arXiv subjects

Francisco Melo

Publications and source records attributed to Francisco Melo.

22 records · Page 2Linked to original sources

arXiv2005

How Hertzian solitary waves interact with boundaries in a 1-D granular medium

We perform measurements, numerical simulations, and quantitative comparisons with available theory on solitary wave propagation in a linear chain of beads without static preconstrain. By designing a nonintrusive force sensor to measure the impulse as it propagates along the chain, we study the solitary wave reflection at a wall. We show that the main features of solitary wave reflection depend on wall mechanical properties. Since previous studies on solitary waves have been performed at walls without these considerations, our experiment provides a more reliable tool to characterize solitary wave propagation. We find, for the first time, precise quantitative agreements.

physics.gen-ph↗

arXiv1999

Collective motion and solid-liquid-type transitions in vibrated granular layers

From pressure and surface dilation measurements, we show that a solid-liquid-type transition occurs at low excitation frequencies in vertically vibrated granular layers. This transition precedes subharmonic bifurcations from flat surface to standing wave patterns, indicating that these waves are in fact associated with the fluid like behavior of the layer. In the limit of high excitation frequencies, we show that a new kind of subharmonic waves can be distinguished. These waves do not involve any lateral transfer of grains within the layer and correspond to excitations for which the layer slightly bends alternately in time and space. These bending waves have very low amplitude and we observe them in a vibrated two-dimensional layer of photoelastic particles.

cond-mat↗

arXiv1998

Crescent singularities and stress focusing in a developable cone

we investigate developable cones (d-cones) topology and mechanical properties. We found that for a sample of a finite thickness the singularity is never pointlike but has a spatial extension in form of a crescent. The variations of the sheet local curvature versus the distance from the d-cone tip for all deformations showed that the d-cone tip is rejected by a distance which depends on the deformation and on the singularity extension. A further deformation of the d-cone leads to a transition to a plastic deformation equivalent to a decrease in the singularity size characterized from curvature and profile analysis. The crescent radius of curvature is measured both at small deformations and at large deformations. It is found that during the buckling process, the curvature of the crescent exhibit two different scaling versus the deformation.From the cone profile, we measured the reaction force of the plate to deformation and from force measurements, the energy necessary to create the singularity is characterized.

cond-mat.mtrl-sci↗

arXiv1995

Hexagons, Kinks and Disorder in Oscillated Granular Layers

Experiments on vertically oscillated granular layers in an evacuated container reveal a sequence of well-defined pattern bifurcations as the container acceleration is increased. Period doublings of the layer center of mass motion and a parametric wave instability interact to produce hexagons and more complicated patterns composed of distinct spatial domains of different relative phase separated by kinks (phase discontinuities). Above a critical acceleration, the layer becomes disordered in both space and time.

patt-sol↗