Caractérisation de l'endommagement et de la rupture des composites à fibres longues et discontinues (DLF) sollicités en traction

L'une des barrières à l'usage des matériaux composites dans les nouvelles générations de moteurs pour l'aviation civile est la géométrie complexe des pièces à réaliser. Un matériau composite novateur (HexMC ®), composé de bandelettes (ou chips) unidirectionnelles de renforts fibreux longs discontinus et disposées aléatoirement, semble être un bon candidat. Cette étude s'intéresse à la caractérisation des premiers endommagements qui amorcent la rupture en traction dans le cas particulier du HexMC ®. Pour cela, différents types d'essais de traction multi-instrumentés (Corrélation d'images numériques (CIN), émission acoustique (EA), microscopie post-mortem/in-situ) ont été menés. Ainsi, les types d'endommagements présents (fissurations intra-chips, délaminage inter-chips, décohésions) ont été déterminés mais aussi leur séquencement d'apparition et leur méthode de propagation. Les chips orientées à 90° par rapport au chargement ont été directement incriminées comme étant les éléments déclencheurs des premiers endommagements. Ce sont dans ces chips en particulier qu'apparaissent les premières fissures intra-chips transversalement au chargement. Le niveau de charge d'apparition de ces premiers endommagements a également été déterminé. L'analyse combinée de l'ensemble de l'instrumentation mise en place a permis de proposer un scénario d'endommagement depuis le seuil d'endommagement jusqu'à la rupture fragile du matériau. Abstract Among the factors limiting the use of composite materials are the complex shapes to be found, for example, in aircraft engines. A new and innovative composite material (HexMC ®) unidirectional prepreg based, made of discontinuous and long strands (or "chips"), randomly oriented seems to match the demands. The goal of this study is to characterize the first damages that initiate the failure under tensile loading in the particular case of HexMC ®. For this purpose, various and multi-instrumented (Digital Image Correlation (DIC), Acoustic Emission (AE), post-mortem/ in-situ microscopy) tensile tests were conducted. Not only the types of damage were determined (intra-chips cracks, inter-chips delamination, debonding) but also the sequence in which they appear and the way they propagate. Cause of the first damages is attributed to chips oriented at 90° with respect to the loading direction. These particular chips are the ones in which appear the first intra-chips cracks transversely to the loading direction. The loading level at which occur the first damages is determined as well. Through this study and the multi-instrumented analyses, a damage scenario was created from the first damages until to catastrophic failure

A micromechanics model for 3D elasticity and failure of woven-fibre composite materials

International audienc

Structural Health Monitoring (SHM) Study of Polymer Matrix Composite (PMC) Materials Using Nonlinear Vibration Methods Based on Embedded Piezoelectric Transducers

Nowadays, nonlinear vibration methods are increasingly used for the detection of damage mechanisms in polymer matrix composite (PMC) materials, which are anisotropic and heterogeneous. The originality of this study was the use of two nonlinear vibration methods to detect different types of damage within PMC through an in situ embedded polyvinylidene fluoride (PVDF) piezoelectric sensor. The two used methods are nonlinear resonance (NLR) and single frequency excitation (SFE). They were first tested on damage introduced during the manufacturing of the smart PMC plates, and second, on the damage that occurred after the manufacturing. The results show that both techniques are interesting, and probably a combination of them will be the best choice for SHM purposes. During the experimentation, an accelerometer was used, in order to validate the effectiveness of the integrated PVDF sensor

Experimental Linear and Nonlinear Vibration Methods for the Structural Health Monitoring (SHM) of Polymer-Matrix Composites (PMCs): A Literature Review

The goal of this article is to provide a review of the experimental techniques and procedures using vibration methods for the Structural Health Monitoring (SHM) of Polymer-Matrix Composites (PMCs). It aims to be a guide for any researchers to carry out vibration experiments. The linear methods are first introduced. But, as PMC is a complex material, these classic methods show some limits, such as low accuracy for small damages and a high environmental dependency. This is why the nonlinear methods are secondly studied, considering that the complexity of PMCs induces a nonlinear behavior of the structure after damage occurrence. The different damage mechanisms are well-explained in order to evaluate the potential of each vibration method to detect them

Effet du vieillissement artificiel sur les paramètres d'un critère de rupture interlaminaire en mode mixte (I+II) d'un matériau composite à armure tissée hybride

International audienc

In-situ structural health monitoring of glass fiber reinforced composites by tufted reinforcement

International audienc

Effects of the environmental conditions on the mechanical behaviour of the corrugated cardboard

International audienc

Digital image correlation, acoustic emission and in-situ microscopy in order to understand composite compression damage behavior

International audienc

The effect of ageing on the damage events in woven-fibre composite materials under different loading conditions

International audienc