Question

Explain why in welded components, residual compressive stresses are as detrimental as residual tensile stresses, but in unwelded components residual compressive stresses are beneficial.

Answer 1

The residual stresses whether they are tensile or compressive type predominantly affect dimensional stability and soundness of the weld joint. The affect of Residual stresses can be seen in the form of hot cracking, cold cracking or destortion of the weld. Residual stress of same type as that of external load increases the failure tendency while opposite decreases the failure tendency.

Failure of weld joint kept in corrosive environment also acclerated in presence of tensile residual stresses. The tensile stress adversely affect their load carrying capacity.

So residual stresses must be releived from the weld joint before undertaking any operations.

Compressive residual stresses are intentionally induced to enhance tensile and fatigue performance. Fatigue crack initiation usually occur on metal surface due to cyclic loading. That's why compressive residual stresses filed are intoduced in the material by the method of " Shot Peening" . In this method metal surface is shot with high velocity particles which leads to the formation of a layer of plastically compresses material upto a certain depth. This reduces magnitude of tensile compressive stresses on surface when crack initiate or propagate.