LEDS IN ULTRA-HIGH STRAIN-RATE DEFORMATION

Regimes involving very high strains (epsilon approximate to 900%) and high strain rates (epsilon approximate to 10(4) to 10(7) s(-1)) provid e intriguing and often systematic examples of low-energy dislocation s tructures (LEDS). In this broad study, microstructure evolution in pla ne-wave shock-loaded Ni and Cu is compared with microstructures observ ed in starting Cu and Ta shaped charge liner cones, and recovered jet fragments and slugs. These microstructures, in turn, are compared with corresponding end-paint microstructures in a Ta explosively formed pe netrator (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 refine ment (subgrain formation) and recovery play varying and important role s in the evolution and features of observed LEDS, and are a manifestat ion of adiabatic heating due to high strain and strain-rate effects (c c(epsilon) (epsilon)). LEDS, which are characteristic of high strain a nd ultra-high strain-rate deformation, cause an inversion in hardness and now stress profiles since as these microstructures decrease in siz e, hardness will decrease. By contrast when low-temperature LEDS decre ase in size, hardness increases.