Caractérisation de la morphologie des pièces obtenues en moulage par injection et en injection-soufflage par la technique de spectroscopie infrarouge

Principe de mesure de l'orientation moléculaire par la technique de spectroscopie infrarouge en mode de réflexion -- Principe de la technique de microtomie -- Synthèse des articles et lien avec l'ensemble des travaux -- Moulage par injection -- Moulage par soufflage -- The build-up and measurement of molecular orientation, crystalline mophology and residual stresses in injection-molded parts -- An experimental technique for the characterization of molecular orientation through the thickness of plastic products -- Effect of polymer properties on the structure of injection-molded parts -- A new approach to the characterization of molecular orientation in uniaxially and biaxially oriented samples of poly(éthylène terephthalate)

Microstructure investigation of hydrothermal damage of aged SMC composites using Micro-computed tomography and scanning electron microscopy

This paper presents an investigation on the effects of hydrothermal aging on Sheet Molding Compound (SMC) composite. Two different techniques were carried out to study the inner structure of aged SMC composite. Firstly, X-ray micro computed tomography (XµCT) was used to evaluate the changes using 3D images. The results showed cracks in all the composite structure with different shapes and volume in response to the hydrothermal conditions. The cracks results from the build up of an osmotic pressure in microcavities, which is proportional to water concentration. However, it was not possible to quantify separately the hydrothermal induced damage in the studied SMC composite material. Therefore, the XµCT analyzes were supplemented by a microscopic study. This step has been studied in terms of crack density evolution and crack propagation rate. The results obtained by XµCT technique and SEM observations show that the damage increases continuously with time and temperature during aging. The damage was found to be located in the voids contained in the matrix at early stage of aging. Then it is mostly developed into the fiber interface in the form of fiber/matrix interfacial debonding.This work is supported by Ecole des Arts et Metiers – France and Ecole Nationale d’Ing´enieurs de Sousse – Universit´e de Sousse – Tunisie

Micromechanical Modelling of Dynamic Behavior of Advanced Sheet Molding Compound (A-SMC) Composite

Passive safety, particularly in the transport industry, requires maximizing the dissipation of energy and minimizing the decelerations undergone by a vehicle following a violent impact (crash). This paper proposes a strategy for identifying an anisotropic local damage criterion in a moderate dynamic loading for Advanced Sheet Molding Compound (A-SMC) composite materials. Multi-scale damage modelling based on the Mori-Tanaka approach is put forward. Previously, the results of an experimental campaign carried out on a range of strain rates varying from quasi static to 200 s−1 were used to identify a probabilistic local damage criterion based on Weibull’s formulation and integrate the effect of damage at a fiber-matrix interface scale. Therefore, the progressive local damage occurring under a fast loading may be described. A two-step homogenization procedure allows describing the strain rate effect on the stress-strain curves. The model gives also rise to the prediction of the progressive anisotropic loss of stiffness. Comparing between the experimental and numerical results confirms the ability of the proposed approach to describe the visco-damage effect (delay of damage threshold and decrease in damage kinetics) emphasized in A-SMC composites

Effet de la nature et des caractéristiques du milieu d’immersion sur le comportement hygrothermique des composites polyester/fibre de verre

Dans ce travail, nous caractérisons les effets des caractéristiques du milieu d’immersion sur la cinétique d’absorption d’humidité des différents matériaux composites. Les résultats obtenus montrent que les caractéristiques des courbes de l’humidité changent beaucoup avec la variation de la température et la vitesse de l’eau. L’effet de la direction d’écoulement a montré qu’un échantillon orienté perpendiculairement absorbe plus d’humidité qu’un échantillon orienté dans le sens parallèle

UV degradation of clay-reinforced polypropylene nanocomposites

The aim of this work is to experimentally characterize the UV-degradation process at both the surface and at different layers across the thickness of injection-molded polypropylene (PP) matrix containing different amounts of nanosized montmorillonite (MMT) clay particles. These nanocomposite materials have been exposed to UV irradiations (\u3bb=320 nm) at different preset temperatures (25, 45, and 65\ub0C) in the presence of oxygen and during different exposure times. The extent of such process at these layers was determined using both the FTIR spectroscopy and the wide-angle X-ray diffraction analyses. The micromechanical properties across the thickness have been characterized using the nanoindentation technique. The obtained results have indicated that the UV-degradation process for the nanocomposite materials is much more intense than the one observed for the neat PP. Moreover, it has been noted that such degradation process is not uniform across the thickness of the exposed materials. Results obtained from the X-ray analysis have shown an increase of the crystallinity of the polymer molecules at only the external surface of the exposed materials. This was confirmed using the nanoindentation test as an increase of the Young's modulus at this layer was noted.Peer reviewed: YesNRC publication: Ye

6th Conference on Design and Modeling of Mechanical Systems

This book offers a collection of original peer-reviewed contributions presented at the 6th International Congress on Design and Modeling of Mechanical Systems (CMSM’2015), held in Hammamet, Tunisia, from the 23rd to the 25th of March 2015. It reports on both recent research findings and innovative industrial applications in the fields of mechatronics and robotics, dynamics of mechanical systems, fluid structure interaction and vibroacoustics, modeling and analysis of materials and structures, and design and manufacturing of mechanical systems. Since its first edition in 2005, the CMSM Congress has been held every two years with the aim of bringing together specialists from universities and industry to present the state-of-the-art in research and applications, discuss the most recent findings and exchange and develop expertise in the field of design and modeling of mechanical systems. The CMSM Congress is jointly organized by three Tunisian research laboratories: the Mechanical Engineering Laboratory of the National Engineering School of Monastir; the Mechanical Laboratory of Sousse, part of the National Engineering School of Sousse; and the Mechanical, Modeling and Manufacturing Laboratory at the National Engineering School of Sfax

On the mechanical properties and damage mechanisms of short fibers reinforced composite submitted to hydrothermal aging: Application to sheet molding compound composite

Sheet Molding compound (SMC) composites were subjected to water immersion tests in order to study their durability since such composites are of interest in automotive applications. Water sorption tests were conducted by immersing specimens in distilled water at 25-90°C for different time durations. In order to investigate the combined action of water and temperature over time on composite mechanical behavior, tensile tests and quasi-static loading were conducted. The mechanical properties of water immersed specimens were evaluated and compared alongside to dry composite behaviour. The tensile tests and quasi-static properties of the studied composite were found to decrease with the increase in moisture uptake. This decrease was attributed toinner structure dégradations by means of osmosis phenomenon. It was shown that hydrothermal aging affects mainly the fiber/matrix interfacial zone while a good adhesion between the reinforcement and the matrix was observed for the virgin samples. In order to well understand the damage mechanisms, scanning electron microspy (in-situ three point bending) tests were performed on aged and non aged specimens. Damage mechanisms were identified for different material states. Results display clearly that damage evolution always begins at the interface regions. Furthermore, a quantitave analysis was performed at a local scale in a representative zone of the tensile area

Digital image correlation to reveal mechanical anisotropy in 3D printing of polymers

International audienceIn this work, we propose to study the mechanical anisotropy inferred in printed acrylonitrile butadiene styrene polymer using fused deposition modelling by combining digital image correlation and mechanical testing. Tensile specimens are printed utilising different design orientations and raster angles. Monitoring of deformed samples is performed and strain fields are derived for each configuration. The results show that a heterogeneous strain field develops leading to a more significant strain localisation for samples printed with the dimensions mainly aligned with the building direction. An optimal printing angle allowing the filament to be crossed at −45°/+45° shows the best behaviour even with a larger elongation at fracture compared to the raw material. The digital image correlation based on optical imaging indicates, however, scaling limits to reveal the effect of the filament orientation on strain localisation