11 research outputs found
ModÚle numérique pour la simulation de la propagation des fissures de fatigue en mode I des plaques en aluminium réparées par patch en matériaux composites
Par la prĂ©sente Ă©tude, une simulation numĂ©rique dynamique en 3D a Ă©tĂ© effectuĂ©e pour prĂ©dire le facteur d'intensitĂ© des contraintes Ă la pointe de fissure ainsi que la durĂ©e de vie en fatigue d'une plaque en aluminium 2124-T3 rĂ©parĂ©e par un patch en composite. Par la suite, une Ă©tude d'optimisation a Ă©tĂ© menĂ©e pour estimer la durĂ©e de vie adĂ©quate justifiant une forme optimale du patch en composite. ConsidĂ©rant les variables de conception telle que, la hauteur, la largeur et l'Ă©paisseur du patch, en plus de l'Ă©paisseur d'adhĂ©sif, une importante rĂ©duction du volume de patch peut ĂȘtre rĂ©alisĂ©e en appliquant le modĂšle dĂ©veloppĂ©. La sensibilitĂ© des paramĂštres optimaux du patch est Ă©tudiĂ©e sous diffĂ©rentes tailles de fissures. DiffĂ©rentes sĂ©quences d'empilement et propriĂ©tĂ©s mĂ©caniques du patch sont Ă©galement considĂ©rĂ©es afin de rĂ©duire la concentration de contraintes au voisinage de la pointe de fissure, en aboutissant Ă une forte rĂ©duction du volume. Â
Etude en rupture d'un composite à fibres végétales d'Alfa
National audienceThe behavior under monotonic loading of reinforced natural fibre composites begins to be fairly well known today. However, the fracture behavior is still poorly controlled. This work describes a numerical approach developed to simulate the propagation mechanism of a matrix crack in natural fibre reinforced composites.To this end, the fracture behavior of a REV; constituted of alfa fibre, with linear anisotropic behavior, surrounded by a matrix with non-linear viscoelastic behavior, was investigated using a finite element model. The analysis of the fracture behavior of the composite alfa fibre / epoxy resin shows that under uniaxial longitudinal or transverse load to the fibre, a crack initiated in the matrix is propagated perpendicularly to the direction of the load. Near the interface, the energy release rate decreases and this energy is higher in the presence of interfacial debonding areas generated by problems of fibre wettability. Reaching the interface, the crack is either blocked or deflected. Once deflected, the crack propagates along the interface and causes the complete debonding of the fibre.Le comportement sous chargement monotone des composites renforcĂ©s par des fibres naturelles commence Ă ĂȘtre assez bien connu aujourd'hui. Cependant, le comportement Ă la rupture est encore mal maĂźtrisĂ©. Le prĂ©sent travail dĂ©crit une approche numĂ©rique dĂ©veloppĂ©e pour simuler le mĂ©canisme de propagation d'une fissure matricielle Ă l'interface fibre vĂ©gĂ©tale alfa / rĂ©sine Ă©poxy dans les composites Ă matrice polymĂšre. A cette fin, le comportement Ă la rupture d'un VER constituĂ© d'une fibre unitaire d'alfa, de comportement linĂ©aire anisotrope, entourĂ©e d'une matrice de comportement non linĂ©aire viscoĂ©lastique, a Ă©tĂ© Ă©tudiĂ© Ă l'aide d'un modĂšle Ă©lĂ©ments finis. L'analyse du comportement Ă la rupture du composite fibre alfa/rĂ©sine Ă©poxy montre que sous l'action d'un chargement uniaxial, longitudinal ou transversal par rapport Ă la fibre, une fissure initiĂ©e dans la matrice se propage perpendiculairement au sens de la sollicitation. Au voisinage de l'interface, le taux de restitution d'Ă©nergie diminue et ce taux est plus Ă©levĂ© en prĂ©sence de zones de non adhĂ©sion gĂ©nĂ©rĂ©es par des problĂšmes de mouillages. ArrivĂ©e Ă l'interface, la fissure est soit bloquĂ©e soit dĂ©viĂ©e. Une fois dĂ©viĂ©e, la fissure se propage le long de l'interface et entraĂźne la dĂ©cohĂ©sion de la fibre
Impact de renforts FRP précontraints sur la valeur des contraintes interfaciales des structures renforcées par composites collés
Cet article prĂ©sente une nouvelle approche thĂ©orique dâanalyse des contraintes
interfaciales sur les structures renforcées par composites FRP précontraints, en tenant
compte du modĂšle de chargement mĂ©canique, de lâeffet shear lag et de
lâimpact des prĂ©contraintes. Ces renforts FRP prĂ©contraints sont, en particulier, utilisĂ©s
pour rĂ©habiliter les structures par composites collĂ©s, en arrĂȘtant la propagation des
fissures, en donnant plus de rigidité et de résistance à la structure permettant ainsi de
prolonger leur durée de vie. Dans ce travail, un aspect original est présenté, il permet
de prévoir et déterminer la concentration des contraintes aux bords des renforts FRP par
une approche analytique et de donner plus de précision par rapport aux méthodes
prĂ©cĂ©dentes qui ont nĂ©gligĂ© lâeffet des renforts FRP prĂ©contraints couplĂ©s avec les
différentes charges appliquées. La résolution numérique a été finalisée en tenant compte
des paramÚtres physiques et géométriques des éléments de la structure qui peuvent jouer un
rĂŽle important dans la diminution de la valeur des contraintes
Experimental and Numerical Model of CFRP Retrofitted Concrete Beams with Intermediate Notches Subjected to Drop-Weight Impact
International audienc
Experimental and numerical models to study the creep behavior of the unidirectional Alfa fiber composite strength by the photoelasticity method
International audienceIn this paper, we propose an experimental and numerical model to study the creep behavior of the unidirectional Alfa fiber composite strength by the photoelasticity method. To have better mechanical properties, chemical treatment is made for Alfa fibers. Tensile tests are made to predict the Young modulus and tensile strength. These tests confirm that the chemical treatment during 48 Hours of Alfa fibers collected from the south region gives the best results. After that, specimens are made in Medapoxy STR resin and treated Alfa fibers of the south region. All fibers of specimens are arranged approximately in multiple hexagonal clusters embedded in the matrix. For the micromechanical fiber stress redistribution or load sharing theory to be applied, clusters must minimally contain one broken fiber. Consequently, we have a stress perturbation due to a fiber fracture, which propagates to the nearest-neighbor fibers. This perturbation enables us the photoelastic visualization of the fracture events during the creep tests. The contour diagram and fringe values give us the accurate distribution of stress near broken fibers showing local shear stress concentrations during the time. To simulate the creep response and failure mechanism, the TsaiâWu failure criterion was applied on ANSYS explicit dynamic software. Because it merges between experimental tests and numerical simulation, the present study offers a real scientific contribution in the creep behavior of biobased composite strength by the photoelasticity method
Morphology, static and fatigue behavior of a natural UD composite: The date palm petiole âwoodâ
International audienc
Experimental and numerical studies on the low-velocity impact response of orthogrid epoxy panels reinforced with short plant fibers
Experimental and numerical studies were conducted to analyze the low-velocity impact response of orthogrid stiffened panels reinforced with short alfa fibers. Tensile specimens and orthogrid panels were fabricated with two types of epoxy resins and different fractions of crushed and sieved alfa fibers (fiber volume fraction (V f ) from 10% to 50%). Impact tests were conducted on the orthogrid panels to investigate their low-velocity transverse impact behavior. The resistance to damage increased with an increase in fiber content and improvement in the mechanical properties of the composites (measured in static). Bending tests carried out on pre-impacted and non-impacted panels revealed a change in the linearity of the initial bending behavior, which could be justified by the small cracks generated by impact. A numerical model of impact on the orthogrid stiffened composite panels was developed using the nonlinear Hertz's contact model. To simulate the failure mechanism and load-time history, a standard Tsai-Wu failure criterion was used on ANSYS explicit dynamic software. The simulations show a good correlation with the experimental data. The dominant stresses for damage evolution are found to be normal stresses. The presence of a stiffener reduces the stress, which confirms that stiffeners limit the propagation of damage. © 201