rollover and roof crush analysis of low

ROLLOVER AND ROOF CRUSH ANALYSIS OF LOW-FLOOR MASS TRANSIT BUS
A Thesis by
Pankaj S. Deshmukh
B. E., Dr Babasaheb Ambedkar Marathwada University, 2002
Submitted to the Department of Mechanical Engineering
and the faculty of the Graduate School of
Wichita State University
in partial fulfillment of
the requirements for the degree of
Master of Science
December 2006
ROLLOVER AND ROOF CRUSH ANALYSIS OF LOW-FLOOR MASS TRANSIT BUS
I have examined the final copy of this thesis for form and content and recommend that it be
accepted in partial fulfillment of the requirements for the degree of Master of Science, with a
major in Mechanical Engineering.
Hamid M. Lankarani, Committee Chair
We have read this thesis and recommend its acceptance:
Bob Minaie, Committee Member
Bayram Yildirim, Committee Member
ii
DEDICATION
To my parents
iii
ACKNOWELDGEMENTS
I would like to thank my advisor, Dr. Hamid Lankarani, for his guidance and support.
Thanks are also due to Dr. Gerardo Olivares. His support and coaching in completing my
research were invaluable and greatly appreciated.
Also, I would like to thank to Dr. Bob Minaie and Dr. Bayram Yildirim for being part of
my committee, and reviewing this report and making valuable suggestions. I extend my gratitude
to my friends in the computational mechanics laboratory and Aniruddha Deo for their help and
support in all stages of this work. I also thankful to Kristie Bixby for her help in making this
report.
A special acknowledgement goes to my parents for their infinite faith, support, and love.
iv
ABSTRACT
Today transit buses are an integral part of the national transportation system. According
to National Transportation Statistics from 1990 to 2002, the number of transit motor buses in the
U.S. has increased 30 percent. Although buses are one of the safest means of transportation,
occupant injuries and fatalities in bus crashes do occur. Rollover strength has become an
important issue for bus and coach manufacturers. Today European regulation “ECE-R66” is in
force to prevent catastrophic rollover accidents. The Standard Bus Procurement Guidelines
(SBPG) of the American Public Transit Association (APTA) also mentions the roof crush test for
the assessment of bus superstructure and roof.
This thesis discusses the development of a finite element (FE) model of a bus, and the
analysis of its roof crush and rollover in LS-DYNA. The FE model was validated for the roof
crush test carried according to the standard bus procurement guidelines (SBPG). ADAMS-View
software was used to simulate the rollover of the bus. Bus accelerations, velocities, and its angle
with the ground just before impact were measured in ADAMS and then used as input for the LSDYNA analysis. According to the ECE-R66 regulation, a passenger’s survival space is defined
in the bus model to check whether there is any intrusion into the survival space during or after
the rollover. This ensures that the bus structure has sufficient strength to avoid intrusions into the
survival space. The effect of passengers’ weight on energy absorbed by the bus structures during
rollover is also discussed. Development of the MADYMO bus model and its rollover simulations
were also included in this research. Dummy kinematics and injuries sustained during rollover for
various seated and standing positions were studied as well.
v
TABLE OF CONTENTS
Chapter
1.
LITERATURE REVIEW OF PHYSICAL AND VIRTUAL ROLLOVER TESTS .........1
1.1
1.2
1.3
1.4
2.
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
HyperMesh ........................................................................................................14
Finite Element Modeling....................................................................................16
2.2.1 Meshing .................................................................................................16
2.2.2 Mesh Quality Criterion...........................................................................17
2.2.3 Non-Structural Components ...................................................................19
Material Data Definition ....................................................................................20
Creation of FE Joints..........................................................................................21
Suspension System.............................................................................................22
Sub-Assemblies and Implicit Eigenvalue Shakedown Analysis ..........................24
Assembly of Whole Transit Bus.........................................................................25
Accelerometers ..................................................................................................27
Addition of Residual Space in the FE Model......................................................28
Model Validation for Roof Crush .......................................................................29
Limitations of the Bus Model for the Rollover ...................................................34
STRUCTURAL ANALYSIS.........................................................................................35
3.1
3.2
3.3
3.4
3.5
3.6
4.
Introduction .........................................................................................................1
Standards and Regulations ...................................................................................3
Previous Research and Testing.............................................................................8
Objectives ..........................................................................................................13
NONLINEAR FINITE ELEMENT MODEL CREATION AND VALIDATION ..........14
2.1
2.2
3.
Page
ECE-R66 Rollover Test Set Up in ADAMS’s View ...........................................35
ADAMS Rollover Simulation without Passenger Weight Consideration ............37
Consideration of the Passengers’ Weights in the Bus Model...............................38
ADAMS Rollover Simulation with Passenger Weight Consideration .................40
LS-DYNA Rollover Simulation without Passenger Weight Consideration .........41
LS-DYNA Rollover Simulation with Passenger Weight Consideration ..............46
MADYMO BUS MODEL DEVELOPMENT AND OCCUPANT KINEMATICS AND
INJURIES……..............................................................................................................51
4.1
4.2
MADYMO ........................................................................................................51
4.1.1 Reference / Inertial Space in MADYMO ................................................53
4.1.2 Multibody Systems in MADYMO ..........................................................53
4.1.3 Numerical Integration Methods in MADYMO........................................55
4.1.4 Dummy Database ...................................................................................56
Injury Parameters...............................................................................................57
vi
TABLE OF CONTENTS (continued)
Chapter
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
5.
Page
General Injury Mechanisms in Crash Scenarios..................................................59
MADYMO Bus Model Development.................................................................62
Contact Properties for MADYMO Model...........................................................64
Dummy Selection...............................................................................................66
Madymo Analysis Results..................................................................................68
4.7.1 Hybrid III 50th Percentile Dummy at Side-Facing Seat............................68
4.7.2 EuroSID Dummy at Front-Facing Lower Platform Seat..........................71
4.7.3 EuroSID Dummy at Front-Facing Upper Platform Seat ..........................75
4.7.4 Standing Hybrid III 50th Percentile Dummy at Lower Platform...............79
Comparison of Injuries for Different Dummy Positions......................................83
Dummy Interactions...........................................................................................85
Addition of Handle Bar to Front-Facing Seats....................................................91
CONCLUSIONS AND RECOMMENDATIONS..........................................................94
4.11
4.12
Conclusions .......................................................................................................94
Recommendations..............................................................................................95
REFERENCES .........................................................................................................................97
APPENDIX
.........................................................................................................................100
Accelerations and Velocities of ADAMS Rollover Simulations ...................................101
vii
LIST OF TABLES
Table
Page
1.1
Injury Distribution in Coach Accidents............................................................................3
2.1
Mesh Quality Criterion ..................................................................................................18
2.2
Joints Defined in the Bus ...............................................................................................22
2.3
Finite Element Model Summary of the Bus ...................................................................27
3.1
Velocities of the Bus without Passengers’ Weights Just Before the Impact ....................38
3.2
Velocities of the Bus with Passengers’ Weights Just Before the Impact .........................41
3.3
Occupant Mass Coupled to the Structure during an ECE-R66 Rollover Test ..................46
4.1
Comparison of Injury Parameters for Four Different Dummy Positions .........................84
4.2
Comparison of Injury Parameters for Dummy Interactions ............................................87
5.1
Roof Crush and Rollover Analysis Results ....................................................................94
viii
LIST OF FIGURES
Figure
Page
1.1
All crashes ................................................................................................................................ 1
1.2
Buses involved in crashes with fatalities by rollover occurrence ......................................2
1.3
Specification of residual space.........................................................................................6
1.4
Specification of the rollover test ......................................................................................7
1.5
Identification of occupants’ initial positions...................................................................10
1.6
Deformation stops when the waist rail touches the ground .............................................12
1.7
Technical solution to new rollover test...........................................................................12
2.1
FE modeling process .....................................................................................................16
2.2
Solid to mid-surface conversion.....................................................................................17
2.3
Non-structural components of the bus............................................................................19
2.4
Front axle kinematics joints ...........................................................................................23
2.5
Typical air springs stiffness and damper functions .........................................................23
2.6
Rear axle kinematic joints..............................................................................................24
2.7
Sub-assemblies ..............................................................................................................25
2.8
Transit bus FE model assembly .....................................................................................26
2.9
Transit bus FE model.....................................................................................................26
2.10
Accelerometer locations ................................................................................................28
2.11
Residual space ...............................................................................................................29
2.12
Roof crush frame ...........................................................................................................30
2.13
Roof crush test setup......................................................................................................31
2.14
Validation of the roof crush test .....................................................................................32
ix
LIST OF FIGURES (continued)
Figure
Page
2.15
Force vs. roof crush plot for static roof crush test...........................................................33
2.16
Energy vs. roof crush plot for static roof crush test ........................................................33
3.1
Geometry of the tilting bench ........................................................................................35
3.2
ECE-R66 test setup in ADAMS-View ...........................................................................36
3.3
Rollover simulation in ADAMS-View...........................................................................37
3.4
Dimensions for CoG of anthropomorphic ballast ...........................................................39
3.5
Seat configuration of the bus model...............................................................................39
3.6
ECE-R66 simulation using ADAMS-View with passengers’ weight ..............................40
3.7
ECE-R66 rollover test setup in LS-DYNA.....................................................................42
3.8
Deformation of the bus without passengers’ weights......................................................43
3.9
Survival space for the bus without passengers’ weights .................................................44
3.10
Von Mises stress contour for the bus without passengers’ weights .................................44
3.11
Force Vs Roof crush plot for bus without passengers’ weights.......................................45
3.12
Energy Vs Roof crush plot for bus without passengers’ weights ....................................45
3.13
Deformation of the bus with passengers’ weights...........................................................47
3.14
Survival space for the bus with passengers’ weights ......................................................48
3.15
Von Mises stress contour for the bus with passengers’ weights......................................48
3.16
Force vs. roof crush plot for the bus with passengers’ weights .......................................49
3.17
Energy vs. roof crush plot for the bus with passengers’ weights.....................................49
4.1
MADYMO 3D Structures..............................................................................................51
4.2
Reference space.............................................................................................................53
x
LIST OF FIGURES (continued)
Figure
Page
4.3
Types of joints...............................................................................................................54
4.4
Constrained load in a spherical joint ..............................................................................55
4.5
Ellipsoidal dummy models ............................................................................................57
4.6
MADYMO model of the bus .........................................................................................63
4.7
Bus interior modeled in MADYMO...............................................................................64
4.8
Contact characteristics for MADYMO model ................................................................65
4.9
Seat positions selected for dummies...............................................................................66
4.10
Injuries in roll/ no roll events .........................................................................................67
4.11
Kinematics of Hybrid III dummy at side-facing seat position.........................................69
4.12
Accelerations and forces of side-facing Hybrid III dummy ............................................70
4.13
Neck and chest injury results of side-facing Hybrid III dummy......................................71
4.14
Kinematics of EuroSID dummy positioned at front-facing lower platform seat ..............72
4.15
Accelerations and forces of EuroSID dummy positioned at front-facing lower
platform seat.......................................................................................................................73
4.16
Neck and rib injury results of EuroSID dummy positioned at front-facing lower
platform seat ......................................................................................................................74
4.17
Lower rib deflection of EuroSID dummy positioned at front-facing lower platform
seat.....................................................................................................................................75
4.18
Kinematics of EuroSID dummy positioned at front-facing upper platform seat ..............76
4.19
Accelerations and forces of EuroSID dummy positioned at front-facing upper
platform seat…………………………………………………………………………….. 77
4.20
Neck and rib injury results of EuroSID dummy positioned at front-facing upper
platform seat.......................................................................................................................78
xi
LIST OF FIGURES (continued)
Figure
Page
4.21
Lower rib deflection of EuroSID dummy positioned at front-facing upper platform
seat……............................................................................................................................ 79
4.22
Kinematics of Hybrid III standing dummy at lower platform .........................................80
4.23
Accelerations and forces of Hybrid III standing dummy at lower platform.....................81
4.24
Neck and chest injury results of Hybrid III standing dummy at lower platform ..............82
4.25
Neck injuries for different seat positions........................................................................85
4.26
Interactions between dummies positioned at side-facing seats........................................88
4.27
Interactions between dummies positioned at front-facing lower platform seats...............89
4.28
Interactions between dummies positioned at front-facing upper platform seats...............90
4.29
Kinematics of the dummies positioned at the front-facing lower platform seat with
handle bar...........................................................................................................................92
4.30
Kinematics of the dummies positioned at the front-facing upper platform seat with
handle bar ..........................................................................................................................93
xii
CHAPTER 1
LITERATURE REVIEW OF PHYSICAL AND VIRTUAL ROLLOVER TESTS
1.1
Introduction
Automotive manufacturers are investing large capital in crashworthiness and automobile
safety research. As a result, according to Traffic Safety Facts reports, the fatality rate dropped to
a new historic low of 1.44 fatalities per 100 million of vehicles traveling in 2004 [1]. Now
automotive industries are concentrating more on vehicle rollover, as rollover accidents have only
decreased a little more than a half percent in the last decade. Vehicle rollover is one of the
serious highway accidents. The risk of fatal injuries is more in a rollover than any other type of
accident.
Figure 1.1. All crashes [2].
1
Figure 1.1 shows the data from the 1997-2001 National Automotive Sampling System
(NASS) and Crashworthiness Data System (CDS). It is observed that although the percentage of
rollover accidents is less, occupant fatalities (31%) and seriously injured occupants (21%) in
rollovers are more than in any other type of accidents [2].
Of all vehicle types, the situation for mass transit buses is not that different. Although
buses are one of the safest means of transportation, occupant injuries and fatalities in bus crashes
do occur. From 1999 to 2002, the number of transit buses in the United States increased 30
percent, becoming an integral part of the national transportation system. According to Traffic
Safety Facts reports from 1999 to 2003, an average of 40 fatalities and 18,430 injuries of bus
occupants occurred per year [3]. During 1999 to 2003, rollovers occurred in less than 3.1 percent
of buses involved in crashes with fatalities and 0.1 percent of buses involved in crashes with
injuries.
Buses Involved in Crashes with Fatalitites by Rollover Occurrence
1999-2003
350
300
Bus Crash
250
200
Roll
No Roll
150
100
50
0
1999
2000
2001
2002
2003
Average
Figure 1.2. Buses involved in crashes with fatalities by rollover occurrence, 1999-2003 [3].
2
In Europe, bus and coach manufacturers also are focusing more on passenger safety in
case of catastrophic rollover accidents. Thus, rollover strength has become an important issue for
all bus manufacturers. Spanish data from 1995 to 1999 showed a rollover frequency of 4 percent
of all coach accidents on roads and highways, and the risk for fatalities in a rollover was five
times higher than in any other type of coach accident [4]. Table 1.1 shows the probability of
fatalities and other injury severity observed in coach rollover versus other coach accidents [4].
Table 1.1
Injury distribution in coach accidents, Spain 1995-1999 [4]
Injury Severity
Rollover
Others
Fatalities
9.6%
2.5%
Serious Injured
32.1%
7.7%
Minor Injured
55.6%
43.3%
Not Injured
2.6%
46.5%
Total number of occupants
1037
14151
Thus, it was observed that rollover seriously threatens the lives of coach passengers.
Rollovers are complex, chaotic, and unpredictable events involving the interaction of the driver,
road, vehicle, and environmental factors. A rollover is a crash in which a vehicle revolves at least
one-quarter turn (which would be on its side), regardless of whether the vehicle ends up laying
on its side or roof, or even returning upright on all four wheels [2].
3
1.2
Standards and Regulations
Both static and dynamic tests have been studied to determine their effectiveness in
predicting rollovers. Since there are many different causes for rollover, it is difficult to create a
dynamic test which can predict any type of rollover. Rollovers are widely divided into two
categories: tripped and untripped. A tripped rollover is described as one that occurs when a
vehicle’s tires come in contact with an object or soft soil that abruptly stops lateral motion of the
tire and sends the vehicle into a roll around that object. Possible tripping objects are curbs, rocks,
ramps, and soil. These usually occur when a vehicle leaves the road surface. Untripped rollovers
usually happen on the road, and their main causes are severe steering maneuvers such as J-hooks,
lane changes, and fast turns. These types of untripped rollover are the main focus of safety
research because they depend more on vehicle properties and can be prevented [5].
The National Highway Traffic Safety Administration (NHTSA) issues the Federal Motor
Vehicle Safety Standards (FMVSS) to which manufacturers of motor vehicles and equipments
must conform and certify compliance. At present, two federal regulations are applicable to
vehicle rollovers, FMVSS 208 and FMVSS 216. The former is a dynamic roof crush test
standard and the most widely used industry test for rollover. Although it is useful, it lacks
repeatability, since two vehicles with identical roof structures can have tremendously differing
roof crush results. Even the number of times the same vehicle model rolls can change between
tests runs [6]. FMVSS 216 is issued for “Roof Crush Resistance”. It became effective in 1973
and is a mandatory requirement for all vehicles in the United States. This standard specifies
requirements for roof crush resistance over the passenger compartment for passenger cars
(except convertibles), multi-purpose vehicles (MPV), trucks and buses (except school buses)
with a gross vehicle weight rating of 6000 pounds or less. According to this standard, the
4
vehicle roof is loaded quasi-statically up to a specific level, and its roof crush resistance is
checked. Since it is a static test, it does not involve the rollover forces and velocities that are
encountered during an actual scenario. In addition, it has incurred much criticism for its
deficiencies:
a) It applies force in a manner that permits the windscreens to play a significant but
unrealistic role in limiting roof deformation.
b) It applies force at a more vertical roll angle than is typically the case in actual rollover
conditions.
c) The total force applied is substantially less than the forces actually experienced by the
roof in typical rollover accidents.
On August 19, 2005, the NHTSA proposed improvements to its current roof crush
standard [8] as follows:
a) Extend the application of the standard to a vehicle with a gross vehicle weight rating of
4,536 kg (10,000 pounds) or less.
b) Increase the applied force to 2.5 times the unloaded vehicle weight, and eliminate an
existing limit on the force to passenger cars.
c) Replace the current limit on the amount of roof intrusion with a new requirement in
order to maintain enough headroom to accommodate a mid-size adult male occupant.
Test conditions for transit buses are mentioned in the Standard Bus Procurement
Guidelines (SBPG) of the American Public Transit Association (APTA). According to the
SBPG, the bus body and roof structure shall withstand a static load equal to 150 percent of the
curb weight, evenly distributed on the roof with no more than a six inch reduction in any interior
dimension [7]. During a bus or coach rollover, the occupant will have a larger distance from the
5
center of rotation compared to other vehicle types. Some regulations of the Economic
Commission for Europe (ECE) deal with the general construction of buses and coaches.
European regulation “ECE-R66” titled “Resistance of the Superstructure of Oversized Vehicles
for Passenger Transportation” is in force to prevent catastrophic rollover accidents to ensure the
safety of bus passengers [8]. It applies to single-decked vehicles constructed for carrying more
than 16 passengers, whether seated or standing, in addition to the driver and crew.
“Superstructure” refers to the parts of a vehicle structure that contribute to the strength of the
vehicle in the event of a rollover accident. The purpose of this regulation is to ensure that the
vehicle superstructure has sufficient strength so that the residual space during and after the
rollover test on the complete vehicle is unharmed. This means that no part of the vehicle that is
outside the residual space at the start of the rollover, like luggage, is intruding into the residual
space and no part of the residual space projects outside the deformed structure. The envelope of
the vehicle’s residual space is defined by creating a vertical transverse plane within the vehicle
which has the periphery described in Figure 1.3. The SR point is located on the seatback, 500 mm
above the floor under the seat, 150 mm and 250 mm from the inside surface of the sidewall [8].
Figure 1.3. Specification of residual space [8].
6
The rollover test is a lateral tilting test (see Figure 1.4) specified as follows:
The complete vehicle is standing on the tilting platform, with blocked suspension and is tilted
slowly on its unstable equilibrium position. If the vehicle type is not fitted with occupant
restraints it will be tested at unladen curb mass. If the vehicle is fitted with occupant restraints, it
will be tested at total effective vehicle mass. The rollover test starts in this unstable vehicle
position with zero angular velocity, and the axis of rotation passes through the wheel-ground
contact points. The vehicle tips over into a ditch, having a horizontal, dry, and smooth concrete
ground surface with a nominal depth of 800 mm [8].
Figure 1.4. Specification of the rollover test [8].
The rollover test shall be carried out on the side of the vehicle that is more dangerous
with respect to the residual space. This decision was made by the technical service on the basis
of the manufacturer’s proposal, considering at least the following:
7
a) The lateral eccentricity of the center of gravity and its effect on the reference energy in
the unstable starting position of the vehicle.
b) The asymmetry of the residual space.
c) The different asymmetrical construction features of the two sides of the vehicle, and
the support given by the partition or inner boxes (e.g. wardrobe, toilet, and kitchenette).
The side with less support shall be chosen as the direction of the rollover test.
Computer simulation of a rollover test on a complete vehicle is an equivalent approval
method. Today, computer simulation is becoming an irreplaceable mathematical tool in the
vehicle design and development process. It allows manufacturers to test designs and safety
features virtually in the crash scenario until they obtain the safest and optimum design, thus
saving time and money in developing costly prototypes.
1.3
Previous Research and Testing
In research published by CADFEM GmbH, an ECE-R66 calculation procedure was
performed for a TEMSA bus [9]. They developed a finite element (FE) bus model using
specialized pre-processing software, ANSA, and calculations made by the dynamic FE computer
code LS-DYNA. First they prepared two specimens of breast knot and roof edge knot extracted
from the vehicle. These parts were subjected to boundary conditions and quasi-static loads as in
an actual real-life scenario. The same test scenarios were simulated using LS-DYNA. Forcedeflection curves for both the experiment and simulation were compared, and simulation results
were verified. They prepared a FE model of the full vehicle with seats and matched its center of
gravity (CoG) with the measured CoG of the actual vehicle. They obtained the material data, i.e.,
true stress-strain curves, by doing tension tests on several specimens.
8
According to the formula indicated in the ECE-R66 regulation they applied energy of E
= 0.75 Mgh (Nm) by a rotational velocity to all parts of the vehicle. M is the unladen kerb mass
of the bus structure, g is the gravitational acceleration, and h is the vertical distance between the
vehicle CoG at a free fall position and the vehicle CoG which is kinematically rotated up to the
ground contact position. They performed four non-linear explicit dynamics solutions for four
different scenarios:
1. The baseline vehicle (BIW of the vehicle modeled with no seats, no passenger, and no
luggage mass introduced, according to current ECE-R66 regulation).
2. The vehicle with the seat structure introduced (to observe the effect of the seat
structure)
3. The vehicle with the seat structure and passenger mass introduced.
4. The vehicle with the seat structure, passenger mass, and luggage mass introduced.
In the results, they observed that the total energy remains constant which is one
indication of correct analysis. They also observed that the kinetic energy drops and transforms
into internal energy (strain energy + sliding energy) over time, and the hourglass energy remains
negligible. When they introduced the passenger mass on the seat structure, the bus’s center of
gravity of the bus shifted up, and the energy applied to the system increased by almost 37
percentages. Intrusion to the survival space was also increased. Therefore, in the future, experts
are also contemplating introducing the passenger mass into the regulation [9].
In a study conducted in the Polytechnic University of Madrid, Spain, three rollover cases
from the Enhanced Coach and Bus Occupant Safety (ECBOS) project database were selected [4].
They found that the initial occupant position when they are not restrained had a great influence in
9
the kinematics and free flight inside the coach during rollover. They grouped the coach seats in
four columns depending upon the rollover (left or right) event, as shown in the Figure 1.5.
Figure 1.5. Identification of occupants’ initial positions [4].
They found that the most hazardous positions in coach rollover are the rollover window
(P1), followed by the external side window (P4). Occupants of the external seats to the rollover
(P3 and P4) have the largest free flying distance until their body impacts with the internal
elements of the coach.
Their results showed that the seat belt could mitigate the injuries suffered by occupants
located in the positions P2, P3, and P4, since there was no hard contact between the occupant and
any internal part of the coach. In the rollover window cases, even using seat belts, the injuries
suffered by occupants were severe. Seat belts could not prevent the contact of the occupant’s
head, shoulder and ribs with the window, pillar and interior elements of the coach. Therefore,
they suggested use of a restraint system based on lateral airbags. Their results showed that the
presence of passengers increased the angular velocity before the impact by almost 5 percent.
10
They also found that, depending upon the passenger restrain system (two- or three-point seat
belt), the energy absorbed by the coach structure could be increased up to 60 percent.
In the study conducted by Belingardi et al in Politecnico di Torino [10], a new parameter
called Rollover Injury Parameter (RIP) was developed. RIP is defined as the weighted linear
combination of some injury parameters. These injury parameters are the Head Injury Criterion
(HIC), Thoracic Trauma Index (TTI), Viscous Criterion (VC), and the Pubic Symphisis Force
(PSF). They defined RIP as
 HIC 
 TTI 
 VC 
 PSF 
RIP = 0.3
 + 0.25
 + 0.25
 + 0.2

 1000 
 85 
 1 
 6000 
They faced a problem with opposite requirements: to keep the survival space intact, a
very stiff structure is needed, while to keep the biomechanical injury parameters low below the
limits a structure with large energy absorption capability is needed. They used design of
experiment (DOE) tool to obtain a design solution satisfying each request. They also found that
the formation process of plastic hinges along the pillars is fundamental for adequate energy
absorption.
On the 80th meeting of GRSG, Hungary raised the problem of the geometrically limited
deformation of higher deck (HD) coaches (with a height > 3.4m) in the standard rollover test
[11]. According to Hungary, in the case of an HD coach tested according to the standard rollover
test, if its superstructure has a four plastic hinges deformation mechanism, the structural
deformation stops when the waist rails touch the ground.
As shown in Figure 1.6, if ω < υ, the distortion of the superstructure in a standard rollover
test will be stopped because of the geometrical configuration of the test bench, even in the case
of a weak superstructure. According to Hungary for higher deck buses, the standard rollover test
cannot separate the strong superstructure from the weak one.
11
Figure 1.6. Deformation stops when the waist rail touches the ground [11].
The IKARUS Vehicle Manufacturing Company, Hungary, suggested one possible
solution for this scenario [12]. They kept the depth of the ditch at 800 mm as it exists in Reg. 66,
but they made the ground level shaped and deeper to avoid the too early contact of the waist rail,
as shown in the Figure 1.7.
Figure 1.7. Technical solution to new rollover test [12].
12
1.4
Objectives
Rollover occurs less frequently than all other types of automotive accidents, but the
probability of fatalities and severe injuries is more in rollover type accidents. Today, transit
buses are becoming an integral part of the nation’s transportation system. In a bus rollover,
occupants are further away from the axis of rotation compared to other types of vehicles. Hence,
occupants are at greater risk in a rollover crash. It is essential that the bus superstructure be stiff
enough to protect the occupant survival space from any intrusion, while absorbing the maximum
crash energy.
Full-scale rollover tests are expensive and instrumenting the vehicle correctly is not easy.
Hence, computer simulations are becoming more important and sophisticated in automotive
industries to make design process fast and affordable. The objective of this thesis is to simulate
the different roof strength tests, like the roof crush test, according to bus procurement guidelines
and rollover test according to ECE-R66 using the nonlinear finite element code LS-DYNA. A
method of modeling a bus rollover test in MADYMO is also discussed to investigate occupant
injuries and kinematics using the Hybrid III and EuroSID dummy models. It is also necessary to
study occupant interactions with the interior bus features. Unlike the seating compartment in a
school bus, the surfaces in a transit bus are not designed to absorb the impact energy. At the
same time, since real-world crash events may take greater time, the CPU time to perform these
situations and advantages and limitations of the mathematical codes are also discussed.
13
CHAPTER 2
NONLINEAR FINITE ELEMENT MODEL CREATION AND VALIDATION
2.1
HyperMesh [13]
Altair HyperMesh is a high-performance finite element pre- and post-processor that is
compatible with most widely used finite element solvers. HyperMesh’s user-interface is easy to
learn and supports many CAD geometry and finite element model files, thus increasing
interoperability and efficiency. Advanced functionality allows users to efficiently mesh highly
complicated models. It also allows user-defined quality criteria and controls, morphing
technology to update existing meshes to new design proposals, and automatic mid-surface
generation for complex designs with varying wall thicknesses. Automated tetra-meshing and
hexa-meshing minimizes meshing time, while batch meshing enables large-scale meshing of
parts with no model clean-up and minimal user input.
HyperMesh incorporates a variety of tools for seamless integration into any existing
engineering process. It allows customizing the layout of HyperMesh's menu system through an
easy-to-use interface according to the user’s convenience. Users can take advantage of the power
within the Tcl/Tk toolkit to build custom applications fully integrated with HyperMesh. One can
create macros that automate a process or series of steps. Export templates and input translators
increase the flexibility making Hypermesh compatible with many solvers. The export templates
allow the HyperMesh database to be written out to formats to non-supported solvers. The input
translators support by adding the user’s own input translators for reading different analysis data
decks.
HyperMesh provides direct access to a variety of industry-leading CAD data formats for
generating finite element models. It also provides robust tools to clean imported geometry
14
containing surfaces with gaps, overlaps, and misalignments, which prevent auto meshing and
high quality mesh generation. By eliminating misalignments and holes, and suppressing the
boundaries between adjacent surfaces, users can mesh across larger, more logical regions of the
model while improving overall meshing speed and quality. Boundary conditions can be applied
to these surfaces for future mapping to underlying element data.
HyperMesh includes a sophisticated suite of easy-to-use tools to build and edit models.
For 2D and 3D model creation, users have access to a variety of mesh generation panels besides
HyperMesh's
powerful
auto-meshing
module.
Automatic
mid-surface
generation,
a
comprehensive laminate modeler and morphing (to stretch existing FE meshes to new design
geometries), and creating surfaces from the existing mesh offer new levels of model
manipulation.
The surface auto-meshing module in HyperMesh is a robust tool for mesh generation that
provides users the ability to interactively adjust a variety of mesh parameters for each surface or
surface edge. These parameters include element density, element biasing, mesh algorithm, and
more. This gives very high user control over the meshing process enabling meshing of even
highly complicated surfaces with desired quality.
HyperMesh supports a host of different solver formats for both import and export. Along
with fully supported solvers, HyperMesh also provides the flexibility to support additional
solvers via a complete export template language and C libraries for development of input
translators. Some of these are stated below:
OptiStruct
LS-DYNA
ANSYS
ABAQUS
RADIOSS
MADYMO
NASTRAN
PAMCRASH
MOLDFLOW/C-MOLD
15
MARC
2.2
Finite Element Modeling
2.2.1
Meshing
Computational vehicle models need to capture the deformation and interaction of vehicle
parts and subsystems occurring during impact. The accuracy with which the crash behavior of a
vehicle is simulated depends on the quality of the computer aided design (CAD) data and its
meshing. CAD geometry should be accurate in shape and size to resemble the actual vehicle. The
FEM mesh should be dense enough to ensure computational convergence and to keep the
computational time reasonably low.
Catia / ProE
3D Cad Data
Hypermesh
2D or 3D
Elements
Geometry Defeature
2D
Mid-Surface
Extraction
3D
Hypermesh
Mesh Quality
Check
Meshing
No
Excell
Yes
Hypermesh
No
Part Assembly:
-Spotweld
-Kinmeatic Joint, etc
Boundary
Conditions
Contact Definitions
Hypermesh
Excell
Primer
Initial
Penetrations
Documentation
Final Model Check
Documentation
LS Dyna Solver
Implicit Check
Explicit Solution
Material and
Section Properties
Adjust
Normals
Motion View
Post Processing
Model Archive
Figure 2.1. FE modeling process.
Figure 2.1 shows the methodology adopted for the preparation of a finite element model
of a bus. For meshing purposes, HyperMesh software was used. HyperMesh is a high
performance finite element pre- and post-processor that allows building finite element models,
views their results, and performs data analysis. First all CAD models generated in softwares like
16
Pro-E and CATIA were converted into IGES format. These CAD models of the bus were
provided by the local bus manufacturing company. Then models were called into the
HyperMesh. In this software, first mid-surfaces were extracted from these models, as shown in
Figure 2.2. Then geometry cleaning was done by using options like “geom cleanup” and
“defeature” to modify the geometry data and prepare it for meshing operations. This process
involved deletion of holes and curvatures of a very small radius (less than 5 mm), which have
less structural significance. The geometries with holes were always difficult to mesh, because
they distort mesh generation. Holes with a radius of more than 5 mm were meshed by
surrounding it with minimum six elements. Very small parts, like nut-bolts, also were removed
from the geometry, and then spot-welds were created in their places to represent bolts, rivets, and
welds.
Figure 2.2. Solid to mid-surface conversion.
17
2.2.2 Mesh Quality Criteria
Some default quality criteria are available in HyperMesh, including the following:
•
Min Side Length: Length of the smallest side of an element.
•
Max Side Length: Length of the largest side of an element.
•
Aspect Ratio: Ratio of longest side to the shortest side of an element.
•
Warpage: Deviation of an element or element face from being planar.
•
Min/Max Quad Internal Angle: The minimum/maximum angle of a quad element.
•
Min/Max Tria Internal Angle: The minimum/maximum angle of a triangle element.
•
Percent of Triangular Elements: Ratio of the number of triangular elements to the total
number of elements.
For quality criterion was prepared as listed in the table 2.1 and it is maintained
throughout the meshing process. While meshing it was made sure that minimum element size
should not be less than 5 mm in order to maintain the minimum time step of one micro second
without using mass scaling.
Table 2.1
Mesh quality criteria
No
Quality Parameter
Allowable Min / Max
1
Minimum Side Length
5
2
3
4
5
6
7
8
9
Maximum Side Length
Maximum Aspect Ratio
Maximum Warpage Angle
Minimum Quad Internal Angle
Maximum Quad Internal Angle
Minimum Tria Internal Angle
Maximum Tria Internal Angle
Percent of Triangular Elements
100
5
15
45
135
15
120
5
18
If the part thickness exceeded 1.5 mm, a minimum of five integration points were
assigned. Belytscho Tsay elements were used primarily, because they are recommended for crash
analysis to save computational time. Constant stress solid elements were used for solid elements.
Every part that was meshed was checked for its elements normal directions. For the contact
between parts, their directions of normal should be kept toward each other. No splits and cracks
were allowed in the mesh. It was also checked for duplicate elements, free nodes, and free edges.
A smooth transition from fine mesh to coarse mesh was also maintained.
2.2.3 Non-Structural Components
Some non-structural components move relative with the main bus structure such as the
engine, fuel tank, battery compartment and roof air-conditioning unit. These parts contribute
significantly to weight, but their deformation is less. Therefore, they were meshed as rigid bodies
just to maintain the mass and center of gravity (CoG) of the bus. Bus interiors were also modeled
to check their interactions with FE dummies when the bus model was subjected to a crash test.
Some mass nodes also were assigned to match the CoG of the bus model to that of the calculated
CoG of the actual bus. The engine differential was modeled with beam elements. Tires were
meshed with the enclosed volumes to allow the internal pressure definition.
Engine
Bus Interior
Fuel Tank
Figure 2.3. Non-structural components of the bus.
19
Radiator
2.3
Material Data Definition
The bus structure mainly consists of steel and aluminum members. A vehicle collision is
a highly dynamic process in which structural members deform under different strain rates. This
bus model was used for various crash configurations with impacting velocities of 0 to 60 km/hr;
hence, it was necessary to consider the strain rate effect on the mechanical properties of the
structural members. Three types of testing are available for obtaining the material data, i.e.,
stress-strain curve:
1)
Mechanical or Servo-Hydraulic: quasi-static condition and strain rates below 0.1/s.
2)
Servo-Hydraulic: strain rate range from 0.1 to 500/s.
3)
Split Hopkinson Bar System: strain rate range 100 to 1000/s, and higher.
A mechanical or servo-hydraulic system was used to extract the material data, because
strain rate increments of 0.1, 1, 10, 100, 250, and 500/s were sufficient for describing strain rate
sensitivity in this application. Material testing was done by the third party. Results of the
material testing showed that the steel materials are more strain-rate sensitive than the aluminum
materials. Engineering stress and strain were obtained from the tension test. Therefore, true stress
and true strain was calculated by using following formulas:
σ
true
=
fl
AA
o
c
= σ e (1 + ε e )
ε
true
l 
= ln  = ln(1 + ε e )
 
 lo 
Now the effective stress and strain curves were calculated by using following equations:
σ
eff
ε
= σ vm = σ xx
eff
= ε xx − σ xx
E
and then used as input for the FE model.
LS-DYNA material type 24 (*MAT_PIECEWISE_LINEAR_ PLASTICITY) was used
for all structural members. This is an elasto-plstic material with arbitrary stress vs. strain curve
20
and arbitrary strain rate dependency [14]. This material uses the Young’s modulus if stresses are
below the yield stress and the measured stress-strain curve if the stresses are above the yield
stress. Windshield and passenger window glass properties were also modeled with material type
24 with a defined plastic strain failure model.
LS-DYNA material DS4, i.e., MAT_S04 or MAT_SPRING_NONLINEAR_ELASTIC
was used for the discrete spring elements. LS-DYNA material DS5, i.e., MAT_S05 or
MAT_DAMPER_NONLINEAR_VISCOUS
(damper
nonlinear)
was used
for
damper
suspensions. Components of the bus with negligible deformations such as the engine block and
transmission were modeled using material type 20 (MAT_RIGID), and inertial properties were
defined per component as specified in the engineering documentation. For the tires, material
type-1, i.e., MAT_ELASTIC (linear elastic material model) was used. To define the internal
pressure of 110 psi in enclosed volumes of tires *AIRBAG_SIMPLE_AIRBAG_MODEL_ID
card was used. Spot-welds were modeled with material type 100 (MAT_SPOTWED). Failure
criterion was not used for the spot-weld. The final FE bus model contained 26 material
definitions.
2.4
Creation of FE Joints
Joints were created in HyperMesh. The “fe joints” option in HyperMesh allows creating,
reviewing, or updating joint elements. A joint element is a connection between two rigid bodies
[13].
Hence,
parts
in
which
joints
are
defined
must
be
rigid.
The
*CONSTRAINED_EXTRA_NODES_SET option was used to connect the joint elements with
the rigid parts. Joint elements store property and orientation information. These elements are
config-22. There are total 32 joints defined in the FE model of the bus, as listed in Table 2.2.
These FE joints are used to define the suspension system of the bus.
21
Table 2.2
Joints defined in the bus
Name of the joint
2.5
Description
Number of joints
Translational joint
12
Revolute joint
18
Spherical joint
2
Suspension System
The bus uses air-ride suspension to dampen shock that is transmitted from the road
surface to the passengers. A height control valve is used to maintain the proper ride height. This
valve controls the volume of the air in the springs.
Figure 2.4 shows the kinematics joints used for the front-axle suspension system. The
front axle has four air springs that were modeled with four translational kinematic joints with
nonlinear spring functions, and two hydraulic shock absorbers that were modeled with two
translational joints with nonlinear damper functions. Two additional spherical joints in the
control arms and two revolute joints in the wheels were also defined. Typical spring and damper
functions are shown in Figure 2.5.
22
Figure 2.4. Front axle kinematics joints.
Figure 2.5. Typical air spring stiffness and damper functions.
The rear axle has four air springs that were modeled with four translational kinematic
joints with nonlinear spring functions, and two hydraulic shock absorbers that were modeled
with two translational joints with nonlinear damper functions. Eight additional revolute joints in
the four control arms and two revolute joints in the wheels were defined as shown in Figure 2.6.
The same spring and damper functions as shown in Figure 2.5 were used. The FE model allows
changes in riding height and air spring pressures.
23
Figure 2.6. Rear axle kinematic joints.
2.6
Subassemblies and Implicit Eigenvalue Shakedown Analysis
Subassemblies were prepared by connecting the meshed parts. Deformable parts were
connected by spot-welds, and rigid bodies were connected to deformable parts by the constrained
rigid body option. The rigid body merge option was used to connect two rigid bodies. Some of
the sub-assemblies are shown in the Figure 2.7.
All the subassemblies were run for the implicit eigenvalue shakedown analysis. The
purpose of this implicit shakedown analysis is to check the proper attachments of the every part
in the assembly. To run theses shakedown analysis CONTROL_IMPLICIT_GENERAL and
CONTROL_IMPLICIT_EIGENVALUE cards were used. In this analysis, assemblies were
vibrated at their natural frequencies. If some parts are not properly attached, they will dislodge.
Hence, this implicit analysis is a good way to check all spot-welds and joints of the assembly.
Although implicit analysis takes less computational time, it requires very high memory
allocation.
24
Roof with windshield
Chassis with side panels
Rear suspension
Front suspension
Figure 2.7: Sub-assemblies
2.7
Assembly of Whole Transit Bus
After all subassemblies were checked by shakedown analysis, they were assembled to
form the whole FE model of the bus, as shown in Figures 2.8 and 2.9. This figure shows the bus
superstructure; bus interior components are not shown. When whole bus is modeled with interior
components, it becomes a very large detailed FE model of the low-floor mass transit bus with
282,025 elements, 20,306 spot-welds, and 26 materials. A summary of the FE bus model is listed
in the Table 2.2.
25
Figure 2.8. Transit bus FE model assembly.
Figure 2.9. Transit bus FE model.
26
Table 2.2
Finite element model summary of the bus
No. of Parts
1,338
No. of Nodes
298,833
No. of Elements
282,025
No. of Spot Welds
20,306
No. of Materials
26
No. of Sectional Properties
2.8
1,348
No. of Sub-assemblies
43
No. of Kinematic Joints
32
No. of Tire Models (Control Volumes)
6
Accelerometers
Whenever computed accelerations are compared to experimental results or whenever
computed accelerations are compared between different runs, accelerometers are essential. Raw
nodal accelerations contain considerable noise, and their comparisons are generally meaningless
and, therefore, misleading. In the bus model, accelerometers were located at several locations, as
shown in Figure 2.10. An accelerometer is a solid 3D element with rigid (steel) material
properties (MAT_RIGID). These elements are constrained to the bus parts. They are placed at
every important location like floor, side beams, seats, bumpers, and roof. This accelerometer has
its own local coordinate system. The NODOUT file, including all the accelerometer nodes, was
written. This NODOUT file has the motion history of all accelerometer nodes.
27
Figure 2.10. Accelerometer locations.
The cross-sectional forces were measured at the structural members by using
DATABASE_SECFORC and DATABASE_CROSSSECTION_PLANE_ID cards. Crosssections were defined for resultant forces written into ASCII file SECFORC.
2.9
Addition of Residual Space in FE Model
Residual space is a space to be preserved in the passengers’, crew, and driver’s
compartment(s) to provide better survival possibility for passengers, driver and crew in case of a
rollover accident. Residual space is defined as mentioned in the section 1.2 of this thesis.
In the FE model, an envelope of the vehicle’s residual space is defined by two vertical
transverse planes within the vehicle which have a periphery described in Figure 2.11 and move
through the length of the vehicle. This was defined for viewing purposes only, so MAT_RIGID
was assigned to this space and no contacts with the other parts were given. It should not be
displaced from its position and should move along with the bus model during the rollover.
Therefore, it was attached to the floor parts, which do not get deformed in a rollover analysis, by
using the CONSTRAINED_EXTRA_NODES_SET card.
28
Figure 2.11. Residual space.
2.10
Model Validation for Roof Crush
The model has been validated for a variety of impact conditions specified in the Bus
Procurement Guidelines [7]. The data for these guideline test conditions was provided by the bus
manufacturer, and additional higher-speed crashworthiness evaluations were compared to data
from previous publications of similar class transit buses [15]. Validation parameters were limited
to the test data provided, including bus CG displacements, velocities, acceleration, rigid wall
reaction forces, and measurements of permanent structural deformations. The bus model was
validated for a frontal impact test (5 mph), side impact test (21.5 mph), rear impact test (2 mph),
and roof structure. In this thesis, only validation of roof crush test is discussed. Roof crush was
validated according to section 5.4.1.2 of the Bus Procurement Guidelines [7]. This section says
that the bus body and roof structure shall withstand a static load equal to 150 percent of the curb
weight, evenly distributed on the roof with no more than a six-inch (152 mm) reduction in any
interior dimension. Windows shall remain in place and shall not open under such a load. These
29
requirements must be met without such components as a roof-mounted air conditioning unit.
Therefore, the air conditioning unit was removed from the bus FE model.
The roof crush frame was modeled using softwares CATIA and HyperMesh, as shown in
the Figure 2.12. Its mesh size was kept the same as that of the bus roof. The MAT_RIGID card
was assigned to it. The mass of the bus FE model without the air conditioning unit was 9.712
tons. Hence, density of the frame material was adjusted such that frame mass measured 1.5 times
that of the bus mass i.e. 14.568 tons.
Figure 2.12. Roof crush frame.
This roof crush test was done by supporting the bus on its floor chassis frames, not on the
tires. This allows the bus structural frames to carry the entire load without any contribution from
the suspension system. Therefore, one rigid plate was modeled on which the bus floor was
supported. This plate was constrained in all degrees of freedom (DOF). The roof crush frame
was placed on the bus roof such that its horizontal beams were exactly on top of the bus roof’s
beams, as shown in the Figure 2.13.
30
Figure 2.13. Roof crush test set up.
The roof crush frame moves down on the bus roof because of applied gravity. Self
contact was given between all parts of the bus using the AUTOMATIC_SINGLE_SURFACE
card.
The AUTOMATIC_SURFACE_TO_SURFACE card was used to provide contact
between the crush frame and the bus roof. It was also used to define contact between the bus
floor and the rigid plate. The roof crush test results data were provided by the bus manufacturer
as follows:
Roof Test Load Obtained = 1.65 x 105 N
Maximum Permanent Interior Deflection = 111.2 mm
As shown in Figure 2.14, in the simulation, the maximum dynamic displacement
obtained was 143 mm. But after recovery of the elastic deformation, the permanent plastic
deformation obtained was in the range of 95 to 115 mm, which is within the range of physical
test results. On the support platform, there was load of both the bus and the crush frame.
(load on the platform) = (mass of the bus) + (mass of the crush frame)
= 9.712 + 14.568 = 24.28 tons =24280 kg
Hence, force on the platform = 24280 * 9.71 = 2.3575 * 105 N
31
Figure 2.14. Validation of the roof crush test.
From the simulation, the resultant contact force obtained at the support platform was
around 2.3e5 N, which is very close to the calculated force. Figure 2.15 shows the force vs. roof
crush plot, where there is maximum roof crush of around 148 mm, but again reduced to 115 mm.
This is because the whole deformation is a combination of elastic and plastic deformation again,
the roof comes up and pushes the crush frame in an upward direction to recover its elastic
deformation. The final permanent deformation of 115 mm is the plastic deformation.
32
Force Vs Roof Crush
2.5E+05
Force (N)
2.0E+05
1.5E+05
1.0E+05
5.0E+04
0.0E+00
0
20
40
60
80
100
120
140
160
Roof Crush (mm)
Force Vs Roof Crush
Figure 2.15. Force vs. roof crush plot for static roof crush test.
A force vs. roof crush plot was used to calculate the energy. The area under this curve
gives the energy absorbed by the system during a crush. Energy vs. roof crush plot was plotted
by integrating the force vs. roof crush curve in the LS-POST, as displayed in the Figure 2.16. Its
nature is linear, and energy absorbed is more, causing more roof crush. The slope of the curve
was found using the Linear Trend Line in Microsoft Excel. The slope gives the rate of energy
absorbed by the system for a given roof crush.
Roof Energy in Static Crush Test
2.0E+07
y = 124972x
2
R = 0.9764
1.8E+07
Energy (Nmm)
1.6E+07
1.4E+07
1.2E+07
1.0E+07
8.0E+06
6.0E+06
4.0E+06
2.0E+06
0.0E+00
0
20
40
60
80
100
120
140
160
Roof Crush (mm0
Roof Energy in Static Crush Test
Linear (Roof Energy in Static Crush Test)
Figure 2.16. Energy vs. roof crush plot for static roof crush test.
33
2.11
Limitations of the Bus Model for the Rollover
Implicit analysis was also tried for the roof crush test, but there was a limitation to the
model. Implicit analysis gave the error of the over-constrained nodes (error code -19), which
belongs to spot-welds. Therefore, using HyperMesh, these spot-weld configurations changed to
rigid links. CONSTRAINED_NODAL_RIGID_BODY cards were created in HyperMesh for all
MAT_SPOTWELD cards. But LS-DYNA still gave an error code of type -2.
For ECE-R66 rollover, the DEFORMABLE_TO_RIGID_AUTOMATIC card was used
to switch all deformable parts of the bus into rigid parts during rollover until it touches the
ground. But after this conversion, LS-DYNA gave the error that some nodes were already used
in the rigid body definition. It was found that those nodes were used to constrain the rigid bodies
like engine with the deformable parts. Many rigid parts in the bus model were constrained with
the deformable parts, so it was very difficult to run the bus model for rollover using the
DEFORMABLE_TO_RIGID card.
So it was decided that ADAMS-View should be used with LS-DYNA for the rollover. It
was easy to make the simple bus model and tilting table assembly in the ADAMS-View. So after
running the rollover in the ADAMS, it was possible to extract all velocities, accelerations, and
angle of the bus with the ground at the time of its impact. In LS-DYNA, the bus can be tilted at
an angle obtained in ADAMS, and all velocities can be assigned to it. This approach was
considered to be appropriate to simulate the ECE-R66 rollover.
34
CHAPTER 3
STRUCTURAL ANALYSIS
3.1
ECE-R66 Rollover Test Setup in ADAMS View
According to ECE Regulation 66, the tilting table geometry is shown in Figure 3.1 [8].
The tilting table shall be sufficiently rigid and the rotation sufficiently controlled to ensure
simultaneous lifting of the axles of the vehicle with a difference of less than one degree in the
platform’s tilt angles measured below the axles. The height difference between the horizontal
lower plane of the ditch and the plane of the tilting platform on which the bus is standing, shall
be 800 ± 20 mm. The axis of its rotation is 100 mm maximum from the vertical wall of the ditch
and 100 mm maximum below the plane of the horizontal tilting platform. Wheel supports shall
be applied at the wheels being close to the axis of rotation against sliding of the vehicle sideways
when tilting it. The tilting platform shall be constructed to prevent the vehicle moving along its
longitudinal axis. The impact area of the ditch shall have a horizontal, uniform, dry and smooth
concrete surface.
Figure 3.1. Geometry of the tilting bench [8].
35
Figure 3.2. ECE-R66 test setup in the ADAMS-View.
In ADAMS View, one block of the bus’s dimensions was created as shown in Figure 3.2.
The mass of the bus without the air conditioning unit (9.76 ton) was assigned to this block. Using
the Easy Crash Dyna software center of gravity (CoG) of the bus was measured. The CoG was
closer to the rear axle due to the presence of heavy parts like the engine at the rear end. In
ADAMS View, the bus block’s CoG was positioned according to this measured CoG. Blocks of
the tilting table and ground were created with the height difference of 800 mm between them
according to ECE-R66 regulation. Wheel supports were drawn exactly at the position of the bus
tires to prevent its sliding motion. A revolute joint was defined between the tilting table and the
ADAMS default ground part. In the R66 regulation, the bus platform was pulled up by a crane at
maximum rotational speed of 1o per sec to let the bus rollover [16]. Rotational motion of one
degree per second
was assigned to the revolute joint. Points of the ground block were
constrained with lock joints to fix the ground in the space. Contact for the bus block with the
tilting table and the ground was defined with coefficient of frictions of 0.2 and 0.7, respectively.
36
3.2
ADAMS Rollover Simulation without Passenger Weight Consideration
For this simulation, passenger weights were not considered. Figure 3.3 shows the position
of the bus block just before its impact with the ground. Simulation was run for 68 seconds.
Figure 3.3. Rollover simulation in the ADAMS View.
When tilted, the bus remained in equilibrium position until the tilting table surface made
an angle of 57.4 degrees with the horizontal direction. At this angle, the bus became unstable and
left the surface of the tilting table. According to the Delhi Transport Corporation’s bid document
in order to obtain approval for the stability of the bus model, when the surface on which the
vehicle stands was tilted to both sides in turn at an angle of 35 degrees from the horizontal, the
vehicle should not overturn [17]. Since in the ADAMS simulation bus block was overturned at
an angle more than 35 degrees, the bus model is stable. At the simulation time of 65.8011
seconds, the bus was in position just before impact. The bus made an angle of approximately 17º
with the ground just before the impact. At that time, all angular and translational velocities of the
bus block about its center of gravity were noted down, as listed in Table 3.1.
37
Table 3.1
Velocities of the bus without passengers’ weights just before the impact
3.3
ADAMS Simulation
Magnitude
Angular velocity in X-axis
-0.05º/ sec ≈ 0
Angular velocity in Y-axis
-0.003º/ sec ≈ 0
Angular velocity in Z-axis
11.22º/ sec = 0.19 rad/ sec
Translational velocity in X-axis
-751.34 mm/ sec
Translational velocity in Y-axis
-1026.67 mm/ sec
Translational velocity in Z-axis
6.29 mm/ sec
Consideration of Passenger Weights in the Bus Model
In the ECE-R66 regulation test, passenger weights were not included. Therefore, to check
the effect of passengers mass, a bus model with passengers mass was introduced. It was assumed
that all passengers were restrained with safety belts. The passenger mass was imposed on the seat
structure assuming a single passenger mass of 68 kg and the number of passengers on board to
be 23. Hence, the bus’s weight was increased by 1,564 kg. In the FE model of the bus, a lumped
mass element was used to attach passenger weights. In the ECE-R66 regulation, position of the
center of gravity of the anthropomorphic ballast is mentioned, as shown in Figure 3.4 [8]. This
was used as a reference to position the single solid element above every seat. These elements
were made rigid (MAT_RIGID) and constrained with the seats using the LS-DYNA card
CONSTRAINED_NODAL_RIGID_BODY. Then a nodal mass of 0.068 tons was attached to
these elements. Since this mass was constrained with the seat, it moved with the seat like a fully
restrained occupant.
38
Figure 3.4. Dimensions for CoG of anthropomorphic ballast [8].
Figure 3.5 shows bus seats with solid elements to which nodal masses were attached.
There were a total of 23 seats, and the numbers of the seats were more on the driver’s side of the
aisle. Hence, due to this weight addition, there was a considerable change in position of the CoG
of the bus. The CoG shifted upwards by 5.6 mm, toward the rear side by 8.87 mm, and toward
the driver’s side by 50.92 mm.
Figure 3.5. Seat configuration of the bus model.
39
3.4
ADAMS Rollover Simulation with Passenger Weight Consideration
As calculated before when the bus was fully boarded with 23 passengers, its weight
increased from 9.71 tons to 11.324 tons. For the second ADAMS simulation, the weight of the
bus block was changed to 11.324 tons to consider passengers’ weights. Due to this addition, the
bus CoG shifted its position, as discussed in the previous section. Hence, in ADAMS, the bus
block CoG was changed accordingly.
Figure 3.6. ECE-R66 simulation using ADAMS View with passenger weights.
In the simulation, it was observed that during tilting, the table bus block also moved in
the longitudinal direction which was undesirable. Therefore, a stopper block was added to the
tilting table to prevent the bus block’s longitudinal movement, as shown in Figure 3.6. This
simulation was run using the same conditions and same contact definitions as the previous one.
At the simulation time of 64.4232 seconds, the bus was in position just before impact.
The bus model made an angle of 16.5816 degrees with the ground at the time of impact. At this
time, all angular and translational velocities of the bus block about its center of gravity were
noted down as listed in Table 3.2.
40
Table 3.2
Velocities of the bus with passengers’ weights just before the impact
ADAMS Simulation
Magnitude
Angular velocity in X-axis
0.31º/ sec ≈ 0
Angular velocity in Y-axis
0.005º/ sec ≈ 0
Angular velocity in Z-axis
11.97º/ sec = 0.21 rad/ sec
Translational velocity in X-axis
-826.23 mm/ sec
Translational velocity in Y-axis
-2129.01 mm/ sec
Translational velocity in Z-axis
0.13 mm/ sec
In this simulation, the bus block became unstable when the tilting table made an angle of
56.1 degrees with the horizontal. At this angle, the bus block left the tilting table. Since this
angle is more than 35 degrees, bus model was stable, even fully loaded with passengers.
This addition of passenger weights affected the falling velocity of the bus block. The
translational velocity in the Y-axis represents the falling velocity of the bus, whereas angular
velocity around the Z-axis represents the rotational velocity around the tilting axis. The results of
both ADAMS simulations show that when the bus was fully loaded with passengers, its falling
velocity increased by 74.89 mm/s over that of the bus without passengers, and its rotational
velocity around the tilting axis also increased by 0.0132 rad/s. There was an almost 6 percent
increase in the rotational velocity of the bus.
3.5
LS-DYNA Rollover Simulation without Passenger Weight Consideration
The bus was tilted to create the desired angle obtained in the ADAMS simulation with
the ground, as shown in Figure 3.7.
41
Figure 3.7. ECE-R66 rollover test setup in LS-DYNA.
The ground was simulated a rigid plane (MAT_RIGID) with all degrees of freedom
constrained. The angular and translational velocities obtained in the ADAMS simulation as listed
in
Table
3.1,
were
assigned
to
all
parts
of
the
bus
using
the
INITIAL_VELOCITY_GENERATION card. For the contact between the bus and the ground,
the AUTOMATIC_SURFACE_TO_SURFACE card was used. Static and dynamic coefficient of
frictions was kept at 0.7 because of the hard nature of the concrete ground used for the rollover
test.
Contact
was
given
between
all
parts
of
the
bus
by
using
the
CONTACT_AUTOMATIC_SINGLE_SURFACE_ID card. Deformation of the bus during the
rollover is shown in Figure 3.8. There was not much significant deformation that could cause
harm to the survival or residual space of the passenger. Figure 3.9 shows the survival space of
the passenger before and after the rollover simulation. There is no intrusion in the survival space,
which remains intact during the rollover.
The von Mises stress contours are shown in Figure 3.10. Most of the energy is absorbed
by the “A” pillar, the last vertical pillar, and the floor beams. Both the “A” pillars and the last
vertical pillars start bending with increasing forces.
42
Time = 0 sec
Time = 0.1 sec
Time = 0.2 sec
Time = 0.3 sec
Time = 0.4 sec
Time = 0.5 sec
Figure 3.8. Deformation of the bus without passenger weights.
43
Time = 0 sec
Time = 0.5 sec
Figure 3.9. Survival space for the bus without passenger weights.
Figure 3.10. von Mises stress contour for the bus without passenger weights.
44
Force Vs Roof Crush for bus without passenger weight
2.0E+06
1.8E+06
1.6E+06
Force (N)
1.4E+06
1.2E+06
1.0E+06
8.0E+05
6.0E+05
4.0E+05
2.0E+05
0.0E+00
0
50
100
150
200
250
300
Roof Crush (mm)
Force Vs Roof Crush
Figure 3.11. Force vs. roof crush plot for bus without passenger weights.
Force vs. roof crush curve was plotted in Figure 3.11. Maximum force was reached about
1.75E+06 Newton at 230 mm of roof crush. This curve was integrated in LS-POST to obtain the
energy vs. roof crush plot shown in Figure 3.12. Here, energy of the system is 2X107 Nmm for a
crush of 250 mm. Thus, in the rollover simulation, energy of the system and deformation are
more than the static roof crush test. But the slope of the trend line is less than that of the static
crush test. This signifies that the rate of energy absorption is more in the static crush test than
dynamic rollover test without passenger weights.
Roof Energy in ECE R66 test without passenger wt
2.5E+07
y = 82125x
2
R = 0.9446
Energy (Nmm)
2.0E+07
1.5E+07
1.0E+07
5.0E+06
0.0E+00
0
50
100
150
200
250
300
Roof Crush (mm)
Roof energy in ECE R66 test without passenger wt
Linear (Roof energy in ECE R66 test without passenger wt)
Figure 3.12. Energy vs. roof crush plot for bus without passenger weights.
45
3.6
LS-DYNA Rollover Simulation with Passenger Weight Consideration
During a rollover, only part of the total passenger mass is coupled to the structure,
depending on the kind of restraint system used. Within the ECBOS project, some studies were
performed to assess the mass of the occupant that is effectively coupled to the structure during
the ECE-R66 rollover test. The results of such studies are found in Table 3.3 [18].
Table 3.3
Occupant mass coupled to the structure during an ECE-R66 rollover test [18]
Mass coupled to the structure
Unrestrained passenger
20 %
2-point belted passenger
70 %
3-point belted passenger
90 %
A second analysis was run by considering all 23 seats of the bus as fully occupied by
passengers restrained with a three-point belt system. The single passenger mass was assumed to
be 68 kg. Figure 3.13 shows that deformation of the bus during rollover was greater without
passenger weight, but the survival space of passenger was still unharmed, as shown in Figure
3.14.
The von Mises stress contours are shown in Figure 3.15. This analysis also shows that
most of the energy was absorbed by the “A” pillars, the last vertical pillars, and the floor beams.
But bending of the “A” pillars and last vertical pillars was more than that in the bus without
passenger weights.
46
Time = 0 sec
Time = 0.1 sec
Time = 0.2 sec
Time = 0.3 sec
Time = 0.4 sec
Time = 0.5 sec
Figure 3.13. Deformation of the bus with passenger weights.
47
Time = 0 sec
Time = 0.5 sec
Figure 3.14. Survival space for the bus with passenger weights.
Figure 3.15. von Mises stress contour for the bus with passenger weights.
48
Force Vs Roof Crush for the bus with the passengers' weights
4.5E+05
4.0E+05
3.5E+05
Force (N)
3.0E+05
2.5E+05
2.0E+05
1.5E+05
1.0E+05
5.0E+04
0.0E+00
0
100
200
300
400
Roof Crush (mm)
Force Vs Roof Crush
Figure 3.16. Force vs. roof crush plot for the bus with passenger weights.
The force vs. roof crush graph is shown in Figure 3.16. Two peaks of force of 4.14E+05
Newton are shown at crushes of 7.61 mm and 139 mm. Integration of this curve gives the energy
vs. roof crush curve as shown in Figure 3.17. This curve is also linear with more slope than that
of roof crush and the bus without passenger weights simulations. Energy of the system was
6.56x107 Nmm for a crush of 416 mm.
Energy Vs Roof crush for the bus with the passengers' weights
7.0E+07
y = 158034x
2
R = 0.994
Energy (Nmm)
6.0E+07
5.0E+07
4.0E+07
3.0E+07
2.0E+07
1.0E+07
0.0E+00
0
50
100
150
200
250
300
350
400
450
Roof Crush (mm)
Roof Energy in ECE R66
Linear (Roof Energy in ECE R66)
Figure 3.17. Energy vs. roof crush plot for the bus with passenger weights.
49
Since the deformation was greater, the energy absorbed by the system (6.5X107 Nmm)
was very high compared to the bus without passenger mass (2X107 Nmm). The trend line slope
of energy vs. roof crush curve is greater than that of the static crush test and rollover without
passenger weights, which signifies that the rate of energy absorption is more when passenger
weight included in the model.
Results show that the presence of passengers on board affects the deformation level of the
structure in a rollover accident. As expected, the deformation rises by increasing the percentage
of the passenger mass coupled to the structure. An additional mass in the vehicle increases the
energy assumed to be absorbed by the structure in order to pass the ECE-R66 test. Consequently,
a structure that fulfils test requirements with no passengers on board may not pass the same test
with passengers on board. This may lead to building stronger structures in order to fulfill the
requirement of no intrusion into the survival space stated in the regulation. But a more rigid
structure may cause higher levels of injury to passengers if an inadequate restraint system is
adopted.
50
CHAPTER 4
MADYMO BUS MODEL DEVELOPMENT AND OCCUPANT KINEMATICS AND
INJURIES
4.1
MADYMO [19]
A Mathematical Dynamic Models (MADYMO) is a worldwide standard software for
occupant safety simulations. It is a software package that allows users to design and optimize the
crash safety performance of vehicles efficiently, quickly, and cost-effectively. It is a generic
multibody and finite element software with a range of specific features for impact simulation.
MADYMO provides analysis in the time domain based on explicit integration techniques.
Increasingly demanding legislative crash test standards, with occupant injury measurements as
the pass/fail criterion, demand that detailed modeling be undertaken at an early stage in the
design to avoid costly late changes. MADYMO allows the designer to develop the multibody
occupant model and carry out predictive occupant simulation, thereby contributing to design
modification in the early stages.
Figure 4.1. MADYMO 3D Structures [19].
51
To create a MADYMO input data file, the user first selects the number of multibody
systems and/or finite element structures to be included in the simulation model. For instance, a
simulation model of the bus rollover can consist of one multibody system for a dummy, one for
the bus model, and one for the ground ellipsoid. For crash dummies, standard databases are
available. Next, for each multibody system the number of bodies and their configurations and
load deformations curves must be specified.
Planes, ellipsoids, cylinders, and facet surfaces can be attached to a body to represent its
shape. These surfaces are also used to model contact with other bodies. The contact surfaces are
of major importance in the description of the interaction of the occupant with the vehicle interior.
The elastic contact forces, including hysteresis, are a function of the penetration of the contact
surfaces. In addition to elastic contact forces, damping and friction can be specified.
The final section of the input file deals with output required from the simulation. The
output generated by MADYMO is specified through a set of output control parameters. A large
number of standard output parameters are available, such as accelerations, forces, torques, and
kinematic data. In addition to standard output quantities, MADYMO offers the possibility to
calculate injury parameters like femur and tibia loads, Head Injury Criterion (HIC), Gadd
Severity Index (GSI), Thoracic Trauma Index (TTI) and Viscous Injury Response (VC). Special
output can be obtained through user-defined output routines. Results of the simulation are stored
in a number of output files, which are accessible by post-processing programs.
Once a given crash situation has been modeled with the MADYMO package, it is
relatively straightforward for users to determine how the scale of potential injuries can be
reduced by introducing special safety features or by changing certain design parameters. This
makes the MADYMO package an extremely useful tool for enhancing vehicle safety.
52
4.1.1 Reference / Inertial Space in MADYMO
A coordinate system (X, Y, and Z) is connected to the reference space, as shown in the
Figure 4.2. The origin and orientation of this reference space coordinate system can be selected
arbitrarily. Usually the positive Z-axis is chosen pointing upwards, opposite to the direction of
gravity. The motion of all systems is described relative to this coordinate system. Contact
surfaces such as planes and ellipsoids, restraint systems, spring-damper elements, and nodes of
finite element structures in MADYMO can be attached to the reference space.
Figure 4.2. Reference space [19].
4.1.2 Multibody Systems in MADYMO
A multibody system is a system of bodies. A kinematic joint can interconnect any pair of
bodies of the same system; kinematic joints cannot connect bodies of different systems. For each
system, one body can be connected to the inertial space by a kinematic joint, or the motion
relative to the inertial space of one body can be prescribed as a function of time. A kinematic
joint restricts the relative motion of the two bodies it connects. In MADYMO, twelve types of
joints are available - spherical joints, translational joints, revolute joints, cylindrical joints, planar
joints, and universal joints - as shown in Figure 4.3.
53
Figure 4.3. Types of joints [19].
The way a specific type of kinematic joint constrains the relative motion of two bodies is
characteristic for that type of joint. The relative motion allowed by a joint is described by
quantities called joint degrees of freedom. Their number depends on the type of joint. The
constraints imposed by a kinematic joint cause a load on the pair of interconnected bodies, the
constraint load. Due to this load the relative motion of the pair of bodies is restricted to a motion
that does not violate the constraints imposed by the kinematic joint. The constraint loads on the
separate bodies are equal but opposite loads. Figure 4.4 shows the constraint load in a spherical
joint. Constraint loads can be used to assess the strength of the joint.
54
Fi
j
i
Fj
Figure 4.4. Constrained load in a spherical joint [19].
4.1.3 Numerical Integration Methods in MADYMO [19]
The equations of motions are solved numerically. IN MADYMO three methods are
available:
•
Modified Euler method with a fixed time step.
•
Runge-Kutta method with fixed time step.
•
Runge-Kutta Merson method with variable time step.
These are one-step explicit methods, which mean the solution at a time point tn+1 can be
written explicitly in terms of the solution at the preceding time point tn. The Runge-Kutta Merson
method cannot be used for applications with finite element models because these do not allow
the repeated time integration over the same time interval, which occurs when the step size is
reduced. For a given time step, the modified Euler method is less accurate than the Runge-Kutta
methods. In order to obtain the same accuracy, the time step in the modified Euler method should
be one-eighth of the Runge-Kutta method and one-sixteenth of the Runge-Kutta Merson method.
When stability determines the step size, the modified Euler method is more stable than the
Runge-Kutta method. When finite element model is supported on a rigid body, the Runge-Kutta
method may become unstable.
55
4.1.4 Dummy Database [20]
To simulate a human being in crash scenario MADYMO dummy models are used. These
models are well validated using the Anthropomorphic Test Dummy (ATD) database. Three
MADYMO model types are available. These model types are:
•
Ellipsoid models.
•
Facet models.
•
Finite Element models.
Ellipsoid models are those that are based fully on MADYMO’s rigid-body modeling
features. Their geometry is described by means of ellipsoids, cylinders, and planes. They are the
most CPU-time efficient type of models. Therefore, they are particularly suitable for concept,
optimization, and extensive parameter sensitivity studies. It is recommended for all models to
use the Euler time-integration method. For the ellipsoid and facet models, the recommended
maximum multibody timesteps lie in the order of 1.0e-4 s to 1.0e-5 s.
A wide range of MADYMO ATD models are available. The standard models of the adult
and child Hybrid III dummies are the 5th percentile female, the 50th percentile male, the 95th
percentile male, 6-year-old child and 3-year-old child Hybrid III dummy models. The size and
weight of the Hybrid III 50th percentile male ATD represents an “average” of the American adult
male population. In order to cover the extremes of this population, two other versions of the
Hybrid III have been developed, the 5th percentile small female and the 95th percentile large
male.
Figure 4.5 shows the dummies used for this research. The Hybrid III 50th percentile
dummy is the most widely applied dummy for the evaluation of automotive safety restraint
systems in frontal crash testing.
56
Hybrid III 50th percentile
EuroSID-1
Standing Hybrid III 50th
percentile
Figure 4.5. Ellipsoidal dummy models [20].
The EuroSID-1 side impact dummy has been designed to represent a 50th percentile adult
male subject during side-impact crash conditions, and is used in European and Japanese side
impact test procedures. The EuroSID is a lateral impact dummy, which is specified in the
96/27/EG directive for the protection of motor vehicle occupants.
The standard Hybrid III 50th percentile dummy has been developed for seated automotive
applications. The standing Hybrid III contains some adapted parts and thereby has a wider range
of application including standing and testing pedestrian accidents.
4.2
Injury Parameters
The field of injury biomechanics deals with the effect of mechanical loads, in particular
impact loads, on the human body. Due to this mechanical load, a body region will experience
mechanical or physiological changes. These changes are called biomechanical responses. An
injury will occur if the biomechanical response is of such a nature that the biological system
57
deforms beyond a recoverable limit, resulting in damage to anatomical structures and alteration
in normal function. The mechanism involved is called the injury mechanism, and the severity of
the resulting injury is called as the injury severity. An injury criterion is a physical parameter or a
function of several physical parameters, which correlates with the injury severity of the body
region under consideration. There are many proposals for ranking and quantifying injuries.
Anatomical scales describe the injury in terms of its anatomical location, type of injury, and
relative severity. The most accepted anatomical scale worldwide is the Abbreviated Injury Scale
(AIS). The AIS distinguishes the following levels of injury:
0 - No injury
1 - Minor
2 - Moderate
3 - Serious
4 - Severe
5 - Critical
6 - Maximum Injury (cannot be survived)
9 - Unknown.
The AIS is a so-called “threat to life” ranking. The numerical values have no significance
other than to designate order. Many injury criteria are based on acceleration forces,
displacements, and velocities. These quantities can be obtained with the standard features offered
by MADYMO. These qualities must be requested with standard output options. Some injury
criteria need mathematical evaluation of a time-history signal. MADYMO offers the possibility
to perform some of these injury parameter calculations.
calculations are available:
58
The following injury parameter
Gadd Severity Index (GSI)
Head Injury Criterion (HIC)
Neck Injury Criteria (FNIC)
3 ms Criterion (3MS)
Thoracic Trauma Index (TTI)
4.3
General Injury Mechanisms in Crash Scenarios [19]
In motor vehicle crashes, three types of collision forces can cause injuries. The first is
direct impact due to the collision between the motor vehicle and another object. The second is
any collision that may occur between the intruded parts of the vehicle and the passenger body.
The third involves the violent collision of body organs within the body frame. The last two
forces increase the importance of consistent use of safety restraints in motor vehicles.
Injuries to head are divided into skull injuries, brain injuries, and scalp injuries. Scalp
injuries are quite common in accidents but are considered to be of minor importance. In general
terms, it is convenient to view head injuries as comprising three distinct varieties.
Skull Fracture
Skull fracture can occur with or without damage to the brain but is itself not an important
cause of neurological death or disability. Skull fractures can be classified in many ways and are
considered open fractures if the dura is torn, or closed fractures if it is not. More conveniently,
fractures are categorized into those of the base. Injuries to the neural substance of the brain are
primarily cause of neurological dysfunction and can readily be divided into two categories.
Focal Brain Injuries
Focal brain injuries are those in which a lesion large enough to be visualized with the
naked eye has occurred and comprise contusion, subdural hematoma, epidural hematoma, and
59
intracerebral hematoma. These injuries comprise approximately 50 percent of all head injury
patients admitted to the hospital and are responsible for two-thirds of head injury deaths.
Diffuse Brain Injuries
Diffuse brain injuries, on the other hand, are associated with more widespread or global
disruption of neurological function and are not usually associated with macroscopically visible
brain lesions. Rather, they cause widespread disruption of either the function or structure of the
brain. Since diffuse brain injuries, for the most part, are not associated with visible microscopic
lesions, they have historically been lumped together to mean all injuries not associated with focal
lesion.
Some injury criteria are as follows:
Head Injury Criterion (HIC)
The head injury criterion was used to asses head injury. Values greater than 1,000
indicate that there is likelihood of serious head injury. The HIC is calculated when the head of
the occupant comes in hard contact with another rigid object during a frontal (contact) impact (9
pg 7 yanu).
It is evaluated as
2.5

 1 t2
HIC = max 
a
(
t
)
dt
 (t 2 − t 1 )
∫
t
t
−

 2 2 t1
Where:
t1, t2 = arbitrary instants of time when the head experiences acceleration or deceleration
a(t) = resultant linear acceleration at the center of gravity of the head
60
Neck Injury Criterion
The neck injury occurs due to excessive compressive or tensile forces along the neck axis
or excessive shear forces acting perpendicular to the neck axis. The duration of the load acting
on the neck also affects the level of injury. The neck injury criteria formulated by Mertz and
Patrick was used.
The criteria for compressive loading were as follows:
F > 900 – 20t
t< 30 ms
F > 250 lb (f)
t> 30 ms
The criteria for tensile loading were as follows:
F> 740 – 2.6 t
t < 34 ms
F> 1888 - 36.4 t
34ms < t > 45 ms
F> 250 lb (f)
t > 45 ms
Neck injuries can also occur due to excessive moments. The limiting values of 504 in-lb and
1,680 in-lb were set for moments in extension and flexion respectively (SI equivalent of 1 lb-f is
4.484 N and in 1 in-lbf is 0.1130 N-m).
Thoracic Trauma Index (TTI)
The thorax consists of vital organs like the heart, chest which are vulnerable to rapid
changes in the acceleration pulse. It has been shown in cadaver tests that the peak lateral
acceleration on the struck side of the rib and lower thoracic spine greatly influences injury to the
thorax. The TTI for side impact has been defined as
TTI (d) = 0.5 (RIBg + T12g)
Where:
RIBg = Peak acceleration of the 4th and the 8th rib
61
T12 g = Peak absolute value of the 12th Thoracic vertebrae in lateral direction (G)
TTI (d) = Thoracic Trauma Index for the side impact dummy
Viscous Injury Response (VC)
Vital organs of the chest, heart, and blood vessel are built of soft tissues. Therefore, an
understanding of the mechanism of soft tissue is critical to the safety of the occupant. It has been
seen from experiments that soft tissue injury is induced by rate-sensitive deformation of the
chest. In some cases, pulmonary and cardiac injuries occurred during conditions of high-impact
velocities with very little chest deformations. This is also supported by injuries caused by fatal
impacts.
The viscous criterion is the maximum value of a time function formed by the product of
the velocity of deformation (V) and the instantaneous compression function (C). It is represented
by
 dD(t ) D (t ) 
V ∗ C = max 
×

To 
 dt
Where:
D (t) = deflection of the chest
T0 = initial torso thickness
A value of 1.5 m/s was used as a reference value for the human tolerance for the chest
and a value of 2 m/s for the abdomen of SID in a lateral collision.
4.4
MADYMO Bus Model Development
To develop the bus model in MADYMO, only the passenger area was considered. Since
the bus was turned over on the door side, only its door side was modeled with details like
windows, door, and window pillars. For the other side of the bus, only a single ellipsoid was
62
drawn. The wheels were not modeled. The ground and tilting table were modeled for viewing
purposes only because analysis was run until the bus contacted the ground. The height difference
between the tilting table and ground was kept at 800 mm, according to the ECE-R66 regulation.
Figure 4.6 shows this MADYMO model, which was made up of ellipsoids and planes only.
Figure 4.6. MADYMO model of the bus.
It is important to model the bus interior to study its interaction with the dummies. Bus
interiors can greatly influence dummy kinematics and injuries. Hence, interior components, such
as stanchions, seats, and modesty panels, were also modeled. Figure 4.7 shows the bus interior
parts.
There are three separate systems defined for the bus model, dummy, and ground. The
CHARACTERISTIC.CONTACT card was used to assign the appropriate force-deflection
properties to these parts. The CONTACT.MB_MB card was used to define the contact between
parts. Gravity was applied to all systems by using the card LOAD.SYSTEM_ACC.
63
Figure 4.7. Bus interior modeled in MADYMO.
There was a joint (JOINT.FREE) between the bus system and the reference space. This
joint was moved to position it with the bus tilting axis. The MOTION.JOINT_ACC card was
used to give the translational and rotational accelerations obtained from the ADAMS simulations
to this bus-reference space joint. This rotated the bus system according to the ADAMS input.
Status of the JOINT.FREE joint between the ground and the reference space was made LOCK to
constrain all motions of the ground.
4.5
Contact Properties for MADYMO Model
One of the important factors for the MADYMO simulation is to define the contact
characteristics between the systems. MADYMO calculates these contacts according to the user
input of force deflection characteristics. To study the interactions between the dummy and the
bus interior, it is important to define suitable contact between them. To obtain these Forcedeflection curves, FE bus model was used. Analysis was run with a force of 15,000 N applied on
64
certain bus locations for 50 ms, and then deflections were plotted. Four main locations were
selected to apply the forces: window glass, window pillar, roof, and stanchions. From this
analysis force-deflection curves were plotted, as shown in Figure 4.8, and used in MADYMO
model. A suitable force-deflection characteristic obtained from earlier studies was given to the
seats to obtain a validated response of the setup.
Contact Characteristics for Roof Structure
16000
16000
14000
14000
12000
12000
10000
10000
Load (N )
Load (N )
Contact Characteristics for Window Pillars
8000
6000
8000
6000
4000
4000
2000
2000
0
0
0
0.02
0.04
0.06
0.08
0.1
0
0.12
0.01
0.02
Deformation (m)
0.04
0.05
0.06
Contact Characteristics for Roof Panels
Window Pillar Load Deformation
Contact Characteristic for Window & Door Glasses
Contact Characteristic for Stanchions
16000
5000
14000
4500
4000
12000
3500
10000
Load (N )
Load (N)
0.03
Deformation (m)
8000
6000
3000
2500
2000
1500
4000
1000
2000
500
0
0
0
50
100
150
200
250
300
350
400
0
450
0.1
0.2
0.3
0.4
0.5
Deformation (m)
Deformation (m)
Contact Characteristic for Stanchions
Contact Characteristic for Window & Door Glasses
Figure 4.8. Contact characteristics for MADYMO model.
4.6
Dummy Selection
The MADYMO dummy database provides with validated dummy models to represent
their counterparts used in full-scale or sled testing. These dummy models, as described earlier,
are available in ellipsoidal, facet, and FE models. Dummies were selected according to their
65
positions in the bus. For MADYMO analysis, three sitting positions and one standing position
were chosen, as shown in Figure 4.9. Of these, one seat position is side-facing seat and the other
two are front-facing at upper and lower platforms.
Figure 4.9. Seat positions selected for dummies.
For the side-facing seat, a Hybrid III 50th percentile dummy was selected, while EuroSID
dummies were used for the front-facing seat positions. These lateral-impact SID dummies were
chosen because 97 percent of rollover accidents that happen in the field occur over the vehicle’s
longitudinal axis. Only 3 percent of rollover accidents occur over the vehicle’s transverse axis.
These are also described as end-over-end cases [21]. A standing Hybrid III 50th percentile
dummy was used for the passenger standing on the lower platform of the bus.
66
Figure 4.10. Injuries in roll/ no-roll events [21].
There are higher chances of head injuries from rollover accidents as listed in Figure 4.10.
The test dummies developed for frontal impact react very stiffly under lateral loads, particularly
the neck-head areas. The neck-head area of the EuroSID dummies consists of a construction
which is more flexible. Therefore, these dummies do not show stiffness like other
anthropometric test dummies. The standard simulation dummy model maps only translational
load directions. The rotational movement which occurs during a rollover, is not considered. A
dummy simulation model, which takes such a behavior into account, is not available currently
[21]. For the standing position, a Hybrid III standing dummy was used.
67
4.7.
MADYMO Analysis Results
MADYMO shows the kinematics and injuries sustained by the occupant during the crash
scenario. The injury criterion is widely used in automobile safety to check the probability and
severity of injuries. The various commonly used injury criterion are described in the first chapter.
The MADYMO model presented in this thesis is not validated with actual laboratory tests. But
this model is useful to predict the occupant kinematics and injuries sustained during bus rollover.
4.7.1. Hybrid III 50th Percentile Dummy at Side-Facing Seat
This dummy was placed on the side-facing the lower platform seat opposite the rollover
side. The dummy kinematics is shown in Figure 4.11. Since the dummy was not restrained, it
was thrown out of its seat and took flight in space. Consequently it impacted its head on the side
panel, which increased its HIC injury value. Accelerations, forces, and injuries sustained by the
dummy during the rollover are shown in Figures 4.12 and 4.13. Since this model is not validated,
the analysis gives only approximations, not exact results. The HIC value was 889.794, which is
more than the tolerable injury limit of 700. The maximum neck-up force in the negative Zdirection, i.e., neck peak compression force, was 9,243.46 N, which much higher than the
tolerable injury limit of 4,000 N. The neck injury values of compression extension and
compression flexion were 1.416 and 2.211, which are more than the safe limit of 1. This
simulation shows that rollover will cause severe head and neck injuries to the occupant sitting in
the side-facing seat on the rollover side.
68
Time = 0 sec
Time = 0.3 sec
Time = 0.6 sec
Time = 0.9 sec
Time = 1.2 sec
Time = 1.5 sec
Time = 1.725 sec
Figure 4.11. Kinematics of Hybrid III dummy at side-facing seat position.
69
Figure 4.12. Accelerations and forces of side-facing Hybrid III dummy.
70
Figure 4.13. Neck and chest injury results of side-facing Hybrid III dummy.
4.7.2. EuroSID Dummy on Front-Facing Lower-Platform Seat
On the front-facing seat at the lower platform, the lateral impact dummy EuroSID was
placed. Here the bus rollover threw the dummy out of its seat, causing it to impact its head on the
side panels, as shown in Figure 4.14. Figures 4.15, 4.16, and 4.17 show the forces, accelerations,
and injuries sustained by the dummy during rollover. However, the HIC value was 319.34, which
is much lower than the tolerable injury limit of 700. The neck peak compression of 3,646.21 N
also was less than 4,000 N. But neck-low moments about Y-axis (Max My) is 72.09 Nm, which
is more than the tolerable injury limit of 57 Nm. Thus, the occupant at this position may have
neck injuries.
71
Time = 0 sec
Time = 0.3 sec
Time = 0.6 sec
Time = 0.9 sec
Time = 1.2 sec
Time = 1.5 sec
Time = 1.725 sec
Figure 4.14. Kinematics of EuroSID dummy positioned at front-facing lower-platform seat.
72
Figure 4.15. Accelerations and forces of EuroSID dummy positioned at front-facing lowerplatform seat.
73
Figure 4.16. Neck and rib injury results of EuroSID dummy positioned at front-facing lowerplatform seat.
74
Figure 4.17. Lower rib deflection of EuroSID dummy positioned at front-facing lower-platform
seat.
4.7.3. EuroSID Dummy in Front-Facing Upper-Platform Seat
At this position, the bus rollover also threw the dummy out of its seat, as shown in Figure
4.18. Since this seat position is on the upper platform, the height difference between the dummy
head and the bus roof is less. Due to this small distance, the dummy first struck its head on the
roof and then it impacted on the side panel. When the dummy struck the side panel, its neck
twisted generating considerable neck moment. Figures 4.19, 4.20, and 4.21 show the forces,
accelerations, and injuries sustained by the dummy during rollover. This simulation gave an HIC
value of 1,356.21, which is much higher than the tolerable limit of 700. It also shows the chest 3
ms value of 69.5717 g’s more than that of the tolerable limit of 60 g’s. The neck extension was
76.0378 Nm, exceeding the safe limit of 57 Nm. The neck peak compression was 3,991.35,
which is very close to the safe limit of 4,000 N. All other forces and moments were within the
safe limits. Thus, at this seat position, the occupant may sustain severe injuries to the head, neck,
and chest.
75
Time = 0 sec
Time = 0.3 sec
Time = 0.6 sec
Time = 0.9 sec
Time = 1.2 sec
Time = 1.5 sec
Time = 1.725 sec
Figure 4.18. Kinematics of EuroSID dummy positioned at front-facing upper-platform seat.
76
Figure 4.19. Accelerations and forces of EuroSID dummy positioned at front-facing upperplatform seat.
77
Figure 4.20. Neck and rib injury results of EuroSID dummy positioned at front-facing upperplatform seat.
78
Figure 4.21. Lower rib deflection of EuroSID dummy positioned at front-facing upper-platform
seat.
4.7.4. Standing Hybrid III 50th Percentile Dummy on Lower-Platform
Since this model is for a transit bus, some of the passengers may travel standing.
Therefore it is important to consider a standing dummy for simulations in order to study the
kinematics and injuries of the standing passenger during bus rollover. The standing dummy was
positioned on the lower platform in front of the door, because this is the place where passengers
are most likely to stand. Figure 4.22 shows the dummy kinematics. During bus rollover, the
dummy falls on the nearest seat and then slides down. The dummy impacts the side panels with
its legs; hence, there are no threatening forces acting on the head or neck, as in the other dummy
positions. Figures 4.23 and 4.24 show the forces, accelerations, and injuries sustained by the
dummy during rollover. The HIC is 450.407, and all NIJ values are less than 1. Thus, HIC and
neck forces are below the tolerable injury limits. All other forces and moments are also within
safety limits. Of all the positions, only the standing dummy does not have any severe injuries.
However, if its position changed so that it struck its head on the seat’s handle bar or stanchions,
then it may have higher injury values.
79
Time = 0 sec
Time = 0.3 sec
Time = 0.6 sec
Time = 0.9 sec
Time = 1.2 sec
Time = 1.5 sec
Time = 1.725 sec
Figure 4.22. Kinematics of Hybrid III standing dummy at lower-platform.
80
Figure 4.23. Accelerations and forces of Hybrid III standing dummy at lower-platform.
81
Figure 4.24. Neck and chest injury results of Hybrid III standing dummy at lower-platform.
4.8
Comparison of Injuries for Different Dummy Positions
Table 4.1 shows the comparison of injuries sustained by all four dummies at different
positions with tolerable injury limits. The values highlighted in yellow show that they exceed the
tolerable injury limits. The dummy in the upper-platform front-facing seat sustained higher HIC
values of 1356.21 and chest 3 ms of 69.57 compared to the other dummies. With the exception of
the standing dummy, all dummies showed severe neck injuries. The dummy at the side-facing
seat showed severe neck compression of 9,243.46 N. Dummies in the front-facing seats showed
severe neck extension values of 72.09 N and 76.04 N positioned at the lower platform and upper
82
platform, respectively. Only the dummy in the standing position showed less probability of
injuries.
Figure 4.25 shows the neck injuries with corresponding forces and moments plotted on Y
and X axes, respectively. The quadrilateral area represents the safe region within which all
injuries were less than the tolerable injury limits. For the dummy in the lower-platform sidefacing seat, two values from the III and IV quadrants lie outside the safe region, which indicates
that the dummy had very high compression-extension and compression-flexion values. The
dummy in the lower-platform front-facing seat had higher tension-extension and compressionextension injury values. For the upper-platform front-facing seat-positioned dummy, only the
tension-flexion value was in the safe region and all other injury values were outside the safe
region. The standing position dummy had all injury values in a safe region.
83
Table 4.1
Comparison of injury parameters for four different dummy positions
Injury
Parameters
Hybrid III 50%
dummy at
Side-facing seat
position
EuroSID at
Front-facing
lower-platform
position
EuroSID at
Front-facing
upper-platform
position
Hybrid III 50%
standing
dummy at
lower-platform
Tolerable
Injury
Limits
(FMVSS208 Injury
Criterion)
HIC 15
889.79
319.34
1356.21
450.41
700
Chest 3 ms
(g’s)
Femur Force Right
(N)
Femur Force Left
(N)
Chest Deflection
(mm)
Rib Deflection
(mm)
Up
Mid
Low
31.74
30.78
69.57
41.16
60
1307.85
1028.59
1350.56
2919.78
10000
2751.56
576.25
1943.45
1520.67
10000
2
-
-
6
63
-
9
10
11
1
8
4
-
-
Neck Peak Tension
(N)
812.21
578.72
1433.06
611.47
4170
Neck Peak
Compression (N)
9243.46
3646.21
3991.35
1257.31
4000
Neck Flexion
(Nm)
11.00
17.14
81.59
22.36
190
Neck Extension
(Nm)
9.15
72.09
76.04
19.67
57
Neck Shear
(N)
268.12
710.34
749.08
622.47
3100
0.6
0.22
1.42
2.21
-
-
0.19
0.07
0.18
0.22
1
1
1
1
NIJ Values
NTE
NTF
NCE
NCF
84
I – Tension-Flexion
III – Compression-Extension
II – Tension-Extension
IV – Compression-Flexion
Figure 4.25. Neck injuries for different seat positions.
4.9
Dummy Interactions
Until now, analyses were run with only a single dummy. It is important to consider the
interactions between the dummies, because interactions may affect the kinematics and injuries
sustained by the dummies. Table 4.2 shows a comparison of injury parameters for the dummy
interactions. Figure 4.26 shows the interactions between dummies positioned in the side-facing
seats. One dummy was positioned opposite the rollover side, as in the previous case, whereas
two dummies were positioned on the rollover side, i.e., door side. When the dummy opposite the
rollover side impacted the side panels, the two dummies opposite to it were colliding with it.
This collision slowed down the dummy before impact with the side panels, which in turn reduced
85
the HIC value of the dummy to 481.09, which is less than the tolerable injury limit. Also neck
peak compression and neck injuries NCE and NCF reduced to values of 6163.85 N, 0.38, and
1.13, respectively. This indicates that the presence of other dummies reduced the injury values of
the dummy positioned at the side-facing seat opposite the rollover side.
Figure 4.27 shows the interactions between the dummies positioned at the front-facing
lower-platform seats. It is observed that for the dummy placed at the inner side, i.e., window
side, neck extension and chest 3 ms increased to values of 120.05 and 61.41 g’s, respectively,
which are more than the tolerable injury limits. Thus, in this case, the presence of another
dummy increased the neck injury values and chest acceleration.
Figure 4.28 shows the interactions between the dummies positioned at front-facing upperplatform seats. Due to the presence of the other dummy beside it, the HIC value decreased to
473.11, which is less than tolerable HIC limit of 700. But injury values of chest 3 ms, neck
compression, and neck extension increased to 81.39 g’s, 4097.34 N, and 119.39 Nm,
respectively, which are more than tolerable limits. Hence, although HIC is reduced, chest
acceleration and neck injury values increased severely.
86
Table 4.2
Comparison of injury parameters for dummy interactions
Tolerable
Injury
Limits
(FMVSS-208
Injury
Criterion)
Injury
Parameters
Hybrid III 50%
dummy at
Side facing seat
position
EuroSID at
Front facing
lower platform
position
HIC 15
481.09
301.62
473.11
700
Chest 3 ms
(g’s)
Femur Force Right
(N)
Femur Force Left
(N)
Chest Deflection
(mm)
Rib Deflection
(mm)
Up
Mid
Low
25.57
61.41
81.39
60
1160.52
1501.07
1480.49
10000
2649.13
1406.05
3084.12
10000
3
-
-
63
-
18
24
37
24
8
7
-
Neck Peak Tension
(N)
513.89
1362.53
1235.03
4170
Neck Peak
Compression (N)
6163.85
2799.81
4097.34
4000
Neck Flexion
(Nm)
39.26
144.714
48.04
190
Neck Extension
(Nm)
60.10
120.05
119.39
57
Neck Shear
(N)
1485.43
2200.42
1239.23
3100
0.35
0.12
0.38
1.13
-
-
1
1
1
1
NIJ Values
NTE
NTF
NCE
NCF
87
EuroSID at
Front facing
upper platform
position
Time = 0 sec
Time = 0.3 sec
Time = 0.6 sec
Time = 0.9 sec
Time = 1.2 sec
Time = 1.5 sec
Time = 1.725 sec
Figure 4.26. Interactions between dummies positioned at side-facing seats.
88
Time = 0.3 sec
Time = 0 sec
Time = 0.6 sec
Time = 0.9 sec
Time = 1.2 sec
Time = 1.5 sec
Time = 1.725 sec
Figure 4.27. Interactions between dummies positioned at front-facing lower-platform seats.
89
Time = 0 sec
Time = 0.3 sec
Time = 0.6 sec
Time = 0.9 sec
Time = 1.2 sec
Time = 1.5 sec
Time = 1.725 sec
Figure 4.28. Interactions between dummies positioned at front-facing upper platform seats.
90
4.10
Addition of Handle Bar to Front-Facing Seats
Handle bars were attached to the front-facing seats to check their effect on dummy
kinematics and injuries. Figure 4.29 shows the kinematic of the dummies positioned at the frontfacing lower-platform seats with handle bars. The handle bar obstructed the dummy on the aisle
side when it took flight during the bus rollover. Hence, its flight height was reduced. But the
dummy on the window side suffered no effect on its kinematics. Chest 3 ms and neck extension
injury values obtained for the dummy on the window side were 110.73 g’s and 145.24 Nm,
respectively, which are more than the tolerable injury limits. The addition of a handle bar
increased the injury values of the neck extension and chest acceleration slightly more than in the
other cases. Thus, the presence of a handle bar did not have any prominent effect on kinematics
or injuries.
Figure 4.30 shows the kinematics of dummies positioned at the front-facing upperplatform seats. It is observed that dummies took flight without touching the handle bar. Thus, on
the upper platform as well, the presence of the handle bar did not have any effect on dummy
kinematics.
91
Time = 0 sec
Time = 0.3 sec
Time = 0.6 sec
Time = 0.9 sec
Time = 1.2 sec
Time = 1.5 sec
Time = 1.725 sec
Figure 4.29. Kinematics of the dummies positioned at the front-facing lower-platform seat with
handle bar.
92
Time = 0 sec
Time = 0.3 sec
Time = 0.6 sec
Time = 0.9 sec
Time = 1.2 sec
Time = 1.5 sec
Time = 1.725 sec
Figure 4.30. Kinematics of the dummies positioned at the front-facing upper-platform seat with
handle bar.
93
CHAPTER 5
CONCLUSIONS AND RECOMMENDATION
5.1
Conclusions
There were three main objectives of this research: (a) to study the roof crush analysis
according to bus procurement guidelines, (b) to study the rollover carried out according to the
ECE-R66 regulation with and without passengers’ weights, and (c) to study dummy kinematics
and injuries in the MADYMO rollover simulation.
In the case of rollover, three parameters define the worst case scenario: structural
strength, reference energy, and residual space. Table 5.1 shows the results of roof crush and
rollover simulation carried out in LS-DYNA. Roof crush and the energy absorbed are more in
the rollover analysis than in the roof crush analysis. But in the rollover analysis, the presence of
passengers’ weights increased the roof crush and energy absorbed by almost 40 % and 69 %
respectively.
Table 5.1
Roof crush and rollover analysis results
Test
Roof Crush (mm)
Energy Observed (Nmm)
Roof crush
111
1.50x107
Rollover without passengers’ weight
250
2.02x107
Rollover with passengers’ weight
416
6.56x107
This suggests that the bus without passengers’ weights passing the ECE-R66 test may not
pass the same test if the passengers’ weights are included. In both cases of the rollover analysis,
there was no intrusion in the passenger’s survival space. Thus, the FE bus model was stiff
94
enough to protect the survival space from any intrusion. It was also seen that the “A” pillars and
the last vertical pillars of the bus play an important role in preventing roof crush. They absorb the
maximum amount of energy. ADAMS analysis results showed that the presence of passengers
increased the angular velocity reached before the impact by almost 6 percent. In ADAMS
analysis, bus was leaving the surface of the tilting table at an angle of around 57º, which is more
than 35º where the bus model is stable.
Although the MADYMO model of the bus was not validated, from the study of various
results of MADYMO analyses, it can be predicted that bus rollover may cause severe head and
neck injuries to the occupants. Occupants in side-facing and front-facing upper-platform seats,
both opposite the rollover side, sustain the severest injuries. An occupant standing on the lower
platform has a low probability of getting injured since it impacts on the seat and then simply
slides down. A study of the dummy interactions shows that presence of other occupants has an
effect on the kinematics and injuries.
5.2
Recommendations
The following recommendations can be made:
1) The FE model developed was very detailed and has limitations using the
DEFORMABLE_TO_RIGID card and to run the implicit analysis. A model containing only the
superstructure of the bus with a very fine meshed roof could be developed to obtain more
accurate results. This would also help to avoid all the limitations of the model, and the full
rollover would be feasible in LS-DYNA instead of using the ADAMS view.
2) In MADYMO analysis, seat belts could be used to avoid the free movement of the
dummies inside the bus during rollover.
95
3) In this research, only 50th percentile dummies were used. Other dummies could be
studied such as the 95th percentile dummy, 5th percentile female dummy, or child dummy.
4) Studies have shown that the most common body parts injured in a rollover, when no
ejection occurs, are the head, the neck, and the shoulder. Currently side-impact dummies are not
ready to assess the injuries suffered by the occupants of buses during rollover. Simulations
showed that during rollover, the neck is subjected to combined loads namely lateral bending,
lateral shear, and torsion. Today, there are no injury criteria that take into account these types of
loads [22]. A dummy should be developed for rollover crash scenarios.
5) The bus driver also plays a major role in the rollover accident. Seatbelts are provided
for the bus driver. Therefore, driver kinematics with a restraint system could be studied.
96
REFERENCES
97
LIST OF REFERENCES
[1]
Traffic Safety Facts 2004.
[2]
“Initiatives to Address the Mitigation of Vehicle Rollover,” NHTSA, June 2003.
[3]
Report # FTA-002, “Mass Transit Crashworthiness Statistical Data Analysis,” prepared
by National Institute of Aviation Research, 12 Dec 2005.
[4]
Martinez L, Aparicio F, Garcia A, Paez J, Ferichola G, “Improving occupant safety in
coach rollover,” INSIA, Polytechnic University of Madrid, Spain, 2003.
[5]
Meghan Elizabeth Henty, “Virtual Simulation of a Pickup Truck Rollover Test using the
Nonlinear Finite Element Code PAM-CRASH,” Master Thesis, The Pennsylvania State
University, May 2003.
[6]
M Mao, E.C. Chirwa, W. Wang, “Assessment of vehicle roof crush test protocols using
FE models: inverted drop tests versus updated FMVSS No. 216,” The University of
Bolton, UK, 2006.
[7]
Standard Bus Procurement Guidelines Commercial Terms and Conditions, APTA, 31
March 1997.
[8]
ECE Regulation No. 66, Agreement, E/ECE/TRANS/505, Rev. 1/Add. 65/Rev.1, United
Nations, 22 Feb 2006.
[9]
Elitok K, Dr Guler M A, Bayram B, Stelzmann U, “An investigation on the rollover
crashworthiness of an intercity coach, influence of seat structure and passenger weight”,
9th International LS-DYNA Users Conference, 2006, Dearborn, MI, USA.
[10]
Belingardi G, Chiandussi G, Gaviglio I, and Giorda A, “Multi-point optimization
methodologies for enhancement of coach passive safety in rollover accidents,” VIII
International Conference on Computational Plasticity, Barcelona, 2005.
[11]
“The Problem of High-Decker Coaches in the Standard Rollover Test” Presented by
Hungary, Informal document # 6, 83rd GRSG 15-18 Oct 2002.
[12]
Matyas Matolcsy, “Development possibilities in relation to ECE Regulation 66 (Bus
Rollover Protection)”, Hungary Paper No. 98-S4_O-04, IKARUS Vehicle Manufacturing
Company, Sixteenth International Technical Conference on the Enhanced Safety of
Vehicles, Windsor, Canada, 1998.
[13]
Altair HyperMesh 7.0 Tutorials, Altair Engineering Inc., 2004.
98
[14]
LS-DYNA keyword user’s manual version 970, Livermore Software Technology
Corporation, April 2003.
[15]
Anon., Final Report Enhanced Coach and Bus Occupant Safety (ECBOS), European
Commission 5th Framework, Project Number 1999-RD.1130.
[16]
Kazuhiro Fukamachi, Shuji Miyamoto, Hiroshi Nagasawa, Shinji Uchino, “Study of
Crash Worthiness of Super High-Decker Large-sized Bus by CAE approach,” Seoul 2000
FISITA World Automotive Congress, Seoul, Korea, June 2000.
[17]
BID Documents, Delhi Transport Corporation, Nov 2005.
[18]
G Belingardi, P Martella, L Peroni, “Coach Passenger Injury Risk during Rollover:
Influence of the Seat and the Restraint System,” Paper Number 05-0439, Politecnico di
Torino, Italy.
[19]
MADYMO Theory Manual Ver. 6.3, TNO, Dec 2005.
[20]
MADYMO Model Manual Ver. 6.3, TNO, Dec 2005.
[21]
Linstromberg M, Scholpp G, Scherf O, “Test and Simulation Tools in a Rollover
Protection Development Process,” Siemens restraint Systems GmbH, ESV Conference,
Washington, USA, June 2005.
[22]
“Results and Conclusions - Enhanced Coach and Bus Occupant Safety,” European
Commission, 5th Framework, Project Nº: 1999-RD.11130, Aug 2003.
99
APPENDIX
100
APPENDIX
Accelerations and Velocities of ADAMS Rollover Simulations
Velocities Obtained in ADAMS View Simulation for Bus Rollover without Passenger Weights
Translational Velocity in X-axis
0.08
400
0.06
200
Transl Velocity - X (mm/sec)
Ang Velocity - X (deg/sec)
Angular Velocity in X-axis
0.04
0.02
0.00
-0.02
0
10
20
30
40
50
60
70
-0.04
0
-200
0
10
20
30
70
60
70
60
70
-400
-600
-800
Time (sec)
Time (sec)
Translational Velocity in X-axis
Angular Velocity in X-axis
Translational Velocity in Y-axis
Angular Velocity in Y-axis
0.03
2500
0.02
2000
Transl. Velocity - Y (mm/sec)
Ang Velocity - Y (deg/sec)
60
-1200
-0.08
0.01
0.00
0
10
20
30
40
50
60
70
-0.01
-0.02
-0.03
1500
1000
500
0
-500
0
10
20
30
40
50
-1000
-1500
-0.04
Time (sec)
Time (sec)
Translational Velocity in Y-axis
Angular Velocity in Y-axis
Translational Velocity in Z-axis
Angular Velocity in Z-axis
20.00
7
15.00
6
Transl. Velocity - Z (mm/sec)
Ang Velocity - Z (deg/sec)
50
-1000
-0.06
10.00
5.00
0.00
-5.00
40
0
10
20
30
40
50
60
70
-10.00
-15.00
-20.00
5
4
3
2
1
0
0
-25.00
10
20
30
40
50
Time (sec)
Time (sec)
Translational Velocity in Z-axis
Angular Velocity in Z-axis
101
APPENDIX (continued)
Accelerations Obtained in ADAMAS View Simulation for Bus Rollover without Passenger
Weights
Translational Acceleration in X-axis
10
50000
8
40000
Transl Accln - X (mm/sec2)
Ang Accln - X (deg/s2)
Angular Acceleration in X-axis
6
4
2
0
-2
0
10
20
30
40
50
60
70
-4
-6
30000
20000
10000
0
0
10
20
30
60
70
60
70
60
70
Time (sec)
Angular Accln in X-axis
Translational Acceleration in X-axis
Translational Acceleration in Y-axis
Angular Acceleration in Y-axis
50000
1.50
0
Transl accln - Y (mm/s2)
1.00
Ang Accln - Y (deg/s2)
50
-20000
Time (sec)
0.50
0.00
0
10
20
30
40
50
60
70
-0.50
-1.00
-50000
0
10
20
30
40
50
-100000
-150000
-200000
-250000
-300000
-1.50
-350000
Time (sec)
Time (sec)
Angular Acceleration in Y-axis
Translational Acceleration in Y-axis
Translational Acceleration in Z-axis
Angular Acceleration in Z-axis
100
3.00
2.50
0
10
20
30
40
50
60
70
Transl Accln - Z (mm/s2)
0
Ang Accln - Z (deg/s2)
40
-10000
80
-100
-200
-300
-400
2.00
1.50
1.00
0.50
0.00
-0.50
0
10
20
30
40
50
-1.00
-500
Time (sec)
Time (sec)
Translational Acceleration in Z-axis
Angular Acceleration in Z-axis
102
APPENDIX (continued)
Velocities Obtained in ADAMS View Simulation for Bus Rollover with Passenger Weights
Angular Velocity in X-axis with passengers weight
Translational Velocity in X-axis with passengers weight
0.80
500.00
Transl. Velocity - X (mm/sec)
Ang Velocity - X (deg/sec)
0.60
0.40
0.20
0.00
-0.20
0
10
20
30
40
50
60
70
-0.40
-0.60
-0.80
-1.00
0.00
0
10
20
30
40
50
60
70
60
70
60
70
-500.00
-1000.00
-1500.00
-2000.00
Time (sec)
Time (sec)
Angular Velocity in X-axis
Translational Velocity in X-axis
Translational Velocity in Y-axis with passengers weight
Angular Velocity in Y-axis with passengers weight
2500.00
0.10
Transl. Velocity - Y (mm/sec)
Ang. Velocity - Y (deg/sec)
2000.00
0.05
0.00
0
10
20
30
40
50
60
70
-0.05
-0.10
1500.00
1000.00
500.00
0.00
-500.00 0
10
20
30
40
50
-1000.00
-1500.00
-2000.00
-2500.00
-0.15
Time (sec)
Time (sec)
Translational Velocity in Y-axis
Angular Velocity in Y-axis
Angular Velocity in Z-axis with passengers weight
Translational Velocity in Z-axis with passengers weight
25.00
1.50
Transl. Velocity - Z (mm/sec)
Ang. Velocity - Z (deg/sec)
20.00
15.00
10.00
5.00
0.00
-5.00 0
10
20
30
40
50
60
70
80
-10.00
-15.00
1.00
0.50
0.00
0
10
20
30
40
50
-0.50
-1.00
-20.00
-1.50
-25.00
Time (sec)
Time (sec)
Translational Velocity in Z-axis
Angular Velocity in Z-axis
103
APPENDIX (continued)
Accelerations Obtained in ADAMS View Simulation for Bus Rollover with Passenger Weights
Angular Acceleration in X-axis with passengers weight
Translational Acceleration in X-axis with passengers weight
60000.00
Transl. Acceleration - X (mm/sec2)
Ang. Acceleration - X (deg/sec2)
60.00
40.00
20.00
0.00
-20.00
0
10
20
30
40
50
60
70
-40.00
-60.00
-80.00
50000.00
40000.00
30000.00
20000.00
10000.00
0.00
0
-10000.00
10
20
30
60
70
Time (sec)
Time (sec)
Translational Acceleration in X-axis with passenger weight
Angular Acceleration in X-axis
Angular Acceleration in Y-axis with passengers weight
Translational Acceleration in Y-axis with passengers weight
100000.00
Transl. Acceleration - Y (mm/sec)
6.00
Ang. Acceleration - Y (deg/sec2)
50
-20000.00
-100.00
4.00
2.00
0.00
0
10
20
30
40
50
60
70
-2.00
-4.00
-6.00
0.00
0
10
20
30
50
60
70
-200000.00
-300000.00
-400000.00
-500000.00
Time (sec)
Time (sec)
Translational Acceleration in Y-axis with passenger weight
Angular Acceleration in Y-axis
Angular Acceleration in Z-axis with passengers weight
Translational Acceleration in Z-axis with passengers weight
30.00
Transl. Acceleration - Z (mm/sec2)
60.00
40.00
20.00
0.00
-20.00
40
-100000.00
-600000.00
-8.00
Ang. Acceleration - Z (deg/sec2)
40
0
10
20
30
40
50
60
70
-40.00
-60.00
-80.00
-100.00
20.00
10.00
0.00
0
10
20
30
40
50
60
-10.00
-20.00
-30.00
-40.00
Time (sec)
Time (sec)
Angular Acceleration in Z-axis with passenger weight
Translational Acceleration in Z-axis with passengers weight
104
70