Multiscale Experimental and Numerical Design of a Self-Healing Epoxy Adhesive

在从微电子到航空航天结构的许多应用中，聚合物基胶粘剂通常被认为是粘接结构的薄弱环节，包括那些承受循环载荷的结构。在这项合作实验和分析工作中，伊利诺伊大学厄巴纳-香槟分校的研究人员正在设计和展示一种新型的异质、多功能环氧基粘合剂，这种粘合剂具有在疲劳载荷下自主愈合(即，无需任何外部干预)的独特能力，从而显著延长粘接接头的预期寿命。这类新材料的灵感来自生命系统，在生命系统中，损伤(例如，割伤或瘀伤)会触发自主愈合反应。在生物系统中，损伤部位释放的化学信号会引发系统反应，将修复剂运送到损伤部位并促进愈合。为了在本项目所研究的胶粘剂系统中实现自我修复能力，将含有单体愈合剂的亚微米尺寸的纳米胶囊嵌入到环氧胶粘层中，同时将活性催化剂分散在环氧胶粘层中。当疲劳引起的微裂纹出现并在粘结层中扩展时，纳米胶囊破裂并释放出愈合剂。然后，单体与催化剂相混合，引发聚合并重新粘合裂纹表面。该研究项目的重点是(I)材料的开发，纳米胶囊的加工和表征，以及环氧胶粘剂可行的自愈化学物质的鉴定，以及(Ii)自愈胶接接头疲劳响应的多层次数值和实验研究。该项目的成功完成将导致一种全新类型的粘接系统的开发，这种粘接系统具有更强的抗疲劳破坏能力。对“大体积”自愈合复合材料的初步观察表明，环氧基组件的疲劳寿命增加了五到十倍。此外，通过将多层次实验技术与新的多尺度粘结有限元框架相结合，该项目有望产生一个多功能胶接接头的集成设计工具，其应用远远超出所提出的自愈环氧基胶粘剂系统。这项研究项目在自主材料实验室进行，是贝克曼高级科学技术研究所跨学科研究小组的一部分，该小组涉及来自航空航天工程、工程力学、化学和材料科学的学生和教职员工。

Used in many applications ranging from microelectronics to aerospace structures, polymer-based adhesives are often considered as the weak link of bonded structures, including those subjected to cyclic loading. In this collaborative experimental and analytical effort, researchers from the University of Illinois at Urbana-Champaign are designing and demonstrating a new class of heterogeneous, multifunctional, epoxy-based adhesives that possess the unique ability to heal autonomically (i.e., without any external intervention) under fatigue loading, thereby substantially expanding the expected lifetime of adhesive joints. This new class of materials is inspired by living systems, in which damage (e.g., a cut or bruise) triggers an autonomic healing response. In biological systems, chemical signals released at the site of injury initiate a systemic response that transports repair agents to the site of damage and promotes healing. To achieve self-healing capability in the adhesive system studied in this project, sub-micron-size "nanocapsules" containing a monomer healing agent are embedded in the epoxy adhesive layer, together with a living catalyst dispersed in the epoxy matrix. As fatigue-induced microcracks appear and propagate in the adhesive layer, the nanocapsules rupture and release the healing agent. The monomer then mixes with the catalyst phase initiating polymerization and rebonding the crack faces. The research project focuses on (i) materials development with processing and characterization of nanocapsules and identification of viable self-healing chemistries for epoxy adhesives, and (ii) a multi-level numerical and experimental investigation of the fatigue response of a self-healing adhesive joint. The successful completion of this project will lead to the development of a radically new type of adhesive system that present a much enhanced resistance to fatigue failure. Initial observations obtained on "bulk" self-healing composites indicate a five- to ten-fold increase in the fatigue life of epoxy-based components. Furthermore, by integrating multi-level experimental techniques with a new multiscale cohesive finite element framework, this project is expected to yield an integrated design tool for multifunctional adhesive joints with application well beyond the proposed self-healing epoxy-based adhesive system. This research project takes place at the Autonomic Materials Laboratories as part of an interdisciplinary research group at the Beckman Institute for Advanced Science and Technology that involves students and faculty from Aerospace Engineering, Engineering Mechanics, Chemistry and Materials Science.