Non local approach for prediction of delamination onset

International audienceThis study is mainly focused on two major types of damage: intra-laminar ply cracking and inter-ply delamination in fiber-reinforced composite under static and fatigue loading. Off-axis and angle-ply non woven laminate have been used to study matrix cracking. Damage evolution based on continuum damage mechanics is considered for prediction intra-laminar ply cracking. While, angle-ply woven laminate is used to study the delamination. The delamination onset criterion based on average stress has been proposed. Identification of the different parameters of damage evolution model of matrix cracking and delamination onset has been made with classical rectangular specimen. Validation was made with static and fatigue tests performed on non woven and woven laminates with drilled circular hole. The numerical predictions are in good agreement with experimental results

A continuum damage model for composite laminated structures submitted to static and fatigue loadings

International audienceThis study is mainly focused on two major types of damage: intra-laminar ply cracking and inter-ply delamination in fiber-reinforced composite under static and fatigue loading. Off-axis and angle-ply non woven laminate have been used to study matrix cracking. Damage evolution based on continuum damage mechanics is considered for prediction intra-laminar ply cracking. While, angle-ply woven laminate is used to study the delamination. The delamination onset criterion based on average stress has been proposed. Identification of the different parameters of damage evolution model of matrix cracking and delamination onset has been made with classical rectangular specimen. Validation was made with static and fatigue tests performed on non woven and woven laminates with drilled circular hole. The numerical predictions are in good agreement with experimental results

Rhombohedral calcite precipitation from CO2-H2O-Ca(OH)2 slurry under supercritical and gas CO2 media

The formation of solid calcium carbonate (CaCO3) from aqueous solutions or slurries containing calcium and carbon dioxide (CO2) is a complex process of considerable importance in the ecological, geochemical and biological areas. Moreover, the demand for powdered CaCO3 has increased considerably recently in various fields of industry. The aim of this study was therefore to synthesize fine particles of calcite with controlled morphology by hydrothermal carbonation of calcium hydroxide at high CO2 pressure (initial PCO2=55 bar) and at moderate and high temperature (30 and 90 degrees C). The morphology of precipitated particles was identified by transmission electron microscopy (TEM/EDS) and scanning electron microscopy (SEM/EDS). In addition, an X-ray diffraction analysis was performed to investigate the carbonation efficiency and purity of the solid product. Carbonation of dispersed calcium hydroxide in the presence of supercritical (PT=90 bar, T=90 degrees C) or gaseous (PT=55 bar, T=30 degrees C) CO2 led to the precipitation of sub-micrometric isolated particles (<1$\mu$m) and micrometric agglomerates (<5$\mu$m) of calcite. For this study, the carbonation efficiency (Ca(OH)2-CaCO3 conversion) was not significantly affected by PT conditions after 24 h of reaction. In contrast, the initial rate of calcium carbonate precipitation increased from 4.3 mol/h in the "90bar-90 degrees C" system to 15.9 mol/h in the "55bar-30 degrees C" system. The use of high CO2 pressure may therefore be desirable for increasing the production rate of CaCO3, carbonation efficiency and purity, to approximately 48 kg/m3h, 95% and 96.3%, respectively in this study. The dissipated heat for this exothermic reaction was estimated by calorimetry to be -32 kJ/mol in the "90bar-90 degrees C" system and -42 kJ/mol in the "55bar-30 degrees C" system

Caractérisation d'une colle structurale polyuréthane

National audienceLe projet MP32 du pôle de compétitivité EMC2 vise la maîtrise des assemblages multimatériaux pour ses industriels partenaires. Des essais sur une colle structurale polyuréthane employée par l'un d'eux ont fait ressortir un comportement mécanique de type viscoélastoplastique avec une entrée en plasticité sensible à la pression hydrostatique. Une modélisation originale en a été proposée, avec notamment un critère de plasticité qui est dérivé de celui de Drucker-Prager. La procédure d'identification des paramètres de la loi de comportement dépendants du matériau est ici détaillée. Le dispositif de sollicitation multiaxiale d'interfaces Arcan-Mines est employé pour l'identification du critère. La modélisation et l'identification sont validées par la simulation d'un essai fait sur assemblage à quatre recouvrements de colle

Study of delamination of fibre harness satin weave composites molded by hot pressing. The example of high strength carbon fiber and PEEK matrix

International audienceIn recent years, the use of continuous fiber thermoplastic composites has been growing steadily, especially in the transportation industry. The purpose of the work reported here consists in developing an experimental and numerical approach to bring help in the design of laser welded TP reinforced composites. The current paper proposes a test procedure for a multi-axial mechanical characterization of the laser welded seam using the ARCAN-MINES device. This set up allows varying the loading direction while controlling the state of stress inside the joint. On the basis of experimental observations, a non-linear phenomenological material model based on a generalized Drucker-Prager criterion is used. An estimation of strains and stress inside the laser-welded seam could be computed and related to failure observations

Multi-scale statistical approach of the elastic and thermal behavior of a thermoplastic polyamid glass fiber composite

International audienceThe strong heterogeneity and the anisotropy of composite materials require a rigorous and precise analysis as a result of their impact on local properties. First, mechanical tests are performed to determine the macroscopical behavior of a polyamid glass fiber composite. Then we focus on the influence of the heterogeneities of the microstructure on thermal and mechanical properties from finite element calculations on the real microstructure, after plane strain assumptions. 100 images in 10 different sizes (50, 100, 150, 200, 250, 300, 350, 400, 450, 600 pixels) are analysed. The influence of the area fraction and the spatial arrangement of fibers is then established. For the thermal conductivity and the bulk modulus the fiber area fraction is the most important factor. These properties are improved by increasing the area fraction. On the other hand, for the shear modulus, the fibers spatial arrangement plays the paramount role if the size of the microstructure is smaller than the RVE. Therefore, to make a good prediction from a multi-scale approach the knowledge of the RVE is fundamental. By a statistical approach and a numerical homogenization method, we determine the RVE of the composite for the elastic behavior (shear and bulk moduli), the thermal behavior (thermal conductivity), and for the area fraction. There is a relatively good agreement between the effective properties of this RVE and the experimental macroscopical behavior. These effective properties are estimated by the Hashin-Shtrikman lower bound

Influence de la microstructure sur les propriétés mécaniques des joints collés

International audienceL'objectif de cette étude est de déterminer les propriétés mécaniques intrinsèques d'un adhésif au sein des assemblages structuraux puis d'examiner l'évolution de ces propriétés en fonction de l'épaisseur des joints de colle. Nous nous plaçons dans le cas d'une résine époxy DGEBA-DDA, chargée ou non. Des essais mécaniques et ultrasonores ont été réalisés sur des assemblages de différentes épaisseurs. Dans le but de déterminer l'influence de la microstructure sur le comportement du joint, ces résultats d'essais ont été couplés à des analyses microscopiques fines au microscope électronique à balayage (MEB). La composition de cette microstructure (charges minérales lamellaires), occasionne un endommagement d'autant plus important que les épaisseurs de colle sont faibles. Les propriétés mécaniques mesurées sont donc très dépendantes de l'épaisseur des joints considérée