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

Benchmarking of strength models for unidirectional composites under longitudinal tension

Several modelling approaches are available in the literature to predict longitudinal tensile failure of fibre-reinforced polymers. However, a systematic, blind and unbiased comparison between the predictions from the different models and against experimental data has never been performed. This paper presents a benchmarking exercise performed for three different models from the literature: (i) an analytical hierarchical scaling law for composite fibre bundles, (ii) direct numerical simulations of composite fibre bundles, and (iii) a multiscale finite-element simulation method. The results show that there are significant discrepancies between the predictions of the different modelling approaches for fibre-break density evolution, cluster formation and ultimate strength, and that each of the three models presents unique advantages over the others. Blind model predictions are also compared against detailed computed-tomography experiments, showing that our understanding of the micromechanics of longitudinal tensile failure of composites needs to be developed further

Stochastic factors controlling the failure of carbon/epoxy composites

The 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

Damage accumulation in a carbon/epoxy composite: comparison between a multiscale model and computed tomography experimental results

High-resolution computed tomography has been carried out for carbon/epoxy laminates loaded in situ to failure. The experimental data allows major damage mechanisms to be quantified in 3D, in an unambiguous and mechanically representative way, where previous experimental analysis is limited.A multi-scale model that predicts damage accumulation in tensile loaded composites is compared to the experimental analysis, to validate the underpinning assumptions within the model and overall performance. The model considers the random nature of fibre-strengths, stress transfer resulting from fibre breaks, fibre/matrix debonding and viscosity of the matrix. Assumptions within the model are made to reduce computational times whilst considering the microscopic behaviour of the whole structure.Both model and experimental results indicate failure of the composite progresses via single fibre breaks, which, at higher loads, evolve into clusters of broken fibres. The model resulted in reasonable predictions of the preceding damage accumulation and final failure load of the structure

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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