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F. V. LawrenceUniversity of Illinois

At Urbana

Overview of Weldment Fatigue Life Prediction

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The fatigue-prone machine

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Lecturer

Professor Frederick LawrenceCivil and Environmental EngineeringUniversity of Illinois at Urbanaflawrenc@uiuc.edu

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Outline

I IntroductionII Fatigue FundamentalsIII Fatigue ModelsIV Modeling Weldment Fatigue BehaviorV Predicted Weldment Fatigue BehaviorVI Classifications of WeldmentsVII Improving the Fatigue Life of Weldments

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Overall objective

To understand the factors which control the fatigue life of weldments.

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Underlying ideas…

No two weldments are alike!The fatigue of weldments is a complex, non-linearproblem.Weldment fatigue life is strongly dependent upon initial conditions.Models help us understand what may happen and how to control it!Fatigue is caused by the fluctuation of local stresses and strains.There is nothing more practical than a good theory!

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I Introduction

Fatigue of Weldments

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AM - Cracked Hsg 1

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AM - Front Axle

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AM - Rear weld overall

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AM - Front weld

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What to do?Reduce the local stresses and strains.

Redesign componentReduce stress concentrations.

Avoid lousy weld geometries.Make the weld toes nice.Control weld distortions.

Avoid tensile residual stresses.Avoid high strength materials.

Calculate, don’t guess.Use fatigue life improvement techniques.