In-Situ Mesoscale Characterization of Dynamic Crack Initiation and Propagation Using X-Ray Phase Contrast Imaging

Predicting and controlling the failure of brittle materials against impacts have important applications in defense, mining, and medicine. To that end, the key is understanding at the mesoscale the events of crack initiation, propagation, branching, multiple crack interactions, and coalescence. Therefore, we developed an x-ray phase contrast imaging-based technique to directly visualize and quantify the cracking process. We chose to test our technique on single-crystal quartz because it has well-defined material and mechanical properties which computational models can use to accurately simulate the cracking process. Also, quartz serves as an ideal model material to developing experimental techniques/analysis and high-fidelity damage models for energetic materials and heterogenous geomaterials. To achieve the micron and nanosecond resolution required to resolve and track cracks in real-time, we use the high brilliance, spatially coherent synchrotron source at the Dynamic Compression Sector (Advanced Photon Source, Argonne National Laboratory) and the 8-frame LANL/DCS detector system coupled to a 150-μm thick single crystal LYSO scintillator. Quartz samples are uniaxially compressed at 103–104 s−1 strain rates with a custom-built Kolsky bar and stress-strain histories are measured using PDV probes. To characterize the evolving crack morphology, a physics-based inverse model is developed that converts the phase contrast-enhanced image intensity of the cracks into crack volume orientation distributions inside the sample. Using this model, we study how sample surface finish affects the dynamic behavior of cracks.