Dynamic Characterization of Pressure-Dependent Elastic Moduli of Iron

Characterizing the inelastic response of materials under high strain-rates and pressures is critical for developing material models under these extreme conditions. It was previously shown that pressure effects on yield strength are more significant than strain-rate dependence under these condensed matter states. However, it is generally difficult to characterize the pressure dependence on yield strength, therefore, it is inferred from pressure-dependent shear modulus data. Recent experiments on phase transformed $varepsilon-$iron have shown a significant strength increase compared to its ambient $alpha-$phase with a change in the pressure dependent yield scaling as a possible key mechanism. In this study, symmetric pressure-shear plate impact experiments with window interferometry are conducted on iron at pressures ranging from $10-25$ GPa to extract the evolution of the elastic moduli of the phase transforming material. A diffration grating is sandwiched between the iron sample and a c-cut sapphire window which enables measurement of in-material normal and transverse particle velocities. The shear and normal release wave arrival times are used to determine the shear and longitudinal moduli at constant pressures. These elastic moduli are used to understand the role of pressure on the dynamic strength of iron while consequently probing the effect of shear on the phase transformation.