Zinc single-crystal deformation experiments using a "6 degrees of freedom" apparatus

A new experimental technique to study crystallographic slip system activity in metallic single crystals deformed under a condition of uniaxial stress is applied to study the behavior of Zn single crystals. The experimental apparatus promotes unconstrained shape change of inherently anisotropic materials under a condition of uniaxial stress by allowing three translational and three rotational degrees of freedom during compression; hence, we have named the experiment "6 degrees of freedom" (6DOF). The experiments also use a three-dimensional (3-D) digital image correlation (IC) system to measure full-field displacements, which are used to calculate strain and make direct observations of slip system activity. We show that the experimental results associated with a pristine zinc single crystal are precisely consistent with the theoretical predicted shape change (sample distortion) assuming that the most favored slip system on the basal plane is the only one that is active. Another experiment was performed on a processed and annealed Zn single crystal to investigate slip that is inconsistent with the critical resolved shear stress (CRSS) theory. These experiments on zinc illustrate the ability of the 6DOF experiment, together with image correlation (IC) data, to measure slip system activity with a high degree of fidelity.