| Summary: | An investigation of the high-strain-rate mechanical properties, deformation
mechanisms, and fracture characteristics of a Zr-based bulk metallic glass (BMG) and its composite with tungsten was conducted through the use of controlled impact experiments and constitutive modeling. The overall objective of this research was to determine the high-strain-rate deformation and failure mechanisms of a BMG and its composite as a function of stress state and strain rate, and
describe the mechanical behavior over a range of loading conditions. The research involved performing controlled impact experiments on BMG
composites consisting of an amorphous Zr57Nb5Cu15.4Ni12.6Al10 (LM106) with
crystalline tungsten reinforcement particles. Monolithic LM106 was also examined to aid in the understanding of the composite. The mechanical
behavior of the composite was investigated over a range of strain rates (10^3 s^-1 to 10^6 s^-1), stress states (compression, compression-shear,
tension), and temperatures (RT to 600 C) to determine the dependence of mechanical properties and deformation and failure modes (i.e., homogeneous deformation vs. inhomogeneous shear banding) on these parameters. Mechanical
testing in the quasi-static to intermediate strain rate regimes was performed using an Instron, Drop Weight Tower, and Split Hopkinson Pressure
Bar, respectively. High-strain-rate mechanical properties of the BMG-matrix composite and monolithic BMG were investigated using dynamic compression (reverse Taylor) and dynamic tension (spall) impact experiments performed using a gas gun instrumented with velocity interferometry and high-speed digital photography. These experiments provided information about dynamic strength and deformation modes, and allowed for validation of constitutive models via comparison of experimental and simulated transient deformation profiles and free surface velocity traces. Hugoniot equation of state measurements were performed on the monolithic BMG to investigate the high
pressure phase stability of the glass and the possible implications of a high pressure phase transformation on mechanical properties. Specimens were recovered for post-impact microstructural and thermal analysis to gain information about the mechanisms of dynamic deformation and fracture, and to examine for possible shock-induced phase transformations of the amorphous phase.
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