Effect of Strain Rate on the Dynamic Hardness in Metals

Traditionally, the hardness of materials is determined from indentation tests at low loading rates (static). However, considerably less work has been conducted in studying the dynamic hardness of materials using relatively high loading rates. In the present work, two models are used to predict strain rate dependency in hardness. The first model is a power law expression that is based on the dependence of the yield stress on the strain rate. This model is relatively simple in implementation, and it is quite easy to determine its parameters from simple uniaxial experiments. The second model is a micromechanical based model using Taylor’s hardening law. It utilizes the behavior of dislocation densities at high strain rates in metals in order to relate dynamic hardness to strain rates. The latter model also accounts for any changes in temperature that could exist. A finite element is also run and compared with the two models proposed in this work. Results from both models are compared with available experimental results for oxygen-free high-conductivity copper and 1018 cold rolled steel, and both models show reasonably good agreement with the experimental results.