Collaborative Research: Gel rupture under simple and dynamic loading: manipulation of failure mode via patterned heterogeneity in soft materials

非技术性质的软材料在自然界中普遍存在(植物、组织、食品)，也是先进工程应用(植入式医疗设备等)的理想材料。软材料具有令人难以置信的多功能性，特别是聚合物网络和凝胶，因为它们可以设计成与复杂环境(生物系统、组织、水环境等)兼容。虽然众所周知，软材料可以承受比脆性塑料或金属更大的变形，但它们仍然遭受突然的灾难性破坏，例如几乎瞬间形成的横跨整个材料的快速形成的裂纹。这限制了软材料的潜力，因为工程材料通常旨在避免或消除灾难性故障事件的可能性。虽然在传统的弹性固体中已经探索了几何和破坏模式之间的基本关系，但在为软材料建立类似的设计原则方面所做的工作有限。因此，了解如何定制软材料的失效响应，特别是在使用之前，是至关重要的。该项目通过研究几何结构(例如，晶格图案)以及夹杂物的存在(例如，晶格结构中的填充磁区)如何影响软材料(主要是聚合物凝胶)的失效模式来解决这一问题。此外，该项目还为来自不同学科(材料科学、物理和土木工程)的学生提供了独特的培训机会，使他们能够合作并参与两个机构之间的研究交流。这些交流为学生提供了从事自己以外的学科和系的机会，以加强他们的培训，扩大他们的专业科学网络，并确立自己作为STEM工作人员的成员。技术摘要复合材料，如穿孔结构或具有嵌入域的结构，提供了特殊的自由来改变材料特性，如刚性、韧性和破坏模式。例如，塑料格子在应变作用下的破坏模式可以通过几何形状来定制；较薄的压杆提供缓慢和扩散的破坏。虽然这种几何形状和破坏模式之间的关系已经在传统的弹性固体中得到了探索，但在为软材料建立类似的设计原则方面所做的工作却很有限。这个项目通过研究晶格结构的几何形状以及工程夹杂物如何影响软材料(聚合物凝胶)的失效模式来解决这一问题。本研究采用实验和计算相结合的方法，系统地研究了这种材料体系的一个大的参数空间，包括晶格几何形状、凝胶硬度以及晶格结构和工程夹杂物之间的力学性能差异。在本项目中，使用光刻技术制作试件，并将使用光弹成像来建立应力传递与破坏模式之间的关系。光弹成像使用扩展有限元方法(Xfem)来通知计算模型。这个项目提供了关于软材料失效行为的关键信息，软材料在自然界和工程材料中普遍存在。此外，这些信息将促进生物医学设备和软机器人等应用领域的发展，这些领域大量使用软材料，但在解决这些平台的故障和机械性能时会出现挑战。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。

Non-technical Abstract Soft materials are ubiquitous in nature (plants, tissue, foods) and are also of interest for advanced engineering applications (implantable medical devices, etc.). Soft materials are incredibly versatile, particularly polymer networks and gels, as they can be engineered to be compatible with complex environments (biological systems, tissues, aqueous environments, etc.). While it is well known that soft materials can withstand larger deformations than brittle plastics or metals, they still suffer from sudden and catastrophic failure, such as a rapidly forming crack spanning the entire material nearly instantaneously. This limits the potential of soft materials, as engineered materials are typically designed to avoid or eliminate the likelihood of catastrophic failure events. While fundamental relationships between geometry and failure mode have been explored in traditional elastic solids, limited work has been done to establish similar design principles for soft materials. Therefore, understanding how to tailor the failure response of soft materials, particularly prior to use, is essential. This project addresses this gap by investigating how the geometry (e.g., lattice pattern), as well as the presence of inclusions (e.g., filled-in domains within a lattice structure) influence the failure mode of soft materials, mainly polymer gels. Furthermore, this project provides unique training opportunities for students from varied disciplines (materials science, physics, and civil engineering) by enabling them to work together collaboratively and participate in research exchanges between the two institutions. These exchanges provide students with the opportunity to engage in a discipline and department outside of their own to enhance their training, broaden their professional scientific network, and establish themselves as members of the STEM workforce.Technical Abstract Composite materials, such as perforated structures or structures with embedded domains, offer exceptional freedom to alter material properties such as stiffness, toughness, and failure mode. For example, the failure mode of a plastic lattice subjected to strain can be tailored via geometry; thinner struts afford slow and diffuse failure. While this type of relationship between geometry and failure mode has been explored in traditional elastic solids, limited work has been done to establish similar design principles for soft materials. This project addresses this gap by investigating how the geometry of a lattice structure, as well as engineered inclusions, influence the failure mode of soft materials (polymer gels). This study uses a combined experimental and computational approach to systematically address a large parameter space for this material system, including lattice geometry, gel stiffness, and the differential in mechanical properties between the lattice structure and engineered inclusions. In this project, samples are fabricated using photo-lithography techniques, and photoelastic imaging will be used to establish the relationship between stress transmission and failure mode. The photoelastic imaging informs computational models using the eXtended Finite Element Method (XFEM). This project provides crucial information regarding the failure behavior of soft materials, which are ubiquitous in nature and engineered materials. Furthermore, this information will advance application fields including biomedical devices and soft robotics, where soft materials are heavily employed but challenges arise when addressing the failure and mechanical performance of these platforms.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.