Quantifying Dislocation Drag at Ultra-High Strain Rates with Laser-Induced Microprojectile Impact

With increasing deformation rates, the thermally activated dislocation glide transitions to a continuous glide of dislocations influenced by their interactions with phonons. Understanding dislocation-phonon drag is critical for designing materials for extreme conditions, but remains largely qualitative due to the difficulty of measuring materials mechanics at ultra-high rates. Here, we develop an impression-based approach combining laser-induced microprojectile impact and spherical nanoindentation to study the dislocation-phonon drag regime. We isolate and quantify dislocation-phonon drag by leveraging the similar deformation length scales and geometries, but different mechanistic regimes that are operative during microprojectile impact and spherical nanoindentation. We also develop a physically based constitutive framework that when combined with nanoindentation and LIPIT enables a full quantification of the dislocation-phonon drag regime. We present a discussion on the mechanistic contributions to the plastic work during microprojectile impact in a range of impact velocities producing strain rates up to 109 s-1.