We have multiple projects where we are studying the dependence of dynamic behavior of materials on microstructure and loading conditions. To achieve this goal, the material microstructure is characterized before shock loading followed by use of a gas-gun to induce damage in material via spall recovery experiments. The samples are recovered after the experiments and post-mortem characterization performed to understand where and when damage nucleated in a material.

The past several years has witnessed a surging popularity of two techniques for defect characterization in crystalline materials: (i) scanning transmission electron microscopy (STEM) using diffraction contrast imaging, and (ii) electron back-scattered diffraction (EBSD) mapping. We have linked these capabilities by employing a field emission SEM equipped with a transmission detector for defect characterization – termed transmission SEM (TSEM). Imaging modes that are similar to conventional CTEM bright field (BF) and dark field (DF) and STEM have been explored. We have further demonstrated how the richness of information encoded in EBSD patterns is amplified by a new generation of direct electron detectors that enable high speed mapping and acquisition of high-fidelity patterns that can be used for statistically-meaningful defect analyses. We plan to employ these techniques for in situ tensile experiments to study the nature of dislocations dynamics in the structural alloys of interest to this program.

The Boechler Research Group is broadly interested in designing materials with new mechanical properties. Two major mechanisms that are studied to this end are designed material microstructure and strong nonlinearities. These mechanisms have drastic implications for a material's dynamic (e.g. impact, vibration, and signal transmission) response, and thus their effective properties. In the above animation, Boechler Research Group researchers measured, via high speed video, the impact dynamics of a microstructured material that has a microstructure-derived nonlinear softening response in compression.

It is widely accepted that most materials are heterogeneous and possess a hierarchical structure where the coarse-scale behavior is greatly affected by the fine-scale details (i.e., the microstructure). Because the traditional one-scale continuum mechanics does not suffice to investigate the effect of microstructure on materials’ properties, significant effort has been devoted to the development of multiscale computational models. Leveraging these models for uncertainty quantification or designing architectured materials with tailored properties relies on microstructure characterization and reconstruction (MCR) techniques which systematically build spatially varying unit cells at various length scales. In this project, we will exploit our expertise in MCR to understand how the dynamic response of a multiscale system is affected by spatially varying micro- and meso-structures of various classes.

To understand the dynamic behaviors of the microscale grain structures, we will apply physics-based multiscale models to determine grain-level strength and plastic deformation and reveal how their deformation behaviors depend on structural features in nano- and micro-scales. We will use three simulation techniques involving atomistic simulation, dislocation dynamics, and mesoscale crystal plasticity to uncover dislocation slip, pile-up, and dislocation patterning.

The team works closely with multidisciplinary researchers at the interface of engineering, computer science and applied mathematics and strives to find simple and powerful engineering solutions.