mike weaver
TRANSCRIPT
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Fatigue Estimation of Welds with FEA:Modeling, Criteria, Approaches, and Issues
• Introduction• Weld Fatigue and Physical Influencing Factors
• Methods of Analysis and Prediction and
Application of FEA
• FEA Tool Development Specific to Weld Fatigue
• Concluding Remarks
WEAVER E GINEERINGSeattle, Washington. http://www.weavereng.com
Presentation to SAE Fatigue Committee, Mike Weaver, October 2003, Cedar Rapids, Iowa
8/7/2019 Mike Weaver
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Factors in Weld Fatigue Life Prediction
LIFEFABRICATION
VARIANCE
DESIGN
LIMIT STATE
TRUE
LIMIT STATE
ANALYSIS
UNCERTAINTY
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Weld Fatigue and Physical Influencing Factors• Material State Variations: Mill Heat,
Electrode, Moisture
• Material Damage Due to Welding -
Hydrogen Cracking, Hot Short Cracking,
Lamellar Tearing, Other Base Metal Damage
• Fit-up and Joint Preparation.
• Process and Position
• Operator and Machine Variations
• Starts and Stops
• Sequence, Restraint, and Residual StressState
• Heat Affected Zone - Grain Structure, Local
Brittle Areas, Strength Mismatch
Impoverishment, Overaging, etc
• As Welded Profile - Local Stress
Concentrations• Flaw Density and nature.
• Load History and Environmental
Uncertainties -
Multi-axial Loading, Non-Proportional
Loading
Improvements:
- Mechanical: Burr Grinding, Machining, Peening
- Thermal: PWHT, TIG Dressing, Selective Spotand Line Heating.
- NDT: Improves distribution by truncating tail.
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Methods of Analysis and Prediction
Per IIW Guidelines, Four
Categories:• Nominal Stress Method - Classical
Analysis
• Geometric (Structural, Hot-Spot)Stress Method
• Effective Notch Stress
• Fracture Mechanics … Fitness for
Purpose
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Methods of Analysis: Nominal Stress Method
• P/A … Mc/I• Structural Load Path Variations in Criteria
• Weld Notch Effect in Criteria
• Joint Performances Tabulated and Classified invarious Codes, Design Guides, etc.
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Methods of Analysis: Geometric Stress
• A.K.A. Structural Stress Method, HotSpot Stress
• Structural Load Path Determined by
Analysis or Physical Measurement
• Weld Notch Effect in Criteria• Joint Performances Classified based on
Weld Notch Geometry and Weld Quality.
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Methods of Analysis: Effective Notch Stress
• Geometry of Weld Modeled to 1 mm Resolution
• Sharp Features Rounded with 1 mm radius to allow for fatigue notchsensitivity.
• One S-N curve. The Most Refined Stress Based Approach.
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Methods of Analysis: Fracture Mechanics• da/dN material evaluations with∆K and R
determined by Analysis.
• Detailed and Simplified Methods
• Tabulated (Simplified) Equivalent Stress
Categories for S-N Evaluation
• Fitness for Purpose Evaluations, As Fabricated
Quality Level, Joint Design
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Application of FEA to Prediction Methods
• Nominal Stress: Beam Element Models
• Geometric Stress, Shell and Continuum Models
• Effective Notch Stress - Continuum Models or Shell Models with SCF
• Fracture Mechanics: Continuum Models with Flaws Modeled or FEA
Combined with Classical Fracture Mechanics
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FEA Evaluation of Geometric Stress:
Continuum Models
• Examples of Hot Spot -
Plane Strain Evaluationof Condition (1 of )
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FEA Evaluation of Geometric Stress:
Continuum Models
• Examples of Hot Spot -Plane Strain Evaluation
of Condition (2 of 3)
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FEA Evaluation of Geometric Stress:Continuum Models
• Examples of Hot Spot -Plane Strain Evaluation
of Condition (3 of 3)
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FEA Evaluation of Geometric Stress:
Shell Element Models
• A fair amount of Literature and Current Work on the Subject:
Neimi, Radaj, Hobbacher - IIW
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FEA Evaluation of Geometric Stress:
Shell Element Models
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FEA Evaluation of Geometric Stress:Shell Element Models: Issues
• Nodal Stress Averaging
WELD
FREEEDGE
Correct TerminatedPart Element Selection
The Offending Elementfor Incorrect TerminatedPart Element Selection
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FEA Evaluation of Geometric Stress:Shell Element Models: Issues
• Shell Element Cross Section Singularity(1 of 2)
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FEA Evaluation of Geometric Stress:
Shell Element Models: Issues
• Shell Element Cross
Section Singularity
(1 of 2)
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FEA Evaluation of Effective Notch Stress:Continuum Models
• Plane Strain for SCF
• Solid
• Resolution to 1 mm radius of sharp features
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FEA Evaluation of Effective Notch Stress:SCF
• Plane Strain Determination of SCF-Shell Element Models
-Classical Calculations
-Determination of Improvement.
71911
2923
..
.=
≥
OldLife
NewLife
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FEA Evaluation of Effective Notch Stress:
SCF
Tensile Load, Toe Bending Load, Toe.
Tensile Load, Root. Bending Load, Root.
K TENSION K BENDING
TOE 1.59 1.36
ROOT 2.45 -2.16
6 mm Sheet Metal Formed and Welded Hollow FrameModeled with Shell Elements
Applied Nominal Axial Load: 1 MPa
Weld at Break in Profile
******** END COMMENT BLOCK *********/
@INPUT{K1_1_Membrane
K1_2_MembraneK1_1_BendingK1_2_Bending
}
Str_Mem = (Sjj_1 + Sjj_2)/2Str_Bend = Sjj_1 - Str_Mem
Notch_Str_M1 = Str_Mem*K1_1_MembraneNotch_Str_M2 = Str_Mem*K1_2_Membrane
Notch_Str_B1 = Str_Bend*K1_1_BendingNotch_Str_B2 = Str_Bend*K1_2_Bending
Notch_Str_1 = Notch_Str_M1 + Notch_Str_B1Notch_Str_2 = Notch_Str_M2 + Notch_Str_B2
@IF(Notch_Str_1 >= Notch_Str_2){Notch_Str_Max = Notch_Str_1
}@ELSE{Notch_Str_Max = Notch_Str_2
}
@STORE{
Notch_Str_Max{description = "Worst Case Transverse Notch Stress, Sides 1 and 2"plotsummarize max unsigned
}
Notch_Str_1{description = "Transverse Notch Stress, Side 1"summarize max unsigned
}
Notch_Str_2{description = "Transverse Notch Stress, Side 2"summarize max unsigned
}
Notch_Str_M1{ "Transverse Notch Stress, Side 1, Membrane Load" }
Notch_Str_M2{ "Transverse Notch Stress, Side 2, Membrane Load" }
Notch_Str_B1{ "Transverse Notch Stress, Side 1, Bending Load" }
Notch_Str_B2{ "Transverse Notch Stress, Side 2, Bending Load" }
Str_Mem{ “Transverse Structural (Geometric) Membrane Stress" }
Str_Bend{ "Transverse Structural (Geometric) Bending Stress" }}
0
0.5
1
1.5
2
2.5
3
3.5
4
0.00 0.50 1.00 1.50 2.00
Notch_Str_Max, Worst Case Transverse Notch Stress, Sides 1 and 2
-2
-1
0
1
2
3
4
0.00 0.50 1.00 1.50 2.00
Notch_Str_1, Transverse Notch Stress, Side 1
Notch_Str_2, Transverse Notch Stress, Side 2
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FEA Evaluation of Effective Notch Stress:Solid Elements
• Example with Radiused, Ground Special Quality Weld on Heavy
Weldment - Not too many degrees of freedom required here because
of the smooth geometry.
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FEA Evaluation Solid Models
• Lack of Fusion Must Be Modeled. Done here in CAD.Would be a nice FEA Meshing Tool.
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FEA Evaluation: Plane Strain Stress Intensity
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FEA Tool Development Specific to Weld Fatigue
• Production Analysis• Computations
• Automation and Data Management
• FEA Systems Interface
• Flexibility and User Input Ease
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FEA Tools: Production Analysis
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FEA Tools: FEWeld
• Mathematics• Data Management
• Data Input
• Results Presentation
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FEA Tools: FEWeld Shell Element Mechanics
Resolution of Weld Loads, Node 340:
t b.3
8in Base Material Thickness
σ t.19560 psi Normal Stress at Top of Joint
σ b.7884 psi Normal Stress at Bottom of Joint
τ zx_avg.390.2 psi Average Shear Stress in Joint
τ yz_av
.2530 psi .1210 psi
2
τ avg τ zx_avg2
τ yz_avg2
=τ avg 1910 psi
Joint Normal Load:
P .σ t σ b
2t b =P 5146
lbf
in
Joint Bending Load:
M .σ t σ b
2
t b2
6=M 136.8
.inlbf
in
Joint Shear Load:
V .τ avg t b =V 716.4lbf
in
tb
σ
σt
b
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FEA Tools: FEWeld Computations******** END COMMENT BLOCK *********/
@INPUT{K1_1_MembraneK1_2_MembraneK1_1_BendingK1_2_Bending
}
Str_Mem = (Sjj_1 + Sjj_2)/2
Str_Bend = Sjj_1 - Str_MemNotch_Str_M1 = Str_Mem*K1_1_MembraneNotch_Str_M2 = Str_Mem*K1_2_Membrane
Notch_Str_B1 = Str_Bend*K1_1_BendingNotch_Str_B2 = Str_Bend*K1_2_Bending
Notch_Str_1 = Notch_Str_M1 + Notch_Str_B1Notch_Str_2 = Notch_Str_M2 + Notch_Str_B2
@IF(Notch_Str_1 >= Notch_Str_2){Notch_Str_Max = Notch_Str_1
}@ELSE{Notch_Str_Max = Notch_Str_2
}@STORE{
Notch_Str_Max{description = "Worst Case Transverse Notch Stress, Sides 1 and 2"plotsummarize max unsigned
}
Notch_Str_1{description = "Transverse Notch Stress, Side 1"summarize max unsigned
}
Notch_Str_2{
description = "Transverse Notch Stress, Side 2"summarize max unsigned
}
Notch_Str_M1{ "Transverse Notch Stress, Side 1, Membrane Load" }
Notch_Str_M2{ "Transverse Notch Stress, Side 2, Membrane Load" }
Notch_Str_B1{ "Transverse Notch Stress, Side 1, Bending Load" }
Notch_Str_B2{ "Transverse Notch Stress, Side 2, Bending Load" }
Str_Mem{ “Transverse Structural (Geometric) Membrane Stress" }
Str_Bend{ "Transverse Structural (Geometric) Bending Stress" }}
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FEA Tools: FEWeld Data Management
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FEA Tools: FEWeld Overview
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FEA Tools: FEWeld FEA Interaction
FEWeld GUI Interaction with Cosmos
(Same for Ansys)
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FEA Tools: FEWeld Generalized Data Layout (Future)
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FEA Tools: FEWeld Future Scripting
MATERIAL E70_ELECTRODE{Fut 485 MPa
}
MATERIAL ASTM_A572GR50{Fut 485 MPaFy 345 MPa
}
LOAD_GROUP EXT_LOADS{ 01 02 03 04 }LOAD_GROUP FAT_LOADS{ 11 - 30 }LOAD_GROUP ALL{ EXTREME FATIGUE 05 - 09 }
WELD_TEMPLATE DOUBLE_SIDED_PREP{CALCULATION EXTREME_THROAT_SHEAR {
MATERIAL E70_ELECTRODEFORMULATION DPF-FVPARAMETERS{
E = 4 mmSa = Fut * .3
}LOADING{ EXT_LOADS }
}
CALCULATION FATIGUE_DAMAGE {
MATERIAL ASTM_A572GR50FORMULATION SoderbergPARAMETERS{
(mean, alt) = mean_alt( FATIGUE )C_Xverse 100 MPaDesign_Life 100e6
}}
}
WELD_SET CONFIG_00{DESCRIPTION "Original Configuration"FEA_MODEL_UNITS{ F=lb, L=in, T=s }WELD 01{
DESCRIPTION "Weld between parts 150Cand 148C"
ELEM COMPONENT BRACE_150CNODE LINE LIST{ 42 43 62 62 }
TEMPLATE DOUBLE_SIDED_PREP}WELD 02{
DESC "Weld between boom and yoke"ELEM AREA LIST{ 7 14 21 28 35 42 49
56 63 70 77 84 91 98 }
NODE LINE COMPONENT YOKE_JOINT
TEMPLATE DOUBLE_SIDED_PREP}
}
WELD_SET CONFIG_01{COPY SET CONFIG_00DESC "Modified Boom wall to 0.625"
}
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Fatigue Estimation of Welds with FEA:Modeling, Criteria, Approaches, and Issues
THANK YOU
WEAVER E GINEERINGSeattle, Washington. http://www.weavereng.com
Presentation to SAE Fatigue Committee, Mike Weaver, October 2003, Cedar Rapids, Iowa