sample volume from in-situ x-ray diffraction data. X-ray diffraction abilities The design of the anvils used in the D-DIA allows for the transmission of synchrotron X-ray radiation through the sample. This X-ray data can be used for both in-situ stress and strain measurements to be taken during the deformation of the sample. Strain In-situ [strain] measurements can be made by collecting and analyzing x-ray radiographs. Typically this is achieved by utilizing a fluorescent yttrium aluminum garnet (YAG) crystal in combination with a charge coupled device (CCD) camera. By placing metal foils (typically platinum or nickel) on the top and bottom of the sample, the total sample length can be easily observed in the x-ray radiographs during the deformation experiment. Using the initial length measurement and subsequent length measurements during deformation, the following relation can be used to calculate strain. ε = (L0 – L)/L0 Where strain is equal to the difference of the initial and final length, divided by the initial length. Stress The determination of stress is made utilizing data gathered from in-situ [x-ray diffraction]. Diffraction data is used to determine the d-spacing of certain crystallographic planes within the sample and from these values of d-spacing there exists various ways to determine the stress state. A common way of calculating the differential stress inside the polycrystal utilizes the d-spacing values measured in the radial and axial directions of the cylindrical sample. This technique takes advantage of the cylindrically symmetric stress field that is imposed by the D-DIA, but also requires the assumption of a Reuss state (or isostress state) of stress throughout each grain in the polycrystal. The other common technique of deviatoric stress determination utilizes differential lattice strains and single crystal elastic constants. In this method the lattice strain is first calculated using measured values d-spacing dm(hkl), as well as d-spacing values determined under hydrostatic conditions dp(hkl). εD(hkl) = [dm(hkl)- dp(hkl)] / dp(hkl) Once the lattice strains are calculated, the product of these values and the x-ray shear modulus, also known as the diffraction elastic constant GR(HKL), provides the stress on different lattice planes, τ (HKL). τ(HKL) = [(2GR(HKL)] εD(hkl) References Measurement