research

A Cosserat rod based continuum approach is presented to obtain phonon dispersion curves of flexural, torsional, longitudinal, shearing and radial breathing modes in chiral nanorods and nanotubes. Upon substituting the continuum wave form in the linearized dynamic equations of stretched and twisted Cosserat rods, we obtain analytical expression of a coefficient matrix (in terms of the rod's stiffnesses, induced axial force and twisting moment) whose eigenvalues and eigenvectors give us frequencies and mode shapes, respectively, for each of the above phonon modes.

Preprint here: https://www.researchgate.net/publication/333260238_An_Adaptive_Quasi-Co…

Since their inception, more than two decades ago, phononic crystals and metamaterials have led to advanced materials with exceptional acoustic and elastic characteristics, such as negative effective mass and stiffness. In these materials, the dispersion properties and the energy transfer are controlled by selecting the geometry of the lattices and their constitutive material properties. Most designs, however, only affect one mode of energy propagation, transmitted either as acoustic airborne sound or as elastic structural vibrations.

https://doi.org/10.1016/j.actamat.2019.05.030

Abstract

We have discovered a peculiar form of fracture that occurs in a highly stretchable silicone elastomer (Smooth-On Ecoflex 00–30). Under certain conditions, cracks propagate in a direction perpendicular to the initial pre-cut and in the direction of the applied load. In other words, the crack deviates from the standard trajectory and instead propagates perpendicular to that trajectory. The crack arrests stably, and thus the material ahead of the crack front continues to sustain load, thereby enabling enormous stretchabilities. We call this phenomenon 'sideways' and stable cracking.

ACS Nano (2019), in press (https://pubs.acs.org/doi/10.1021/acsnano.9b01794).

Shuze Zhu, Pascal Pochet, and Harley T. Johnson

Materials Today (2019), in press (https://doi.org/10.1016/j.mattod.2019.03.016).

Yubing Zhou, Chaoji Chen, Shuze Zhu, Chao Sui, Chao Wang, Yudi Kuang, Upamanyu Ray, Dapeng Liu, Alexandra Brozena, Ulrich H.Leiste, Nelson Quispe, Hua Guo, Azhar Vellore, Hugh A. Bruck, Ashlie Martini, Bob Foster, Jun Lou, Teng Li, Liangbing Hu

A recent study has drawn a new aspect on the role played by the surface stress with a torsional profile on silicon nanowires to address the existing controversy from experimental and computational studies (https://www.researchgate.net/publication/327768951_Surface_Stress_Effec…).

This paper aims at assessing the influence of environmental parameters on the modal characteristics of age-old masonry constructions. The results of a long-term ambient vibration monitoring of the San Frediano bell tower in Lucca (Italy) are reported. The tower, dating back to the 11th century, has been fitted along its height with four triaxial seismometric stations, which were left active for about one year.

https://doi.org/10.1016/j.engstruct.2017.10.045

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