Estimating 3D ejecta velocities during high-velocity impact experiments

Hypervelocity impacts into heterogenous materials like concrete are common in defense, industrial, and planetary science applications. The macroscopic strength of concrete is controlled by its constituents at lower length scales, including aggregates, cement phases and their water content, microcracks, and voids. Traditional continuum modelling of concrete does not account for the heterogeneity associated with the material strength due to the presence of these components, instead assuming a uniform strength throughout the material. In this work, we first perform hypervelocity impact experiments on concrete in a two-stage light gas gun with 3 mm spherical aluminum projectiles and impact velocities ranging from 1-2 km/s. Post-mortem analysis of the samples using X-ray tomography and nanoindentation allows us to estimate the extent of the crater and the damage throughout the sample. A Material-Point-Method (MPM) numerical scheme in the multiphysics framework GEOS, capable of simulating large deformations typical of impact problems, is then used to replicate the experiments. The major goal of these simulations is to determine whether spatial strength distributions (e.g., Weibull or other) provided to impact specimens allow us to reproduce the fracture patterns, crater profiles, and sub-surface damage observed in the impact experiments. This study will advance our understanding of the dynamic response of heterogeneous materials subjected to shock loading and assess the applicability of continuum modelling with strength variability to capture such phenomena.