Polycrystalline solids under nonhydrostatic compression: Determination of strength from x-ray diffraction data

Abstract

A polycrystalline sample compressed in a diamond anvil cell (DAC) without any pressure transmitting medium develops a stress state at the centre of the sample that is axially symmetric about the load axis. The axial stress component is larger than the radial component and the difference t between the two is taken as a measure of the compressive strength of the sample material at a confining pressure that equals the mean normal stress. A proper analysis of the diffraction data yields t. The data taken with the radial diffraction geometry, wherein the incident x-ray beam is perpendicular to the load axis of the DAC, give reliable estimates of strength. The diffraction data obtained with the conventional geometry, wherein the incident x-ray beam passes parallel to the DAC axis, provide reasonable estimates of strength. However, even in this case, reliable strength data can be obtained by combining the measured pressure-volume data under nonhydrostatic compression and the hydrostat derived from an independent source. The determination of strength from high pressure diffraction data is discussed.