Measurement of plastic strain induced by seismic loading using EBSD and indentation test

Electron backscatter diffraction (EBSD) measurements and an indentation test were applied to measure the plastic strain induced by tensile and fatigue tests using Type 316 stainless steel. It was shown that the local misorientation obtained by EBSD measurements correlated well with the degree of plastic strain. Furthermore, by investigating the statistical distribution of the local misorientation averaged for each grain, it was possible to distinguish the source of strain (cyclic or uniform strain). By the indentation test, it was shown that the hardness could be a parameter for plastic strain estimation, the accuracy of which was about ±1.5%. A detailed investigation using the nanoindentation method revealed that the variation in hardness was attributed to microstructural inhomogeneity, which was evinced by the local misorientation. Also, the estimation of the standard deviation of hardness allowed the source of strain to be identified. It was concluded that the indentation test can be used for estimating the degree of plastic strain induced by seismic loading in nuclear power plant components. (author)