Abstract: A method, which is used to make controlled defects corresponding to natural flaws and residual stresses in various kinds of test pieces. Defects identical to natural flaws are required to qualify non-destructive testing (NDT) procedures. In the method, sequential, repeated, heating-cooling cycles are used to create defects and residual stresses. The shape of the heating and cooling pattern, the duration of the heating and cooling, and the number of thermal cycles are used to control the size of the defects and residual stresses obtained. The defect is grown without initial flaw or other nucleator. The defects correspond to natural flaws in terms of morphology and also of the signals obtained with NDT methods, and are suitable for use in, for example, NDT-qualification blocks.