Residual stresses are stresses that remain after the original cause of the stresses (external forces, heat gradient) has been removed. They remain along a cross section of the component, even without the external cause.
Residual stresses occur for a variety of reasons, including inelastic deformations and heat treatment.
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.
Castings may also have large residual stresses due to uneven cooling.
While uncontrolled residual stresses are undesirable, many designs rely on them. For example, pre-stressed concrete depend on them to prevent brittle failure.
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