Experimental Measurement of Tearing and Cutting in Highly Deformable Solids Relating to the Mechanical Origin of Crack Blunting-Mediated Toughness

该奖项旨在确定切割和撕裂失效模式之间的关系，以便重新审视和提供对高度变形材料撕裂的机械起源的新见解。在从运输到生物材料的各种应用中，这些橡胶类材料的失效支配着设计规则。与许多刚性材料不同，橡胶类材料的裂纹可以在宏观上钝化，因为材料经历了大变形。这使裂纹尖端的应力状态变得复杂，根据材料的不同而有所不同。目前对破坏机制的理解不能解释切割和撕裂两种不同加载几何形式下的能量差异。潜在的好处包括作为指导新材料制造的目标的设计标准。结果可以概括为描述软组织中的穿刺针和插针；这些失败机制在诊断和引导针疗法中发挥着关键作用。这个项目将提供由PI促进的教育机会，因为这个项目中的许多实验对本科生研究人员来说都是可以访问的。PI将招募女本科生参与整个项目的数据收集。高度变形、裂缝钝化的固体显示的断裂能比简单内聚模型预测的大许多倍。研究人员假设了更复杂的模型，表明骨折是由尖端的局部机制决定的。这些局部力学包括材料的大应变响应、尖端半径和局部断裂能。为了充分描述这些重要特征，PI将用原位和尸检图像补充实验力学失效数据，记录裂纹尖端半径、尖端附近应变和断裂机制。这种实验表征产生的机制图将指导对描述高度变形材料撕裂的机械起源的现有模型的检查，并在必要时重新解释。一旦为标准平面应力几何形状建立了关系，本项目中量化的几何控制(切割)和远程加载(撕裂)失效能量之间的关系将被应用于将针介导的失效与标准的I型断裂能量值联系起来。

This award aims to determine the relationship between cutting and tearing failure modes in order to re-examine and provide new insight into the mechanical origin of tearing in highly deformable materials. Failure in these rubber-like materials governs design rules in applications ranging from transportation to biomaterials. Unlike many rigid materials, cracks in rubber-like materials can blunt macroscopically as the material undergoes large deformations. This complicates the stress state at the tip of the crack, which varies depending on the material. Current understanding of the failure mechanism cannot explain the energy differences in two different loading geometries, cutting versus tearing. Potential benefits include design criteria to serve as targets to guide the fabrication of new materials. Results can be generalized to describe puncture and insertion of needles in soft tissue; these failure mechanisms play a key role in diagnostics and guided-needle therapeutics. This project will provide educational opportunities facilitated by the PI as many of the experiments in this project are accessible to undergraduate researchers. The PI will recruit female undergraduate students to participate in data-gathering throughout the project.Highly deformable, crack-blunting solids exhibit fracture energies many times larger than predicted by simple cohesive models. Researchers have postulated more complex models that indicate fracture is governed by the local mechanics of the tip. These local mechanics include the material's large strain response, tip radius, and local fracture energy. To fully characterize each of these important features, the PI will supplement experimental mechanical failure data with in situ and post-mortem imaging, documenting crack tip radius, near-tip strain, and fracture mechanism. The mechanism map resulting from this experimental characterization will guide examination and, if necessary, re-interpretation of existing models describing the mechanical origin of tearing in highly deformable materials. Once established for the standard plane stress geometry, the relationship quantified in this project, between geometrically controlled (cutting) and remote-load (tearing) failure energies, will be applied to relate needle-mediated failure to standard, mode I fracture energy values.