Fundamental Investigations of Adiabatic Shear Localization in Materials with Mesoscale Heterogeneities

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Progress in critical technologies is often enabled by advances in development of new materials, an important class of which is high-performance structural materials. The primary function of these materials is to withstand severe mechanical loads, often in harsh environments, with minimal weight. This award supports fundamental research to develop new and relatively unexplored materials in which the mesoscale structure of materials can be rationally designed to result in superior performance. The project will advance future materials design strategies for dynamic loading applications, examples of which include high speed impact of protective armor, explosive loading of structures, and high-speed machining, thereby advancing national health, prosperity, and welfare; and securing national defense. The fundamental materials design principles that will emerge from this research can be exploited by modern additive manufacturing technologies in manufacturing materials with rationally designed mesoscale architectures. In addition, the award supports educational activities for undergraduate students who will work in multidisciplinary teams to develop short educational animations and disseminate scientific discoveries in a manner accessible to middle and high school students. The award also supports development of educational modules for an outreach program at Brown University that serves students from underrepresented groups in science and technology. The research program focuses on understanding the role of mesoscale heterogeneities in the formation and propagation of adiabatic shear bands (ASB), which are an important mechanism by which materials and structures subjected to dynamic loading often fail catastrophically. The research aims to experimentally investigate the mechanics of how a propagating ASB interacts with a controlled heterogeneity through in situ high-speed microscopy, which is a new technique capable of high spatial (up to 0.7 micrometer) and temporal (250 nsec) resolutions simultaneously. When a propagating ASB encounters a heterogeneity of controlled geometry and properties, there are several possible outcomes: the ASB can get arrested, deflected or continue to propagate through and across the heterogeneity. Through in-situ measurement of the transient deformation fields during such interactions, the research seeks to determine the conditions under which each outcome prevails. Computational simulations of ASB-heterogeneity interactions will be carried out to interpret the experimental results, guide the experimental design with respect to the choice of material properties and geometry of the heterogeneities, and develop a predictive capability to help design more complex mesoscale architectures. The new fundamental knowledge gained from these studies can help develop novel mesoscale architectures with significantly enhanced resistance to ASB.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.