The relationship between x-ray stress measured value and applied stress in elastic/plastic deformation region in tensile testing

Recently in Japan, the 2D detector X-ray stress measurement equipment has developed, and requests of on-site measuring the stress on structural components are increasing. On the other hand, high residual stress, which exceeds its tensile strength stress, is often observed on welded construction parts, and sometimes it causes defects or damage. We report a result of clarified characteristics of X-ray diffraction stress value (XRD) in which exceeds the yield point in the plastic strain region on steel (SM490) and stainless steel (SUS316). For studying the correlation with XRD measurement results and the stress value, we installed flat plate test specimens in the tensile test machine and cyclically loaded to the plastic strain region to simulate the welding structure under load. The XRD measurement values indicated a high correlation with the actual stress value. These results confirm that the XRD measurement values give the actual stress condition of the material under load, irrespective of elastic-plastic deformation. XRD measurement is not only applicable for measuring internal stress but also measuring combination of internal and external stress on a material. Consequently, XRD measurement can also be used to measure the loaded stress conditions of a structure (this stress is also called dead load or static load). Moreover, this outcome expands function of XRD from a specialized measuring method for residual stress to various structural conditions. (author)