Microstructural examination of quasi-static and dynamic shear in high-purity iron

Numerous studies have examined the microstructural evolution of adiabatic shear bands through the utilization of the forced shear or "tophat" test specimen. While the geometry of this specimen does not allow for the microstructure to play a dominant role in the location of a shear band, the forced shear specimen has been shown to be particularly useful for characterizing the influence of parameters such as strain rate, temperature, strain, and load on the microstructural evolution within a shear band. Additionally, many studies have also utilized this geometry to advance the understanding of shear band development in a number of materials. In this study we systematically examine the influence of integrated loading states on the dynamic shear localization response of high-purity Fe by varying the geometry of the forced shear specimen. Post-mortem characterization was performed to quantify the width of the localizations and to examine the microstructural and textural evolution of shear deformation in a body centered cubic (BCC) metal. Increased instability in mechanical response is strongly correlated with development of enhanced intergranular misorientations and high angle boundary evolution. Stress state was also critical to the localization process. Single-component, simple shear configurations were found to promote instability over multi-component stress states. In addition, these geometries resulted in traditional BCC deformation shear textures, while multi-component stress states led to less developed textures.