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Ramathasan Thevamaran's blog

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A Postdoctoral Research Associate Position at the University of Wisconsin-Madison

A Postdoctoral Research Associate Position is available (Fall 2020) in Professor R. Thevamaran’s laboratory at the Department of Engineering Physics of the University of Wisconsin-Madison to study the dynamic behavior of hierarchical materials.

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Environmentally induced exceptional points in elastodynamics

We study the nature of an environment-induced exceptional point in a non-Hermitian pair of coupled mechanical oscillators. The mechanical oscillators are a pair of pillars carved out of a single isotropic elastodynamic medium made of aluminum and consist of carefully controlled differential losses. The interoscillator coupling originates exclusively from background modes associated with the “environment,” that portion of the structure which, if perfectly rigid, would support the oscillators without coupling.

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Independent control of dynamic material properties by exploiting structural hierarchy and intrinsic structural gradients

Achieving high damping and stiffness is challenging in common materials because of their inter-dependent scaling. Controlling extreme mechanical waves requires synergistically enhanced damping and stiffness. We demonstrate superior damping and stiffness in vertically aligned carbon nanotube (VACNT) foams that are also independently controllable by exploiting their synthesis-tailored structural hierarchy and structural gradients. They exhibit frequency- and amplitude-dependent responses with dramatically tunable dynamic stiffness while maintaining constant damping.

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Superior Energy Dissipation by Ultrathin Semicrystalline Polymer Films Under Supersonic Microprojectile Impacts

Distinct deformation mechanisms that emerge in nanoscale enable the nanostructured materials to exhibit outstanding specific mechanical properties. Here, we present superior microstructure- and strain-rate-dependent specific penetration energy (up to ∼3.8 MJ/kg) in semicrystalline poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) thin films subjected to high-velocity (100 m/s to 1 km/s) microprojectile (diameter: 9.2 μm) impacts.

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Dynamic Martensitic Phase Transformation in Single-crystal Silver Microcubes

The ability to transform the crystal structure of metals in the solid-state enables tailoring their physical, mechanical, electrical, thermal, and optical properties in unprecedented ways. We demonstrate a martensitic phase transformation from a face-centered-cubic (fcc) structure to a hexagonal-close-packed (hcp) structure that occurs in nanosecond timescale in initially near-defect-free single-crystal silver (Ag) microcubes impacted at supersonic velocities.

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Asymmetric acoustic energy transport in non-Hermitian metamaterials

One of our studies on linear and nonlinear non-Hermitian metamaterials has been published on the recent special issue of the Journal of the Acoustical Society of America: Non-Reciprocal and Topological Wave Phenomena in Acoustics.

Abstract

Ramathasan Thevamaran's picture

Postdoctoral Research Associate Position at the University of Wisconsin-Madison, Madison, WI.

A Postdoctoral Research Associate Position is available in Professor R. Thevamaran's laboratory at the Department of Engineering Physics to study the dynamic behavior and properties of nanostructured metals and hierarchical materials. A strong background in experimental solid mechanics and materials science is required for this research.

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Dynamic creation and evolution of gradient-nano-grained structures in single-crystal metallic microcubes

In an article published today in Science, we have demonstrated the creation of an extreme gradient-nano-grained (GNG) structure in single-crystal microcubes through high-velocity impact. We use the defect-free single-crystal silver microcubes, synthesized using a seed-growth process, as the model system, and fire them at supersonic velocities onto a rigid target to create the GNG structure.

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A few experimental studies on the dynamic behavior of foam-like aligned carbon nanotubes

I'm posting a few experimental studies we have conducted on the dynamic behavior of hierarchical fibrous materials, using vertically aligned carbon nanotubes as a model material. I hope these will be useful to those who are interested in buckle-instabilities, multiscale behavior, and energy absorption mechanisms.

An overview:

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