Inverting Multiple Residual Stress Components from Multiple Cuts with the Contour Method

An extension of the contour method is presented which allows the measurement of multiple stress components by making multiple cuts. In the contour method, a body is carefully cut in two using wire electric discharge machining (EDM). The contours, or shapes, of the cut surfaces are then measured and used to calculate the original residual stress normal to the cut plane using a simple finite element calculation. In the extension presented here, the two pieces from the original body can be cut again in a transverse direction, and the contours of the new cut surfaces are measured. The stresses calculated on the planes of these second cuts have been affected by the first cut. Then a simple inverse reconstruction using information already provided by the calculation for the first cut gives the original stresses on the plane of the subsequent cuts, removing the effect of the first cut. The method is demonstrated first by means of 3D FE simulations, and possible errors are explored. In order to validate the method, an experimental test on a quenched plate of HSLA-100 steel was carried out.