A Planar Biaxial Experiment Platform for In Situ High-Energy Diffraction Studies

Abstract

An experimental platform for multiscale studies of materials subjected to plane stress loads is presented. Coupling with far-field high-energy diffraction microscopy for grain-by-grain measurements of elastic strains and rotations provides an additional benefit; it enables the direct assessment of elastic vs. inelastic deformation of the gauge sections of cruciform specimens subjected to plane stress loadings, without any a priori assumptions of the form of constitutive relationships, resolving a long-outstanding challenge of multiaxial mechanical testing. Specifically, a planar biaxial mechanical load frame with four independent hydraulic actuators capable of applying arbitrary loading paths and ratios of tension and compression was designed and built for in situ diffraction experimentation. The load frame is integrated for use at the Argonne National Laboratory Advanced Photon Source (APS) synchrotron, Sector 1, 1-ID-E endstation and the Los Alamos Neutron Science Center (LANSCE) spallation neutron source, Spectrometer for Materials Research at Temperature and Stress (SMARTS) instrument. Cruciform specimen geometries were designed to experience loading ratios in the gauges commensurate with those applied at the grips, and to minimize interference with diffracted X-rays and neutrons. The finite element models used to design the cruciform specimen geometries were experimentally validated using stereo digital image correlation measurements. This complete planar biaxial in situ diffraction platform provides a new capability for studying multiaxial micromechanics of crystalline materials (e.g., elastic, slip, twinning, phase transformation) and their dependencies on grain size, location, texture, and neighborhood characteristics.