Displacement field measurements in traditional and rotational diamond anvil cells

摘要

A digital image correlation-based method has been developed to measure the displacement field during compression in a traditional diamond anvil cell (DAC) and torsion in rotational DAC (RDAC) employing ruby fluorescence microscopy imaging. The optical arrangements for these measurements are adaptable at any commercial or customized micro-confocal system used for in situ high-pressure Raman or ruby fluorescence spectroscopy. In this paper, we describe details of the setup developed at Iowa State University along with a few demonstrative measurements for a zirconium sample. In particular, under compression in DAC, no adhesion zone is found, and relative sliding increases almost linearly along the radius. During torsion in RDAC, actual angular displacement of the material is found to be 5 times smaller than the rotation angle of an anvil, which is routinely used in the definition of the plastic shear for the determination of stress-strain curves and plastic strain-induced kinetics of phase transformations and grain refinement in materials. Obtained displacements can be used as the boundary conditions for finite element method (FEM) simulations of processes in DAC and RDAC instead of hypothetical friction conditions. After iterative fitting of FEM simulations and all measured fields from x-ray diffraction and absorption experiments, this will allow us to more precisely determine contact friction conditions and material parameters in the constitutive equations for elastoplastic flow and strain-induced phase transformations.