RESIDUAL STRESS MEASUREMENT SIMULATION IN A TYPE 316 STAINLESS STEEL GIRTH-BUTT WELD JOINT

Several techniques exist to measure residual stresses, but most only work close to the surface of a component. The deep-hole drilling (DHD) method [1] provides complete, through-thickness, measurements of residual stress with high spatial resolution which can be used to validate numerical models. In common with all mechanical strain release methods of residual stress measurement, extra care must be taken when making measurements on components containing highly triaxial residual stress fields which are close to yield. This is because the introduction of a free surface, created as part of the measurement procedure, can lead to plastic redistribution of the residual stress field which is not accounted for in the elastic inversion algorithms of the experimental procedure. This paper seeks to demonstrate the usefulness and accuracy of the DHD method in a component predicted to contain a triaxial residual stress field by comparing measurements and the results of a DHD simulation on a type 316 stainless steel pipe with girth-butt weld joint. Step 1, results are presented from three-dimensional finite element (FE) simulations of the original girth weld. Step 2, the residual stresses predicted from these simulations are mapped onto a new mesh, designed in order to permit a simulation of the DHD measurement method detailed above. Step 3, an FE simulation of the DHD procedure was undertaken, and the predictions of the radial distortion of the initial reference hole were used in the usual experimental inversion algorithm. This permitted a simulation of the DHD measured residual stresses to be obtained and compared with the predictions of the initial FE model. The effects of different material models as well as the measurement paths were also considered. Finally, step 4, FE predicted residual stresses, DHD simulated residual stresses and actual DHD measured residual stresses were compared and conclusions concerning the accuracy of the DHD measurement procedure were made.