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Dennis M. Kochmann
ETH Zurich & California Institute of Technology
Thursday, March 21, 2019 | Onizuka | 12:00 P.M.
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Abstract: Instabilities in solids and structures are ubiquitous across length and time scales, and our engineering design principles commonly aim to prevent those. We aim for the exact opposite: exploiting instabilities to create mechanical systems with beneficial properties. At the core of all instabilities lies a non-convex energy landscape that is responsible, e.g., for structural buckling and localization but also – at much smaller scales – for phase transitions in materials or pulse propagation in cardio- and neurophysiology. The existence of multiple stable configurations can lead to nonlinear dynamic or kinetic effects, including strongly nonlinear transition waves that switch between stable configurations (e.g., propagating domain walls in materials or the snapping of structures between buckled shapes). Understanding the underlying physics enables us to create new interesting mechanical systems that utilize the effects of instability, and to mimic material-level mechanisms at the structural level. Here, we review the underlying theory and discuss opportunities for structural systems whose nonlinear response shows intriguing analogies with phenomena found in materials at small scales. We show how periodic snapping structures can be exploited for propagating signals in lossy media as well as for soft mechanical logic, nonlinear diodes and shape-morphing structures. We further demonstrate that the presented soft architectures may be interpreted as structural-level analogs of solid-solid phase transitions such as those found in ferroelectric ceramics undergoing domain switching. To show that the analogy is not only qualitative, we compare the underlying governing equations and, by passing from a discrete structure to the continuum limit, reveal quantitative analogies that help us learn from one system about the other. Besides theory and simulations, we demonstrate through experiments the instability-driven nonlinear dynamic effects in a variety of mechanical systems.

Bio: Dennis M. Kochmann received his Diploma and his doctoral degree in Mechanical Engineering from Ruhr-University Bochum as well as a Master’s in Engineering Mechanics from the University of Wisconsin-Madison. He was a postdoc and Fulbright fellow at Wisconsin and a Humboldt fellow at Caltech before joining the Aerospace Department at Caltech as Assistant Professor in September 2011. In October 2016 he became Professor of Aerospace at Caltech, in April 2017 he became Professor of Mechanics and Materials at ETH Zurich, where he is now Head of the Institute of Mechanical Systems and Deputy Head of the Department of Mechanical and Process Engineering. His research focuses on the link between structure and properties of a variety of materials and develops and applies methods of theoretical, computational and experimental mechanics (including continuum and atomistic modeling, scale-bridging multiscale models, phase field techniques, and experimental characterization). His research has been recognized by, among others, the Bureau Prize in Solid Mechanics form IUTAM, the Richard von Mises Prize by GAMM, an NSF CAREER Award, the T.J.R. Hughes Young Investigator Award by the ASME, and an ERC Consolidator Grant.

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