Static and Dynamic Analysis of the Roll Cage for an All-Terrain

Transcription

Imperial Journal of Interdisciplinary Research (IJIR)
Vol-2, Issue-6, 2016
ISSN: 2454-1362, http://www.onlinejournal.in
Static and Dynamic Analysis of the Roll
Cage for an All-Terrain Vehicle
Bharat Kumar Sati1, Prashi Upreti2, Anirudh Tripathi3 &
Shankar Batra4
1,3,4
Department of Industrial and Production Engineering, College of Technology Pantnagar
2
Department of Mechanical Engineering, College of Technology Pantnagar
Abstract: A roll cage is a skeleton of an All-Terrain
Vehicle (ATV). The roll cage forms a structural
base and a
3-D shell around the driver. The
objective of the study is to analyze and optimize the
roll cage designed under a set of particular rules
given by Society of Automotive Engineers (SAE).
This paper outlines static and dynamic analysis of
the roll cage of ATV. Static analysis of the roll cage
is done using ANSYS Static Structural for different
collisions like front, side, rear and roll over.
Dynamic analysis of different crash conditions like
head-on, front, side, rear and roll over of the roll
cage is done using ANSYS Explicit Dynamic. The
main objective of analysis is to obtain optimum
factor of safety which ensures that the roll cage of
ATV will be safe in all conditions.
analysis there is no need to take any assumptions
which means that results of dynamic analysis are
more accurate and better than results of static
analysis. Also optimum mesh size is taken for all
analysis in this research. Mesh size is selected by
checking the independency of mesh size for results.
2. Dimensions
The roll cage must ensure enough clearances
from members for free movement of the driver. In
order to reduce the weight two members with
different cross sections are used to construct the
roll-cage. The diameter of the primary member is
1.25” (inch) and thickness is 0.065” (inch) and that
of the secondary members is 1’’ (inch) and
thickness is kept 0.065” (inch).
Attributes
Values
Length x Width x
Height
Weight of the
vehicle (including
the driver)
Weight of the rollcage
Wheelbase
Track-width
Ground Clearance
Vehicle: 81”x60”x61”
Roll cage: 72.125”x31.25”x50.25”
300 kg
1. Introduction
The roll- cage is a structure to protect the
driver and to support all control systems like
suspension, steering, and the engine. The design
factor contains safety, easy manufacturing,
durability & maintenance of the frame and a
compact, lightweight & ergonomic design. The roll
cage is designed under the guidelines of BAJA
SAE rulebook. The objective of BAJA SAE
competition is to design and fabricate an All
Terrain Vehicle. It is very important to check all
failure modes of roll cage. Aru et al., 2014 [1],
Noorbhasha, N., 2010 [2] and Raina et al., 2015 [3]
have done static analysis for predicting failure
modes of roll cage. Noorbhasha , N., 2010 [2]
have also done dynamic analysis for frontal impact
for validating the results of static analysis.
Noorbhasha, N., 2010 [2] and Raina et al., 2015 [2]
have used grid independency for selection of mesh
size during analysis. This research discusses about
static analysis of all possible impact cases during
event site. As static analysis is done using
theoretically calculated value of forces by
assuming impact time, so to validate results of
static analysis, dynamic analysis is also done in this
research for all possible impact cases. In dynamic
31 kg
59”
50”
12”
Table 1. Dimensions of the roll-cage
3. Material properties
ERW2 steel pipes are used for the roll-cage
fabrication. It was selected because of its high yield
strength. In addition to this, its easy availability and
low cost compared to other materials also make it
to select over other.
S. no
Property
value
1.
Composition
C, Fe, Mn, S, P, Si, Al
2.
Density(g/cm^3)
7.85
Page 43
3.
4.
5.
6.
Yield strength, σyt
(MPa)
Ultimate tensile
strength(MPa)
Modulus of
elasticity(GPa)
Poisson’s ratio
407
470
205
0.29
Table 2. Properties of ERW2 steel
4. 2-D views of roll cage and ATV
4.1 Front views
Figure 4. Side view of ATV
4.3 Top views
Figure 5. Top view of Roll cage
Figure 1. Front view of Roll cage
Figure 6. Top view of ATV
4.3 Isometric views
Figure 2. Front view of ATV
4.2 Side views
Figure 7. Isometric view of Roll cage
Figure 3. Side view of Roll cage
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Figure 11. Side impact condition
Figure 8. Isometric view of ATV
5. Possible conditions at event site
ATV can face various conditions at event site
like front impact, side impact, rear impact, roll over
impact and head-on collision. All conditions with
maximum possible velocity are describes as
follows.
Figure 12. Rollover condition
Figure 9. Front impact condition
Figure 13. Head-on collision condition
6. Mesh size selection for analysis
Figure 10. Rear impact condition
Mesh size is calculated by checking the
mesh independency. As per earlier studies [3] static
analysis of front impact with force value 20000 N
is carried out for various mesh size from 15 mm to
1 mm and then a graph is plotted between
deformation and mesh size.
Page 45
7.2 Dynamic analysis
In dynamic analysis ATV is considered to be
in state of motion and it is given maximum
possible velocity and allows hitting the wall, ATV
as per corresponding different impact cases.
Dynamic analysis is done in ANSYS Explicit
Dynamic.
8. Impact force calculation & analysis
images in case of Static analysis
8.1. Front impact
Graph 1. Deformation vs. Mesh size
Figure 14. Roll cage meshing (4 mm)
Hence a mesh size of 4 mm is selected, as the
deformation becomes constant (= 4.270 mm). It
means that there will be negligible changes in
accuracy of results on further reduction in mesh
size.
7. Finite element analysis
Using the solid modeling in CATIA V5 and
Finite Element Analysis (FEA) in ANSYS 14.5 roll
cage is designed and optimized to maximize
strength and minimize weight. Static analysis is
carried out for all cases front impact, rear impact,
side impact and roll over impact and dynamic
analysis is carried out for head-on collision, front
impact, rear impact, side impact and roll over
impact.
7.1 Static analysis
In static analysis ATV is considered in static
state and maximum possible force is applied to roll
cage with suitable constraints as per different
conditions. Static analysis is done in ANSYS Static
Structural. As per earlier studies [1] impact time of
roll cage in case of impact with rigid body (wall,
floor etc.) is taken as 0.13 sec, while that in case of
impact with a deformable object (another ATV),
impact time is taken as 0.30 sec.
During front impact, the ATV may hit a
tree, another ATV or a wall. Time of impact
will be greater for deformable bodies as
compare to that of rigid bodies so impact force
in the case of wall will be more than that in case
of another ATV or tree. Impact time in case of
impact with wall is taken as 0.13 seconds. For
analysis, ATV is considered to be in static state
and force corresponding to velocity 60 km/h
with impact time 0.13 seconds is applied to
front part of the roll cage of ATV keeping rear
suspension members fixed.
Calculations:
Weight of the ATV, M =300 kg
Initial velocity before impact, vinitial = 16.67 m/s
Final velocity after impact, vfinal will be zero.
Impact time = 0.13 seconds
Work done = change in kinetic energies
As per earlier studies [3]
From work energy principal,
W = (0.5 × M × vfinal2 - 0.5 × M × vinitial2)
│W│ = │- 0.5 × M × vinitial2│
=│- 0.5 × 300 × 16.672│
= 41666.67 Nm
Now,
Work done = force × displacement= F × s ……...
(1)
s = impact time × vmaximum
= 0.13 ×16.67
= 2.1671 m
So, from (1) we get,
F = W/ s
= 41666.67 / 2.1671
= 19,226.925 ≈ 20,000 N
Page 46
F = W/ s
= 41666.67 / 5.001
= 8331.67 ≈ 9,000 N
Figure 15. Analysis Condition
Figure 16. von-Mises stress for front impact
8.2. Rear impact
In actual condition during rear impact, another
ATV is going to hit ATV on its rear part. As the
ATV is a deformable body so the impact time is
taken as 0.30 seconds. For analysis, ATV is
considered to be in static state and force
corresponding to velocity 60 km/h with impact
time 0.30 seconds is applied to rear part of the roll
cage of ATV keeping front suspension members
fixed.
Calculations:
W
= (0.5×M×vfinal2 - 0.5×M×vinitial2)
│W│ = │- 0.5×M×vinitial2│= -0.5*300*16.672
= 41666.67 Nm
Now,
Work done = force × displacement= F × s
= 0.30 × 16.67
= 5.001 m
So, from (1) we get,
Figure 18.von-Mises stress for rear impact
8.3. Side impact
During side impact another ATV will hit ATV
on side and as ATV is deformable body, so the
impact time is taken as 0.30 seconds. For analysis,
ATV is considered to be in static state and force
corresponding to velocity 60 km/h with impact
time 0.30 seconds is applied to side of the roll cage
of ATV keeping suspension members of other side
fixed.
Calculations:
W = (0.5 × M × vfinal2 - 0.5 × M × vinitial2)
│W│ = │- 0.5×M×vinitial2│
=│- 0.5 × 300 × 16.672│
= 41666.67 Nm
Now,
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= 0.30 × 16.67
= 5.001 m
So, from (1) we get, F = W/ s = 41666.67 / 5.001 =
8331.67 ≈ 9,000 N
During the fall, the whole potential changes into
kinetic energy,
M × g × h = 0.5 × M × v2
v = √ (2 × g × h)
= √ (2 × 9.81 × 3.048)
= 7.73 m/sec (or 27.83 km/h)
Now from work energy principal
│W│ = │- 0.5 × M × vinitial2│
=│- 0.5 × 300 × 7.732│
= 8962.935 Nm
Now,
= 0.13 × 7.73
= 1.0049 m
Figure 20. von-Mises stress for side impact
8.4. Roll over
In roll over impact, ATV is considered to be
dropped on its roof on road or ground from a height
of 10 feet.10 feet for the drop height is selected
because it is sufficiently greater than anything
expected at the event site. Since road and ground
are non-deformable bodies, so impact time is taken
as 0.13 seconds. For analysis, ATV is considered to
be in static state and force corresponding to the
calculated velocity 27.83 km/h for 10 feet with
impact time 0.13 seconds is applied to top of the
roll cage of ATV keeping bottom members fixed.
Calculations:
Impact time = 0.13 s
Figure 22. von-Mises stress for roll over impact
9. Analysis conditions & analysis images
in case of Dynamic analysis
9.1 Head on collision
Head on collision of two similar ATV will be
the worst condition at event site for ATVs. In head
on collision two similar ATVs are allows hitting
each other with maximum possible velocity. For
Page 48
analysis roll cage of two Similar ATVs are allows
hitting each other with velocity 60 km/h.
Figure 26 von-Mises stress for front impact
9.3. Rear impact
For worst case scenario in rear impact, the ATV is
considered to hit another similar ATV on its rear
part with a maximum velocity of 60 km/h. For
analysis the roll cage of 2nd ATV is given a
velocity of 60 km/h and allows hitting the roll cage
of 1st ATV which is at rest on its rear part.
Figure 24. von-Mises stress for head-on collision
9.2. Front impact
For worst condition in front impact ATV is
assumed to hit a wall at velocity of 60 km/h.
Hitting a wall will give maximum possible stress as
wall is non-deformable body and impact time will
smaller. For analysis the roll cage of ATV is given
velocity 60 km/h and allows hitting wall.
Figure 28. von-Mises stress for rear impact
Page 49
9.4. Side impact
For worst case scenario in case of side impact, the
one ATV is considered to be in rest and impact is
subjected on its side by a similar ATV having a
velocity of 60 km/h. For analysis the roll cage of
ATV is given velocity 60 km/h and allows hitting
the roll cage of 2nd ATV which is at rest on its side.
Figure 32. von-Mises stress for roll over impact
10. Summary of results
10.1. Static analysis
9.5. Roll over impact
Front
Force
applied
(N)
20000
In roll over impact, ATV is considered to be
dropped on its roof on road or ground with a
velocity of 7.73 m/sec. For analysis the roll cage of
ATV is given a velocity of 7.73 m/sec and allows
hitting wall on its roof.
Rear
9000
197.14
2.613
2.06
Side
9000
221.04
5.997
1.84
Roll
over
9000
166.77
1.765
2.44
Figure 30. von-Mises stress for side impact
Maximum
stress
(Mpa)
273.61
Maximum
Deformation
(mm)
4.270
Factor
of
safety
1.49
Table 3. Results of static analysis
Page 50
dynamic analysis ensure the enhancement in results
which is important.
10.2. Dynamic analysis
Relativ
e
Velocit
y
(m/sec)
120
Maximu
m stress
(Mpa)
Maximum
Deformatio
n
(mm)
Facto
r of
safety
351.85
5.354
1.16
60
239.46
4.249
1.70
60
170.25
2.481
2.39
Side
60
180.85
5.341
2.25
Roll
over
27.83
153.43
1.653
2.65
Head
-on
Front
Rear
Table 4. Results of dynamic analysis
11. Conclusion
This study explores concepts of static analysis,
dynamic analysis and selection of mesh size in
finite element analysis. The main objective of the
study was to obtain optimum factor of safety in all
impact cases. During the study roll cage of All
Terrain Vehicle was analyzed & optimized and
optimum factor of safety is obtained in all possible
impact cases at event site in static as well as in
dynamic analysis which ensures that the roll cage
of ATV will be safe in all conditions. Greater
values of factor of safety for different cases in
12. References
[1] Aru, S., Jadhav, P., Jadhav, V., Kumar, A. and
Angane, P. ‘DESIGN, ANALYSIS AND
OPTIMIZATION OF A MULTI- TUBULAR SPACE
FRAME’, International Journal of Mechanical and
Production Engineering Research and Development
(IJMPERD) ISSN(P): 2249-6890; ISSN(E): 2249-8001
Vol. 4, Issue 4, Aug 2014, 37-48© TJPRC Pvt. Ltd.
[2] Noorbhasha, N. "Computational analysis for
improved design of an SAE BAJA frame structure"
.UNLV Theses, Dissertations, Professional Papers,
and Capstones. Paper 736, 12-2010.
[3] Raina, D., Gupta, R. D. and Phanden, R.K. ‘Design
and Development for Roll Cage of All- Terrain Vehicle’,
International Journal for Technological Research in
Engineering (IJTRE) Volume 2, Issue 7, March-2015
ISSN: 2347-4718
[4] 2015 Collegiate Design Series Baja SAEINDIA®
Rules
http://www.bajasaeindia.org/pdf/2015_Baja%20SAE%
20India%20Rules.pdf
Page 51

Static and Dynamic Analysis of the Roll Cage for an All-Terrain

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