CAREER: The Mechanics of Hierachically Multistable Metastructures

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This Faculty Early Career Development (CAREER) grant will support research investigating the mechanics of a new class of material systems exhibiting intrinsic reshaping and property adaptation. Conventional engineering materials have fixed macroscopic properties that are derived from specific atomic compositions. This limits the available design possibilities when compared to biological systems that exhibit many unconventional and time-varying properties, like inherent self-shaping. This biological characteristic can be attributed to unique microstructures comprising hierarchical geometrical arrangements, spanning several length scales. A unique geometrical characteristic enabling property adaptation is multistability; i.e. a system’s capacity to exhibit several coexisting states. Pursuing this concept, this research aims to derive models to harness (locally) multistable arrangements, or metastructures, that display macroscopic adaptability from changes at the local scale. Understanding the mechanics of such multistable structures will facilitate the development of advanced structures and robotic materials relevant to the aerospace, biomedical and robotics industries. This will expand the U.S. scientific and technological edge, ultimately benefiting the economy and society at large. Furthermore, this effort’s multidisciplinary (engineering and material science) nature allows for promoting STEM education. This is pursued by establishing teaching strategies for courses with multidisciplinary content and offering design experiences partnering undergraduate and graduate students.The novel concept of hierarchical multistability in material systems entails the appearance of multiple coexisting global configurations for a single combination of local (multistable) states, thereby breaking the one-to-one correspondence between local and global states commonly found in multistable metamaterials. The objective of this project is to understand the fundamental mechanics responsible for the manifestation of hierarchical multistability. Specifically, this effort aims to determine the local (unit-cell) and global (metastructural) interaction mechanisms responsible for the appearance of hierarchical multistability. The central hypothesis is that long-range effects in the strain field develop compliant deformation modes in the metastructure due to local distortions introduced from changes of state at the unit scale. Building on this hypothesis and departing from considering nearest-neighbor coupling, this research aims to derive long-range interaction models between unit cells. The characteristics of hierarchical multistability opens novel avenues for designing programmable structures that couple sensing, computation and property adaptation. The resulting metastructures are relevant to the aerospace, biomedical and robotic industries. Furthermore, the results from this effort are leveraged to develop an educational plan to encourage multidisciplinary STEM education and research by: 1) offering multidisciplinary design experiences partnering with Purdue University’s EPICS program; and 2) establishing pedagogical strategies for teaching courses with multidisciplinary content.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.