Stress in DAC
Stress in DAC Knowing the deviatoric stress in a DAC is important not only because it causes uncertainties in pressure measurement in the DAC, but also because it produces interesting shear-induced phenomena and can be used to estimate the yield strength of materials.
Deviatoric stress in a diamond anvil cell with gold as a pressure and stress indicator is measured by two complementary techniques using synchrotron radiation. The first method employs a white X-ray beam using energy dispersive X-ray diffraction. The incident X-ray beam is parallel to the load axis (coaxial) and the diffraction pattern is recorded at a low two-theta angle. Using powder diffraction patterns of polycrystalline gold, we measured the elastic strain of two crystal planes oriented normal to the diffraction vector. Stresses nearly parallel and perpendicular to the load axis can be calculated by stress-strain tensor relationship. The other method uses a monochromatic wiggler X-ray beam. In this case, the diamond cell is oriented so that the incident beam is perpendicular to the load axis (cross-axial). The diffraction pattern is recorded on an image plate area detector. Elastic strains responding to stresses perpendicular and parallel to the load axis can be measured and stresses of the same orientations can be calculated from the strain data. These measurements provide a lower bound of the actual differential stresses in a diamond cell. The measurement on non-hydrostatically loaded dayalite sample shows good agreement between those two methods
The stress measurement on forsterite sample by the coaxial geometry shows different stress distribution across the sample diameter. This may has to do with the different rheological properties of these two minerals.
