CAREER: Constrained Slip, Cracking and Instability in Extremely Anisotropic Nanolayered Solids

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This Faculty Early Career Development (CAREER) grant will focus on quantifying the effects of microstructural deformation mechanisms on the mechanical response of materials with nanolayered crystal structures, such as zinc, mica, and certain carbides. These materials hold tremendous promise for technologies where reliable performance is required under extreme environments, such as at elevated temperatures. However, their use in critical applications is severely limited as they exhibit extremely direction-dependent (anisotropic) behavior, cannot accommodate an arbitrary shape change, and are essentially brittle. On the other hand, the anisotropy of these materials enables them to undergo macroscale deformation via crystal slip, cracking, and/or instability at smaller scales, which in turn can significantly enhance their damage tolerance and ductility. This research project will provide the fundamental understanding of the microstructure-based mechanical response of nanolayered crystalline materials, paving the possibility of microstructural engineering to harness their damage tolerance and ductility for applications. This objective will be achieved with an integrated experimental-computational approach, which will result in a predictive modeling framework and experimental data at several length scales. The research activities will be complemented with a series of fully integrated educational and outreach activities. The educational activities will enhance undergraduate and graduate level engineering education through development of interactive instructional materials and a new course. The outreach activities will increase awareness of engineering by engaging Texas high school teachers in research and students in a summer camp, respectively.The objective of this research is twofold. First, develop an understanding of the synergistic effects of crystallographic slip, cracking, and instability in extremely anisotropic nanolayered materials, oxides, carbides and nitrides, via novel small-scale in-situ experiments. Second, develop and validate a crystal plasticity-based constitutive model incorporating non-Schmid effects, cleavage-like cracking, and local instability to predict microstructure-sensitive mechanical response of these materials. This will provide answers to following key fundamental questions: (i) What material property or a combination of properties affect the onset and propagation of slip, cracking and instability in single crystals? (ii) What are the synergistic effects of slip, cracking and instability on overall plastic deformation and damage tolerance? (iii) What is the role of non-Schmid effects on the onset of cracking and instability? (iv) How does intergranular cracking affect the damage tolerance of polycrystals of these materials?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.