Structural dynamics

Résumé

Structural dynamics is a type of structural analysis which covers the behavior of a structure subjected to dynamic (actions having high acceleration) loading. Dynamic loads include people, wind, waves, traffic, earthquakes, and blasts. Any structure can be subjected to dynamic loading. Dynamic analysis can be used to find dynamic displacements, time history, and modal analysis. Structural analysis is mainly concerned with finding out the behavior of a physical structure when subjected to force. This action can be in the form of load due to the weight of things such as people, furniture, wind, snow, etc. or some other kind of excitation such as an earthquake, shaking of the ground due to a blast nearby, etc. In essence all these loads are dynamic, including the self-weight of the structure because at some point in time these loads were not there. The distinction is made between the dynamic and the static analysis on the basis of whether the applied action has enough acceleration in com

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https://en.wikipedia.org/wiki/Structural_dynamics

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Crystallization is a fundamental natural phenomenon and the ubiquitous physical process in materials science for the design of new materials. So far, experimental observations of the structural dynamics in crystallization have been mostly restricted to slow dynamics. We present here an exclusive way to explore the dynamics of crystallization in highly controlled conditions (i.e., in the absence of impurities acting as seeds of the crystallites) as it occurs in vacuum. We have measured the early formation stage of solid Xe nanoparticles nucleated in an expanding supercooled Xe jet by means of an X-ray diffraction experiment with 10-fs X-ray free-electron laser (XFEL) pulses. We found that the structure of Xe nanoparticles is not pure face-centered cubic (fcc), the expected stable phase, but a mixture of fcc and randomly stacked hexagonal close-packed (rhcp) structures. Furthermore, we identified the instantaneous coexistence of the comparably sized fcc and rhcp domains in single Xe nanoparticles. The observations are explained by the scenario of structural aging, in which the nanoparticles initially crystallize in the highly stacking-disordered rhcp phase and the structure later forms the stable fcc phase. The results are reminiscent of analogous observations in hard-sphere systems, indicating the universal role of the stacking-disordered phase in nucleation.

NATL ACAD SCIENCES2021

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Ultrafast Structural Dynamics of Nanoparticles in Intense Laser Fields

Christoph Bostedt, Giorgio Rossi

Femtosecond laser pulses have opened new frontiers for the study of ultrafast phase transitions and nonequilibrium states of matter. In this Letter, we report on structural dynamics in atomic clusters pumped with intense near-infrared (NIR) pulses into a nanoplasma state. Employing wide-angle scattering with intense femtosecond x-ray pulses from a free-electron laser source, we find that highly excited xenon nanoparticles retain their crystalline bulk structure and density in the inner core long after the driving NIR pulse. The observed emergence of structural disorder in the nanoplasma is consistent with a propagation from the surface to the inner core of the clusters.

2019

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Post-tensioned structural glass beams, experimental investigations

Thibaut Jordan, Jean-Paul Lebet, Pieter Christian Louter, Arno Pérez

In this study the structural response of post-tensioned structural glass beams is investigated. This is done through four-point bending tests on two series of post-tensioned glass beam specimens. The beams consist of three layers of annealed float glass and are posttensioned by means of two stainless steel tendons positioned along the upper and lower edge of the beams. In addition, a series of reference beams, with identical geometry but without tendons, is tested. From the results it is concluded that post-tensioning a glass beam is a feasible concept, which provides the beams enhanced initial breakage strength and enhanced post-breakage performance. More specifically, the post-tensioned beams reach up to 80% higher initial breakage loads than the reference beams. Furthermore the post-tensioned glass beams reach postbreakage load levels up to 200% of their initial glass breakage load and demonstrate highly ductile post-breakage response. Further studies will focus in more detail on this promising concept of post-tensioning glass beams.

Taylor & Francis Group2013

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