In practice, a material or component can fail without reason even though no external load is applied. It is very puzzling, at first, to observe that failure can occur without a load. After careful analysis, however, it has been discovered that stresses can be introduced inside a material or component during the manufacturing and machining process. Therefore, the internal stress state of a material or component has a significant influence on its reliability and service life. In order to eliminate these processing defects, it is necessary to measure and evaluate the residual stresses in a material or component and to take appropriate measures to reduce residual stresses or change their distributions.