Recent experiments have proved that sonic crystals containing locally resonant structures exhibit strong sound attenuation bands at frequencies about two orders of magnitude smaller than predicted by Bragg’s theory. The effect is well reproduced here by means of two-dimensional numerical simulations of the elastic wave propagation in a 13 cm slab of locally resonant sonic crystals. Three strong attenuation bands are found in the frequency range from 0.3 to 6.0 kHz. A heuristic model is proposed, which allows one to predict the resonance frequencies in good agreement with the numerical simulations.

The applicability of voxel meshes to model the mechanical behavior of woven composites at the mesoscopic scale is studied and compared to consistent Finite Element (FE) meshes. The methods are illustrated by mechanically modeling a Representative Unit Cell (RUC) of a composite made of four layers of glass fiber plain weave fabric embedded in an epoxy matrix.Mesh convergence is studied to determine the minimum element size necessary to obtain a correct yarn volume fraction. The comparison between both methods is based on (i) homogenized macroscopic elastic properties, (ii) local stress fields, and (iii) first damage prediction.Even if a good agreement is obtained for the elastic properties, the stress concentrations due to the steplike shape of voxels induce significant differences between both methods in terms of first damage prediction.

This paper presents a viscoelastic temperature- and degree-of-cure-dependent constitutive model for an epoxy resin. Multi-temperature relaxation tests on fully and partially cured rectangular epoxy specimens were conducted in a dynamic mechanical analysis apparatus with a three-point bending clamp. Master curves were constructed from the relaxation test results based on the time–temperature superposition hypothesis. The influence of the degree of cure was included through the cure-dependent glass transition temperature which was used as reference temperature for the shift factors. The model parameters were optimized by minimization of the differences between the model predictions and the experimental data. The model predictions were successfully validated against an independent creep-like strain history over which the temperature varied.

No abstract

International audienceThe crack onset configuration at damage onset in a four-layer plain weave glass fiber/epoxy matrix composite is studied at the mesoscopic scale using a coupled criterion based on both a stress and an energy condition. The possible crack shapes are selected based on optical microscope observations of damage mechanisms on a specimen edge during a tensile test. The crack location, length and orientation, the decohesion length and the strain at damage onset are determined. The damage onset strain is underestimated compared to the experimental value determined by acoustic emission if only a stress criterion is considered. The coupled stress and energy criterion leads to a more reasonable estimate of strain at damage onset