Hole-Drilling Method
The hole-drilling method is the most widely used general-purpose technique for measuring residual stresses in materials. It is convenient to use, has standardized procedures and it has good accuracy and reliability. The test procedure involves some damage to the specimen but the damage is often tolerable or repairable. For this reason, the method is sometimes called "semi-destructive".
The hole-drilling method involves drilling a small hole in the test specimen at the place where the residual stresses are to be evaluated. This removal of stressed material causes a redistribution of the residual stresses in the remaining material around the hole and associated localized deformations. The diagram schematically illustrates the deformations around a hole drilled into material with tensile residual stresses. The consequent stress release causes elastic springback that slightly expands the hole edge, with a small local surface rise due to Poisson strain. The reverse happens with compressive stresses. For experimental evaluations, strain gauge or optical techniques can be used to quantify the surface deformations of the surrounding material, from which the residual stresses originally existing within the hole can be determined.
