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. Using an experiment-driven approach, supported by analytical and computational modeling, we strive to answer fundamental open questions that concern the underlying physics and mechanics of structured materials over multiple scales (macro- to nanoscales), and to gain insight into how microstructure may yield unprecedented properties. Because of the importance of wave propagation in many engineering applications, our research is applicable to a broad range of areas including sound and vibration management, blast mitigation, signal processing, biomedical devices, and energy conversion and storage.

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

Contact dynamics of low-dimensional 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. As such, by configuring the microscale granular media to act as sub-wavelength local resonances we are exploring a new type of locally resonant metamaterial, namely a “granular-elastic metamaterial”. 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, and biomedical ultrasound imaging and therapy, and will lead to an improved understanding of the dynamics of granular media.

Shock propagation and failure of ordered 3D microscale granular media


While granular materials are known to be highly effective at absorbing shocks from blast and impact, because of the material complexity, many fundamental questions remain open regarding the mechanisms that lead to their shock absorption properties and ultimate failure. This is in part because previous studies have focused on highly complex disordered granular materials (macro- and microscales) or ordered macroscale granular media (which do not take into account critical effects such as the role of interparticle adhesive forces). The proposed approach of simplifies the problem via ordered granular media, while maintaining relevance via micro- to nanoscale grains. In this project, we are characterizing highly nonlinear shock velocities, decay rates, and spall and blast crater failure mechanisms in 3D ordered microscale granular materials. This research will enable the improved prediction of strength, damage initiation, and failure in complex granular media and lay the foundation for future light-weight and high-performing shock-mitigation material systems.

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.

Non-reciprocal elastic wave propagation via photoelasticity


Non-reciprocal media whose broken symmetry is associated with non-conventional topology are
a new frontier in wave propagation. This project aims to leverage spatiotemporal modulation of photoelastically-sensitive solid media’s elastic properties to create topologically protected states that enable non-reciprocal (one-way) elastic wave propagation. Similar to the advent of the electrical diode, in which non-reciprocal elements formed the basis for modern electronics and computing, we anticipate that this research will help take steps towards a new class of phonon-based information processing and phase-based quantum-like computing strategies.

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?” and “how does microstructural geometric nonlinearity enable any effective material nonlinearity?”

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