Combined Computational-Experimental Study of Shock Induced Plasticity in Tantalum

The shock induced elastic-plastic transition in body-centered cubic (BCC) metals has been measured experimentally and displays a unique behavior of the Hugoniot elastic limit (HEL). Kositski and Mordehai [1] proposed that competition between dislocation nucleation and glide, which depend on initial microstructure, is responsible for this abnormality. To understand the HEL, both experiments and computations were performed: Experimentally, as-received and annealed Ta samples were shocked in a gas gun setup and their free surface velocities were measured. The differences in the HEL between the different samples are attributed to dislocation nucleation, thus one needs to quantify it. Dislocations are more likely to be nucleated from defects and thus the activation parameters for dislocation nucleation from grain boundaries were calculated: Molecular Dynamics (MD) simulations to study these processes in Ta bi-crystals were performed and analyzed in a range of temperatures. Finally, incorporation of the MD results in a multiscale model was examined.

[1] R. Kositski, D. Mordehai, “A dislocation-based dynamic strength model for tantalum across a large range of strain rates”, J. Appl. Phys. 129, 165108 (2021).