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

Northwestern University, Evanston IL

Investigators

Abstract

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.