Response of a Zr-based bulk amorphous alloy to shock wave compression

Plane shock wave experiments were performed on bulk amorphous alloy (BAA) samples having a nominal composition of Zr56.7Cu15.3Ni12.5Nb5.0Al10.0Y0.5. Peak compressive stresses ranged from 4 to 16.4 GPa. Piezoelectric pins and a velocity interferometer were used to measure elastic shock speeds and particle velocity histories, respectively. The elastic Hugoniot curve was determined and the Hugoniot elastic limit (HEL) was measured to be approximately 7.0 GPa, a value significantly higher than expected from quasistatic uniaxial stress data. Impact loading beyond the HEL results in a distinct two wave structure due to elastic-plastic deformation. Our data also show clear evidence for strength loss under shock loading above the HEL. Unlike most metals, the present data show distinct elastic response during unloading. We present a continuum model to describe the deformation response of the BAA to shock loading. Simulations using this time-dependent, strain-softening strength model were able to successfully match the measured wave profiles. The calculated profiles indicate that the characteristic time for stress relaxation is very small (few nanoseconds) and confirm that a significant loss of strength occurs as the plastic wave propagates through the material. When the material is shocked to a peak stress of 16.4 GPa, our model indicates that the yield stress in the shocked state is reduced by at least 0.7 GPa from its value of 2.7 GPa at the HEL. (c) 2006 American Institute of Physics.