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The use of composite materials undergoes a significant growth in many industries including aeronautic, railway, and automotive. Laminated composites are often subjected to severe loading conditions...

Weight reduction of truck cabs can be achieved by using structural parts made from composite materials and adhesively bonded with a flexible adhesive. This paper presents an experimental study on the behaviour of adhesively bonded joints of fibre reinforced thermoplastic composites. U-shaped glass-polyamide substrates are joined with a flexible polyurethane adhesive and the specimens, inspired from spot weld characterization, are tested in a device allowing loading in different directions. Effect of load orientation, temperature, loading speed and adhesive thickness on the stiffness, the strength and the energy absorption of the joints are presented and discussed. Results show that the assembly overall mechanical behaviour is mainly controlled by the polyurethane adhesive. Such an adhesive/substrates combination is able to sustain high dynamic loadings when loaded in shear direction. High temperatures have a detrimental effect on the performances of the adhesively bonded joints.

International audience; An end notched flexure (ENF) test was used to study the effect of growth stability on mode II interlaminar fracture toughness (GIIC) of a carbon/PEEK composite. The instability of the ENF test was used to induce both stable and unstable crack growth with a static loading. Two techniques were used to evaluate mode II fracture toughness: the traditional compliance method and the infra-red thermography technique. The compliance technique has the advantage of being simple and it has already been confirmed for standard tests. Nevertheless its results may be inaccurate for unstable crack growth propagation. The infra-red thermography technique enables fracture toughness to be accurately measured for non-standard tests in which the crack growth may be unstable. Both methods are complementary and this study came to the conclusion that GIIC is sensitive to crack growth velocity. Fracture toughness showed a low value for crack growth start and unstable propagation, and a high value for stable crack growth. The transition between a ductile fracture mode (for low crack growth velocity) and a brittle fracture mode (for high crack growth velocity) explained the important variability in GIIC values.

This work is motivated by increasingly used of composite structures under severe loading conditions. During their use, these materials are often subjected to impact as for example, in the aeronautical field the fall of hailstone on structure composites. In fact, the low energy traditional impact tests don’t allow to see the evolution of the damage and don’t permit also to compare the best tolerance to impact between different stratifications. The multi-impact tests made it possible to find a solution to this problem. In this work, multi-impact tests are performed on three carbon/epoxy stratifications. The final goal is to predict the durability of the composite structures during impact loading for their design. This study brings to light the response of multi-impact tests through force-time and force-displacement curves obtained experimentally. On the other hand, a parameter D has introduced following the experimental results. This made it possible to rank the three stratifications from their tolerance to multi-impact tests. To evaluate the post impact damage, ultrasonic testing techniques are used. The results allow to find the relationship between the damaged surface obtained by the ultrasonic control and the parameter D and to rank the three laminates configurations.

International audience; Bio materials have seen an increase of interest from the scientific community and the industry as a possible future generation of mass produced materials, some of the main arguments being their renewability, low production costs and recyclability.The current work is focused on the experimental data required for the viscoelastic characterization of a composite material. Similar work has been conducted on different types of composite materials by Tuttle and Brinson [1] who verified for a carbon epoxy laminate the possibility of long term predicament of creep. Nordin et al [2] studied paper impregnated with phenol-formaldehyde under compression. Muliana [3] conducted experiments on E-glass/vinyl ester materials. Behavior characterization was based on a model presented by Schapery [4]. The main objective of this work is to understand the mechanical behaviors of bio-laminates structures subjected to long and severe operating conditions.The studied material is a bio composite laminate consisting in long flax fibers embedded in an epoxy resin system. The laminates were obtained from pre-impregnated unidirectional fibers, which were cured though a thermo-compression cycle followed by a post curing cycle. Test specimens were cut down to sizes, with the help of an electric saw. The concerned fiber direction was 0° with sample dimensions of 250x25x2 mm.First, testing consisted in quasi static mechanical tests. Second, to characterize linear viscoelastic behavior of the bio-laminates, creep – recovery tests with multiple load levels have been performed for the chosen fiber direction.

International audience; L’effet de massification automobile qui accompagne les besoins croissants de mobilité terrestre et l’offre de nouvelles infrastructures routières qui soutient de nouvelles demandes rendent les modèles de mobilité actuels de plus en plus difficilement acceptables. En effet, les personnes souffrent de l’inconfort des villes engorgées (nuisances), de l’insécurité lors de transports du fait de défaillances techniques ou humaines, de la très grande difficulté d’optimiser ses itinéraires en fonction des horaires ou circonstances exceptionnelles (accident par exemple). Par ailleurs, la mobilité se heurte toujours aux contraintes liées aux rigidités des infrastructures composées de nœuds, et de contraintes permanentes qui étouffent nos villes.Pour répondre à ces enjeux, la transition vers la mobilité autonome est en marche et l’écosystème véhicules – infrastructures doit évoluer pour désengorger nos villes. Ces nouveaux systèmes de transport sous-tendent une révolution technologique dans le domaine des transports et devront répondre à des préoccupations socio-économiques capitales en étant tout à la fois adaptables, résilients, et évolutifs, coopératifs et acceptables des points de vue économiques, juridiques et sociaux.

Recycling waste tires being important for both economical and environmental reasons, ground tire rubber can be blended with other polymers, modifying their properties. In order to characterize and explain these modifications, an experimental study was carried out concerning the improvement in the dynamic damping properties when adding recycled ground tire rubber (GTR) fillers to an elastomeric matrix (ethylene vinyl acetate, EVA).To evaluate the influence of both the GTR and the porosity in a GTR/ EVA composite, three samples have been elaborated by injection:the EVA matrix alone, a GTR/EVA composite, and a GTR/EVA porous composite. Dynamic measurements of the samples were performed using dynamic mechanical thermal analysis. The Young’s modulus and loss factor of these materials are estimated using the frequency—temperature equivalence introduced by Williams—Landel—Ferry expanding the measurement of the dynamic properties over a wider range of frequencies. This method showed that in low-frequency bandwidth, the loss factor has been improved by the addition of GTR to the EVA matrix. The α-relaxation study showed lower activation energy for both the GTR-filled composites leading to the conclusion that the mobility of the polymer chains has been improved by addition of GTR. The impact behavior study carried out using a weight drop test experiment also concluded to better impact energy absorption for the GTR-filled composites at the expense of a larger maximum displacement.

This article concerns the injection manufacturing process of molded foam sheets and their intrinsic shock and noise performances. The main goal is to optimize the physical performances of molded plastic foams at an early stage in their design and manufacturing. The effects of injection process parameters on the properties of molded LDPE foams are investigated. The input optimization parameters considered are as follows: injection temperature, mold temperature, injection speed, plasticization back pressure, and screw rotation speed during the plasticization phase. The output optimization parameters considered are as follows: density, shock absorption, and acoustic absorption. The experimental design method made use of the central composition design. This allows us to identify simplified mathematical models for input/output and to detect the most influential input in the injection process. Ultimately, models are used to carry out multiobjective optimization of injected foams characteristics in the presence of a few constraints on decision variables. This optimization is done using a very robust technique, NSGA-II. Several two-objective functions involving sometimes the maximization and other times minimization of foam characteristics have been studied to illustrate the procedures and explain and interpret the results obtained. One needs to solve several simpler optimization problems with just one or two decision variables (smaller amount of freedom), to gain insight and to provide help in formulating the more general multiobjective optimization problem. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The aim in this paper is first and foremost to present an experimental method for measuring the dynamic characteristics of granular rubber. Dynamic measurements on recycled granular rubbers are performed here using dynamic mechanical thermal analysis. The Young’s modulus and loss factor of these materials are estimated by using the frequency—temperature equivalence introduced by Williams—Landel—Ferry. It allows us to describe the dynamic properties over a wide range of frequencies. An increase in the wave speed and a decrease in the loss factor were observed with an increase in the frequency for ground tire rubber (GTR) and compound particles obtained by extrusion of GTR—ethylene vinyl acetate blend. However, for recycled polyurethane particles, the loss factor increases with increasing frequency. Then, we investigate the damping efficiency of granular rubbers introduced into a metallic tube, which was subjected to vibrating bending loads. A numerical model is presented to predict the frequency response for the displacement—force function of the tube—particles system. Model prediction is hence validated through a comparison with experimental results. Second, this paper also aims at calculating the optimum weight of granular material with maximum allowable damping effects on tube subjected to bending vibrations. For this purpose, a technique is proposed from the model developed by optimizing the apparent mass of granular material and the dissipation energy of the tube—particles system. Optimization is achieved by a nondominated storing genetic algorithm (NSAG-II). From the results, this technique can be successfully used to optimize the frequency dependence of wave speed and the loss factor of granular rubber with optimized weight.

The article concerns the injection manufacturing process of molded foam sheets and their intrinsic shock and noise performances. The main goal is to optimize the physical performances of molded plastic foams at an early stage in their design and manufacturing. The effects of injection process parameters on the properties of molded LDPE foams are investigated. The input optimization parameters considered are: injection temperature, mold temperature, injection speed, plasticization back pressure, and screw rotation speed during the plasticization phase. The output optimization parameters considered are: density, shock absorption, and acoustic absorption. The experimental design method made use of the Taguchi table and central composition design. This allows us to identify simplified mathematical models for input/output and to detect the most influential input in the injection process. We conclude by validating the models and their robustness. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

In the present paper, the Transformation Filed Analysis (TFA) methodology is used in the multi-scale analysis of cracking localisation in masonry. The related assumption of uniform inelastic strain field in each sub-domain allows reducing the computational cost of such computations without significantly compromising on solution accuracy. The relations underlying the TFA averaging scheme are recalled. The evaluation of the corresponding consistent tangent homogenised stiffness, required in acoustic tensor-based localisation analysis, is also derived. The average RVE mechanical response is performed for two sets of micro-mechanical material laws for mortar joints, based on both damage and damage coupled with plasticity. For these two sets of fine-scale laws, localisation analyses are performed for RVEs under stress proportional loading, showing that meaningful average localisation orientations are properly detected by the acoustic tensor-based loss of ellipticity criterion. Furthermore, the capability of the pure damage micromechanical model combined with TFA to reproduce the failure envelope of typically running bond masonry subjected to uniform biaxial loads is demonstrated through a comparison with available experimental data. Finally, the energetic aspects for the selection of localised solutions are discussed. As a result, the TFA-based averaging scheme is shown to yield meaningful homogenised localisation results, thereby allowing envisioning its use in nested multi-scale computations., info:eu-repo/semantics/published

This paper uses the ZPST multilayered shell element developed by Sulmoni et al. to compute the dynamic response of multilayered viscoelastic structures such as windscreens or car bodyworks. It is based on the P-order shear deformation theory with an added zigzag function. The viscoelastic properties are taken into account with frequency dependent elastic moduli measured with a Dynamic Mechanical Thermal Analyzer. A method based on Pade approximant is also used to reduce the computation time. This acceleration technique enables to achieve fast frequency sweep computations compared to a standard direct method. Finally, validations are made on plates and cylindrical geometries.

National audience; La théorie de déformation en cisaillement d'ordre p combinée avec la théorie de zig-zag (zig-zag p-order shear deformation theory - ZPST) a été utilisée pour l'analyse modale de structures multicouches. Dans la théorie traditionnelle de Reissner-Mindlin, le champ de déplacement inclus un déplacement linéaire dans le plan qui se traduit par une déformation en cisaillement transverse constante dans l'épaisseur nécessitant ainsi l'introduction d'un facteur de correction de cisaillement. La théorie ZPST généralise tous les modèles basés sur une approximation polynomiale du déplacement d'ordre &_leq; p dont les termes de zig-zag assurent les conditions de continuité de la contrainte en cisaillement transverse aux interfaces. La présente étude s'inscrit dans le cadre de la réduction du bruit et des vibrations par le développement de modèles numériques précis permettant de prédire correctement le comportement vibroacoustique des structures composites contenant des matériaux viscoélastique et/ou poroélastiques. La performance numérique de l'élément ZPST est analysée pour des structures sandwichs à matériaux viscoélastiques. Ces résultats montrent que l'élément est robuste et très précis.

This paper presents an improved numerical simulation of bulk metal forming processes. It takes into the account the advanced formalism of large displacements and large deformations. Also, the interface workpiece formalism is considered. Metallographic studies are conducted to determine the evolution of the micro hardness as a function of annealing time and that to characterize accurately the plastic range of aluminum alloy for a range of plasticity 160%. The obtained results of metallographic studies are used to simulate a upsetting under the friction law of the plastic wave. A numerical simulation by FEM of bulk forming alloy is carried out by replacing the real profile of the surface roughness by two triangular profiles, the first has the same height as the real profile and the second has the same area then by a trapezoidal profile of the same height. The obtained results are compared to Challen and Oxley results in order to validate the triangular profile used in the friction model of plastic wave.

The purpose of this work is the investigation of meta-models quantifying shock and acoustic indicators. The vehicle design of the engine block insulating poroelastic materials is considered. An analytical tool is proposed. It facilitates decision-making. Modelling tools (Design of Experiments techniques, kriging models,) are used to build empirical models expressing the Head Injury Criterion (HIC) and the acoustic absorption coefficient of poroelastic materials. Models defined here allow HIC and acoustic absorption predictions to be made for any porous material whose intrinsic characteristics are included in the design space. Such models offer effective alternative to finite-element formulations, with considerable time saving.