NSF-SNSF: Crack Path Prediction and Control in Nonlinearly Viscoelastic Materials: in-silico to Experiments with Viscoelastic and Tough Hydrogels

软机器人、软电子和医疗植入物方面令人难以置信的进步已经超过了我们对这些设备中使用的材料是如何失效的理解。这种装置通常是由承受平面载荷条件下的非线性粘弹性材料构成的，因此我们必须了解这些材料是如何断裂的。这项研究项目将以水凝胶为模型系统，研究非线性粘弹性固体中的裂纹扩展。它的成功将极大地推动粘弹性固体断裂力学的发展。此外，该项目还在教育和技术方面产生了更广泛的影响。它为不同的本科生和研究生提供培训机会，国际合作和交流机会将进一步使学生学习新的文化和观点。研究成果将在科学界广泛传播，并用于为K-12外联活动制定示范。作为长期的成果，这项工作可能会对工程设计产生强烈的影响，并提高软机器人、软电子和医疗植入物的可靠性。本项目的目标是通过对不同加载速率下混合模式平面加载下的裂纹扩展的数值和实验研究，努力确定粘弹性固体中裂纹扩展和路径选择的准则。具体地说，将使用粘弹性水凝胶作为模型体系。本研究分为四个子任务。首先，将对所使用的水凝胶进行表征，并进行基线拉伸断裂研究。同时，将建立一个相场断裂模型来模拟非线性粘弹性固体中与速率相关的裂纹扩展。下一步，将进行平行的实验和数值研究，重点放在更复杂的裂纹加载条件和加载速率上。最后，开发的预测能力将通过在对光敏感的固体中驾驶裂缝来展示。预计复杂裂纹加载条件的验证数值模型、受控加载速率下非线性粘弹性断裂的全场、近裂纹尖端位移测量以及裂纹扩展和路径选择标准的识别将是关键的科学成果。这个美国和瑞士的合作项目得到了美国国家科学基金会(NSF)和瑞士国家科学基金会(SNSF)的支持，其中NSF资助美国研究人员，SNSF资助瑞士的合作伙伴。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The incredible advances in soft robotics, soft electronics and medical implants have outpaced our understanding of how the materials used in these devices fail. Such devices are often constructed of nonlinearly viscoelastic materials subject to planar loading conditions, and thus it is imperative that we understand how these materials fracture. This research project will investigate crack propagation in nonlinearly viscoelastic solids, using hydrogels as a model system. Its success will significantly advance the fracture mechanics of viscoelastic solids. In addition, this project has broader impacts in education and technology. It provides training opportunities to a diverse group of undergraduate and graduate student, and the international collaboration and exchange opportunities will further enable the students to learn new culture and perspectives. The research results will be disseminated broadly in the scientific community and used to develop demonstrations for K-12 outreach activities. As long-term deliverables, this work may strongly influence the engineering design and enhance the reliability of soft robotics, soft electronics and medical implants.The objective of this project is to perform research that strives to identify the criteria governing crack growth and path selection in viscoelastic solids through a combined numerical and experimental study of crack propagation under mixed-mode planar loading at different loading rates. Specifically, viscoelastic hydrogels will be used as a model system. This research is subdivided into four sub-tasks. First, the hydrogels used will be characterized, and baseline tensile fracture studies will be carried out. In parallel, a phase-field fracture model will be established to simulate rate-dependent crack propagation in nonlinearly viscoelastic solids. As a next step, parallel experimental and numerical studies that focus on more complex crack loading conditions and loading rates will be conducted. Finally, developed predictive capabilities will be demonstrated by steering a crack in a photo-responsive solid. It ois anticipated that the validated numerical model for complex crack loading conditions, the full-field, near-crack tip displacement measurements for nonlinearly viscoelastic fracture under controlled loading rates, and the identification of crack growth and path selection criteria will be the key scientific outcomes.This collaborative US-Swiss project is supported by the US National Science Foundation (NSF) and the Swiss National Science Foundation (SNSF), where NSF funds the US investigator and SNSF funds the partners in Switzerland.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.