HR: 09:15h
AN: V41B-06    [PDF]
TI: Deformation Experiments in the D-DIA Using High-Resolution Monochromatic Diffraction
AU: * Wang, Y
EM: wang@cars.uchicago.edu
AF: GSECARS, Univ. Chicago, 9700 S. Cass Ave., Argonne, IL 60439 United States
AU: Uchida, T
EM: uchida@cars.uchicago.edu
AF: GSECARS, Univ. Chicago, 9700 S. Cass Ave., Argonne, IL 60439 United States
AU: Rivers, M
EM: rivers@cars.uchicago.edu
AF: GSECARS, Univ. Chicago, 9700 S. Cass Ave., Argonne, IL 60439 United States
AU: Durham, W
EM: durham1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550 United States
AB: Differential stresses in polycrystalline MgO and CsCl samples under controlled axial strain are determined as a function of pressure and temperature in the Deformation DIA (D-DIA: Wang et al., RSI, 74, 3002, 2003) using monochromatic diffraction, with a two-dimensional X-ray detector and X-ray transparent sintered cubic boron nitride (cBN) anvils. Radiographic images and diffraction Debye rings are repeatedly recorded at various pressures during constant strain rate deformation. From the sample length change in the X-ray image, total sample axial strain can be determined. From the distortion of the diffraction rings recorded over the entire 360$\deg$ azimuth angles, elastic lattice strains can be accurately measured as a function of pressure, temperature, and differential stress. Linear lattice elastic theory is applied to convert lattice strains to differential stress (Singh, J. Appl. Phys., 73, 4278, 1993). The ability of the D-DIA to control differential stress separately from pressure (by deforming the sample while maintaining constant pressure) allows us to establish criteria for detecting yielding and to examine pressure and total strain dependence on yield strength. Analyses indicate that Singh's theory is adequate in describing the stress-strain behavior within the elastic regime. However, as some crystallites begin to yield, stress state becomes heterogeneous on the grain scale, resulting in significant change in the apparent anisotropy factor. This change can be considered as an indicator for the onset of yielding. Such details contain important information on rheology but previously could not be observed in conventional deformation and high-pressure (such as the diamond-anvil cell or multianvil) devices. Work is underway to model the stress distribution in polycrystalline samples after yielding, in order to connect stresses measured at the grain-to-grain level to conventional the force-over-the-area measurements. Our findings also raise questions on previous elastic constant measurements using diffraction, where differential stress levels are expected to be high. These data are likely to be influenced by heterogeneous yielding, in which case the elastic data thus obtained would be erroneous.
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 3902 Creep and deformation
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 5120 Plasticity, diffusion, and creep
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting