CAREER: Integrated Research and Education on the Dynamic Behavior of Metal-ceramic Layered Solids

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This Faculty Early Career Development Program (CAREER) award supports research to generate new knowledge related to an emerging class of unique materials, known as MAX phases. These hybrid metal-ceramic materials form layers on the atomistic scale, much like pieces of paper stacked together, which allows the layers to locally kink instead of crack under load. This kinking behavior has only recently been discovered, yet if understood, has the potential to provide tougher, lighter and more damage-tolerant materials for our nation's aging energy, communication and transportation systems. As a result, MAX phases will be investigated with varying stacking sequences and layer orientations across a variety of real-world loading conditions, including impact, and dynamic fatigue and fracture. In addition, experimental techniques utilizing cutting edge high-speed imaging coupled with surface acceleration mapping under these complex-loading scenarios will be performed, that are able to extract more material behavior information than classical techniques. These findings will provide meaningful input for predictive computational models in structural design leveraging MAX phases, as well as other similar advanced materials. This work brings together multidisciplinary efforts in materials science, and applied and theoretical mechanics. Novel means to reach untapped local communities at all ages will be enabled through a dance-mechanics education and outreach program. The research and outreach components highlight the innate creativity and correlations involved in both, and aims to inspire the next generation of STEAM (science, technology, engineering, arts and mathematics) enthusiasts. This research focuses on an emerging class of materials, MAX phases, a family of layered hexagonal early transition-metal carbides and nitrides. These materials exhibit a newly classified defect deformation mechanism termed ripplocations, a nanoscale buckling phenomena, which accommodates strain in a different manner than dislocation motion in plasticity or bond rupture in fracture, and leads to the formation of nonlinear kind bands (NKB) under load. While a notable portion of the materials science community is examining these 3D layered solids, relatively little research exists pursuing their behavior on the meso- to continuum level. This effort aims to fill that gap through three highly integrated experimental research foci. The first characterizes deformation behavior varying strain rate and stress states, as well as layer orientation and stacking sequences, utilizing nonlinear buckling theory to determine the driving parameters in NKB formation. The second quantifies crack tip energetics in dynamic fracture leveraging a hybrid experimental-numerical scheme, as well as explores impact fatigue, extending the classic Paris Law for temporal effects. The third pursues damage behavior, conducting inertial impact experiments exploiting the Grid Method and the Virtual Fields Method, an emerging inverse technique. The extensive investigations on MAX phases will shed light on competing ductile, pseudo-ductile and brittle deformation mechanisms across length and time scales, thus making a significant contribution towards systemically capturing, understanding and optimizing these unique layered solids. More broadly, the findings will help understand how anisotropic materials accommodate strain under complex loading conditions, and paves the way for specifically textured (defect engineered), functionally graded, and/or hierarchical material design.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.