Experimental and numerical modelling of LRI process

The aim of this study is to gain knowledge concerning the process and its physics, as well as to become able to optimize the fabrication of large and complex composite parts in aeronautics applications. Composite materials have many advantages and the use of this technology is increasing in the aeronautic industry. In the L.R.I. process, dry textile preforms are impregnated by a thermoset liquid resin. All the elements are enclosed in a vacuum bag of known pressure. Once preforms are totally impregnated, the resin system begins the curing reaction to obtain the composite part. This study contains two major sections. Firstly, numerical modeling was done with the Pam- Rtm finite element code to determine the evolution of the flow front during the infusion. Simulations were performed to analyze the infusion of sandwich composite parts with perforate foam, which allows the inferior skin to be impregnated in the same operation. Secondly, experimental work was conducted to confirm the numerical results

Étude du comportement mécanique des matériaux composites par corrélation volumique : Application à l’analyse des effets du cisaillement transverse

De nombreuses études ont été menées sur les matériaux composites, concernant le comportement mécanique à l’échelle macroscopique. D’autre part, le développement continu des techniques de détection et de mesures de champs permet d’aller plus loin dans l’analyse des structures complexes, dont les matériaux composites. Ainsi, la corrélation volumique (DVC) basée sur des acquisitions de la structure interne à différents états de déformation, permet la mesure du champ des déplacements dans le volume des échantillons. Le gauchissement des sections dû aux contraintes de cisaillement transverse est un phénomène propre aux structures anisotropes comme les structures composites. De nombreuses études traitent du développement des modèles analytiques pour la modélisation numérique et la détermination des déplacements avec le plus de précision possible. Ainsi, de nombreux modèles existent, certains très complexes, pour la prise en compte de ce phénomène dans l’étude des structures multicouches. L'objectifs de ce travail doctoral est d’utiliser les mesures de champs issues de la corrélation volumique couplée à la tomographie rayons X, pour visualiser le gauchissement des sections pour un cas de sollicitation de flexion trois points. Une méthode de mesure ainsi qu’un système de chargement in-situ spécifique sont développés dans ce travail de recherche. Les modèles analytiques existants sont évalués et comparés à partir de mesures expérimentales. Aussi, un nouveau modèle est également proposé à partir d'une identification numérique, basée sur les mesures de champs volumiques réalisées. Les résultats de ce travail de thèse permettront une meilleure compréhension du phénomène physique rencontrés lors de l’utilisation des matériaux composites et pourront envisager des pistes d’optimisation de leur conception et de leur mise en œuvre. ABSTRACT : The complex mechanical behaviour of composite materials, due to internal heterogeneity and multi-layered composition impose deeper analysis. Several studies have already been conducted on the composite structures mechanical behavior at the macro level. On the other hand, the continuous development of detection techniques and field measurements can now go further in the analysis of complex structures, including composites. Thus, the digital volume correlation (DVC) based on the acquisition of the internal structure at different deformation states, allows the measurement of displacement fields through the thickness of the specimen. Warping sections due to transverse shear is a phenomenon linked to anisotropic structures, such as composite structures, which has been the subject of many studies to develop analytical models for the numerical modeling and the determination of displacements with the greatest possible precision. Many theories and models exist, some very complex, for the consideration of this phenomenon .. One goal of this doctoral work is to use measurements from the density correlation to determine whether these models the effects of transverse shear are physically consistent, and if their validity is good in the case of a kinematic measurement volume. A second objective of this thesis is to acquire know-how in the processing of information resulting from acquisitions by X-ray tomography In this sense, several studies are planned for the treatment and use of this information in an industrial context. The results of this work will provide a better understanding of physical phenomena encountered in the use of composite materials to generate optimization of their design and implementation paths

One Class Splitting Criteria for Random Forests

Random Forests (RFs) are strong machine learning tools for classification and regression. However, they remain supervised algorithms, and no extension of RFs to the one-class setting has been proposed, except for techniques based on second-class sampling. This work fills this gap by proposing a natural methodology to extend standard splitting criteria to the one-class setting, structurally generalizing RFs to one-class classification. An extensive benchmark of seven state-of-the-art anomaly detection algorithms is also presented. This empirically demonstrates the relevance of our approach

Impact resistance of composite materials under biaxal preloading

The first aim of this study is to analyze the impact behavior of pre-loaded composite. Indeed, a bi-axial load is applied to the composite specimen, in order to keep in touch with a real case of composite fuselage. Then, this pre-loaded specimen is impacted by a pendulum. The used energy and velocity are weak in order to be in the case of low-energy and low-velocity impact. The second aim of this study is to develop and design a pendulum device to be integrated to the biaxial fatigue loading. Moreover, two Non Destructive Inspections (Sonoscan and InfraRed Thermography) is used in order to establish links between pre-load and induced impact damage

Global behaviour of a composite stiffened panel in buckling. Part 2: Experimental investigation

The present study analyses an aircraft composite fuselage structure manufactured by the Liquid Resin Infusion (LRI) process and subjected to a compressive load. LRI is based on the moulding of high performance composite parts by infusing liquid resin on dry fibres instead of prepreg fabrics or Resin Transfer Moulding (RTM). Actual industrial projects face composite integrated structure issues as a number of structures (stiffeners, …) are more and more integrated onto the skins of aircraft fuselage. A post-buckling test of a composite fuselage representative panel is set up, from numerical results available in previous works. Two stereo Digital Image Correlation (DIC) systems are positioned on each side of the panel, that are aimed at correlating numerical and experimental out-of-plane displacements (corresponding to the skin local buckling displacements of the panel). First, the experimental approach and the test facility are presented. A post-mortem failure analysis is then performed with the help of Non-Destructive Techniques (NDT). X-ray Computed Tomography (CT) measurements and ultrasonic testing (US) techniques are able to explain the failure mechanisms that occured during this post-buckling test. Numerical results are validated by the experimental results

X-μCT and DVC use for composite materials analysis

The complex mechanical behaviour of composite materials, due to internal heterogeneity and multi-layered composition imposes deeper studies. This paper presents an experimental protocol to perform volume kinematic measurements in composite materials. This work is centered on the transverse shear effects in relation with the composite materials mechanical behaviour. A lot of theories exist in literature to consider the existing warping section during high transverse shear stresses, but very few studies have been realized in the experimental way. The association of X-ray micro-computed tomography acquisitions and Digital Volume Correlation (DVC) technique allows the measurement of displacements and deformations in the whole volume of composite specimen. To elaborate the latter, composite fibres and epoxy resin are associated with metallic particles to make contrast in X-μCT acquisitions. A specific in-situ loading device is presented for three-point bending tests, which enables the visualization of transverse shear effects in composite structures

Experimental study of 48600 Carbons fabrics behavior using marks tracking technique method

Lightweight and energy saving are the main challenges in the aircraft industry production, that explain the increase of composite demand and the diversity of its applications. The investigation of the shear behavior and stiffness of technical woven fabric are essential to guarantee the performance of the final product. In case of forming process (for example RTM process), the in-plane deformability of the woven fabric is necessary for forming without creating defects. The change of the fiber orientation (warp and weft) have a significant impact on final mechanical properties. In this study, the use of marks tracking technique allow the determination of the rigidity of 48600 C 1300 carbon fabrics, and allow calculation of their shear angle, lock angle during tensile and bias-extension tests

Warping section analysis by numerical modelling and volume measurements techniques

The transverse shear effects is a important phenomenon which have to be taken into account in the composite structures studies. This paper deals whith the use of differents kind of transverse shear functions for the analytical displacement fields calculations of composite materials. Since the old models of Kirchhoff-Love and Reissner-Mindlin to consider the transverse shear stresses, litterature gives a very large number of functions wich can be used to concider the transverse shear effects, especially the warping sections

Damage investigation in CFRP composites using full-field measurement techniques: combination of digital image stereo-correlation, infrared thermography and X-ray tomography

The present work is devoted to damaging process in carbon–fiber reinforced laminated composites. An original experimental approach combining three optical measurement techniques is presented. Image stereo-correlation and infrared thermography, that respectively provide the kinematic and thermal fields on the surface of the composites, are used in live recording during axis and off-axis tensile tests. Special attention is paid to simultaneously conduct these two techniques while avoiding their respective influence. On the other hand, X-ray tomography allows a post-failure analysis of the degradation patterns within the laminates volume. All these techniques are non-destructive (without contact) and offer an interesting full-field investigation of the material response. Their combination allows a coupled analysis of different demonstrations of same degradation mechanisms. For instance, thermal events and densimetric fields show a random location of damage in the early stages of testing. The influence of the material initial anisotropy on damage growth, localization and failure mode can also be clearly put in evidence through various data. In addition to such characterization, this study illustrates at the same time the capabilities of the different full-field techniques and the damage features they can best capture respectively