The effect of pre-strain on micro-scale strain concentration of austenitic stainless steel (Investigation using digital image correlation method)

It is difficult to predict the earthquake loading so the effect of pre-strain on fatigue strength was required to investigate. Especially, surface shape was changed when large plastic strain was applied. Strain concentration may be occurred by this surface changing. In this study, the effect of pre-strain on micro-scale strain concentration was investigated using in-situ observation. Tensile test for austenitic stainless steel, SUS316L, was performed under laser microscope to measure the height distribution. In addition, micro-scale strain distribution was measured using digital image correlation method. Pre-strains were applied range of 0-56 %. Loads were applied in the range of plastic strain after pre-strain. The results show that height of roughness due to pre-strain became large when the pre-strain was larger than 16 %. High strain area due to pre-strain did not depend on pre-strain because strain concentration was dominated by ease of plastic deformation of each grain. When plastic strain was applied after pre-strain, which was smaller than 8 %, strain distribution was not affected by pre-strain. This is because surface shape changing was small and strain concentration was dominated by ease of plastic deformation of each grain. On the other hands, local strain was increased when pre-strain was large. This is because surface shape changing became large and strain concentration due to surface changing was also occurred.