verity rhazime june2008 public -...
TRANSCRIPT
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Center for Welded Structures Research
Fatigue Strength of Welded JointsVerityTM in Fe-safe
Radwan Hazime, PhDSafe Technology (US) Limited
June 3th, 2008
Outline1. The Verity Method
– Background and needs– Stress based existing methods and codes– The VerityTM structural stress definition– Formulation of the master S-N curve– Validations and applications– Concluding remarks
2. Implementation in fe-safe and application examples
3. Modeling Considerations
4. Demo of fe-safe and Verity
1. The Verity Method for Welded Joints
Rails, railway vehicles and
plant
Ship building
Fatigue of welded joints
-
Ships Civil engineering
Fatigue of welded joints Fatigue of welded joints
Power generation Car bodies and car assembly plant
Car bodies and car assembly plant
“This will save millions of dollars” - Ford
Truck, bus and off-highway vehicles
Fatigue of welded joints
Truck, bus and off-highway vehicles
Caterpillar and John Deere have expressed strong interest. Caterpillar has more than 30 fe-safe™ licences
Pressure vessels
Fatigue of welded joints
-
Pressure vesselsMedical equipment -
X-ray treatment and mobile MRI scanners
Fatigue of welded joints Issues: welded joints
1. Welding process induces highly localized heating and cooling
3. Randomly distributed discontinuities or defects
Planar discontinuitiesVolumetric discontinuities(slag inclusion, Porosity)
2. Material Heterogeneity
Buckling Distortion
Issues: welded joints
4. Residual stresses can be as high as material yield
5. Stress concentration at weld toe or notch
6. Stress concentration at weld ends
7. Estimation of local stresses in HAZ is complex, costly, time consuming and are sensitive to mesh sizes
8. Structures will be subjected to complex time varying loads
Mesh-Sensitivity in Stress Calculations for Welded Joints
• Stress singularity at sharp notches
1.0
2.0
3.0
4.0
0.0
Norm
alize
d St
ress
Element Size (Δl/t)
F/A
Peak stress at Weld Toe from FE Model
1.0
2.0
3.0
4.0
0.0
Norm
alize
d St
ress
Element Size (Δl/t)
F/A
Peak stress at Weld Toe from FE Model
• Mesh-sensitivity in stress calculations
• Existing Codes/Standards: based on nominal stress –the distance from the weld toe is very subjective
-
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 subjectiveDifferent S-N curves for each type of weld.
B C F F2
Mesh-Sensitivity in Stress Calculations for Welded Joints
• Stress singularity at sharp notches
1.0
2.0
3.0
4.0
0.0
Norm
alize
d St
ress
Element Size (Δl/t)
F/A
Peak stress at Weld Toe from FE Model
1.0
2.0
3.0
4.0
0.0
Norm
alize
d St
ress
Element Size (Δl/t)
F/A
Peak stress at Weld Toe from FE Model
• Mesh-sensitivity in stress calculations
• Existing Codes/Standards: based on nominal stress –the distance from the weld toe is very subjective
σtF
σtF
σσtF
0.4t1t
• … or on extrapolated hot-spot stress HSS
Extrapolated hot-spot stress (HSS)
σtF
σtF
σσtF
0.4t1t
Should it be 0.4t and 1t ?0.5t and 1.5t ?
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
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
0 5 10 15 20 25 30
Distance from Weld Toe
Stress
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
.5t/1
.5t
.4t/1
.0t
0.5t
Ext
rap o
lat e
dst
ress
es
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
.5t/1
.5t
.4t/1
.0t
0.5t
Ext
rap o
lat e
dst
ress
es
SCF
ExtrapolationProcedures
Extrapolated hot-spot stress (HSS)
-
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
0 5 10 15 20 25 30
Distance from Weld Toe
Stress
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
.5t/1
.5t
.4t/1
.0t
0.5t
Ext
rap o
lat e
dst
ress
es
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
.5t/1
.5t
.4t/1
.0t
0.5t
Ext
rap o
lat e
dst
ress
es
SCF
ExtrapolationProcedures
ExperimentShell4Shell4Shell8Shell8Shell4(css)Shell4Shell8w1Solid20wSolidpw2Solid20w4Solid8w4Solid8w2Solid20w(f)
Extrapolated hot-spot stress (HSS)
Extrapolated HSS is very mesh-sensitive and very sensitive to extrapolation method
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
Fatigue of welded joints –Verity™…. Welded joint behavior
Fatigue of welded joints –Verity™…. Welded joint behavior
-
Fatigue of welded joints –Verity™…. Welded joint behavior
Fatigue of welded joints –Verity™…. Welded joint behavior
e
Fatigue of welded joints –Verity™…. Welded joint behavior
Fatigue of welded joints –Verity™…. Welded joint behavior
-
Fatigue of welded joints –Verity™ in fe-safe™
• Developed and patented by the Battelle Institute
- Licensed exclusively to Safe Technology - world-wide agreement in place
• Dr Pingsha Dong has received many awards -Society of Automotive Engineers Henry Ford II medal - Time Magazine 2005 maths innovator
Verity Basics
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
y’x’
N1
N2
N3NiE1
E2
E3Ei
WeldNodes at Weld Toe
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
The equilibrium-equivalent structural stresses can be extracted using:• Balanced nodal forces
“NLOAD” in ANSYS“NFORC” in Abaqus“GPFORCE” in Nastran
• “Work equivalent” based mapping from nodal force/moments to line force/moments
FEA Numerical Implementation Automated Procedures for Shell/Plate Models: Transforming Nodal Forces/Moments to Line Force and Moments
N1
y’x’
N2
N3NiE1
E2
E3Ei
WeldNode at Weld Toe
x
y
z
⎪⎪⎪⎪
⎭
⎪⎪⎪⎪
⎬
⎫
⎪⎪⎪⎪
⎩
⎪⎪⎪⎪
⎨
⎧
⎥⎥⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢⎢⎢
⎣
⎡
+
+=
⎪⎪⎪⎪
⎭
⎪⎪⎪⎪
⎬
⎫
⎪⎪⎪⎪
⎩
⎪⎪⎪⎪
⎨
⎧
nn f
fff
llll
llll
ll
F
FFF
.
.
......0063
)(6
0
063
)(6
0063
.
.3
2
1
3322
2211
11
3
2
1
Coordinate rotations and solving simultaneous equations:
-
Line forces along the weld line - work equivalent argument
⎩⎨⎧
=⎭⎬⎫
forces lineby donework
forces GP
by donework
Mesh Independent Structural Stress Evaluation – line forces
F1,u1
1 2 3
F2,u2 F3,u3
∫∫ +=++21 L
0
''L
0332211 dl u f dlu f u F u F u F
1 32
f1
f2
L1 L2
f3f,u
dl
f’,u’ 22112211
fN fN fuN uN u
+=+=
3221'
3221'
fN fN f
uN uN u
+=
+=
⎪⎭
⎪⎬
⎫
⎪⎩
⎪⎨
⎧
⎥⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢⎢
⎣
⎡
+=
⎪⎭
⎪⎬
⎫
⎪⎩
⎪⎨
⎧
3
2
1
22
2211
11
3
2
1
fff
3L
6L0
6L
3L L
6L
06
L3
L
FFF
GP forces line forces
Line forces
⎪⎪⎪⎪
⎭
⎪⎪⎪⎪
⎬
⎫
⎪⎪⎪⎪
⎩
⎪⎪⎪⎪
⎨
⎧
⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢
⎣
⎡
+
+
=
⎪⎪⎪⎪
⎭
⎪⎪⎪⎪
⎬
⎫
⎪⎪⎪⎪
⎩
⎪⎪⎪⎪
⎨
⎧
+++
=
⎪⎪⎪⎪
⎭
⎪⎪⎪⎪
⎬
⎫
⎪⎪⎪⎪
⎩
⎪⎪⎪⎪
⎨
⎧
nn
nnn f
fff
l
l
llll
llll
ll
F
FFFFF
F
F
FFF
.
.
6..............
..................
.........6
00
......63
)(6
0
......063
)(6
......0063
.
...
3
2
1
3
3322
2211
11
)(
)4(3
)3(3
)3(2
)2(2
)1(2
)1(1
3
2
1
Element forcesGP forces
System of equations for a general curved weld line
•Mesh independent•Numerically robust•Consistent line forces
Similarly, line moments along the weld line - work equivalent argument
⎩⎨⎧
=⎭⎬⎫
moments lineby donework
moments GP
by donework
Mesh Independent Structural Stress Evaluation-stresses•Calculate structural stress components fromline forces and moments
2bms tm6
tf
stress structural Total
+=+=⎭⎬⎫
σσσ
Bending structural stress
Line moment
Thickness of sheetMembrane structural stress
•Work equivalent arguments are coupled with a special virtual nodemethod to capture the stress concentration at weld ends
X’, f
Y’,m
Line force
0.25tx0.25t 0.25tx0.25t
(a) Tubular T-JointHot Spot
Chord
BraceHot SpotHot Spot
Chord
Brace
0.5tx5t 1tx1t 2tx2t
Saddle
0.5tx5t 1tx1t 2tx2t 2tx2t
Saddle
Mesh Insensitivity:A Tubular Joint (Zerbst et al, 02)
2
4
6
8
10
12
0 30 60 90Angle from Saddle Point (Deg.)
SCF 2tx2t
1tx1t0.5tx0.5t0.25tx0.25t
(c) Structural stress SCF results
SaddleCrown
Peak SS
Structural stress is mesh-insensitive
0.5tx5t 0.5tx5t 0.5tx5t 0.5tx5t
-
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 30 60 90 120 150
Distance from top of attachment, mmSt
ruct
ural
Str
ess,
MPa
shell-0.5tx0.5trshell-1.0tx1.0trshell-2.0tx2.0tr
Mesh-Insensitive SS Demonstration – Gussets on Plate Edge (FPSO Detail 5)
0.25tx0.25t 0.5tx0.5t
1.0tx1.0t 2.0tx2.0t
Weld End (Peak Stress)
Structural stress is mesh-insensitive
σtF
σtF
σσtF
0.4t1t
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
0 5 10 15 20 25 30
stre
sses
at R
OP
's
ExperimentShell4Shell4Shell8Shell8Shell4(css)Shell4Shell8w1Solid20wSolidpw2Solid20w4Solid8w4Solid8w2Solid20w(f)
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
.5t/1
.5t
.4t/1
.0t
0.5t
Ext
rapo
late
d st
ress
es
Distance from Weld ToeExtrapo lationProcedure s
SCF
Attachment
Base Plate
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
0 5 10 15 20 25 30
stre
sses
at R
OP
's
ExperimentShell4Shell4Shell8Shell8Shell4(css)Shell4Shell8w1Solid20wSolidpw2Solid20w4Solid8w4Solid8w2Solid20w(f)
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
.5t/1
.5t
.4t/1
.0t
0.5t
Ext
rapo
late
d st
ress
es
Distance from Weld ToeExtrapo lationProcedure s
SCF
Attachment
Base Plate
FPSO Phase 1 Results (Fricke,01)
Extrapolated HSS is mesh-sensitive
Focus on rat hole end
Bracket
Web Frame
Side Shell
Longitudinal Stiffener Web
Web Frame Stiffener Web
Mesh Insensitivity: Recent Comparative Study on HSS and Structural Stress Methods (B. Healy)
Focus on rat hole endFocus on rat hole end
0
1000
2000
3000
4000
5000
abaqus-8r abaqus-4 abaqus-4r nastran-8r nastran-4
2t
t
0.5t
0.25t0.125t
Structural Stress Method
0
1000
2000
3000
4000
5000
abaqus-8r abaqus-4 abaqus-4r nas tran-8r nas tran-4
2t
t
0.5t0.25t
0.125t
HSS (.5t/1.5t)HSS (.4t/1t)
0
1000
2000
3000
4000
5000
6000
0
1000
2000
3000
4000
5000
6000
Focus on rat hole end
Bracket
Web Frame
Side Shell
Longitudinal Stiffener Web
Web Frame Stiffener Web
Mesh Insensitivity: Recent Comparative Study on HSS and Structural Stress Methods (B. Healy)
Stress Intensity Factor Estimation Using Structural Stresses
2c
a tr
General 3D Welded Joints
The structural stress at the weld toe in mesh-insensitive, but is that enough – what about crack growth / specimen compliance effects ?
-
Crack growth / compliance
t
σs
σb
σb
(a) Membrane Dominated
(b) Bending Dominated
Smalls
brσσ
=
Larges
brσσ
=
(a) Remote Loading Mode Effects
(b) Thickness Effects
t
t
F
8t
25t
1
1.1
1.2
1.3
1.4
1.5
1.6
No
rma
lize
d S
tru
ctu
ral
Str
ess
Dimensions are Proportional for 3 Joints
t 2t 3t
Stress Intensity Factor Estimation Using Structural Stresses
2c
a tr
General 3D Welded Joints
[ ] where
)(
:Cracks Edge
r
bms
bmbms ffftKσσσ
σσ+=
−−= ta
σbσm
ta
σbσm
Newman and Raju or alet Shiratori either from Y and Y where
2-
:Cracks Elliptical
10
b 10 2)( YQaY
QaK bs
πσπσσ +=
Weld
t σx (y)τ(y)
mσ bσ
Weld
t τm
Structural Stress: Equilibrium Equivalent
Notch Stress: Self -equilibrating
Weld
t
FE Model
Mesh sensitive
•Uses far field nominal stress •OK for a/t >0.1• Long crack
•Using local stress concentration (notch)• a/t< 0.1 • Short crack
a= crack size at weld tow
The VerityTM Structural Stress Definition Local Analysis – Mode I Crack Growth Stress Intensity Factor Approach
Complex geometry &loading in Global analysis
Simple geometry &loading
t
σm σb
a
Problem definition: A finite width plate with a surface crack “a”subjected to remote loads
Structural stress components are the remote loads (tension and bending) for local analysis
-
⎟⎠⎞
⎜⎝⎛Δ=Δ
⎭⎬⎫
taftK
load tensile todue RangeFactorIntensity Stress
mmm σ
functions compliance bending and membrane are f andf taftK
load bending todue RangeFactorIntensity Stress
bm
bbb ⎟⎠⎞
⎜⎝⎛Δ=Δ
⎭⎬⎫
σ
bm K K Kload combined todue RangeFactorIntensity Stress
Δ+Δ=Δ⎭⎬⎫
s
b
bm
br ratio, bending definingBy σσ
σσσ
ΔΔ
=Δ+Δ
Δ=
⎥⎦
⎤⎢⎣
⎡⎥⎦
⎤⎢⎣
⎡⎟⎠⎞
⎜⎝⎛−⎟
⎠⎞
⎜⎝⎛−⎟
⎠⎞
⎜⎝⎛Δ=Δ
taf
tafr
taftK bmmsσ
The stress intensity factor range can be written as
f= compliance functions
Factorion MagnificatIntensity Stress is M
andconstant a is C ere whK)()C(MdNda
kn
mnkn Δ=
Two-stage crack growth law:
) and s thickneson through (basedKeffects)notch localwith (KM
bm
Notchkn σσ=
Life prediction in cycles to final failure
∫∫=
=
=
= Δ=
Δ=
1a/t
0a/tmn
kn
aa
0amn
kn K)()C(Mtd(a/t)
K)()C(MdaN
f
m= Paris law exponentn= (taken as = 2) unifies short crack growth rate with long crack growth.
Master SN curve
∫∫=
=
=
= Δ=
Δ=
1a/t
0a/tmn
kn
aa
0amn
kn K)()C(Mtd(a/t)
K)()C(MdaN
f
∫=
=
−
Δ=
faa
0a
2/1
)/()/(1N tadtaFC
tms
m
σ
)(1N2/)2(
rIC
tms
m
σΔ=
−
)((N)(C)2/)2(
rItms
m
σΔ=
−
m
s
mmm rItC /1
2/)2(/11/m )]([N
σΔ=
−
mmmsm
rItC
/12/)2(/11/m-
)]([N
−
− Δ=σ
Taking C, t, and Δσs out of the integral,
Equivalent Structural Stress
after substituting for ΔK and Mkn,
m-1
m-1
S N C SStress StructuralEquivalent
=Δ⎭⎬⎫
where,
m1
2mm-2
SS
I(r) t S σΔ=Δ
Master S-N curvem=Paris law exponent
This equivalent structural parameter includes the effects of thickness, geometry, bending ratio and test conditions I(r).
Structural stress
Two-stage crack growth law:
-
1a/t
0a/tm
bmmn
kn ta
fta
frta
f)M(
d(a/t)I(r) ∫
=
=⎥⎦
⎤⎢⎣
⎡⎟⎠
⎞⎜⎝
⎛⎟⎠⎞
⎜⎝⎛−⎟
⎠⎞
⎜⎝⎛−⎟
⎠⎞
⎜⎝⎛
=
I(r) is a dimensionless function of r and is given by,
I(r) function can be expressed in actual test loading conditions (e.g. displacement controlled condition or load controlled condition).
Two-stage crack growth law: The Fatigue Governing Parameter: Equivalent Structural Stress Parameter Δss
Modify the structural stress for effects of
s
b
sm
brσσ
σσσ
=+
=- loading mode
- Thickness t
… to produce an equivalent structural stress
“Loading Mode Effect”
mmm
ss
rItS 1
22
)(⋅
Δ=Δ −
σ
“Thickness Effect”
“Stress Concentration Effect” I(r)^(1/m), m=3.6
1
1.1
1.2
1.3
1.4
1.5
1.6
0 0.2 0.4 0.6 0.8 1Bending Ratio (r)
I(r)^
(1/m
)
Load Controlled Disp Controlled
s
b
sm
brσσ
σσσ
=+
=
mrI1
)( as a function of r
The Fatigue Governing Parameter: Equivalent Structural Stress Parameter Δss
Notch Stress Intensity Magnification Factor (Mkn) Estimation
Sym.
Notched specimen
Remotebending
Mkn is dominant approximately within a/t < 0.1
Mkn=
-
“Loading Mode Effect”
mmm
ss
rItS 1
22
)(⋅
Δ=Δ −
σ
“Thickness Effect”
“Stress Concentration Effect”
Equivalent structural stress
s
b
sm
brσσ
σσσ
=+
=…loading mode
…thickness
…is calculated at the weld toe
How well does it correlate with test results ?
The Fatigue Governing Parameter: Equivalent Structural Stress Parameter Δss
pp
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 30 60 90 120 150
Distance from Top Weld Toe on Attachement, mm
Nor
mal
ized
Str
uctu
ral S
tres
s
0.5tx0.5t1tx1t2tx2t4tx4t
Top Weld Toe
Bottom Weld Toe(b) Comparison of structural stress distributions
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 30 60 90 120 150
Distance from Top Weld Toe on Attachement, mm
Nor
mal
ized
Str
uctu
ral S
tres
s
0.5tx0.5t1tx1t2tx2t4tx4t
Top Weld Toe
Bottom Weld Toe(b) Comparison of structural stress distributions
Virtual Node Method – Stress Concentration at Weld Ends
Before Virtual node treatmentAfter Virtual node treatment
Stress concentration with different mesh sizes
A Plate to Frame Joint
-
Correlation: All Pipe and Vessel Weld S-N Data (~500 tests) – ASME Div 2 Rewrite JIP)
1.E+01
1.E+02
1.E+03
1.E+04
1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08
Life
Equi
vale
nt S
truct
ural
Stre
ss R
ange
, MP
a
Equivalent Structural Stress Range
mmm
ss
rItS 1
22
)(⋅
Δ=Δ −
σ
1.E+01
1.E+02
1.E+03
1.E+04
1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08
Life
Nor
min
al S
tress
Ran
ge, M
Pa
ASME Mean
ASME III Design
Markl’s Equation(Mean Line for i =1)
BS5500 Design(Smooth ground butt welds)
Nominal Stress Range
1.E+01
1.E+02
1.E+03
1.E+04
1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08
Life
Stru
ctur
al S
tress
Ran
ge, M
Pa
ASME Mean
ASME III Design
Markl’s Equation(Mean Line for i =1)
BS5500 Design(Smooth ground butt welds)
Structural Stress Range
t
σs
σb
σb
t
t
F
8t
25t
1.E+02
1.E+03
1.E+04
1.E+04 1.E+05 1.E+06 1.E+07
Life
Equ
ival
ent S
truct
ural
Stre
ss R
ange
, MPa
AT122 AT140 AT180 AT222AT240 AT280 Bell Joint G'Joint D Detail_3(Fricke) Joint F joint F(rorup)Joint-Cb(Booth) Joint-Cb(Pook) AC110 AC122AC140W AC140N AC180 AC210AC222 AC240 AC280 AC310AC340 AC380 AC422 AC440Joint C Joint B 13/10/8 AW 50/50/16 AW50/50/16 AW (DW) 100/50/16 AW 100/50/16 AW (QT) Joint EGurney -LW2 HHI_3 9mm-w25 9mm-w509mm-w100 9mm-w160 20mm-w25 20mm-w5020mm-w100 20mm-w160 40mm-w25 40mm-w5040mm-w100
mmm
ss
rItS 1
22
)(⋅
Δ=Δ −
σ
1.E+02
1.E+03
1.E+04
1.E+04 1.E+05 1.E+06 1.E+07
Life
Equ
ival
ent S
truct
ural
Stre
ss R
ange
, MPa
AT122 AT140 AT180 AT222AT240 AT280 Bell Joint G'Joint D Detail_3(Fricke) Joint F joint F(rorup)Joint-Cb(Booth) Joint-Cb(Pook) AC110 AC122AC140W AC140N AC180 AC210AC222 AC240 AC280 AC310AC340 AC380 AC422 AC440Joint C Joint B 13/10/8 AW 50/50/16 AW50/50/16 AW (DW) 100/50/16 AW 100/50/16 AW (QT) Joint EGurney -LW2 HHI_3 9mm-w25 9mm-w509mm-w100 9mm-w160 20mm-w25 20mm-w5020mm-w100 20mm-w160 40mm-w25 40mm-w5040mm-w100
mmm
ss
rItS 1
22
)(⋅
Δ=Δ −
σ
(b)
1.E+02
1.E+03
1.E+04
1.E+04 1.E+05 1.E+06 1.E+07
Life
Equ
ival
ent S
truct
ural
Stre
ss R
ange
, MPa
AT122 AT140 AT180 AT222AT240 AT280 Bell Joint G'Joint D Detail_3(Fricke) Joint F joint F(rorup)Joint-Cb(Booth) Joint-Cb(Pook) AC110 AC122AC140W AC140N AC180 AC210AC222 AC240 AC280 AC310AC340 AC380 AC422 AC440Joint C Joint B 13/10/8 AW 50/50/16 AW50/50/16 AW (DW) 100/50/16 AW 100/50/16 AW (QT) Joint EGurney -LW2 HHI_3 9mm-w25 9mm-w509mm-w100 9mm-w160 20mm-w25 20mm-w5020mm-w100 20mm-w160 40mm-w25 40mm-w5040mm-w100
mmm
ss
rItS 1
22
)(⋅
Δ=Δ −
σ
1.E+02
1.E+03
1.E+04
1.E+04 1.E+05 1.E+06 1.E+07
Life
Equ
ival
ent S
truct
ural
Stre
ss R
ange
, MPa
AT122 AT140 AT180 AT222AT240 AT280 Bell Joint G'Joint D Detail_3(Fricke) Joint F joint F(rorup)Joint-Cb(Booth) Joint-Cb(Pook) AC110 AC122AC140W AC140N AC180 AC210AC222 AC240 AC280 AC310AC340 AC380 AC422 AC440Joint C Joint B 13/10/8 AW 50/50/16 AW50/50/16 AW (DW) 100/50/16 AW 100/50/16 AW (QT) Joint EGurney -LW2 HHI_3 9mm-w25 9mm-w509mm-w100 9mm-w160 20mm-w25 20mm-w5020mm-w100 20mm-w160 40mm-w25 40mm-w5040mm-w100
mmm
ss
rItS 1
22
)(⋅
Δ=Δ −
σ
(b)t
Joint Gb (t=20mm)
t
Joint B(t=12.7mm), Joint B(Kihl)(6.35mm),13/10/8AW(13mm), 50/50/16AW(50mm), 50/50/16AW(DW)(50mm),100/50/16AW(100mm),100/50/16AW(QT Steel)(100mm)
t
Joint C(t=12.7mm)
t
Joint D(t=12.7mm)
t
Joint F (t=12.7mm), Joint F(Rorup)(12.5mm)
t
Bell (t=16mm)
Double Edge Gusset (90mm)
t
Joint G’ (t=12.7mm)
t
Joint-Cb(Booth)(t=38mm), Joint-Cb(Pook)(38mm)
t
Joint E (t=12.7mm)
t
t = 5-80mm
t
Joint Gb (t=20mm)
t
Joint B(t=12.7mm), Joint B(Kihl)(6.35mm),13/10/8AW(13mm), 50/50/16AW(50mm), 50/50/16AW(DW)(50mm),100/50/16AW(100mm),100/50/16AW(QT Steel)(100mm)
t
Joint C(t=12.7mm)
t
Joint D(t=12.7mm)
t
Joint F (t=12.7mm), Joint F(Rorup)(12.5mm)
t
Bell (t=16mm)
Double Edge Gusset (90mm)
t
Joint G’ (t=12.7mm)
t
Joint-Cb(Booth)(t=38mm), Joint-Cb(Pook)(38mm)
t
Joint E (t=12.7mm)
t
t = 5-80mm
Plate Joints with various thickness
Correlation: All Literature Data (> 800 Tests) – Load Controlled
Correlation for spot welds
Thus, we have a fatigue parameter,
•Insensitive to mesh
•Takes into account stress concentration, thickness, and loading mode effects
•A single SN curve for all welded joints of a given class of material (Steel, AL, Titanium, ..)
“Loading Mode Effect”
mmm
ss
rItS 1
22
)(⋅
Δ=Δ −
σ
“Thickness Effect”
“Stress Concentration Effect”
Verity: Equivalent Structural Stress Parameter Δss
-
2. Implementation in fe-safe and application
examples
B.C. & loads
Loading for superpositionStress &
nodal forcesDesign FE model
FEAABAQUS
NASTRANANSYSPro/E
I-DEAS
FE SafeStructural Stress
Life ContourRedesign
Verity for welds
Implementation in fe-safeTM
Implementation in fe-safeTM for scaling and combining load cases
1. For each load case, the membrane and bending structural stresses are calculated
2. Membrane and bending structural stresses are scaled and combined separately
3. I(r)1/m is calculated for each point in time; r = |σb|/( |σb|+|σm|)
4. Membrane and bending structural stresses are added and te equivalent structural stresses are calculated for each point in time
5. The equivalent structural stresses history is cycle counted and the damage is added
Superimposed load histories
Loading
SignalSingle load history
Modal superimposition+
+
Sequencies of FEA solutions
-
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:
Application - MIG welded T-box (Constant Amplitude)
Fine MeshCoarse mesh
Life Contour Plots - Mesh insensitivity
Test results (Initiation + Propagation)75,000Experimental (Deere)w. surf. Rough corr. Factor 0.65
‘text book’ guess based on FEAParticipant 5Not as fixed35,000
Fixed body condition51,000Participant 5Mesh 368,900Mesh 266,100Mesh 177,100Dong, Battelle -Verity90% penetration674,000
50% penetration211,000
10% penetration54,000
3D model, full penetration53,000Participant 3
Hand Calculations30,000Participant 2BS 7608 Class G33,529
BS 7608 Class W21,800Participant 1CommentNf (R=-1)Who
Verity results voted to be the best
Life Predictions from Weld Challenge ParticipantsA 2nd SAE Weld Challenge: Variable Amplitude Loading of Same Specimens
Weld end is much bigger in Challenge 2A
• The Verity method predicted the crack location and the fatigue life
Challenge 1 (2003)
Challenge 2A (2004)
Challenge 2A (2004)
-
Weld Representation at Weld Ends
Challenge 2A (2004)Model 1
Weld Representation at Weld Ends
Challenge 1 (2003)FF
Comparison of FE Models Used for Weld Challenge 1 (03) and Challenge 2A (04)
Identification of Critical Locations after Searching Two Weld Toe Lines
-300
-200
-100
0
100
200
300
-50 0 50 100 150 200 250
Distance from tube end, mm
Stru
ctur
al S
tress
, MPa
Challenge 1 (03)Challenge 2A (04)-Model 1Challenge 2A(04)-Model 2
-300
-200
-100
0
100
200
300
-50 0 50 100 150 200 250
Distance from tube end, mm
Stru
ctur
al S
tress
, MPa
Challenge 1 (03)Challenge 2A (04)-Model 1Challenge 2A-Model 2
2”x6” weld toe 4”x4” weld toe
F=4000 Ibs
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
2A
The method is the only method predicting both failure location and mean life correctly
SAE MIG Weld, MIG welded T-tube subjected to variable amplitude load
Load
(N)
TimeLocation of min life
Grapple skidder torque history (GSTH)
Life (blocks)Load Verity TEST
27.1 x GSTH 364 45019.2 x GSTH 1044 1) 1750
2) 2161
Weld end modeling
Concluding Remarks
mmm
ss
rItS 1
22
)(⋅
Δ=Δ −
σ
The Equivalent Structural Stress based Master S-N curve provides a single parameter description of
• Thickness (t)• Loading mode (r)• Stress concentration (Δss)
Validated by correlating S-N data from about 3500 fatigue tests from 1947 to presentWon SAE “Weld Challenge” twice in a row (2003 and 2004)Adopted by ASME Div 2 Rewrite (Design by Analysis)Implemented in fe-safe from Safe Technology to combine the analysis of welded and non-welded structures
-
Acknowledgement:Many thanks to Dr. Pingsha Dong of Battelle for supplying some of the slides