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External bonding of fibre-reinforced polymer (FRP) plates has emerged as a method for strengthening reinforced concrete structures. The creep of the concrete, adhesive and FRP can accelerate debond...

The present work reports an experimental study on the thermal and mechanical properties of hybrid composites obtained from Petiole Date Palm Fiber (PDPF)/Glass fiber (GF) as reinforcement and vinylester resin (VE). In order to improve the fiber/matrix adhesion, palm fibers were alkali treated with 5% NaOH solution for 24 h–72h. SEM and ATR-FTIR analysis revealed that the 48 h treatment of PDFP with NaOH solution led to rough fiber surface. Vacuum assisted resin transfer molding (VARTM) system was used to produce four hybrid composites (30PDPF/0GF, 20PDPF/10GF, 10PDPF/20GF and 0PDPF/30GF) where the weight ratio of total fiber reinforcement was kept 30%. The treated palm fibers were arranged as a nonwoven mat and placed between woven glass fabrics. Tensile, flexural, dynamic mechanical thermal analysis (DMTA), and thermogravimetric (TGA) were carried out to evaluate the performance of the hybrid composites. The flexural strength and modulus for pure PDPF composite were found to be 60 MPa and 3.87 GPa respectively. Addition of 20%wt glass fiber led an increase in the thermal stability and an enhancement in the tensile and flexural strength by 71.72% and 74.51%, respectively compared to pure PDPF composite. However, the incorporation of 10% of PDPF increases the damping factor from 0.2 for the composite glass/VE to 0.54 for the hybrid 10PDPF/20GF. According to findings of this study, PDPF based composites can be used as non-structural parts in automotive and boat industries.

International audience; Abstract: This experimental study highlights the effect of the geometric form factor (λ=length/diameter) and the fiber mass fraction on the mechanical behavior of an Alfa/Greenpoxy bio-composite. The Alfa stalks, collected in the Djelfa region in the Algeria highlands, were cut into pieces with length of 7 to 10 cm, washed and dried for two days at 70 °C. Using a knife mill coupled to three sieves (1.6, 2 or 2.5 mm), three categories of short fibers, according to their form factor λ, were obtained. Depending on the incorporated mass fraction (5, 10, 15 or 20 %) and the three form factors λ of the fibers, twelve types of plates were manufactured by hand molding followed by a curing cycle to accelerate the polymerization, reduce porosity and improve the final surface state. The main mechanical characteristics were determined with tensile, bending and shock tests on ISO 3167-type A samples, obtained by laser cutting. The results revealed that the increase of the form factor and the mass fraction gives rise to a significant improvement of the mechanical properties. We conclude that optimal processing conditions will maximize the mechanical properties of Alfa/Greenpoxy bio-composites.RÉSUMÉ :Cette étude expérimentale met en valeur l’effet du facteur de forme géométrique (λ=longueur/diamètre) et de la fraction massique de fibre sur le comportement mécanique d’un bio-composite Alfa/Greenpoxy. Les tiges d’Alfa, collectées dans la région de Djelfa des hauts plateaux de l’Algérie, sont découpées en morceaux de 7 à 10 cm, lavées et séchées durant deux jours à 70 °C. Trois catégories de fibres courtes, suivant leur facteur de forme λ, ont été obtenues par passage dans un broyeur à couteaux suivi d'un tamisage (tamis 1,6, 2 ou 2,5 mm). En fonction de la fraction massique incorporée (5, 10, 15 ou 20 %) et des trois facteurs de forme λ des fibres, douze types de plaques ont été élaborés par moulage manuel suivi d’un cycle de cuisson pour accélérer la polymérisation, réduire la porosité et améliorer l’état de surface final. Des échantillons ISO 3167-type A, prélevés par découpe laser, ont été testés en traction, flexion et choc pour déterminer les principales caractéristiques mécaniques. Les résultats ont révélé que l’augmentation du facteur de forme et de la fraction massique engendre une sensible amélioration des propriétés mécaniques. Nous concluons que l’adoption de conditions optimales permettra de maximiser les propriétés mécaniques des bio-composites Alfa/Greenpoxy.

In this work, an experimental investigation was proposed for the evaluation the wear resistance of hybrid polymer composite inter-layer of Petiole date palm fiber (PDPF) and glass fiber (GF). In order to enhance the interfacial of hydrophobic fibers (PDPF) and hydrophilic (Vinylester resin), chemical treatment was proposed based on 5% NaOH for 48 h. Besides, the glass fiber (woven) was used in order to increase the specific stiffness and the dimensional stability of specimens. The manufacturing of four hybrids specimens was done using a VARTM process [(30PDPF/0GF), (20PDPF/10GF), (10PDPF/20GF) and (0PDPF/30GF)]. The wear characteristics were evaluated at a sliding distance of (1000 m), sliding velocity (1.7 m/s) and applied loads (20 and 40 N). Scanning electron microscopy was performed on both treated alkali fiber and worn surfaces of hybrid specimens to evaluate the surface modification and wear mechanisms, respectively. The adding of glass fiber to PDP fibers was advantageous on the wear resistance, where it improved the wear resistance of 30PDPF/0GF around 190 and 310% as compared to (20PDPF/10GF) and (10PDPF/20GF), respectively. The adding of loads was disproportional to wear resistance. The SEM of worn surfaces showed debonding and bending of fibers, and fragmentation, fiber broken, and deformation on the resinous regions. In the end, the hybridization by 20% of glass fibers exhibits a high wear resistance relative to its nature (partially bio-friendly) and price.

This paper presents a probabilistic analysis approach applied to finite element analysis for modeling a cracked aluminum plate repaired with composite patches under cyclic loading. For this, it is necessary to have a mechanical model and a probabilistic model correctly representing the behavior of this type of structures. The finite element method reported in this paper to analyse the evolution of the stress intensity factor and to evaluate the effect of the composite patch on increasing the life of cracked structures. The uncertainty of the geometric characteristics and mechanical properties of the Glass/Epoxy repair patch was presented in this study. The Probabilistic method applied to finite element modeling provides another alternative medium for structural analysis of repairing aluminum plates to achieve a robust and reliable design in a more efficient manner. The Monte Carlo simulation was used in this study and the reliability in this context is defined as the probability that the stress intensity factor is less than the toughness under cyclic stress. According to this study, the most influential parameter that has a significant effect on the stress intensity factor is the thickness of the adhesive and the thickness of the patch that must be tightly controlled.

The present research article investigates the effect of a transverse crack on the flexural vibration of fiber reinforced composite beam based on Euler-Bernoulli beam theory. The presence of a crack in structural elements leads to an energy concentration near to crack’s region and introduce a local flexibility which affect its dynamic response. Linear fracture mechanic theory has been used for crack modeling by using the stress intensity factors expressions. A parametric study has carried out in order to investigate the influence of fiber orientation, crack depth and crack location on the natural frequencies and theirs corresponding shape modes.

This article presents an improved theoretical solution with the new prestressed – fibre-reinforced polymer (FRP) – model. The prestressing technique employed in this article was developed and refined by the prestressed force model coupled with the externally applied load and the fiber orientation effect. The new theoretical improved solution for the shear lag is developed. Comparisons are made with beams externally reinforced with a plate unstressed for different theory and the beams reinforced with a prestressed plate FRP. This research gives a numerical precision in comparison with the other studies that neglect the effect of prestressed plate model coupled with the thermal loads and fiber orientation impact. The physical and geometric properties of materials are taken into account and that may play an important role in reducing the interfacial stresses magnitude.

International audience; Afin de réduire les contraintes circonférentielles engendrées par un chargement mécanique d'un pipeline en composite, nous avons proposé un modèle analytique basé sur la formulation de Tsai. Une étude paramétrique a été proposée pour valoriser ces contraintes à travers l'épaisseur du pipeline. Pour mettre en valeur la variabilité des incertitudes causées par des défauts de fabrication, des erreurs de manipulation en service ou des endommagements statiques ou cycliques du matériau, nous avons proposé une étude fiabiliste qui cerne la sensibilité des paramètres les plus importants lors de la conception d'un pipeline en composite. En se servant de la méthode de Monte-Carlo, nous avons estimé l'effet des incertitudes dues à la variation des caractéristiques mécaniques et géométriques du pipeline ainsi que la charge appliquée. A partir des résultats obtenus, il a été constaté que pour des coefficients de variation bien contrôlés, les paramètres les plus dominants sont l'épaisseur et la charge appliquée