Détection et discrimination par émission acoustique des endommagements dans les composites. Comparaison expérience / modélisation

International audienceOn présente dans cette étude la discrimination des phénomènes de ruptures de fibre, de microfissuration intralaminaire, de macrofissuration intralaminaire ainsi que du microdélaminage au sein des composites stratifiés d'unidirectionnels orientés, dans le cadre d'une méthode de détection des endommagements basée sur la technique de l'Emission Acoustique. Ces résultats expérimentaux sont confrontés aux prévisions issues d'un modèle de comportement de matériaux composites unidirectionnels, basés sur la physique des phénomènes à l'échelle des constituants

Thermal conductivity of refractory glass fibres

In the present study, the current international standards and corresponding apparatus for measuring the thermal conductivity of refractory glass fibre products have been reviewed. Refractory glass fibres are normally produced in the form of low-density needled mats. A major issue with thermal conductivity measurements of these materials is lack of reproducibility in the test results due to transformation of the test material during the test. Also needled mats are inherently inhomogeneous, and this poses additional problems. To be able to compare the various methods of thermal conductivity measurement, a refractory reference material was designed which is capable of withstanding maximum test temperatures (1673 K) with minimum transformation. The thermal conductivity of this reference material was then measured using various methods according to the different standards surveyed. In order to compare different materials, samples have been acquired from major refractory glass fibre manufacturers and the results have been compared against the newly introduced reference material. Materials manufactured by melt spinning, melt blowing and sol–gel have been studied, and results compared with literature values

Stochastic factors controlling the failure of carbon/epoxy composites

International audienceThe intrinsic scatter in tensile properties of unidirectional (UD) carbon/epoxy composites is due to several factors, including variability in fibre strength and fibre volume fraction at the local microscopic level. A model included in a multiscale finite element process, previously developed to simulate fibre failure in composite laminates but having little variation in fibre strength and local fibre volume fraction, has been extended to cover the effects of such material variations. The present study investigates the effects of the variability in material properties which can occur in real UD composite materials subjected to monotonic increasing and sustained loadings. This latter case is one of the originalities of this study. In the interval of variation studied for the Weibull parameters of fibre strength and fibre volume fraction, the mean and standard deviation of the failure stress are never strongly affected. Concerning the time-to-failure, its mean and its standard deviation increase strongly if the mean of fibre volume fraction increases and if the standard deviation of the fibre strength decreases. The standard deviation of local fibre volume fraction was found to have only a secondary effect on failure stress and time-to-failure. Another original and important result concerns the scatter in the time-to-failure of composites due to the level of applied sustained loading

Arguments pour expliquer la dispersion expérimentale sur le nombre de ruptures de fibres au sein d'un composite obtenue par Emission Acoustique

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