Parameterization of a rate-dependent model of shock-induced plasticity for copper, nickel, and aluminum

A mechanistic model of shock-wave-induced viscoplasticity is parameterized for three polycrystalline metals: Cu, Ni, and Al. The model is also extended to higher stress wave amplitudes by incorporating homogeneous dislocation nucleation within the constitutive framework. Steady shock waves are simulated to demonstrate the model and compare results to experimental data. Stress wave amplitudes of up to 30 GPa have been simulated in each metal; these stress waves generate strain rates of up to ∼1010 s−1 in the shock front. Model results compare favorably with experimental velocity profiles, dynamic stress–strain curves, the Swegle-Grady scaling law, and non-invasive measurements of shear strength in the shocked state. Furthermore, simulated stress-strain-rate profiles exhibit points of self-intersection (loops) because the mobile and immobile dislocation densities have been assigned as internal state variables. Such loops, which have been observed in experiments, are not captured by flow functions that are based on a single monotonically-increasing internal state variable. Finally, the model of 6061-T6 Al alloy is revisited to ammend a prior conclusion regarding shear strength in the shocked state and the onset of homogeneous dislocation nucleation.