Weld Design and Specification - Welcome to the University of Delaware
Transcript of Weld Design and Specification - Welcome to the University of Delaware
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Weld Design and Weld Design and SpecificationSpecification
Jim Glancey, PEJim Glancey, PE
Depts. of Depts. of BioresourcesBioresources Engineering Engineering & Mechanical Engineering& Mechanical Engineering
University of DelawareUniversity of Delaware
[email protected]@udel.edu
http://http://udel.edu/~jglanceyudel.edu/~jglancey
I can’t explain everything . . .I can’t explain everything . . .
4 in
6 in
1000 ft
Inside weld entire length
1/4”
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Factors in Weld DesignFactors in Weld Design
Strength (static and/or fatigue)Strength (static and/or fatigue)
Material and the effects of heatingMaterial and the effects of heating
CostCost
DistortionDistortion
Residual StressesResidual Stresses
Easy to WeldEasy to Weld
Static StrengthStatic Strength
Stress - strain diagram
Strain (ε) =
Stress (σ)
= FA
∆ LL
yield ultimate(tensile)
F
F
A
L
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Shear StrengthShear Strength
In general, material fails in shear due to distortion (at a molecular level)
Criteria for failure:• Ductile: Shear Strength ~ 0.5 Tensile Strength
• Brittle: Shear Strength ~ 0.75 Tensile Strength
Weld strength analysis is generally based on Shear Strength
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Static Strength of WeldsStatic Strength of Welds
F F Normal =
Shear =
Fw * hF
w * h
2FF
F
1/875o 3/8
1/4 Max Normal =
Max Shear =
F0.618w * h
F0.707w * h
Butt
Fillet
h = throat size!
Weld Size vs. Throat SizeWeld Size vs. Throat Size
1/875o 3/8
h = plate thickness = weld size
Butt
h = 0.707 * plate thickness0.707 * weld size
1/4
Fillet
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Fatigue StrengthFatigue Strength
Cycles of Loading
FatigueStrength
1000 1,000,0001
EnduranceLimit
Static Tensile Strength
LowCycle
HighCycle Infinite
Life
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Endurance LimitEndurance Limit
For Steel:For Steel:•• Endurance Limit = 0.5 * Tensile StrengthEndurance Limit = 0.5 * Tensile Strength
or 100 or 100 kpsikpsi, which ever is lower., which ever is lower.
For Aluminum:For Aluminum:•• No endurance limit (cannot have an infinite No endurance limit (cannot have an infinite
life)life)
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Factors for Fatigue Stress AnalysisFactors for Fatigue Stress Analysis
Type of Weld Stress Increase
Butt Weld 1.2
Transverse Fillet 1.5
Parallel Fillet 2.7
T-butt with corners 2.0
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Strength ConsiderationsStrength Considerations
Try to minimize the stresses in welds; make the parent materials carry highest stresses.
Butt welds are the most efficient
Avoid stress concentrations
Intermittent weld length should be at least 4 times the fillet size
Minimize weld size to reduce potential for fatigue failure
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Effects of Welding on MetallurgyEffects of Welding on Metallurgy
Depends on the alloy and welding processDepends on the alloy and welding process
In general, cracking is promoted by:In general, cracking is promoted by:•• stress concentrationsstress concentrations
•• brittle parent material after welding (low brittle parent material after welding (low carbon steels)carbon steels)
•• hydrogen in the weld metalhydrogen in the weld metal
•• impurities in the weld metalimpurities in the weld metal
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Reducing DistortionReducing Distortion
Prevent overweldingIntermittent weldingMinimize number of passesPlace welds near the neutral axis of the partBalance welds around the neutral axisAnticipate shrinkage forcesResidual stress relief
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Neutral AxisNeutral Axis
The line (plane) where bending stresses are The line (plane) where bending stresses are zero.zero.
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