Transcription of Weld Design and Specification - University of …
1 1 weld Design and weld Design and SpecificationSpecificationJim Glancey, PEJim Glancey, PEDepts. of Depts. of BioresourcesBioresourcesEngineering Engineering & Mechanical Engineering& Mechanical EngineeringUniversity of DelawareUniversity of can t explain everything ..I can t explain everything ..4 in6 in1000 ftInside weld entire length1/4 2 Factors in weld DesignFactors in weld DesignIIStrength (static and/or fatigue)Strength (static and/or fatigue)IIMaterial and the effects of heatingMaterial and the effects of heatingIICostCostIIDistortionDistortionI IResidual StressesResidual StressesIIEasy to WeldEasy to WeldStatic StrengthStatic StrengthIStress - strain diagramStrain ( ) = Stress ( )= FA LLyieldultimate(tensile)FFAL3 Shear StrengthShear StrengthIIn general, material fails in shear due to distortion (at a molecular level)ICriteria for failure: Ductile: Shear Strength ~ Tensile Strength Brittle: Shear Strength ~ Tensile StrengthIWeld strength analysis is generally based on Shear Strength4 Static Strength of WeldsStatic Strength of WeldsFFNormal = Shear = Fw * hFw * h2 FFF1/875o3/81/4 Max Normal = Max Shear = * * hButtFilleth = throat size!
2 weld Size vs. Throat SizeWeld Size vs. Throat Size1/875o3/8h = plate thickness = weld sizeButth = * plate * weld size1/4 Fillet5 Fatigue StrengthFatigue StrengthCycles of LoadingFatigueStrength10001,000,0001 EnduranceLimitStatic Tensile StrengthLowCycleHighCycleInfiniteLife6 Endurance LimitEndurance LimitIIFor Steel:For Steel: Endurance Limit = * Tensile StrengthEndurance Limit = * Tensile Strengthor 100 or 100 kpsikpsi, which ever is lower., which ever is Aluminum:For Aluminum: No endurance limit (cannot have an infinite No endurance limit (cannot have an infinite life)life)7 Factors for Fatigue Stress AnalysisFactors for Fatigue Stress AnalysisType of WeldStress IncreaseButt with ConsiderationsStrength ConsiderationsITry to minimize the stresses in welds; make the parent materials carry highest welds are the most efficientIAvoid stress concentrationsIIntermittent weld length should be at least 4 times the fillet sizeIMinimize weld size to reduce potential for fatigue failure9 Effects of Welding on MetallurgyEffects of Welding on MetallurgyIIDepends on the alloy and welding processDepends on the alloy and welding processIIIn general, cracking is promoted by:In general, cracking is promoted by.
3 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 metal10 Reducing DistortionReducing DistortionIPrevent overweldingIIntermittent weldingIMinimize number of passesIPlace welds near the neutral axisof the partIBalance welds around the neutral axisIAnticipate shrinkage forcesIResidual stress relief11 Neutral AxisNeutral AxisIIThe line (plane) where bending stresses are The line (plane) where bending stresses are
