Fracture and Fatigue of Liquid Crystal Elastomers

本计画将研究液晶弹性体在单一或多重循环负载下之断裂。液晶弹性体是聚合物网络上的液晶分子沿一定方向排列的弹性体。液晶弹性体在刺激响应致动器和软机器人中有着广泛的应用。因此，了解其断裂行为，预防其失效具有重要的现实意义。研究液晶弹性体的非线性断裂力学，其中包括聚合物网络的拉伸和液晶分子的重取向之间的耦合，也是从根本上独特和重要的。该项目在教育和技术方面具有更广泛的影响。研究工作将被纳入一个新的研究生班，融入研究生和本科生的研究项目，并发展成为K-12推广活动的示范。此外，液晶弹性体断裂的研究将对刺激响应型致动器和软机器人等领域产生深远影响，有助于防止液晶弹性体在工作过程中的失效，并设计出耐用的液晶弹性体用于可靠的设备。本项目的目标是建立液晶弹性体的非线性断裂力学理论，并通过实验表征了它们的断裂和疲劳过程及性能。该项目将使用模拟和实验来确定液晶弹性体在单次或多次载荷循环下的裂纹尖端场、能量释放率和断裂能。将应力场和液晶取向场与内聚区模型沿着耦合的液晶弹性体粘弹性场理论将被建立并用于计算依赖于时间的裂纹尖端场和能量释放率，以模拟裂纹扩展，并确定多畴和单畴液晶弹性体的断裂能。在实验上，液晶弹性体的模式I和模式III断裂能将通过纯剪切和裤形测试进行测量，裂纹尖端场将使用数字图像相关和透射圆偏振镜进行观察。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project will investigate fracture of liquid crystal elastomers under a single or multiple cycles of loading. A liquid crystal elastomer is an elastomer with liquid crystal molecules on a polymer network aligning in a certain direction. Liquid crystal elastomers find broad applications in stimuli-responsive actuators and soft robotics. Therefore, understanding their fracture behavior and preventing their failure have practical significance. Studying nonlinear fracture mechanics of liquid crystal elastomers, which involves coupling between stretching of polymer networks and reorientation of liquid crystal molecules, is also fundamentally unique and important. This project has broader impacts in education and technology. The research work will be included into a new graduate class, integrated into research projects for graduate and undergraduate students, and developed into demonstrations for K-12 outreach activities. In addition, understanding fracture of liquid crystal elastomers will have long-term impacts in the fields of stimuli-responsive actuators and soft robotics by preventing failure of liquid crystal elastomers during operation and designing durable liquid crystal elastomers for reliable devices.The objective of this project is to establish a nonlinear fracture mechanics theory for liquid crystal elastomers, and experimentally characterize their fracture and fatigue processes and properties. This project will use both simulations and experiments to determine the crack-tip fields, energy release rates, and fracture energies of liquid crystal elastomers under a single or multiple cycles of loading. A viscoelastic field theory of liquid crystal elastomers coupling the fields of stress and liquid crystal orientation, along with the cohesive zone model will be established and used to computationally calculate the time-dependent crack-tip fields and energy release rates, to simulate crack propagation, and to determine the fracture energies of polydomain and monodomain liquid crystal elastomers. Experimentally, mode I and mode III fracture energies of liquid crystal elastomers will be measured by the pure shear and trousers tests, and the crack-tip fields will be observed using digital image correlation and transmission circular polariscopy.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.