Building a Computational Framework to Model Microstructure Evolution during Laser-driven In Situ Diffraction and Shock Experiments

The interaction of short-pulsed lasers has enabled the ability to investigate the dynamic response of metals at extremes of high temperatures, high pressures, and high strain rates. Characterizing the material's response under these extremes is primarily based on in situ X-ray diffraction, wherein peak widths, broadening, splitting, and modifications are used to determine the presence of defects, quantify strains, and infer phase transformation. This talk will first demonstrate a computational framework to model microstructure evolution during laser direct-drive experiments wherein the laser interacts with the metal targets, resulting in ablation melting and the generation of a shock wave. The framework is based on modeling the microstructure evolution using classical molecular dynamics (MD) and quasi-coarse-grained dynamics (QCGD) simulations that are coupled with a continuum two-temperature model (TTM). The multi-scale computational framework allows the modeling of microstructure evolution during simulated laser direct-drive experiments to understand the role of laser energies on the melting kinetics of metal targets (Al), the acceleration of metal flyers, and laser-driven spall. Similarly, the computational framework allows the modeling of laser shock experiments to predict the defect (dislocation slip, deformation twinning, and or phase transformation) evolution behavior in BCC (Fe) metals in laser shock experiments wherein the metal targets do not interact with a laser. The microstructures can then be used to generate simulated diffraction patterns of the metal targets at various stages of loading to understand the contributions of microstructure features (phase fractions and defect densities) deformation mechanisms to peak shifts/splitting/broadening behavior and complement the interpretation of experimental in situ diffraction patterns. In addition, a new virtual texture (VirTex) analysis tool has also been developed to generate simulated EBSD maps and compare them with experimentally characterized microstructures of recovered samples. The framework with the various computational methods combined can serve as a digital twin of in situ laser shock and laser direct-drive experiments.