Center for Welded Structures Research

Transcription

The Structural Stress Method for the Fatigue Analysis
of Welded Structures
(The Verity® Method)
Pingsha Dong/Battelle
John Draper/Safe Technology
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1
Outline





Background and needs
The VerityTM structural stress definition
Formulation of the master S-N curve
Validations and applications
Concluding remarks
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


Stress singularity at sharp
notches
Mesh-sensitivity in stress
calculations
Existing Codes/Standards:
based on nominal stress –
the distance from the weld
toe is very subjective
Normalized Stress
The Problem: Mesh-Sensitivity in Stress
Calculations for Welded Joints
4.0
Peak stress at Weld Toe
from FE Model
3.0
2.0
F/A
1.0
0.0
Element Size (l/t)
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


Stress singularity at sharp
notches
Mesh-sensitivity in stress
calculations
Existing Codes/Standards:
based on nominal stress –
the distance from the weld
toe is very subjective
Normalized Stress
The Problem: Mesh-Sensitivity in Stress
Calculations for Welded Joints
4.0
Peak stress at Weld Toe
from FE Model
3.0
2.0
F/A
1.0
0.0
Element Size (l/t)
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4
BS7608 Joint Classification - Currently Used by
Various Industries
Weld Classes and S-N Curves Used by
IIW, Eurocodes, AWS, AASHTO, API, etc
Based on nominal stress
– choice of reference
distance is subjective
Different S-N curves for
each type of weld.
B
C
F
F2
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Extrapolated hot-spot stress (HSS)
Objective – to define a weld toe stress that characterises the fatigue
life of the weld – and therefore a single S-N curve for all welds
1t
0.4t
m+ b
F
t

Should it be
0.4t and 1t ?
0.5t and 1.5t ?
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SCF
3.2
Stress
3.0
2.6
2.6
2.4
2.4
2.2
2.2
2.0
2.0
1.8
1.8
1.6
1.6
1.4
1.4
1.2
1.2
1.0
1.0
0.8
0.8
0.5t
2.8
.4t/1.0t
2.8
.5t/1.5t
Ext rapo l ated st resses
3.0
3.2
0
5
10
15
20
25
30
Distance from Weld Toe
Extrapolation
Procedures
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SCF
3.2
Stress
2.6
2.4
2.4
2.2
2.2
2.0
2.0
1.8
1.8
1.6
1.6
1.4
1.4
1.2
1.2
1.0
1.0
0.8
0.8
0.5t
2.6
.4t/1.0t
2.8
Extrapolation
Procedures
Experiment
Shell4
Shell4
Shell8
Shell8
Shell4(css)
Shell4
Shell8w
1Solid20w
Solidpw
2Solid20w
4Solid8w
4Solid8w
2Solid20w(f)
3.0
2.8
.5t/1.5t
Ext rapo l ated st resses
3.0
3.2
0
5
10
15
20
25
30
Distance from Weld Toe
Extrapolated HSS is very mesh-sensitive
and very sensitive to extrapolation method
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Requirements for a FE Based Stress
Parameter Definition for Fatigue Evaluation

Consistency in stress determination:
• Mesh-insensitive
• Robust for complex structures – always get the same answer

A single S-N curve should apply to:
• different joint geometries
• different loading modes
• different plate thicknesses
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The Verity® Structural Stress Definition
Structural Stress: Equilibrium Equivalent
Weld
Weld
t
tm
m b
t
t (y)
x (y)
Notch Stress: Self- Equilibrating
Weld
t
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The Verity® Structural Stress Definition
Structural Stress: Equilibrium Equivalent
Far-field stress – controls
„Paris‟ crack growth.
Weld
t
tm
m b
Notch Stress: Self- Equilibrating
Local notch effect – influences
„short crack‟ growth.
Not available from FE analysis.
Obtained from fracture
mechanics studies.
Weld
t
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Numerical Implementation in FEA

Displacement based FE procedures:
• Nodal forces and displacements are most reliable solution
quantities
• Equilibrium conditions are only guaranteed in terms of
nodal forces at nodes, but not in terms of stresses
N1
Nodes at
Weld Toe
Weld
N2
E1
Ni
Ei
N3
E2
E3
x’
y’
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Automated Procedures for Shell/Plate Models: Transforming
Nodal Forces/Moments to Line Force and Moments
Coordinate rotations and solving
simultaneous equations:
 F1   l1
F  
 2 3
l

 F3 
 1
   6
.  
.   0
  0

 Fn 
 
l1
6
(l1  l2 )
3
l2
6
0
0
l2
6
(l2  l3 )
3
...
  f1 
0  
f
 2 
 f3 

0 

 . 
l3   
 
6  . 
...  f n 
 
N1
Node at
Weld Toe
Weld
N2
E1
N3
Ni
Ei
E2
E3
x’
y’
y
x
z
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Automated Procedures for Shell/Plate Models: Transforming
Nodal Forces/Moments to Line Force and Moments
Structural stress at any given location:
s  m b 
f y'
t

Weld
6mx '
t2
tm
m b
Is the value of s mesh-insensitive ?
Is it a valid fatigue parameter ?
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A Tubular Joint
( Zerbst et al, 02)
Brace
Hot Spot
(a) Tubular T-Joint
0.25tx0.25t
Chord
0.5tx5t
Structural stress is mesh-insensitive
Saddle
12
(c) Structural stress SCF results
0.5tx5t
10
SCF
Peak SS
2tx2t
1tx1t
8
2tx2t
1tx1t
0.5tx0.5t
0.25tx0.25t
6
4
Crown
Saddle
2
0
30
60
Angle from Saddle Point (Deg.)
90
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Mesh-Insensitive SS Demonstration – Gussets on
Plate Edge (FPSO Detail 5)
Weld End
(Peak Stress)
0.25tx0.25t
0.5tx0.5t
2
shell-0.5tx0.5tr
1.5
shell-1.0tx1.0tr
shell-2.0tx2.0tr
1.0tx1.0t
2.0tx2.0t
Structural Stress, MPa
1
0.5
0
0
-0.5
30
60
90
120
150
Distance from top of attachment, mm
-1
-1.5
-2
Structural stress is mesh-insensitive
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A Recent Comparative Study on HSS and
Structural Stress Methods by B. Healy
Side Shell
Focus on
end
Focus
onrat
rathole
hole
end
Web Frame
Longitudinal
Stiffener Web
Bracket
Web Frame
Stiffener Web
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A Recent Comparative Study on HSS and
Structural Stress Methods by B. Healy
5000
Structural Stress Method
Side Shell
4000
2t
Focus on rat hole end
Web Frame
Longitudinal
Stiffener Web
t
3000
0.5t
2000
0.25t
1000
0.125t
Bracket
Web Frame
Stiffener Web
0
abaqus-8r
abaqus-4
5000
6000
abaqus-4r
nastran-8r
nastran-4
HSS
HSS(.5t/1.5t)
(.4t/1t)
5000
4000
2t
4000
t
3000
3000
0.5t
2000
2000
0.25t
1000
1000
0.125t
00
abaqus-8r
abaqus-4
abaqus-4r
nastran-8r
nastran-4
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Stress Intensity Factor Estimation Using Structural
Stresses
The structural stress at the weld toe in mesh-insensitive, but is that enough
– what about crack growth / specimen compliance effects ?
General 3D Welded Joints
2c
a
tr
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(a) Remote Loading
Mode Effects
(b) Thickness Effects
8t
s
t
t
F
(a) Membrane Dominated
Small r 
t
b
s
25t
b
(b) Bending Dominated
Large r 
s
b
Dimensions are Proportional for 3 Joints
1.6
b
s
N o r m a liz e d S tru c tu ra l S tre ss
s
Crack growth / compliance
1.5
1.4
1.3
1.2
1.1
1
1 /2 " tTh ic k
1" 2t
Th ic k
2 " 3t
Th ic k
P la te T h ic k n e ss (t)
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Stress Intensity Factor Estimation Using Structural
Stresses
General 3D Welded Joints
2c
a
m
Edge Cracks :
K  tr  s f m   b ( f m  f b )
where s   m   b
a
t
tr
b
Elliptical Cracks :
K  ( s - 2 b )
a
Q
Y0  2 b
a
Q
Y1
where Y0 and Y1 from either Shiratori et al
or Raju and Newman
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The Fatigue Governing Parameter: Equivalent
Structural Stress Parameter Ss
Modify the structural stress for effects of
- loading mode
r
b

 b
 m s  s
Notch Stress: Self Equilibrating
-thickness
Weld
-include local notch „short crack‟ effect
t
… to produce an equivalent structural stress
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I (r )
“Structural stress”
1
m
as a function of r
1.6
I(r)^(1/m), m=3.6
1.5
 s
t
“Thickness Effect”
2 m
2m
 I (r )
1
m
“Loading Mode
Effect”
1.4
I(r)^(1/m)
S s 
Load Controlled
Disp Controlled
1.3
1.2
1.1
1
0
0.2
0.4
0.6
0.8
1
Bending Ratio (r)
r
b

 b
 m  b  s
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Equivalent structural stress
“Structural stress”
…loading mode
 s
S s 
t
“Thickness Effect”
2 m
2m
 I (r )
1
m
“Loading Mode
Effect”
r
b

 b
 m s  s
…thickness
…is calculated at the weld toe
How well does it correlate with test results ?
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Correlation: All Pipe and Vessel Weld S-N Data
(~500 tests) – ASME Div 2 Rewrite JIP)
1.E+04
Nominal Stress Range
ASME Mean
Equivalent Structural Stress Range, MPa
Norminal Stress Range, MPa
ASME III Design
Markl’s Equation
(Mean Line for i =1)
1.E+03
1.E+02
BS5500 Design
(Smooth ground butt welds)
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
1.E+02
Life
1.E+04
Structural Stress Range
ASME Mean
Structural Stress Range, MPa
ASME III Design
Markl’s Equation
(Mean Line for i =1)
1.E+03
1.E+02
BS5500 Design
(Smooth ground butt welds)
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
Life
Jo int F
Jo
int-Cb(B o o th)
1.E+04
A C110
A C140W
A C180
A C222
A C280
A C340
A C422
Jo int C
13/10/8 A W
50/50/16 A W (DW)
100/50/16 A W (QT)
Gurney -LW2
1.E+03
9mm-w25
9mm-w100
20mm-w25
20mm-w100
40mm-w25
40mm-w100
A T140
A T222
A T280
Jo int G'
Detail_3(Fricke)
P VRC:SS-1.5"
P1.E+02
VRC:SS-4"
M acfarlane(P ressure)
M arkl's: Flange
M ark's M B -IB (2.2ksi)
M arkl's: M B -OB -Thin
P 1, S1
P 1, S3
P 1, S5
P 1, S7
P 2, S1
P 2, S3
P 3, S1
mean
curve
1.E+01
B S 5500
1.E+06
1.E+07
1.E+08
Jo int F
Jo int-Cb(B o o th)
A C110
A C140W
A C180
A C222
A C280
A C340
A C422
Jo int C
13/10/8 A W
50/50/16 A W (DW)
100/50/16 A W (QT)
Gurney -LW2
9mm-w25
9mm-w100
20mm-w25
20mm-w100
40mm-w25
40mm-w100
A T140
A T222
A T280
Jo int G'
Detail_3(Fricke)
P VRC:SS-1.5"
P VRC:SS-4"
M acfarlane(P ressure)
M arkl's: Flange
M arkl's M B -IB (2.2ksi)
M arkl's: M B -OB -Thin
P 1, S1
P 1, S3
P 1, S5
P 1, S7
P 2, S1
P 2, S3
P 3, S1
mean curve
B S 5500
jo int F(ro rup)
Jo int-Cb(P o o k)
A C122
A C140N
A C210
A C240
A C310
A C380
A C440
Jo int B
50/50/16 A W
100/50/16 A W
Jo int E
HHI_3
9mm-w50
9mm-w160
20mm-w50
20mm-w160
40mm-w50
A T122
A T180
A T240
B ell
Jo int D
P VRC:CS-1.5"
P VRC:CS-4"
M acfarlane(IB )
M arkl's:M B -IB
M arkl's:Girth Welds
B ending(EP RI)
8"pipe (P . Sco tt)
P 1, S2
P 1, S4
P 1, S6
P 1, S8
P 2, S2
P 2, S4
P 4, S1
A SM E III
M arkl's equatio n
1.E+03
jo int F(ro rup)
Jo int-Cb(P o o k)
A C122
A C140N
A C210
A C240
A C310
A C380
A C440
Jo int B
50/50/16 A W
100/50/16 A W
Jo int E
HHI_3
9mm-w50
9mm-w160
20mm-w50
20mm-w160
40mm-w50
A T122
A T180
A T240
B ell
Jo int D
P VRC:CS-1.5"
P VRC:CS-4"
M acfarlane(IB )
M arkl's:M B -IB
M arkl's:Girth Welds
B ending(EP RI)
8"pipe (P . Sco tt)
P 1, S2
P 1, S4
P 1, S6
P 1, S8
P 2, S2
P 2, S4
P 4, S1
A SM E III
M arkl's equatio n
Equivalent Structural Stress Range
 s
S s 
t
1.E+04
1.E+05
1.E+06
2 m
2m
1
 I (r ) m
1.E+07
1.E+08
Life
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25
Correlation: All Literature Data (> 800 Tests) –
Load Controlled
1.E+04
Joint G’ (t=12.7mm)
S s 
t
t
Plate Joints
Joint G’
: Maddox,
S.J., 1982,
“Influence
of Tensile
Residual
Stresses
Joint
G’: Maddox,
S.J., 1982,
“Influence
of Tensile
Residual
Stresseson
onthe
the Fatigue
Fatigue
2 m
2m
 I (r )
Equivalent Structural Stress Range, MPa
t
 s
1
m
Joint
B(t=12.7mm),
B(Kihl)(6.35mm),
Joint
B(t=12.7mm),
JointJoint
B(Kihl)(6.35mm),
Joint
(t=12.7mm)
Joint
G’G’
(t=12.7mm)
13/10/8AW(13mm),
50/50/16AW(50mm),
13/10/8AW(13mm),
50/50/16AW(50mm),
tt
50/50/16AW(DW)(50mm),100/50/16AW(100mm),
50/50/16AW(DW)(50mm),100/50/16AW(100mm),
100/50/16AW(QT
Steel)(100mm)
100/50/16AW(QT
Steel)(100mm)
Behavior
of Welded
JointsJoints
in Steel,”
Residual
Stress
Effects
Behavior
of Welded
in Steel,”
Residual
Stress
EffectsininFatigue,
Fatigue,
STPpp.
776,
pp. 63-96,
ASTM.
ASTM ASTM
STP 776,
63-96,
ASTM.
tt
Joint
G’
: Maddox,
S.J.,
1982, “Influence
of Tensile Residual
Stresses
on”The
the Fatigue
Jointto
B(t=12.7mm),
Joint B(Kihl)(6.35mm),
Joint
: Mantaghi,
Mantaghi,
S. and
and
S.J.,
1993,
Application
of Fatigue
Design
Rules
Large
Joint
G’
: Maddox,
1982, “Influence
of Maddox,
Tensile
Residual
Stresses
on”The
the
Fatigue
Joint
B(t=12.7mm),
Joint
B:BS.J.,
S.
Maddox,
S.J.,
1993,
Application
of Fatigue
Design
Rules
to
Large
Behavior
of Welded Joints
in Steel,”
Residual Stress
Effects
in Fatigue,
13/10/8AW(13mm), 50/50/16AW(50mm),
Welded
Structures,”
Behavior
Welded
Joints
in Steel,” Residual StressJoint
Effects
in Fatigue,Joint B(Kihl)(6.35mm),t
13/10/8AW(13mm), 50/50/16AW(50mm),
B(t=12.7mm),
ASTM
STP
776, pp. Structures,”
63-96, ASTM.
Joint
Gbof
(t=20mm)
Welded
50/50/16AW(DW)(50mm),100/50/16AW(100mm),
Joint B(t=12.7mm),
ASTM
776, pp. Kihl,
63-96,D.P.,
ASTM.
Joint
GbSTP
(t=20mm)
Joint
B(Kihl):
and Sarkani, S.,
1997,
“Thickness
Effects
on the fatiguet Strength
of
13/10/8AW(13mm),
50/50/16AW(50mm),
50/50/16AW(DW)(50mm),100/50/16AW(100mm),
t
100/50/16AW(QT
Steel)(100mm)
Joint B(Kihl):
Kihl,
D.P.,
and
Sarkani,
S.,
1997,
“Thickness
Effects
on
the
fatigue
Strength
of
13/10/8AW(13mm),
50/50/16AW(DW)(50mm),100/50/16AW(100mm),
Welded Steel Cruciforms,”
Journal of 50/50/16AW(50mm),
Fatigue, Vol.19 Supp. No.1, 100/50/16AW(QT Steel)(100mm)
t International
50/50/16AW(DW)(50mm),100/50/16AW(100mm),
100/50/16AW(QT
Steel)(100mm)
Welded
Steel Cruciforms,” International
Journal
of Fatigue, Vol.19 Supp. No.1,
pp.S311-S316.
Joint
B: Mantaghi,Steel)(100mm)
S. and Maddox, S.J., 1993, ”The Application of Fatigue Design Rules to Large
Joint Gb (t=20mm)
100/50/16AW(QT
t
Joint E (t=12.7mm)
pp.S311-S316.
Joint
B100/50/16AW(QT
: ofMantaghi,
S. and Maddox,
S.J., Joint
1993,S.J.,
”The Application
of Fatigue
Design Rules to Large
tt
Welded
Structures,”
13/10/8AW,
50/50/16AW,
50/50/16AW(DW),
B(t=12.7mm),
Joint
B(Kihl)(6.35mm),
Joint B: Mantaghi,
S. and Maddox,
S.J., Joint
1993, Gb
”The(t=20mm)
Application
Fatigue Design Rules toSteel):
Large Maddox,
Joint E (t=12.7mm)
Joint B(Kihl):
Kihl,Strength
D.P.,
and of
Sarkani,
S.,
1997, “Thickness
Effects
on the
fatigue Joint
Strength
of
tt
Welded
Structures,”
13/10/8AW,
50/50/16AW,
100/50/16AW(QT
Steel):
Maddox,
S.J.,
50/50/16AW(50mm),
Joint
B(t=12.7mm),
B(Kihl)(6.35mm),
”The
of 50/50/16AW(DW),
Plate
Thickness
the Fatigue
Fillet
Joints,”
Welded
Structures,”
Joint B: 1987,
Mantaghi,
S.Effect
and Maddox,
S.J.,
1993, ”Theon
Application
of Fatigue Design
Rules
Large 13/10/8AW(13mm),
t toWelded
Welded
Steel
Cruciforms,”
International
Journal
of Fatigue, Effects
Vol.19 Supp.
No.1,
t Effect
Joint
Kihl,
D.P.,
andofof
Sarkani,
S.,50/50/16AW(DW)(50mm),100/50/16AW(100mm),
1997,
“Thickness
on the
fatigue Strength of
13/10/8AW(13mm),
50/50/16AW(50mm),
TWI.
Joint1987,
B(Kihl):
Kihl,
D.P., andof
Sarkani,
S.,Thickness
1997, “Thickness
Effects
on the
fatigue
Strength
”The
Plate
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Welding in the World, Vol., 44(5), pp.20-35.
elded Structures,” Welding in the World, Vol., 44(5), pp.20-35.
Double Gussets(Niemi): Wagner, M., 1998, “Fatigue Strength of Structural Members
Fig. 3: Corner Joints Tested by Yagi (1992)
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26
Aluminum Alloy MIG
Welds (Courtesy of Ford Motor Company)
40
60
48
F
F
Grip
40
Weld all around
40
40
Grip
t
30
4
8
Grip
40
40
24
2
0
1.E+01
60
Grip
40
10
5
Weld (1 side)
40
Grip
Isometric view
160
Fig. 3.2.12 T-Box (tubes - Single weld) (M12)
Fig. 3.2.8 Plate with stiffener – bending (M8)
1.E+04
Equivalent Structural Stress, MPa
1.E+02
240
t
40
Grip
Nominal Stress Range, MPa
1.E+03
M131XX(1.5-1.5)
M162XX(2-2)
M112XX(3-3)
M102XX(1.5-1.5)
M118XX(2-2)
M144XX(3-3)
M125XX(1.5-1.5)
M156XX(2-2)
M138XX(2-2)
M171XX(3-3)
M116XX(1.5-1.5)
M106XX(2-2)
M122XX(3-3)
M152XX(1.5-1.5)
M132XX(2-2)
M165XX(3-3)
M145XX(3-3)
M104XX(1.5-1.5)
M120XX(2-2)
M110XX(3-3)
M130XX(1.5-1.5)
M162XX(2-2)
M139XX(3-3)
1.E+03
M153XX(1.5-1.5)
M108XX(2-2)
M124XX(3-3)
M114XX(1.5-1.5)
M137XX(2-2)
M170XX(3-3)
M147XX(1.5-1.5)
1.E+00
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
Life
M131XX(1.5-1.5)
M138XX(2-2)
M145XX(3-3)
M153XX(1.5-1.5)
M162XX(2-2)
M171XX(3-3)
M104XX(1.5-1.5)
M108XX(2-2)
M112XX(3-3)
M116XX(1.5-1.5)
M120XX(2-2)
M124XX(3-3)
M102XX(1.5-1.5)
M106XX(2-2)
M110XX(3-3)
M114XX(1.5-1.5)
M118XX(2-2)
M122XX(3-3)
M130XX(1.5-1.5)
M137XX(2-2)
M144XX(3-3)
M152XX(1.5-1.5)
M162XX(2-2)
M170XX(3-3)
M125XX(1.5-1.5)
M132XX(2-2)
M139XX(3-3)
M147XX(1.5-1.5)
M156XX(2-2)
M165XX(3-3)
Conventional Method: Nominal Stress
Parameter
m=3.6 load control
F
F
10
0
40
Grip
40
40
40
Grip
100
1.E+02
112
25
25
199
40
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
Weld all
around
(both sides)
40
40
Grip
Life
112
25
Grip
40
48
Verity Equivalent Structural Stress Parameter
F
F
Fig. 3.2.13 Cruciform - Tubes double weld (M13)
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27
Weld Representation Using Shell/Plate
Element Model


Full penetration weld: two
rows of plate elements with
“triangle formation”
Partial penetration: one row
of inclined elements
Thickness based on
equivalent stiffness
t
Plate Elements
An Example:
Partial Penetration Weld:
Nominal weld throat
size
t/ 2
Shell Elements
t
t
t
L
Plate Elements
(a)
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28
Can Resistance Spot Weld S-N Data be Correlated
with Fusion Weld S-N Database?
l, R., and Vosikovsky, O., 1993, “Fatigue Life Prediction of Welded Joints
Journal of Offshore Mechanics and Arctic Engineering, Vol.115, pp.123-130.
Bell (t=16mm)
t
Bell: Bell, R., and Vosikovsky, O., 1993, “Fatigue Life Prediction of Welded Joints
Journal
of Offshore Mechanics and Arctic Engineering, Vol.115, pp.123-130.
LS1 (t=1.5mm)
t
CP1 (t=1.5mm)
, J., Dong, P. and Gao, Y., 2001, “Evaluation of Stress Intensity Factor-Based Predictive
echnique for Fatigue Life of Resistance Spot Welds, SAE paper 2001-01-0830, SAE
t
LS1 (t=1.5mm)
t
CP 1: Zhang, J., Dong, P.and Gao, Y., 2001, “Evaluation of Stress Intensity Factor-Based Pred
Technique forPredictive
Fatigue Life of Resistance Spot Welds, SAE paper 2001-01-0830, SA
LS 1: Zhang,
J., Dong, P. and Gao, Y., 2001, “Evaluation of Stress Intensity Factor-Based
m=3.6, displacement controlled
m=3.6
1.E+04
1.E+04
CP1
Power (m=3.6)
1.E+03
1.E+02
1.E+02
1.E+03
1.E+04
1.E+05
Life, Cycles
1.E+06
1.E+07
Equivant SS Range, MPa
Equivant SS Range, MPa
Load-Controlled I(r)
LS1 (t=90mm, crack=2m
t
Displace-Controlled
I(r)Double Gussets
LS1
CP1
Power (m=3.6)
Double Gussets(Niemi): Wagner, M., 1998, “Fatigue Strength of Structural Members
1.E+03
1.E+02
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
Life, Cycles
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30
SAE FD&E “Fatigue Challenge” Blind Life
Prediction




SAE FD&E issued a “fatigue
prediction challenge”
Actual test results were
given after all participants
presented their predicted
lives
See www.fatigue.org/weld
The Verity method won “The
Best Prediction:
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31
A 2nd SAE Weld Challenge: Variable
Amplitude Loading of Same Specimens
Challenge 1 (2003)
 Weld end is much bigger in Challenge 2A

The Verity method predicted the crack
location and the fatigue life
Challenge 2A (2004)
Challenge 2A (2004)
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32
Comparison of FE Models Used for Weld
Challenge
1 (03) and
Challenge
2A (04) 2A
Finite Element
Modeling:
Challenge
versus 1
Weld Representation at
Weld Ends
Challenge 2A (2004)
Model 1
Entire Model
F
Weld Representation at
Weld Ends
Challenge 1 (2003)
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33
Identification of Critical Locations
after Searching Two Weld Toe Lines
2A
The method is the only method predicting
both failure location and mean life correctly
F=4000 Ibs
300
300
Challenge 1 (03)
Challenge 1 (03)
Challenge 2A (04)-Model 1
Challenge 2A-Model 2
100
0
-50
0
-100
50
100
150
Distance from tube end, mm
-200
-300
2”x6” weld toe
200
Challenge 2A (04)-Model 1
200
Challenge 2A(04)-Model 2
250
200
100
0
-50
0
-100
-200
50
100
150
200
250
Distance from tube end, mm
4”x4” weld toe
-300
Observations:
• If the weld ends are big (modeled as posted in the website), weld end failure occurs on 4”x4”
• if the weld ends are as small as those for Challenge 1, failure occurs at 2”X6” weld toe corner
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34
Weld throat failure can also be assessed
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35
The
module in fe-safe
Loading
Design
FEA
ABAQUS, ANSYS
I-DEAS,
NASTRAN, Pro/E
Stress
results
Fatigue
fe-safe
Redesign
Life
contours
fe-safe
durability analysis from FEA
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37
Loading
Signal
Summary of Tests - DEF STAN 00-35
0.1
PSD
g2/Hz
Single load history
0.01
0.001
0.0001
0.00001
1
10
100
1000
10000
Hz
Rainflow
cycles
Superimposed load histories
Sequencies of FEA solutions
Modal superimposition – steady
state and random dynamic
+
+
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38
The
module in fe-safe
Weld analysed using Verity
equivalent structural stress
Analysed using Brown-Miller
strain-life fatigue
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39
Mesh-insensitive Structural Stress method for fatigue
of welded joints.
Calculated from nodal forces at the weld toe, not some distance from it
Is mesh insensitive
Applies to all types of weld (including spot welds), all thicknesses,
all types of loading
One S-N curve for all steel welds, one S-N curve for all welds in
aluminium alloy
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40
of welded joints.
 Can be used with solid or shell elements
Bell (t=16mm)
t
 For toe failure, weld can be modeled with a fillet, or not at all
Journal of Offshore Mechanics and Arctic Engineering, Vol.115, pp.123-130.
 Transverse or longitudinal welds
 Toe and throat failure
Bell (t=16mm)
t
t
Journal
of Offshore Mechanics and Arctic Engineering, Vol.115, pp.123-130.
LS1 (t=1.5mm)
CP1 (t=1.5mm)
 Spot welds in shear or peal
LS 1: Zhang, J., Dong, P. and Gao, Y., 2001, “Evaluation of Stress Intensity Factor-Based Predictive
t
LS1 (t=1.5mm)
t
 In-house corrections for weld improvement processes
LS 1: Zhang, J., Dong, P. and Gao, Y., 2001, “Evaluation of Stress Intensity Factor-Based Predictive
CP 1SAE
: Zhang,
Dong, P.and SAE
Gao, Y., 2001, “Evaluation of
Technique for Fatigue Life of Resistance Spot Welds,
paperJ.,
2001-01-0830,
Stress Intensity F
Technique for Fatigue Life of Resistance Spot Welds, SAE paper 2
Double Gussets (t=9
t
Double Gussets(Niemi): Wagner, M., 1998, “Fatigue Strength of Structura
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41
of welded joints.
 The Equivalent Structural Stress based Master S-N curve provides
a single parameter description of
• Thickness (t)
• Loading mode (r)
• Stress concentration
 s
S s 
t
2 m
2m
 I (r )
1
m
 Validated by correlating S-N data from about 3500 fatigue tests from
1947 to present (including spot welds in shear and tension)
 Adopted by ASME Div 2 Pressure Vessel Code (Design by Analysis)
 Implemented in fe-safeTM from Safe Technology to combine the analysis
of welded and non-welded structures
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42

Center for Welded Structures Research

Transcription

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