Dynamic strength characterization of phase transformed iron using pressure shear plate impact experiments

Understanding plasticity behavior of iron in its high pressure ε-phase is important to develop accurate models for hypervelocity impacts and to understand deformation mechanisms of planetary cores. Additionally, martensitic phase transformations, of iron and its alloys, provide a unique opportunity to study strength behavior as they play a crucial role in enhanced material properties and expand the material design space for various load-bearing applications. In this study, we investigate the pressure dependent dynamic strength behavior of both the ambient α-phase and high pressure ε-phase of iron at strain-rates of 10⁵ s^-1 and pressures to 42 GPa. High pressure - pressure shear plate impact experiments are conducted using a sandwich configuration to decouple the effect of pressure and shear thereby allowing us to probe strength once the sample reaches an equilibrated state of stress. We report the strength of ε-iron to be more than double the strength of α-iron potentially due to microstructural evolution during phase transition. Additionally, we present the evolution of yield strength with pressure, temperature, and strain for the first time, enabling more accurate modeling of extreme deformation phenomena associated with iron-rich celestial bodies such as planetary collisions.