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Ramathasan Thevamaran's blog

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Mitigating Oblique Impacts by Unraveling of Buckled Carbon Nanotubes in Helmet Liners

Abstract

 

Background: Helmet systems most commonly experience oblique blunt impacts which cause simultaneous linear and rotational accelerations. The ability to attenuate both linear and rotational accelerations by absorbing the normal shock while accommodating large shear deformations with energy dissipation is critical to developing superior helmet liners that prevent traumatic brain injury (TBI).

 

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Block copolymer additives for toughening 3D printable epoxy resin

Dear Colleagues,

Please see our recent article on toughening 3D printable resins with block copolymer additives:

Abstract

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Assistant Professor in Fluid Dynamics at University of Wisconsin-Madison

Dear Colleagues,

The Department of Mechanical Engineering (ME) at the University of Wisconsin-Madison is seeking applicants for a tenure-track Assistant Professor in the area of experimental fluid dynamics with applications to aerodynamics, turbulence, wind energy, flow control, bio-inspired flows, or related fields. Please see the job description here: https://jobs.wisc.edu/jobs/assistant-professor-in-fluid-dynamics-madison-wisconsin-united-states

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Assistant Professor in Polymers and Composites at University of Wisconsin-Madison

Dear Colleagues,

The Department of Mechanical Engineering at the University of Wisconsin, Madison seeks candidates in polymer and composite processing and engineering to join their interdisciplinary advanced manufacturing group as a tenure-track Assistant Professor. Please see the job description here: https://jobs.wisc.edu/jobs/assistant-professor-in-polymers-and-composites-madison-wisconsin-united-states

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Assistant Professor in Structural Dynamics at the University of Wisconsin-Madison

Dear Colleagues,

The Department of Mechanical Engineering at the University of Wisconsin-Madison invites applications for a tenure-track Assistant Professor position in structural dynamics. Please see the job description here: https://jobs.wisc.edu/jobs/assistant-professor-in-structural-dynamics-madison-wisconsin-united-states

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

A Postdoctoral Research Associate Position is available immediately in Professor R. Thevamaran’s laboratory (https://thevamaran.engr.wisc.edu) at the Department of Mechanical Engineering of the University of Wisconsin-Madison. The research will focus on design, fabrication, micro/nanostructural characterization, and thermo-mechanical testing, and modeling of carbon nanotube-based hierarchical composites.

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Orientation-dependent plasticity mechanisms control synergistic property improvement in dynamically deformed metals

Dear Colleagues,

I invite you to read our recent paper on the orientation dependent plasticity mechanisms that control the dynamic creation of nanostructures and their  behavior under subsequent quasistatic microcompression published in the International Journal of Plasticityhttps://doi.org/10.1016/j.ijplas.2023.103657

Abstract

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Synergistic strength and toughness through impact-induced nanostructural evolutions in metals

Dear Colleagues,

I invite you to read our recent paper on the process-structure-property relations in heterogeneous nanostructured metals created through a laser induced projectile impact of single crystal microcubes published in the Extreme Mechanics Lettershttps://doi.org/10.1016/j.eml.2023.102037

Abstract

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Dynamic Hardness Evolution in Metals from Impact Induced Gradient Dislocation Density

Dear Colleagues,

I invite you to read our recent publication on Acta Materialia on the dynamic hardness evolution in metals.

Abstract

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Reconfigurable enhancement of actuation forces by engineered losses in non-Hermitian metamaterials

Dear Colleagues, 

I invite you to read our recent Extreme Mechanics Letters paper presenting a novel viewpoint on enhancing emissivity near exceptional point singularities in a non-Hermitian metamaterial. We present the experiments and numerical modeling in an elastodynamic framework--where the actuation forces from an actuator are enhanced by coupling to a passive dissipative non-Hermitian metamaterial--and present the theory further generalized and applicable to other physical frameworks from acoustics to optics and microwaves.

Abstract

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Exceptional-point-based accelerometers with enhanced signal-to-noise ratio

Exceptional points (EP) are non-Hermitian degeneracies where eigenvalues and their corresponding eigenvectors coalesce. Recently, EPs have attracted attention as a means to enhance the responsivity of sensors, through the abrupt resonant detuning occurring in their proximity. In many cases, however, the EP implementation is accompanied by noise enhancement, leading to the degradation of the sensor’s performance.

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Origins of mechanical preconditioning in hierarchical nanofibrous materials

Dear Colleagues,

I invite you to read our recent paper on Origins of mechanical preconditioning in hierarchical nanofibrous materials, published in Extreme Mechanics Letters.

Abstract

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Extreme Dynamic Performance of Nanofiber Mats under Supersonic Impacts Mediated by Interfacial Hydrogen Bonds

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

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Origins of size effects in initially dislocation-free single-crystal silver micro- and nanocubes

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.

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Universal route for the emergence of exceptional points in PT-symmetric metamaterials with unfolding spectral symmetries

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.

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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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