Our research focuses on the study wave propagation in complex materials and the design of materials with extraordinary properties. Materials of current interest include granular, metamaterial, mechanochemically responsive, soft/elastomeric, and ultralight lattice structures. We are particularly interested in dynamically responsive and highly nonlinear phenomena occurring in such materials. Fundamental advances in these areas have the potential to result in high-performance and adaptive material systems that can be manufactured rapidly and in large quantities, with applications to areas including sound and vibration management, signal processing, and resilient infrastructure.

Please see the sections below for several current and past research topics:

Contact dynamics of micro- to nanoscale granular media


Granular media is simultaneously one of the most common and complex forms of matter. In this topic, we explore the nonlinear contact-based dynamics of low-dimensional and ordered micro- to nanoscale granular media, often referred to as microscale “granular crystals”. Previous studies on ordered granular crystal structures have yielded significant insights into the dynamics of granular media, however they have been typically restricted to macroscopic length scales and designed to affect sonic frequency acoustic waves. Extending granular crystals to the microscale has the potential to enable granular-based devices with a smaller overall system size that operate at MHz-GHz frequencies. This scale factor is also important, as effects which are negligible at the macroscale, such as adhesion, become significant at microscales. Our approach leverages a combination of laser ultrasonic techniques and various computational and analytical modeling techniques drawn from the areas of nonlinear dynamical systems, solid mechanics, and acoustic metamaterials. This project has future applications in areas such as signal processing, non-destructive evaluation and adhesion characterization, biomedical ultrasound imaging and therapy, future light-weight and high-performing shock-mitigation material systems, and will lead to an improved understanding of the dynamics of granular media.

Dynamics of surface instabilities in soft materials


Elastic surface waves have been a topic of significant interest for over a century, with applications ranging from geophysics to signal processing. In recent years, the mechanics of surface instabilities in soft media, such as elastomers and gels, has received massive interest. One of most notable type of phenomena has included the spontaneous, self-formation of patterns such as wrinkles, creases, folds, and ridges. However, despite this great interest, these phenomena have been explored almost exclusively in quasi-static settings. In this project, we seek to answer a question at the intersection of these two fields (elastic waves and surface instabilities in soft materials), namely: how do complex surface instabilities in soft media form and propagate dynamically? We anticipate this investigation will have significance for applications ranging from novel impact-resistant soft composites to flexible elastic wave signal processing devices for use in flexible electronics.

Tailorable nonlinear constitutive laws via microstructural geometric nonlinearity


Materials with nonlinear constitutive laws have proven effective at spatiotemporally redistributing energy for applications such as impact mitigation. However, previous investigations have been restricted to systems with “fixed” nonlinearities. In this project, utilizing additively manufactured structures, we seek the answers to the following questions: “what is the best nonlinearity for a given application?”, “how does microstructural geometric nonlinearity enable any effective material nonlinearity?”, and “what nonlinear constitutive property enables the translation from a given dynamic input to a desired dynamic output?” Major avenues of answering these questions include optimization studies of the dynamic response of continuum and discrete element models, and topological optimization of microstructure design, supported with mechanical and dynamic testing. As such, we seek to understand the mechanics and dynamics of the interplay of mechanochemistry and microstructure, which will result in the development of a new class of highly adaptive microstructured materials.

Dynamics of mechanochemically responsive polymers and enhancement of mechanochemical responsive via designer microstructure

Nature has given rise to composite materials that exhibit large adaptability and multifunctional responses to environmental stimuli. Two key elements that are present in many such materials are complex microstructure and chemical reactions that occur in response to mechanical stimuli. Within the realm of synthetic materials, a class of material known as mechanochemically responsive polymers has recently emerged that has demonstrated related effects. However, current implementations have thus far only been in bulk contexts, are activated preferentially under different types of mechanical loading, and require large strains to activate. As such, we seek to understand the mechanics and dynamics of the interplay of mechanochemistry and microstructure, which will result in the development of a new class of highly adaptive microstructured materials.