Effect of high strain rate on indentation in pure aluminum

The indentation properties of pure aluminum (99.9%, 3N aluminum) and high purity aluminum (99.999%, 5N aluminum) with respect to the strain rate dependence of strength are experimentally investigated in order to clarify the effect of strain rate on the micro-indentation test. A micro-indentation test using a Berkovich indenter was performed at loading rates of 0.7, 7, and 70 mN/s. In all of the specimens, the indenter was loaded to a maximum value of 1200 mN, and then was maintained for 30 s. In the 3N specimen, the dependence of the loading rate on the load was slight at loading rates of 0.7 and 7 mN/s, whereas the load at the loading rate of 70 mN/s was higher than the loads at loading rates of 0.7 and 7 mN/s. On the other hand, the load for the 5N specimen increased with the increasing loading rate. Thus, the effect of the loading rate on the load-displacement curve for the 3N and 5N specimens was similar to the strain rate dependence of strength for theses metals. In addition, the micro-indentation test was demonstrated to be strongly affected by high strain rate at a loading rate of 70 mN/s.