Hardness of Metals Under Strain Rates 103 to 108 S-1

It is challenging to access the dynamic mechanical behavior of metallic materials under ultra-high strain rates up to 108 s-1. In this study, we obtained the dynamic behavior of metallic materials, including copper, aluminum, and steel, at strain rates ranging from 103 to 108 s-1 by Laser-Induced Projectile Impact Test (LIPIT) experiments. By measuring the energy dissipation of the microparticles and the impact-induced craters of the metallic materials, we determined the dynamic hardness of the metallic materials at different strain rates. We observed that the strain-rate-sensitivity of the hardness of the copper increases significantly after exceeding the critical strain rate, showing the transformation of deformation mechanisms from thermally activated mechanism to dislocation drag mechanism at ultra-high strain rates. With the aid of numerical simulations, we determined the critical strain rates of about 6.8×105 s-1, 2.8×106 s-1, and 3.1×106 s-1 for the copper, the aluminum, and the steel, respectively. Based on the relationships between hardness and strain rate, we proposed a modified Johnson-Cook constitutive model, which can describe the dynamic behavior of metallic materials under strain rates 103 ~ 108 s-1. This study presents an effective method for accessing the dynamic mechanical behavior of metals under a wide range of strain rates.