Dear Colleagues,
I invite you to read our recent paper on the Extreme Dynamic Performance of Nanofiber Mats under Supersonic Impacts Mediated by Interfacial Hydrogen Bonds published on ACS Nano.
Abstract
We report phenomenal yield strengths—up to one-fourth of the theoretical strength of silver—recorded in microcompression testing of initially dislocation-free silver micro- and nanocubes synthesized from a multistep seed-growth process. These high strengths and the massive strain bursts that occur upon yield are results of the initially dislocation-free single-crystal structure of the pristine samples that yield through spontaneous nucleation of dislocations.
We introduce a class of parity-time symmetric elastodynamic metamaterials (Ed-MetaMater) whose Hermitian counterpart exhibits unfolding (fractal) spectral symmetries. Our study reveals a scale-free formation of exceptional points in those Ed-MetaMaters whose density is dictated by the fractal dimension of their Hermitian spectra.
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.
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.
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.
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.
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.
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
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.
