Experimental and numerical investigations: effects of defects in laminated L-angles

International audienceConsidering the widespread use of composites in aerostructures and the sector’s high production rates, it is now essential to define standard quality and associated acceptance criteria for composite components. Standard quality is the maximum acceptable defect size that has no detrimental effect on a part’s performance. Therefore, the characterisation of manufacturing defects and a deep understanding of their potential consequences on performance is a key issue. Simulations using physically-based damage and failure approaches are a crucial tool to estimate the influence of initial defects on mechanical properties and, therefore, to establish acceptance criteria adapted to each composite component, thus avoiding conservatisms and “over-quality"

Experimental and numerical investigations: effects of defects in laminated L-angles

International audienceConsidering the widespread use of composites in aerostructures and the sector’s high production rates, it is now essential to define standard quality and associated acceptance criteria for composite components. Standard quality is the maximum acceptable defect size that has no detrimental effect on a part’s performance. Therefore, the characterisation of manufacturing defects and a deep understanding of their potential consequences on performance is a key issue. Simulations using physically-based damage and failure approaches are a crucial tool to estimate the influence of initial defects on mechanical properties and, therefore, to establish acceptance criteria adapted to each composite component, thus avoiding conservatisms and “over-quality"

Analyse expérimentale et numérique de la tenue de matériaux composites tissés 3D : de l’éprouvette élémentaire aux structures aéronautiques complexes

International audienceNew generations of 3D woven composite materials have been recently developed to be used in aeronautics as an alternative to the classical laminated composite materials, for structures exposed to impact. Therefore, it has been necessary to determine precisely the damage and failure scenarios for such materials subjected to different kinds of loadings through a large experimental testing campaign performed at Onera on unnotched coupons. These tests have been multi-instrumented to understand the different damage and failure mechanisms encountered in 3D woven composite materials. Based on these observations, a model, named Onera Damage Model for Polymer Matrix Composites (ODM-PMC), has been developed specifically for such materials. This non-linear material approach takes into account the different observed sources of non-linearity (viscoelasticity of the matrix, in–plane matrix damage, interyarn debondings and fiber yarn failures) and has been validated through comparisons with available tests on unnotched specimens. Moreover, the predicted failure loads, obtained with the ODM-PMC model, on plates containing different kinds of geometrical singularities, such as a hole or a milled groove, have been compared successfully to multi-instrumented test results also performed at Onera . Finally, the ODM-PMC model has been applied to large 3D woven composite structures, quite representative of real industrial components. The predicted damage and failure scenarios seem to be relevant as compared to data available in the literature. Moreover, the obtained computational times are compatible with usage in an industrial environment. Therefore, it has been demonstrated that this approach, implemented in a commercial finite element code, could be used in design offices in aeronautical industries.Les nouvelles générations de matériaux composites tissés 3D à matrice organique ont récemment été développées pour être utilisées dans l'aéronautique comme une alternative aux matériaux composites stratifiés classiques, pour des structures exposées aux impacts. Par conséquent, il a été nécessaire d’étudier finement les endommagements et d’établir les scénarios de rupture de ces matériaux soumis à différents types de chargement à l’aide d’une importante campagne d’essais mécaniques effectués à l'ONERA sur des éprouvettes élémentaires. Ces essais ont été multi-instrumentés afin de comprendre les différents mécanismes d’endommagement et de rupture rencontrés dans les matériaux composites tissés 3D. Sur la base de ces observations, un modèle, appelé ONERA Damage Model pour Composites à Matrice Organique (ODM-CMO), a été développé spécifiquement pour ces matériaux. Ce modèle matériau non linéaire prend en compte les différentes sources de non-linéarité observées (viscoélasticité de la matrice, fissuration matricielle, décohésions inter-torons et la rupture des torons de fibres) et a été validé au travers de comparaisons avec les résultats d’essais disponibles sur des éprouvettes élémentaires. Par ailleurs, les efforts à rupture, prévus par le modèle ODM-CMO, sur des plaques contenant différents types de singularités géométriques, telles que des trous ou des rainures fraisées, ont été comparés avec succès aux résultats des essais multi-instrumentés également effectués à l'ONERA. Enfin, le modèle ODM-CMO a été appliqué à des structures composites tissées 3D représentatives de composants industriels. Les scénarios d’endommagement et de rupture prévus semblent être cohérents avec les résultats disponibles dans la littérature. De plus, les temps de calcul obtenus sont conformes aux exigences industrielles actuelles. Par conséquent, il a été démontré que cette approche, disponible dans un code éléments finis commercial, pourrait être utilisée dans les bureaux d'études de l’industrie aéronautique

On the influence of fabric layer shifts on the strain distributions in a multi-layer woven composite

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Study of the galvanic corrosion in Al/CFRP co-cured hybrid materials

International audienceThe use of hybrid structures where the right material is used at the right place for its best properties is of great interest for structures optimisation, particularly when mass reduction is required. In such hybrid structures, where metal and composite are closely in contact, the strength of the interface between the metal and the composite can be altered by the galvanic corrosion between the aluminium and the composite when Carbon Fibres Reinforced Plastic (CFRP) is used. This paper is related to the corrosion and mechanical properties of an Aluminium/CFRP co-cured hybrid structure. The influence of the aluminium surface treatment on the interface properties obtained after a one step co-curing manufacturing process has been assessed. Al-2024 aluminium alloy treated by either tartaric-sulphuric anodizing (TSA), chromic acid anodizing (CAA) or silane pre-treatment (γ-GPS) has been used and co-cured with CFRP. The galvanic corrosion behaviour of the Al/CFRP hybrid system has been determined with the Evans diagram method and the mechanical strength of the interface has been characterized with a single-lap joint tensile test before and after exposure of the samples in a salt spray chamber. The different surface treatments of the aluminium alloy have been compared in term of both galvanic corrosion and adhesion properties before and after corrosive environment exposure in order to find the best compromise for Al/CFRP structure applications

On the analysis of heat haze effects with spacetime DIC

International audienceLong image series (i.e., movies) can be analyzed via digital image correlation (DIC) techniques. A new spacetime implementation is introduced to extend instantaneous DIC with minimal implementation complexity. With this procedure, a denoised reference image is built considering a series of more than 200 images. Such spacetime approach is very interesting when high temperature experiments are performed since it provides a very effective temporal regularization. The analysis of heat haze effects is carried out on a thermomechanical test in which the sample made of ceramic matrix composite is subjected to temperatures greater than 1,200°C in the heat affected zone of the laser beam. It is shown that the addition of a small fan reduces the spurious displacement fluctuations

Glutamatergic synapse in autism: a complex story for a complex disorder

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