Diffraction Microscopes to Capture Shock-Induced Plasticity

The microscopic origins of how plastic failure starts during shock waves is poorly understood, especially at the atomic scale. Limited techniques can measure the ultrafast and apparently stochastic dynamics required to uniquely describe how localized shear, hotspots and stresses can drive the elastic compression at 10⁸ strain rates to induce kinetically dominated plasticity. My group is developing ultrafast X-ray microscopes with crystallographic contrast to measure plasticity across length- and time-scales. Using X-ray topography and dark-field X-ray microscopy, we collect images along the X-ray diffracted beam (i.e. Diffraction Contrast Microscopy, DCM) that resolve the long-range strain and misorientation fields that emanate from defect cores that project onto that crystallographic plane. In this way, we have been able to resolve the dynamics of dislocation patterning, the evolution of dislocation densities, and discrete dislocation avalanches. In this talk, I will introduce our optical, analytical, and theory framework for DCM in dynamic compression. I will describe our optical developments at XFELs that allow us to image shock mechanics with 2-0.15 μm resolution across hundreds of micrometers. I will then discuss the computer-vision tools we have developed to quantify the information about specific types of defect structures in our images, using simulations we have developed to predict DCM images for DDD-predicted defect structures. With this framework, I will show how our new tools are starting to shed light into shock-induced plasticity and strength in diamond – with experiments we performed at the Linac Coherent Light Source. Our new approach holds key opportunities to map out the potential energy landscape of the kinetically dominated plasticity observed in shock physics.