Abderrezak Bezazi

Flexural fatigue behavior of cross-ply laminates: An experimental approach

Within an experimental approach we describe the mechanical behavior of different resin-epoxy laminates reinforced with cross-ply Kevlar and glass fibers under conditions of static and cyclic three-point bending. In static tests, we consider the effect of stacking sequence, the thickness of 90°-oriented layers, reinforcement type on the mechanical behavior of laminates under loading and on realization of various damage modes leading to rupture. Cyclic loading studies have been performed in two steps. In the first stage, we inquire into the dependence of the behavior and durability of four glass fiber-reinforced laminate-types on the stacking sequence; the second stage is devoted to studying the dependence of cyclic strength and fatigue behavior of laminates on the reinforcement type. Fatigue tests are carried out in load-control regime for glass and hybrid (Kevlar + glass) fiber laminates. Fatigue curves are constructed in coordinates “stress – number of cycles until fracture” from the criteria corresponding to a drop in stiffness by 5 and 10%. Analysis of the results obtained permits evaluation of the effect of the stacking sequence and the reinforcement type on the behavior of cross-ply laminates in cyclic loading. The presence of Kevlar fibers accounts for nonlinear behavior of laminates in static tests and for low cyclic strength in fatigue tests under three-point bending.

Characterization of a novel natural cellulosic fiber from Juncus effusus L.

This study aims to assess the morphology and properties of fibers extracted from a wild natural plant largely available in Algeria known as Juncus effusus L. (JE). The morphology and diameter of the fiber bundles extracted from the stem of the JE plant were characterized by optical and scanning electron microscopy. The functional groups of the extracted lignocellulosic JE fibers were studied by FTIR, their thermal degradation behavior was investigated by TGA and their crystallinity was determined using X-ray diffraction technique. In addition, mechanical characterization was carried out using tensile tests on the lignocellulosic fiber in order to evaluate their strength, strain at break and Youngs modulus. In view of the dispersion in the obtained experimental results, the latter were analyzed using the Weibull statistical laws with two and three parameters.

Nonlinear elasticity of auxetic open cell foams modeled as continuum solids

Structure evolution during deformation of isotropic auxetic foams is investigated by simple compression experiments. It is shown that the main feature observed in the experimental data can be accurately described by an isotropic hyperelastic model with an Ogden-type strain energy function. The model can be easily implemented in a finite element code and, hence, can be used to simulate foams undergoing complex structural deformations.

Analyse Statistique et Effet des Traitements Chimique sur le Comportement Physico - Mécanique des Fibres des Bras de Grappe des Palmiers Dattier = Statistical Analysis and Effect of Chemical Treatment on the Physicomechanical Behavior of Fibres from Date-Palm Fruit Branches

Une methode d’extraction des fibres des bras de grappe du palmier dattier est proposee. La caracterisation mecanique en traction quasi statique des fibres non traitees et de celles traitees chimiquement par une solution de NaOH de 1 et 2% de concentration pendant des durees d’immersions de 48 et 72 h montre que le traitement chimique ameliore les proprietes mecaniques comme la contrainte a la rupture et le module de Young. L’optimum est trouve pour les fibres traitees avec 2% de concentration de NaOH pendant 48h d’immersion. Le taux de cristallinite des fibres traitees et non traitees a ete determine a l’aide d’essais de DRX. Les resultats ont fait l’objet d’une analyse statistique de variance Anova a un facteur. Mots cles : fibres naturelles- palmier dattier – traction – DRX – analyse statistique. Statistical analysis and effect of chemical treatment on the physicomechanical behavior of fibres from date-palm fruit branches In this paper the authors propose a method of extracting fibres from date palm cluster arm as well as the mechanical characterization quasi static tensile untreated fibers and chemically treated by NaOH solution of 1 and 2% concentration during immersions durations of 48 and 72 h. The results show that the chemical treatment improves the mechanical properties (failure stress and Youngs modulus) and the optimum was found for the fibres treated with 2% concentration of NaOH for 48h immersion. XRD tests were performed to determine the degree of crystallinity of the treated and untreated fibres. Finally, all the results of mechanical tests were statistically analyzed by ANOVA with a factor. Keywords : natural fibres - date Palm - traction – XRD – statistical analysis.

Strength of concrete columns externally wrapped with composites under compressive static loading

This work describes the experimental results related to several series of circular cross-section concrete columns reinforced by composite materials glass/polyester. The columns have been wrapped externally with several plies, and subjected to classical static uniaxial compression loading, and a novel compressive technique consisting in repeated loading steps. The authors identify in particular two specific composite layups (bidirectional fabrics (0/90)2 and (+30/−60)2), the first providing the highest time to failure, the second showing an increase up to 70% in strengthening efficiency compared with non-reinforced columns. Six hybrid composite jacket configurations have also been investigated. The authors also provide a cost analysis of the different types of layups used to wrap the columns, showing the enhanced mechanical/cost effectiveness of the reinforcements proposed in this article.