Residual Stress

Residual Stress

Residual stresses are stresses that remain after the original cause of the stresses (external forces, heat gradient) has been removed. They remain in the component, even without external cause. Residual stresses occur for a variety of reasons, including inelastic (plastic) deformations, temperature gradients (during heat treatment) or structural changes (phase transformation). Heat from welding may cause localized expansion, which is taken up during welding by either the molten metal or the placement of parts being welded. When the finished weldment cools, some areas cool and contract more than others, leaving residual stresses. Another example occurs during semiconductor fabrication and microsystem fabrication when thin film materials with different thermal and crystalline properties are deposited sequentially under different process conditions. The stress variation through a stack of thin film materials can be very complex and can vary between compressive and tensile stresses from layer to layer.