5.1.1 Residual stresses are present in almost all materials. They may be created during the manufacture or during the life of the material. If not recognized and accounted for in the design process, residual stresses can be a major factor in the failure of a material, particularly one subjected to alternating service loads or corrosive environments. Residual stress may also be beneficial, for example, the compressive stresses produced by shot peening. The hole-drilling strain-gage technique is a practical method for determining residual stresses.

1.1.1 This test method specifies a hole-drilling procedure for determining residual stress profiles near the surface of an isotropic linearly elastic material. The test method is applicable to residual stress profile determinations where in-plane stress gradients are small. The stresses may remain approximately constant with depth (uniform stresses) or they may vary significantly with depth (non-uniform stresses). The measured workpiece may be thin with thickness much less than the diameter of the drilled hole or thick with thickness much greater than the diameter of the drilled hole. Only uniform stress measurements are specified for thin workpieces, while both uniform and non-uniform stress measurements are specified for thick workpieces.

1.2.1 The hole-drilling method can identify in-plane residual stresses near the measured surface of the workpiece material. The method gives localized measurements that indicate the residual stresses within the boundaries of the drilled hole.

1.2.2 This test method applies in cases where material behavior is linear-elastic. In theory, it is possible for local yielding to occur due to the stress concentration around the drilled hole, for isotropic (equi-biaxial) residual stresses exceeding 50?% of the yield stress, or for shear stresses in any direction exceeding 25?% of the yield stress. However, in practice it is found that satisfactory results can be achieved providing the residual stresses do not exceed about 60?% of the material yield stress.

1.3.1 The hole-drilling method is often described as semi-destructive because the damage that it causes is localized and often does not significantly affect the usefulness of the workpiece. In contrast, most other mechanical methods for measuring residual stresses substantially destroy the workpiece. Since hole drilling does cause some damage, this test method should be applied only in those cases either where the workpiece is expendable, or where the introduction of a small shallow hole will not significantly affect the usefulness of the workpiece.