鋭い圧子押込で得られる荷重変位関係に及ぼすひずみ速度の影響

The effect of strain rate on load-displacement relations by instrumented sharp indentation was investigated in pure copper having strain rate dependence of strength. A micro-indentation test was carried out using sharp indenter (Berkovich type) at a loading rate of 70 mN/s. Finite element method (FEM) was used for the indentation analysis in comparison with experiment. The strain rate dependency of strength for this copper was examined by quasi-static tensile test (2.4×10-5 and 2.4×10-3 s-1) and the impact tensile test by means of one bar method (6.0×102 s-1). It was shown that the load-displacement curve obtained through the static-FEM analysis were inconsistent with that obtained through the micro-indentation test. The Cowper-Symonds model, which includes the strain rate dependence of strength, was then used in the dynamic-FEM analysis. The load-displacement curves calculated by the Cowper-Symonds model showed good agreement with the experimental results. As a result of the dynamic-FEM analysis, the strain rate at the early stage of testing reached the dynamic strain rate, approximately 3.0×101 s-1, underneath the sharp indenter. Thus, the indentation load-displacement relation was affected by the dynamic strain rate.