Browsing by Author "Rechak, S."
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Item Analyse par la transformee d’ondelettes de delaminage et porosite dans les composites stratifies(2009) Si-Chaib, M.O; Yahyaoui, A.; Necib, B.; Nour, Abdelkader; Rechak, S.Le recours aux ultrasons pour l’évaluation non destructive des composites stratifiés constitue un outil d’investigation privilégié pour la recherche, la détection et la caractérisation des défauts critiques dissimulés éventuellement dans ces matériaux. Les défauts recherchés sont les délaminages, les inclusions, les fissures et les porosités. Dans le cas de l’examen des plaques composites minces, la localisation d’un défaut interne ou proche de la surface fournit des signaux ultrasonores complexes dont l’analyse requiert des méthodes de traitement très avancées et plus raffinées que les techniques classiques. Cette étude porte sur l’analyse par ondelettes en intégrant le choix de l’ondelette analysante et le niveau de résolution. Elle est appliquée aux signaux ultrasonores obtenus lors du sondage de plaques minces stratifiées pour la détection et l’identification des défauts dans ces matériaux composites. Ils renferment des défauts incorporés ou artificiels (délaminages) et réels (porosités). Les coefficients calculés de la transformée en ondelettes ont été utilisés pour la détection et la localisation des positions de défauts dont les résultats sont en bon accord avec les données expérimentalesItem Analysis of elliptical cracks in static and in fatigue by hybridization of green’s functions(2009) Hachi, B.K.; Rechak, S.; Haboussi, M.; Taghite, M.; Belkacemi, Y.; Maurice, G.A hybrid weight function technique is presented. It consists of dividing an elliptical crack into two zones, then using the appropriate weight function in the area where it is more efficient. The proportion between zones is determined by optimizing two crack parameters (axis ratio and curvature radius). Stress intensity factors are hence computed by a self developed computer code. Static and fatigue loadings are considered. The results found by the present approach are in good correlation with the analytical and experimental solutions (when available) as well as with those obtained numerically by other researchersItem Computation of stress intensity factor in cracked plates under bending in static and fatigue by a hybrid method(2007) Hachi, B.E.K.; Rechak, S.; Haboussi, M.; Taghite, M.; Maurice, M.A hybrid weight-function technique is presented. It consists of dividing an elliptical crack into two zones, then using the appropriate weight function in the area where it is more efficient. The proportion between zones is determined by optimizing two crack parameters (axis ratio and curvature radius). Stress intensity factors for plates containing elliptical and semi-elliptical cracks are hence computed by a self developed computer code. Static and fatigue loadings of bending are considered. The results found by the present approach are in good correlation with the analytical solutions (when vailable) as well as with those of other researchersItem Damage prediction in composite plates subjected to low velocity impact(2008) Tiberkak, R.; Bachene, M.; Rechak, S.; Necib, B.In this investigation, fiber-reinforced composite plates subjected to low velocity impact are studied by the use of finite element analysis (FE). Mindlin’s plate theory is implemented into the FE approach in which a 9-node Lagrangian element is considered. Dynamic stress analysis is carried out by the use of a constitutive equation of composite laminates without damage. A parametric analysis shows that the increase in the percentage of the 90 plies increases the contact force implying a reduction in the rigidity of the laminate. Stresses are calculated at nine Gaussian points of each element of each interface and then averaged. At first, threshold velocities are evaluated for different stacking sequence to predict matrix crack initiation. Then, the impact induces damage at a higher impact velocity including matrix cracking is predicted by the appropriate failure criteria. The present results indicate that matrix cracking appears in the upper 90 plies with the dominance of transverse shear stressItem Dynamic analysis of cracked plates by the extended finite element method (X-FEM)(2009) Bachene, M.; Bachene, M.; Rechak, S.Dynamic analysis of isotropic and composite plates containing through cracks are analyzed. Since regular finite element needs not only re-meshing at discontinuities, but also requires high mesh density at singularities, a search for an efficient numerical method is thus suitable. Because of its efficiency in not requiring re-meshing at singularities, the extended finite element method (X-FEM) is widely used in fracture mechanics problems. However and according to our knowledge, the XFEM has not yet been used in the dynamic analysis of cracked structures, subject of the present work. The analysis of dynamic behavior of isotropic and composite plates having a through crack located at various positions is conducted. At first, conventional FEM without any discontinuity is carried out; then, enrichment of nodal elements containing cracks is added to the FEM model. Various plates configurations with different kinds of boundary conditions and with different crack lengths and locations are considered. Primary observations show that the frequency of all the modes of vibration decreases with the increase of the crack length. This physical effect is more pronounced for some specific modes as it also depends on the nature of the singularityItem Effects of the modifications of the mechanical properties of the skin on the irrigation of the venous wall by the vasa vasorum(2004) Maurice, G.; Rechak, S.; Amor, N.; Taghite, M.Abstract. It is well known that the nonlinear mechanical properties and the ordering of the muscular fibres of the media and the adventia restrict the expansion of the vascular wall under an intraluminal pressure. On the young persons, the surrounding tissues of the blood vessels also play a part in the effect of these two layers. Particularly, for the veins of the upper and lower limbs, the skin plays a no unimportant part in the restriction of this expansion. With the age, the tissues may become distended or reduce their thickness and clearly allow to show some vessels which then are less restrained by the surrounding tissues like the skin. The deformation of a vein under the influence of intraluminal pressure modifies the cross-section of its vasa vasorum and thus can alter its irrigation. The nonlinear elasticity of the vein depends, as a first approximation, basically on two structural parameters. In some cases, even a small variation of the parameters (behaviour or composition of the wall) can provoke the flattening of the vasa vasorum and thus lead to a local ischemia. Thus, one can think that a vicious cycle could be initiated. Firstly, a permanent overpressure causes a modification of the local mechanical property of the vein, which, if it is not restrained by the surrounding tissues, leads to a large expansion of the vessel wall and enhance the decrease of the irrigation. Secondly, the irrigation being insufficient, the vein wall looses its elasticity, becomes progressively rigidified and keeps its maximum deformationItem Extension of the hybridization weight function approach to corner cracks(2009) Hachi, B.K.; Rechak, S.; Haboussi, M.; Nour, Abdelkader; Maurice, G.Item Fatigue growth of embedded elliptical cracks using paris-type law in a hybrid weight function approach(2008) Hachi, B.E.K.; Rechak, S.; Haboussi, M.; Taghite, M.; Maurice, G.A hybrid weight function method (HWFM), improving the calculation of the stress intensity factor (SIF) in mode I, has recently been proposed and validated in the static case [B.K. Hachi, S. Rechak, M. Haboussi, M. Taghite, Modélisation des fissures elliptiques internes par hybridation de fonctions de poids, C. R. Mecanique 334 (2006) 83–90]. In the present Note, the hybridization approach is presented for the fatigue crack growth prediction of embedded elliptical crack in infinite bodies. Hence, Paris’s law of crack propagation is incorporated into the developed hybridization-based computer code, along with two degrees of freedom technique for managing the crack evolution and the cracked structure fatigue life. Simulations of the evolution of elliptical cracks (in infinite bodies) of different configurations (ellipse axes ratio, maximum crack advance) corresponding to fatigue and brittle fracture have been conducted. Comparisons with other numerical methods such as the classical weight function method (WFM) or the extended finite element methods (X-FEM) show the pertinence of the HWFM in the treatment of an aspect of fatigue cracking problemsItem Long-term bending creep behavior prediction of injection molded composite using stress–time correspondence principle(Elsevier, 2004) Hadid, M.; Rechak, S.; Tati, A.In analogous manner to the time–temperature superposition principle, the stress–time superposition principle approach is used to predict long-term material creep behavior without extensive laboratory test time. The bending creep of the injection fiber glass reinforced polyamide is studied. An improved empirical model is used to construct the creep master curve, to take into account the strong non-linear behavior. An excellent superposition of curves is obtained and, in a long-term, an important curvature in the master curve is registeredItem Modélisation de fissures elliptiques internes par hybridation de fonctions de poids(2006) Hachi, B.E.K.; Rechak, S.; Haboussi, M.; Taghite, M.Une méthode améliorant le calcul des facteurs d'intensité de contrainte par hybridation de deux fonctions de poids est présentée et appliquée aux cas de fissures elliptiques internes sous différents chargements. L'hybridation consiste à utiliser l'une ou l'autre des deux fonctions dans la zone de la fissure où la fonction est la plus efficace. La délimitation des deux zones est faite après optimisation du rapport des axes et du rayon de courbure de la fissure. Lors de l'optimisation on cherche à atténuer l'effet des singularités présentes dans les fonctions de poids et à mieux prendre en compte l'influence de la courbure de l'ellipseItem Modelling of elliptical cracks in an infinite body and in a pressurized cylinder by a hybrid weight function approach(2005) Hachi, B.E.K.; Rechak, S.; Belkacemi, Y.; Maurice, G.In this work, a hybridization technique is proposed. It consists of using two weight functions to model elliptical cracks for computation of the stress intensity factor ‘SIF’ in mode I. The idea of hybridization consists of dividing the ellipse into two zones, then to use each weight function in the area where it is more efficient. The proportion between the two zones is determined by optimization of the ellipse axis ratio. A computer code is developed for the computation of SIF. The treatment of the numerical procedures including singularities are presented in detail. The approach is tested on several applications (elliptical crack in infinite body, semi-elliptical cracks in thin and thick cylinders), to demonstrate its accuracy by minimization of the error of SIF and its correlation with respect to other researchersItem Numerical simulation of the behaviour of cracks in axisymmetric structures by the dual boundary element method(Springer, 2009) Amoura, N.; Kebir, H.; Rechak, S.; Roelandt, J. M.The study of defected axisymmetric structures is among important industrial applications. Detection of such defects, and or the evaluation of intrinsic parameter leads to a better design of those mechanical parts. The first part of the conducting research concerns the evaluation of the stress intensity factors (SIF) in axisymmetric elastic structures with internal or circumferential edge crack using the dual boundary element method (DBEM). Its application to axisymmetric problems requires a stress (hypersingular) boundary integral equation together with the displacement (standard) boundary integral equation, one applied to each side of the crack. This process requires a great algebraic handling due to the complexity of the axisymmetric kernels. Crack surfaces are discretized with discontinuous quadratic boundary elements to satisfy the existence of the finite-part integrals and the continuity of the unit outward normal at corners. SIF evaluation is done using displacements extrapolation at the crack tip. Examples of axisymmetric geometries are analyzed and obtained results are compared to others researchers. Damage and Fracture Mechanics Damage and Fracture Mechanics Look Inside Other actions Export citation About this Book Reprints and Permissions Add to Papers Share Share this content on Facebook Share this content on Twitter Share this content on LinkedIn