RESIDUAL STRESS MEASUREMENTS IN STRUCTURAL MATERIALS BY NONDESTRUCTIVE TECHNIQUE

摘要

Characterization of residual stresses in austenitic Type 304L stainless steel (SS) and martensitic Alloy EP-823 has been performed by positron annihilation spectroscopy (PAS) using cold worked, welded and plastically-deformed materials. Welded specimens consisting of both similar and dissimilar materials have been tested. Cylindrical specimens have been subjected to plastic deformation at stresses beyond the yielding load. The plate materials of both alloys have been subjected to cold reduction at different levels. Characterization of residual stresses in all three types of specimen configuration has been performed in terms of the line shape parameters (S, W & T) obtained from the positron annihilation peak. The results indicate that for cylindrical specimens, the magnitude of S-parameter was enhanced at higher applied tensile stresses, as expected. With respect to the cold worked specimens, the magnitude of the S-parameter was enhanced at the intermediate level of cold-deformation. The preliminary data on a welded specimen consisting of Alloy EP-823 and Type 304 L SS on opposite side revealed compressive residual stresses on the EP-823 side at the fusion line (FL), as indicated. The welded specimen consisting of Type 304 L SS on both sides showed tensile residual stresses at the fusion line as indicated by the T-parameter. Characterization of a specimen having 7.2 percent reduction in thickness by transmission electron microscopy (TEM) revealed dislocations, as anticipated. The comprehensive data are presented in this paper.