Abstract. Indentation is widely used to investigate the elastic and plastic properties of mechanical materials, which includes the strain rate sensitivity. The indentation exhibits an inhomogeneous strain distribution in contrast to compression and tensile tests with homogeneous deformation. Thus, the strain rate of the indentation may form the inhomogeneous distribution. Therefore, the effect of strain rate distribution of the indentation on pure aluminum with respect to the strain rate dependence of strength in order to clarify the effect of the strain rate on the indentation technique. First, the numerical simulation was established using the Cowper-Symonds equation as the dynamic constitutive equation. Secondary, the strain rate distribution was calculated from the equivalent plastic strain distribution. The strain rate distribution was quite different from the strain distribution, which showed that the strain rate at the crater rim was higher than that beneath the indenter. Finally, we try to perform the averaging of strain rate distribution in order to make an index of strain rate in the indentation. The average of strain rate distribution was calculated using the equivalent plastic strain above a boundary value that is the critical strain and the representative strain. There is correlation between the average strain rate and the loading curvature, which shows that the average strain rate can express as the representative of strain rate for the indentation technique.

Indentation is widely used to investigate the elastic and plastic properties of materials, which include strain rate dependence. However, the results of the general micro-indentation test were affected by the microscopic scale of materials (e.g., surface roughness, and crystal grain size distribution), since the displacement was small. In the present study, we develop the sharp millimeter indention expanded displacement without the microscopic scale of materials. Furthermore, the effect of displacement rate on the sharp millimeter indentation was evaluated using the quasi-static and impact indentation test. In this study, high purity aluminum, with 99.99 mass%, was selected as the material with strain rate dependence of strength. The quasi-static indentation test was performed using the universal testing machine at the displacement rate of 8.3×10-7 m/s, 8.3×10-6 m/s, and 8.3×10-5 m/s. The impact indention was carried out at the displacement rate of approximately 3×100 m/s. The loading curvature decreased with increasing displacement immediately after indentation, and then this value was convergent, regardless of the displacement rate. It was clear that this convergent value was affected by the displacement rate.

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