Mécanique
Finite element delamination study of adhesively-bonded patchs used to repairs damaged jute fiber/polypropylene composites
In this work, the mechanical behavior of repaired specimens is studied from both experimental and numerical viewpoints. Tensile testing of the specimens with defect, without defect and repaired is carried out. The finite element method (FEM) model is utilized to simulate the mechanical behavior of the repaired specimen during the test. Cohesive Zone Model (CZM) was used to simulate the inter-laminar fracture of the composite, with the capability of simulating the damage initiation and evolution mechanisms of adhesives. The validations of the numerical results were carried out with the experimental results and are show to be in a good agreement. Voir les détails
Mots clés : PP/jute composite, damage, adhesive bonding, cohesive element
Study of the initiation and propagation of a crack in a heterogeneous media using model of cohesive forces
The behavior of crack defects in a heterogeneous media like the weld is a very interesting subject. The mechanical properties change through the different areas of the welded joint (Base Metal, Heat Affected Zone and Fusion Zone). The crack is solicited in mode III (anti-plane shear loading).A cohesive forces model is applied to study the initiation and propagation of a crack located in the middle of the weld using a semi-analytical method, where the equilibrium equations are solved and the solution is converted to a singular integral equation by using the standard Fourier’s transformers. The equation is solved numerically.The limit load of the fracture is represented as a function of different parameters (opening of the crack, the width of the weld,…). The results obtained shows the variation of the crack opening in accordance with the width of the weld taking into account the critical crack opening. Voir les détails
Mots clés : MDR, Crack, welding, cohesive forces model
Mechanical Properties Study of HDPE Wall Pipes Exposed to Sulfuric Acid and Toluene-Methanol Mixture: Comparison Between Filament and Standard Specimens
In this paper, results of two experimental studies are presented and compared. They concern the evolution of mechanical properties through the wall of a HDPE pipe used to transport natural gas. In the first study, specimens filaments (ISO 3341) machined in the form of continuous and uniform chips are used, while the second considers standard shapes according to ISO 527. Both approaches have shown that there is a significant variation in the mechanical properties through the tube wall from the outer side towards the inner side. The filament method is quicker and easier in preparation compared to the second method which comprises complicated machining operations. Immersion in aggressive environments such as sulfuric acid and toluene-methanol showed degradation of major properties. The mechanical properties obtained with the filaments are generally greater (between 6% and 14% higher), but in the case of H2SO4, the difference can reach up to 32% in comparison with control samples. The linear relationship between E and σy is preserved in those oxidative environments indicating the usefulness of HDPE filaments testing Voir les détails
Mots clés : polyethylene, Pipe, mechanical properties, pipe wall, aggressive environment, degradation
Technique d’Hybridation en Vue d’Améliorer le ComportementMécanique à la Rupture des Composites Stratifiés
Cette etude met en evidence l¡¦effet du changement de la disposition du renfort (unidirectionnelle, tissu et mat) sur la rupturedu materiau composite verre-E/epoxyde. Les stratifies consideres sont symetriques equilibres [+ƒá/-ƒá]3S et travaillant entraction uniaxiale. Une approche mathematique basee sur des criteres de rupture est utilisee. La comparaison de leurscomportements nous permet de proposer des hybrides capables d¡¦ameliorer les performances mecaniques des compositesrenforces seulement par des fibres coupees, d¡¦affaiblir le degre d¡¦anisotropie du materiau et d¡¦avoir par consequent desstructures optimales. Voir les détails
Mots clés : Matériau composite renforcement, comportement mécanique, hybridation
Failure of symmetric composite plates E-Glass /Epoxy with variousreinforcement arrangements
This study puts in evidence the effect of the change of the arrangement of the reinforcement(unidirectional, woven fabric and mat) on the rupture of E-glass/epoxy composite material. The consideredlaminates are symmetric of stacking sequence [+θ/- θ]3S and subjected of uniaxial traction loading. Amathematical approach based on failure criteria was used. The comparison of their behavior allows us to proposehybrids capable of improving the mechanical performances of composites, of decreasing the material anisotropydegree and to have consequently optimal structures. Voir les détails
Mots clés : composite materials, reinforcement, mechanical behaviour, hybridization
Failure of symmetric composite plates E-Glass/Epoxy with variousreinforcement arrangements
Abstract : This study puts in evidence the effect of the change of the arrangement of the reinforcement(unidirectional, woven fabricand mat) on the rupture of E-glass/epoxy composite material. The consideredlaminates are symmetric of stacking sequence [+?/-?]3S and subjected of uniaxial traction loading. Amathematical approach based on failure criteria was used. The comparison of theirbehavior allows us to proposehybrids capable of improving the mechanical performances of composites, of decreasing the materialanisotropydegree and to have consequently optimal structures. Voir les détails
Mots clés : composite materials, reinforcement, mechanical behaviour, hybridization
Experimental and Numerical Study of Polypropylene Composite Reinforced with Jute Fibers
This paper is devoted to the study of the mechanical response of polypropylene (PP) thermoplastic composite reinforced with jute fibers. In order to use these composites in structural applications it is necessary to understand the mechanisms governing their mechanical behavior and damage. For this purpose, we have fabricated two kinds of PP/jute laminates: [0°/90°]2S and [+45/-45°]2S with the fibers direction, using the molding technique under compression. The mechanical properties of the material are then characterized by tensile and compressive tests. The numerical part of this work concerns the incorporation of the Matzenmiller, Lubliner, and Taylor (MLT) damage model to take into account the post-elastic-peak and the post-peak strain softening responses observed in the PP/jute composite. This is possible by using formulation with two criterions. The 3D constitutive law has been implemented into the finite code Abaqus using an explicit scheme. In order to assess the capability of this model to describe the material behavior, comparisons are made between numerical and experimental results. Excellent agreements are found between numerical predictions and experimental observations. The model also captures correctly the zones where damage occurs in the two kinds of laminates. Voir les détails
Mots clés : PP/jute, mechanical behavior, damage, laminate, modeling
Short-term HDPE pipe degradation upon exposure to aggressiveenvironments
Natural gas and drinkable water are regularly transported by underground polyethylene pipenetworks in urban and rural areas. The interaction between materials such as high density polyethylene(HDPE) and contact environments is a critical factor which strongly influences pipe behaviour for short andlong terms. The aim of this study is to establish separate effects of H2SO4, a mixture of toluene–methanoland distilled water on the mechanical properties of HDPE pipes. Two testing geometries representing thepipe wall are considered: (1) orthogonally machined filaments and (2) ASTM standard specimens. Tensiletests are carried out on both specimen types using a computer controlled Zwick machine. It is observedthat chemical environments degrade mechanical properties causing a structural weakening especially thosespecimens exposed to organic solvent and acid. For instance, filaments show a reduction in elastic modulusof 64% after 7 days of exposure to toluene and methanol. Compared to standard specimens, the obtainedproperties are much higher indicating that geometry has an effect on the measured values. Fluctuationsin mechanical properties are most probably caused by cristallinity gradients all the way through the pipewall. This type of results allowed establishing the linear relationship between the elastic modulus and theyield stress and is intended to contribute to a better understanding of properties heterogeneity effects whenexposed to unfavourable environments. Voir les détails
Mots clés : polyethylene pipe, environmental stress effect, short-term degradation, yield stress-Young’s modulus correlations, failure strain, OIT
Amélioration de la qualité de surface par le procédé de brunissage
La vie d'un matériau en service dépend non seulement de la combinaison des facteurs de charge et d'environnement auxquels il est soumis mais aussi de l'état de surface. Donc la caractérisation de la surface (rugosité, et défauts de surfaces) est importante pour relier le processus de fabrication aux propriétés en service, ainsi le procédé de traitement mécanique "brunissage" peut améliorer les caractéristiques de surface. La qualité du fini de la surface dépend de la maitrise des paramètres de régime de traitement lors de la réalisation. Cette étude a pour objectif, l’application de ce procédé pour un alliage d'aluminium du commerce et l'optimisation du régime de traitement. Les paramètres considérés sont : l'effort appliqué " Py ", l'avance " f " et le diamètre de bille " Db ". La relation entre ces paramètres et la rugosité de surface" Ra " a été mise en évidence à l'aide des plans d’expériences de " Box-Behnken ". Au moyen d'un programme sous Matlab, un régime optimal a été déterminé en vue d'obtenir un maximum d’effet " Ramin". Les résultats expérimentaux ont montré que l'application de ce type de traitement offre des améliorations vis-à-vis de l'aspect de surface pour ce matériau, soit Ra = 0,19 ÷ 0,23 µm. Voir les détails
Mots clés : Mots clés : Brunissage, rugosité, optimisation, plans d'expériences, traitement de surface
Comportement au vieillissement et a la restauration par traitement thermique de l’acier inoxydable austenoferritique SAF 2205
Les aciers inoxydables duplex avec une microstructure ferrito - austénitique offrent une bonne combinaison de résistance à la corrosion par piqûres et de haute résistance qui ne sont pas réalisables de façon concomitante en utilisant une seule phase classique telle que les aciers inoxydables austénitiques ou ferritiques. L’acier inoxydable duplex utilisé dans cette étude est un alliage ayant une microstructure stable constitué d'environ 48 % de ferrite et 52% d'austénite à température ambiante. Afin d'étudier le vieillissement et la restauration de cet acier et leurs influences sur les propriétés mécaniques, des traitements de vieillissement à 850 ° C (après recuit à 1080 ° C et 1120 ° C et 1250 ° C) ont été réalisés pendant des durées différentes. Enfin, un traitement de recuit a été réalisé, pour tous les échantillons, à 1080 ° C pendant 60 minutes afin de dissoudre les précipités et restaurer l’équilibre des phases d/g de l'acier 2205. Les échantillons ont été soumis à des tests d'impact et de mesures de dureté avant et après tous les traitements. Enfin, les changements de microstructure en raison des traitements ont été étudiés par microscopie optique et électronique. Les résultats ont montré que le traitement de vieillissement a eu un effet négligeable sur la dureté. En outre, des modifications considérables en termes de précipitation de particules intermétalliques néfastes ont été observées dans la microstructure lors du vieillissement qui a conduit à une diminution significative de la ténacité. La formation de la phase intermétallique σ a été reconnue comme la principale raison des changements observés. Voir les détails
Mots clés : aciers inoxydables Duplex, vieillissement, restauration, ténacité, phase sigma