Study of residual stresses distribution and the influence of restraint for a single weld bead in a low carbon steelusing neutron difraction technique

Residual stress is often the single largest unknown in an industrial damage situation involving welding. They are much more difficult to estimate and possibly larger than in-service stresses on which they superimpose. Fitness for purpose assessments normally require the conservative assumption that residual stress is at the level of the yield stress in tension near welds which have not been stress relieved. Residual stress measurement has up till now been dominated by techniques such as hole drilling, trepanning and cutting. These methods are invasive and can provide coarse or limited information. Neutron diffraction is a non-destructive testing ("NDT") technique relying on the interaction of the crystal structure with penetrating beams of thermal neutrons of known wave length. This paper describes the results of experimental neutron stress studies of residual stresses on two single weld bead specimens, one unrestrained and one restrained. The aim of the research was to start to characterize the residual stress distribution which arises in component due to various restraints during MIG welding.