16. Residual Stresses—The Hole-Drilling Method

Residual stresses are locked-in, self-equilibrating stresses that remain in a material after the external loads are removed. They result from any mechanisms that cause misfits among different parts of a material or structure, such as processing operations, non-uniform plastic deformation, temperature gradients, surface treatments, material forming, and shaping procedures, phase transformations, etc. Residual stresses are developed in composite materials, welds, quenched components, semiconductor fabrication, thin films, etc. They can be tensile or compressive. They are algebraically summed with applied stresses. In some cases, beneficial compressive residual stresses are introduced intentionally, as in pre-stressed concrete, in brittle materials which can be toughened, in shot peening, quenching, tempered glass. Generally speaking, residual stresses are undesirable.