LEDS in ultra-high strain-rate deformation

Abstract

Regimes involving very high strains (ϵ ≈ 900%) and high strain rates (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon \approx 10^4 $\end{document} to 107 s−1) provide intriguing and often systematic examples of low-energy dislocation structures (LEDS). In this broad study, microstructure evolution in plane-wave shock-loaded Ni and Cu is compared with micro-structures observed in starting Cu and Ta shaped charge liner cones, and recovered jet fragments and slugs. These microstructures, in turn, are compared with corresponding end-point microstructures in a Ta explosively formed penetrator (EFP) utilizing TEM techniques. In addition, microstructures associated with a hypervelocity impact crater in Cu are compared with the Cu shaped charge microstructures. Dynamically induced grain refinement (subgrain formation) and recovery play varying and important roles in the evolution and features of observed LEDS, and are a manifestation of adiabatic heating due to high strain and strain-rate effects \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\alpha \left(\varepsilon \right)\left({\dot \varepsilon } \right)} \right) $\end{document}. LEDS, which are characteristic of high strain and ultra-high strain-rate deformation; cause an inversion in hardness and flow stress profiles since as these microstructures decrease in size, hardness will decrease. By contrast when low-temperature LEDS decrease in size, hardness increases.