Deformation experiments using synchrotron X-rays: in situ stress and strain measurements at high pressure and temperature

An experimental technique for in situ stress and strain measurements at high pressure and temperature using synchrotron X-rays has been developed at the X17B beamline of the National Synchrotron Light Source. The strain is measured by correlating sample-length marks in recorded X-ray radiographs. The stress is measured by simultaneously collecting energy-dispersive X-ray diffraction patterns of the sample in two perpendicular diffraction planes. Differential stress in the sample is derived from the different lattice strains along the different orientations relative to principal stress direction. Example measurements are conducted to study rheological properties of fayalite. Accuracy of the measurement is about 10–100 MPa for stress and about 10−4 for strain.