When soft materials are compressed, their surface often spontaneously forms wrinkles, creases, ridges, or folds with periodic patterns. These patterns are called 'surface instabilities'. Over the past several years, there has been significant interest in understanding how surface instabilities form, as they are ubiquitous in biological systems and have found wide use in engineering applications ranging from microfabrication to soft robotics. However, nearly all of the past studies have focused on understanding how surface instabilities form under very slow compression, or have neglected the dynamics leading to this event. This award will investigate how surface instabilities form and propagate across the surface of the material as a result of fast compression or impacts. The speed of the event causing the instability is critical as it yields fundamentally unique phenomena, which are prevalent in most physical systems, but still not well understood. The improved understanding gained as part of this fundamental research will impact a broad range of applications. For example, because of the role of surface instabilities in friction, this research will positively affect engineering applications with moving soft materials in contact. It will also lead to improved understanding of the dynamics of sandwich beam composites, and to improved impact absorbers, shock protective systems, and novel soft electronics devices. In addition to the research goals, this project has a significant education and outreach component that will positively affect students from K-12 through graduate levels, and will increase the involvement of underrepresented students in STEM fields.
The research objective of this multidisciplinary, collaborative project is to investigate the initiation and propagation of surface instabilities in soft materials under dynamic loading, using a combined theoretical, computational, and experimental approach. Experimental characterization will be conducted using a combination of drop tower, high-speed video, and laser ultrasonic test methods. Dynamic surface instability propagation will be modeled analytically, and computationally using nonlinear finite element techniques. This project will provide significant intellectual contribution by answering open questions including: What are the conditions for initiating the propagation of surface instabilities, and how do they propagate? How does the propagation of surface instabilities lead to material failure? And how can the propagation of surface instabilities be manipulated? More generally, as there have been almost no investigations into the dynamics of propagating surface instabilities, this investigation will open a new class of instability-based surface waves and provide an improved understanding of dynamic phenomena in soft materials.
