Effect of dynamic strain rate on micro-indentation properties of pure aluminum

¹ National Defense Academy, School of Systems Engineering, 1-10-20 Hashirimizu Yokosuka Kanagawa, Japan
² National Defense Academy, Graduate Student, School of Systems Engineering, 1-10-20 Hashirimizu Yokosuka Kanagawa, Japan
³ Columbia University, Graduate Student, 500 West 120th Street, New York, USA
⁴ Columbia University, 500 West 120th Street, New York, USA

^a Corresponding author: ymda@nda.ac.jp

Published online: 7 September 2015

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.