CAREER: Fracture Mechanics of Soft Dissipative Materials

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This Faculty Early Career Development Program (CAREER) award will support fundamental research on the fracture resistance of soft elastomers and hydrogels. Soft materials that can undergo large reversible deformation have been widely utilized in industrial applications such as tires and soft adhesives, or emerging technologies such as soft robots, biomedical implants and stretchable display. In these applications, the underlying soft materials are required to be stretchable to enable functionality and yet fracture resistant to enhance reliability. Driven by this need, various physical or chemical mechanisms have been developed to enhance the fracture resistance of soft materials, and they share a common theme: to introduce energy dissipation or consumption by the material during deformation. However, theoretical modeling and experimental characterization of fracture in such soft dissipative materials are challenging due to the lack of understandings on the quantitative relation between energy dissipation and fracture resistance. This research program will establish experimental and modeling capabilities to uncover the complex nonlinear mechanics associated with soft material fracture, which will lead to quantitative principles for engineering new soft functional materials that are mechanically robust, as well as new tools to measure and predict fracture in soft materials. Thus, the research will promote the science of soft material fracture to advance the national health, prosperity, and welfare. As part of research, education and outreach programs will be developed to promote research of soft material fracture in academic, educational and industrial sectors by creating an interdisciplinary summer workshop, integrating research findings into curriculum and K-12 outreach activities, and building collaborations with industrial partners.A major challenge in soft material fracture is the large deformation near the tip of a crack, which causes nonlinear strain and stress fields as well as complex failure and dissipation behaviors. To address this challenge, a particle tracking method will be used to measure the crack tip deformation field in model soft materials under various fracture modes. For elastic materials, the experiments will provide data to assess the region of validity for existing crack tip asymptotic solutions, to discover new structures of crack tip fields, and to enable local evaluation of energy release rate through the J-integral, thus eliminating the requirement of specialized experimental geometries. For dissipative materials, the experimental data of crack tip deformation field, augmented by accurate constitutive models, will be used to identify the crack tip dissipation zone and to separately measure the intrinsic and dissipative toughness. A finite element model will also be developed to couple the crack tip failure process, represented by a cohesive zone, with the bulk material dissipation, which will enable the prediction of crack growth in soft dissipative 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.