Plastic Strain Effect in Progressive Multi-Cycle Nano-Indentation Measurement

Properties of materials and their variations in depth direction in the same location could be measured directly by progressive multi-cycle (PMC) nanoindentation method. But influences of strain-hardening on measured results in this process haven’t been researched thoroughly. Measurements on an austenitic steel sample and a fused silica sample were conducted by PMC nanoindentation and standard nanoindentation methods, and differences of the results by two methods of the two materials were analyzed. It was found that hardness of austenitic steel measured by PMC method decreased monotonously with increased depth, while hardness measured by standard method decreased to stable value with increased depth. And properties of fused silica measured by both methods accorded much well. Based on analysis of plastic strain during indentation process, it was deduced that austenitic steel with high plasticity could introduce second convergence of plastic strain and stress in PMC indentation process, which made measured hardness decrease monotonously with increased depth.