Shockwave Propagation and Dynamic Fracture of Hydrogels via Integrated Computational and Experimental Studies

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This award supports experimental and computational research to study the high deformation rate behavior of hydrogels. Hydrogels consist of a polymer network absorbed in water. Hydrogels are an important class of materials because their properties may be customized to mimic the behavior of many biological tissues. Accordingly, hydrogels are commonly used as tissue simulants for skin, muscles and human organs (lungs, heart, brain, etc.) in experiments to study traumatic injuries. Most prior research has focused on the behavior of hydrogels at low deformation rates. Unfortunately, such experiments do not mimic the conditions associated with tissue injuries caused by high rate deformation (e.g., sudden falls, skiing injuries, automobile accidents) and the effects of shockwave propagation (non-contact blast injuries to lungs, tissue and brain). The results of this research will provide the knowledge necessary to better understand shockwave propagation and related damage in biological tissues. Thus, this research will benefit military veterans and other citizens with traumatic soft tissue injuries. Furthermore, workforce development activities will contribute to the training of graduate and undergraduate students in experimental and simulation techniques. This research will provide an understanding of the fundamental physical mechanisms related to the dynamic behavior of hydrogels, such as variation in wave velocity as a function of propagation distance and water volume fraction. Further, this research will provide a first understanding of high rate viscosity in hydrogels as a function of water content, atomic scale stresses and strains during high rate shearing deformation, and the rate of crack growth in hydrogel samples. Experiments will be conducted using a unique polymer split Hopkinson pressure bar customized to study shockwave propagation and dynamic fracture in hydrogel materials. Molecular dynamics simulations will be conducted to study shockwave propagation and viscosity with atomic resolution. Combined, data from experiments and simulation will be used to improve hyperelastic constitutive models for the dynamic mechanical behavior of hydrogels. Experimental measurement and simulation of the high strain rate viscosity of hydrogels will be used to develop novel rate dependent cohesive zone models for predictive simulation of crack propagation in hydrogels.