A Contribution to X-Ray Measurements of Residual Stresses Induced by Welding

Abstract

The X-ray method of stress measurement is particularly important in the determination of residual stress since it is the only accurate method for measuring residual stress non-destructively and is very useful for determining local stress distribution. With a great progress in the equipment and technique for X-ray stress measurement, its accuracy has been much improved recently. For example, there has been almost no problem for measuring the residual stresses induced by heat treatment.As for the residual stress developed by welding, however, the possibility of applying the X-ray method is not certainly confirmed because of lack of actual data. In the present study, errors in stress measurements were examined for three specimens which were welded by large or small heat input. Especially, the dependence of the errors on the parameters representing the shape of X-ray diffraction profiles was studied.The main results are summarized as follows:(1) The residual stress induced in weld metal by the welding of small heat input can be measured with the error less than ±4kg/mm2 if the limit of confidence is set at 95 percent. The error is much more for the residual stress induced by the welding of large heat input.(2) The residual stress developed in heat affected zones can be measured with the errors less than ±5kg/mm2 irrespective of the level of heat input.(3) A good correlation is observed between the errors in stress measurements and the standard deviations of half-value breadth of X-ray diffraction profiles.(4) The loading of additional stress affects the errors of stress measurements.