Residual Stresses and Fracture Mechanics

Abstract

The measurement of residual stresses in a part and the influence of residual stresses on fracture are related topics which have been studied extensively in the literature. Generally, compressive residual stresses are found to be beneficial in fracture calculations while tensile residual stresses degrade the strength of a part. However, in the first part of this chapter we will point out that the local compressive residual stresses, and sub-surface cracks produced by scratching glass at very low loads are responsible for the low tensile strength of conventional glass specimens. Also, if parts containing surface cracks are exposed to processes, such as shot peening, which induce high, near surface compressive stresses, the internal end of the crack will experience tensile loading. What is often ignored is that the compressive stresses close the crack at the surface and make it more difficult to detect by dye penetrant techniques [83]. An attempt is made here to quantify these observations using procedures based on linear elastic fracture mechanics (LEFM).