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

该奖项支持实验和计算研究，以研究水凝胶的高变形率行为。水凝胶由被水吸收的聚合物网络组成。水凝胶是一类重要的材料，因为它们的特性可以被定制来模仿许多生物组织的行为。因此，水凝胶常被用作皮肤、肌肉和人体器官（肺、心、脑等）的组织模拟物，用于研究创伤性损伤的实验。大多数先前的研究集中在水凝胶在低变形速率下的行为。不幸的是，这种实验不能模拟高速率变形（例如，突然坠落、滑雪受伤、汽车事故）和冲击波传播（对肺、组织和大脑的非接触爆炸伤害）造成的组织损伤相关条件。这项研究的结果将为更好地了解生物组织中的冲击波传播和相关损伤提供必要的知识。因此，这项研究将有利于退伍军人和其他公民创伤性软组织损伤。此外，劳动力发展活动将有助于培养研究生和本科生的实验和模拟技术。这项研究将有助于理解与水凝胶动态行为相关的基本物理机制，例如波速随传播距离和水体积分数的变化。此外，这项研究将首次了解水凝胶中的高速率粘度是水含量、高速率剪切变形时原子尺度应力和应变以及水凝胶样品中裂纹扩展速率的函数。实验将使用一种独特的聚合物分裂霍普金森压力棒进行，该压力棒是为研究水凝胶材料中的冲击波传播和动态破裂而定制的。分子动力学模拟将以原子分辨率研究冲击波的传播和粘度。结合实验和模拟的数据，将用于改进水凝胶动态力学行为的超弹性本构模型。实验测量和模拟水凝胶的高应变速率粘度将用于开发新的速率相关的内聚区模型，用于预测水凝胶中裂纹扩展的模拟。

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.