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A numerical model is developed for analyzing the filtration of suspension through fibrous media, during the particle-filled resin transfer molding process. The modeling approach is based on a coupling between flow and filtration models, and it is validated by comparison to various experimental results. The effect of process parameters on the distribution of the concentration and retention of particles within the preform was studied. Four parameters were considered: (i) the injection velocity, (ii) the injection pressure, (iii) the initial filler concentration, and (iv) the overflow time and the lost suspension. The obtained results reveal that the particle distribution and retention depend strongly on the initial concentration and the injection pressure, but very weakly on the injection velocity. A comparison between the distributions of the concentration and retention obtained was established with the two injection modes (imposed velocity and imposed pressure). A quasi-uniform distribution is obtained with the injection at imposed pressure, while a significant non-homogeneity in the distribution is observed in the case of injection at imposed velocity. In the latter case, a marked improvement in the distribution of the concentration and the retention of the particles is obtained by modifying the injection strategy. This operation consists of continuing the suspension injection after filling the mold and evacuating the suspension overflow through the vent. It was found that a small volume of lost suspension is enough to significantly improve particle distribution.

International audience; In the last two decades, an increasing interest has been observed for the use of natural fibers such as jute fibers in different applications. These fibers are characterized by their low cost and their availability. They are mainly used in fabric bag manufacturing. The objective of this paper is to study the effect of temperature on the mechanical properties of jute yarns. An experimental study was conducted at different temperatures (22 °C; 80 °C; 105 °C and 150 °C) for 24 h. Each degree was followed by tensile testing of the specimen. Besides, the thermo-gravimetric analysis (TGA) was used to investigate the effect of the temperature on the thermal stability and the thermal degradation of the jute fibers. In addition, the statistical analysis was performed using the method of two and three-parameter Weibull distribution to determine the spatial distribution of the properties. The results showed that there was a degradation of the mechanical properties of the jute yarns heated to high temperature compared to the raw yarns (considered as a specimen exposed to 22 °C). The tensile strain and the Young modulus failed by 36% and 13% respectively for the specimens heated at 150 °C and the failure kinematic of the jute fiber was affected by the temperature of heating. The TGA showed that the thermal stability of the jute yarns was affected by two factors: fibers drying and their changing temperatures.

In the last years, the natural fibers have been used in many fields such as composites, auto industry and textiles. The natural fibers are chosen due to their renewability, their biodegradability, the presence with a large amounts and their eco-friendly environmental characteristic. Jute fiber is one of the most tropical fibers produced in the Bangladesh and the India. But, the mechanical properties of these fibers in environmental conditions are influenced by the evolution of the chemical and physical modifications induced inside of the fibers. This work aims to investigate the effects of different environmental conditions on the thermal stability of the jute yarns and their mechanicals properties. The obtained results show that the change in the mechanical properties is correlated with water dried and uptake. The jute yarns stress reduction can be primarily explained by the plasticizer role of water molecules and the friction reduction between fibers.

Carbon black (CB) spherical particles were added to poly(ε-caprolactone) (PCL) polymer to produce strong synthetic tissue scaffolds for biomedical applications. The objective of this paper is to study the mechanical behavior of CB/PCL-based nanocomposites using experimental tests, multi-scale numerical approaches, and analytical models. The mechanical properties of CB/PCL scaffolds were characterized using thermal mechanical analysis and results show a significant increase of the elastic modulus with increasing nanofiller concentration up to 7 wt%. Conversely, finite element computations were performed using a simulated microstructure, and a numerical model based on the representative volume element (RVE) was generated. Thereafter, Young's moduli were computed using a 3D numerical homogenization technique. The approach takes into consideration CB particles’ diameters, as well as their random distribution and agglomerations into PCL. Experimental results were compared with data obtained using numerical approaches and analytical models. Consistency in the results was observed, especially in the case of lower CB fractions. Keywords: Carbon black/poly(ε-caprolactone) nanocomposites, Tissue scaffolds, Computational homogenization, Numerical approaches, Microstructure

International audience; Additive manufacturing, which is referred to as 3D printing, is a new developed process of fabricating metallic, ceramic, plastic and concrete materials. The goal of this article is to provide an overview of 3D printing processing methods and discuss their pros and cons. A comparison with other technologies such as injection molding and cutting-based machinery was discussed. Various modeling approaches and tools at all scale levels were depicted. We have presented a case study concerning the effect of pores formation in the mechanical properties of 3D printed polymer composites using FDM process. The mechanical behavior of 3D printed composites was determined using the homogenization technique based on the RVE notion. Recent uses of this technology in the area of electronics, aerospace and biomedical engineering were highlighted. Finally, important benefits and limitations were identified in order to clarify and motivate future works in this field.

International audience; Split Hopkinson Pressure Bar is one of the main methods used to characterize the dynamic behaviour of composite materials. In this study, we performed several impact tests for unstitched (2DWC) and stitched (3DWC) woven composites in order to obtain a reliable comparison between dynamic properties of these materials. On the other hand, an energetic study was carried out during these tests to draw up the energy balance and to quantify the energy dissipation. The impact energy is the kinetic energy of the striker bar and it is the total energy quantity available at the beginning. At the interface bar/sample, some of this energy is absorbed by the specimens and can cause plastic deformation or damage in a different form, which can lead to heat generation. The remaining energy corresponds to the reflected and transmitted energy and can be determined from the measured deformation profile. The test results shows that stitch reinforcement can increase resistance in comparison with the standard composite. Moreover, the existence of Z-fibres made the fracture more complex and caused several characteristic phenomena, so that the required fracture energy for crack propagation was increased. Stitching does not improve the damage initiation strength but significantly prolongs the duration of the crack propagation phase.

International audience

In the last twenty years, the use of the natural fibers has grown due to their environmental, economic and social aspects. Jute is a tropical plant which is known and popular in South west Asia countries. These fibers are used in many fields such as composites, fabric and agricultural bags. In this work, the thermal and the mechanical characterization of the jute yarns were studied using thermo-gravimetric analysis and static tensile tests. The thermal properties of jute fiber show a high stability before temperature of 220 °C. The evaluation of the obtained experimental data shows a high dispersion of the mechanical properties and there is no significant effect of the loading rate on these properties. That is why a statistical analysis is performed using the two parameters Weibull distribution law.

International audience; Elastic properties of laminate composites based Carbone Nanotubes (CNTs), used in military applications, were estimated using homogenization techniques and compared to the experimental data. The composite consists of three phases: T300 6k carbon fibers fabric with 5HS (satin) weave, baseline pure Epoxy matrix and CNTs added with 0.5%, 1%, 2% and 4%. Two step homogenization methods based RVE model were employed. The objective of this paper is to determine the elastic properties of structure starting from the knowledge of those of constituents (CNTs, Epoxy and carbon fibers fabric). It is assumed that the composites have a geometric periodicity and the homogenization model can be represented by a representative volume element (RVE). For multi-scale analysis, finite element modeling of unit cell based two step homogenization method is used. The first step gives the properties of thin film made of epoxy and CNTs and the second is used for homogenization of laminate composite. The fabric unit cell is chosen using a set of microscopic observation and then identified by its ability to enclose the characteristic periodic repeat in the fabric weave. The unit cell model of 5-Harness satin weave fabric textile composite is identified for numerical approach and their dimensions are chosen based on some microstructural measurements. Finally, a good comparison was obtained between the predicted elastic properties using numerical homogenization approach and the obtained experimental data with experimental tests.

International audience; In this work, polymer laminated composites based on Epon 862 Epoxy resin, T300 6 k carbon fibers and carbon nanotubes (CNTs) were tested with the aim to elucidate the effect of CNTs on impact properties including impact force and capacity to absorb impact energy. The polymer matrix was reinforced by a random distribution of CNTs with fraction ranging from 0.5 to 4.wt%. Composite panels were manufactured by using the infusion process. Taylor impact test was used to obtain the impact response of specimens. Projectile manufactured from a high strength and hardened steel with a diameter of 20 mm and 1.5 kg of mass was launched by a compressed gas gun within the velocity of 3 m/s. Impact force histories and absorbed energy of specimens were recorded. A numerical model was employed to simulate the impact performance. This model has been accomplished by forming a user established subroutine (VUMAT) and executing it in ABAQUS software. Finally, the effect of CNTs amount on dynamic properties of laminated composites was discussed.

International audience; Damage in carbon fibers/Epoxy laminate composites containing carbon nanotubes (CNTs) is described. This investigation presents the third part of paper series on composite materials based CNTs. Experimental characterization and numerical homogenizations were published in order to obtain effective elastic orthotropic properties. Therefore, the homogenized properties are used as input data for investigation of damage initiation and propagations in the specimens for Open Hole tensile tests. The numerical intralaminar damage model is created under ABAQUS software with Hashin's criteria. The model is formulated according to damage mechanics. The prediction of ply delamination in laminated composites containing CNTs is modeled by using interface elements. The numerical approach is based on the cohesive zone model, provides an efficient description of the delamination growth. The numerical study is performed in the quasi-static regime and an implicit finite element scheme is used. The force displacement curves obtained numerically shows a good agreement with the experimental.

International audience; Fused deposition modeling (FDM) based 3D printing) technique involves the fabrication of polymer parts using a thermal process which may induce residual stress, stress concentration, distortion, and the delamination between layers. This paper aims to investigate this defect on ASTM D638 polymer composite specimens. For that purpose, a 3D thermo-mechanical model that simulates the process of FDM capable of calculating stresses and temperature gradients during the additive manufacturing of polymer composites was developed. The 3D model considers the temperature-dependent physical properties of composites which consist of density, thermal conductivity, thermal expansion coefficient, yield stress, and Young's modulus. The simulated process includes the heating, solidification, and cooling phases. Different printed parts were analyzed and compared. The stresses vary continuously because of the temperature gradient occurring through the composite thickness. It appears that the concentration of stresses is higher if the temperatures during printing vary rapidly. Those stresses can favor the delamination between the layers of the printed part and the residual thermal stresses can cause an offset to the failure envelope.

International audience; Composite materials have vast range of engineering applications because of their outstanding mechanical performance, low density and cost effectiveness. Marine industry and naval structures are one of the applications where composites are gaining importance rapidly however, there are confronted with extreme environmental conditions in addition mechanical behaviour. Therefore, it is important to comprehend the behaviour of these materials not only under mechanical loads but also under environmental effects. For that reason, the objective of this paper is to study the effects of hygrothermal aging phenomenon on the behaviour of adhesively bonded composite joints at high strain rates. Dynamic compressive properties and microstructural damage progression is analysed utilizing the Split Hopkinson Pressure Bars (SHPB) technique. The stress-strain behaviour of composite specimens subjected to severe hygrothermal conditions have been studied at high strain rates ranging from 445 to 1240 s−1. In addition, Keyence and scanning electron microscopic (SEM) is used to study the significant damage modes. The results indicated change in dynamic properties and damage behaviour because of the environmental effects.

International audience; The overall goal of the research is to develop a composite simultaneously able to absorb mechanical shocks. In this paper, carbon nanotubes (CNTs) based polymers were used to enhance the wave absorption capacity against shock load. The material consists of an epoxy polymer reinforced with various concentrations of CNTs: 1%, 2% and 4 wt%. An experimental procedure was developed for material characterization. The specimen was sandwiched between two steel bars (incident and transmitted bars), with 20 mm in the diameter. The shock wave was generated by a launching device drives the striker to hit 1 bar, and then the wave propagates throughout the specimen. Two strain gauges were placed on the surface of each bar with 1 m of the distance from the specimen surface. The wave intensity was recorded using a data acquisition system (HBM GEN3i model). The full histories of strain, force and the energy absorption during the shock time were measured. With 4% mass fraction of CNTs, the shock wave intensity was reduced to 33.34% compared to 0% of CNTs. The results show also that the specimen with CNTs is able to absorb high energy impacts.

This study was focused on the effect of carbon nanotubes on the impact resistance and damage evolution in laminate carbon nanotubes/epoxy composites under an impact loading. The composite panels were made from carbon fibers and carbon nanotubes randomly distributed into epoxy resin. The amount of carbon nanotubes dispersion was varied up to 4% by weight. Taylor impact tests were carried out to obtain the impact response of specimens with dimensions of 70×70×4 mm3. A projectile manufactured from a high strength and hardened steel with a diameter of 20 mm and 1.5 kg of mass was launched by a compressed gas gun within the velocity of 3 m/s, 7 m/s and 12 m/s. For the experimental test, three velocity levels were used: 3 m/s for the elastic deformation, 7 m/s for the penetration of the impactor and 12 m/s for the perforation of panels. Deformation histories and damage modes in specimens were recorded during the impact test using a high-speed camera. Processing of carbon nanotubes dispersed in laminates, testing, damage, and key findings is reported. It is observed that the impact resistance of laminates reinforced with a random distribution of carbon nanotubes increases up to 15.6% at high-strain rate compared with that of 0% of carbon nanotubes. It is also observed that the resistance to damage initiation and evolution increases with the addition of carbon nanotubes concentration.

International audience; The main goal of this paper is to predict the elastic modulus of partially intercalated and exfoliated polymer-clay nano-composites using numerical homogenization techniques based on the finite element method. The representative volume element was employed here to capture nano-composites microstructure, where both intercalated exfoliated and clay platelets coexisted together. The effective macroscopic properties of the studied microstructure are obtained with two boundary conditions: periodic boundary conditions and kinematic uniform boundary conditions. The effect of particle volume fractions, aspect ratio, number and distribution of particles and the type of boundary conditions are numerically studied for different configurations. This paper investigate also the performance of several classical analytical models as Mori and Tanaka model, Halpin and Tsai model, generalized self consistent model through their ability to estimate the mechanical properties of nano-composites. A comparison between simulation results of polypropylene clay nano-composites, analytical methods and experimental data has confirmed the validity of the set results.

This paper aims at developing 3D numerical simulations of the mechanical properties of polymer composites based on the aggregates of argan shell. The microstructure is made up of two phases, corresponding to the Poly–Propylene PP matrix and the natural aggregates. Due to the grinding operation of agran shell during the manufacturing process, the aggregates shapes, crushed aggregates, greatly vary with their surfaces. The majority of published works used the spherical or ellipsoidal forms in order to study numerically the mechanical behavior of such composites, because of the inherent simplification in algorithm formulations. However, real microstructures of these composites based simple microscopic, show that the shape of aggregates does not takes a spherical form, but a polyhedral form. In this study, the microstructure is described and modeled as a combination of Poisson polyhedral and PP matrix. In the numerical model, the obtained aggregate morphology is similar to that of many argan shell powders often used as reinforcement of the PP matrix. This technique allows generating models with different reinforcement volume fractions up to 28%. The numerical homogenization technique is used to estimate the mechanical properties of these composites. The set obtained numerical results with 3D polyhedral model are compared with the pertinent experimental data and analytical models reported in the literature. The performance of the most used micromechanical schemes used in predicting the effective elastic properties of biocomposites was discussed.

International audience; The recent developments in the aeronautical structure industry have seen a sharp rise in the use of polymer composite materials. The performances of all aerodynamic surfaces are heavily dependent on the shape and the surface form. The modification of these surfaces due to condensation and melting of ice can cause catastrophic decreases in the aerodynamic performance. In this study polymer composite materials as heater were made and studied. The feasibility of using advanced polymer composites for de-icing application was validated and studied through experiments. It consists of thin carbon nanotubes (CNTs) Bucky paper placed between two glass fibers veils and then infiltrated with an epoxy polymer resin and cured. The composite can be heated up very quickly using an electrical power source. The idea of using this new material as a heater and de-icing material was explored experimentally. For that purpose, the temperature distribution was monitored at different positions of the panel using thermal imaging. Experimental results show that the surface temperature of the panel increases gradually as the heating time increases. This temperature increased in a short time period of heating time, implying that the composite panels with CNTs Bucky paper display an excellent heating performance.

Composite materials are used in many marine structures such as renewable marine energy conversion systems because of their fairly good mechanical properties and especially their low densities compared to traditional materials. The most advanced features currently available in finite element (FE) Abaqus/Explicit have been employed to simulate the behavior of the composite nozzle under hydrodynamic and impact loading. A hydrodynamic analysis was considered to design the nozzle turbine and the hydrodynamic pressure obtained was then implemented as boundary conditions to a FE code. The goal of this article is to evaluate the durability of composite materials of a ducted tidal turbine under critical loads (hydrodynamic and hydrostatic pressures) with the implementation of a failure criterion using the finite element analysis (FEA). The mechanical behavior was analyzed for two materials (Carbon–epoxy/ Glass–polyester). This has been accomplished by forming a user-created routine (VUMAT) and executing it in the ABAQUS software. Keywords: Marine composite structures, Ducted tidal turbine, Finite element analysis, VUMAT

International audience; Delamination progressive in carbon nanotubes reinforced composites under applied Short Beam Shear test was studied. Experimental characterization was carried out using ASTM D2344 standard norms for different carbon nanotubes mass fractions ranging from 0 to 4%. Failure modes and the delamination were experimentally characterized by scanning electron microscopy and Kayence microscopy to assess the failure behavior. The numerical model was created under ABAQUS software based on the cohesive zone models. The numerical model was formulated according to the damage mechanics. In these models, the cohesive interaction was implanted between elements of each fabric ply to control the initiation and the propagation of the delamination for different carbon nanotubes fractions. The force–displacement curves vs. carbon nanotubes added were obtained for the numerical model and shown to be in good agreement with the experimental data. The effect of carbon nanotubes on the progressive delamination was elucidated.

International audience; Polymer composite pipes can be exposed to the thermomechanical loading due to hot and cold fluid flow, which results in the degradation of their properties. In this paper, effect on mechanical properties of composite pipes under different temperatures ranging from −40 to 80 °C is studied experimentally. The composite pipes consist of glass/epoxy tubes having 86 mm internal diameter and 6.2 mm of thickness with ±55° glass filament winding, intended for offshoring applications. TEMA TTC machine and split disk are used for uniaxial tensile tests and the thermal aging is considered with the help of SERVONTAN climatic chamber. Thermal aging is carried out on these specimens in climatic chamber for 8 h at different temperatures and then uniaxial test is performed. Experimental results have shown degradation in the mechanical properties of polymer pipes with an increase in the temperature. For pipes at colder temperature, the rigidity of composite increases progressively with the temperature and results in drastic decrease in the displacement at break. Also there is a decrease in the yield stress and an increase in yield strain with an increase in the temperature.

International audience; In this paper, an experimental study has been performed on thick, ±55° filament wound glass/epoxy tubes using quasi-static tests to examine their offshore applications. A new design for the experimental test is developed in which the end tabs and fixture system are made in a way that the stress concentration at the edges of the composite pipe can be reduced. Split disk uniaxial tensile test has been performed on composite pipes with 86 mm of the internal diameter and the thickness of 6.2 mm, in order to evaluate the mechanical properties and to quantify the effect of geometric non-linearities. These pipes can be subjected to different phenomena which can result in introducing a defect in the structure. Two types of pipe specimens are tested which include the composite with notch and the other without notches. The objective of the using a notched specimen is to examine the evolution of the damage and to study the mechanical properties as a function of this damage. The experimental results are described as the influence of the number and the size of notches on the mechanical behavior. These results have shown that the yield stress decreases and yield strain increase with increasing of the notch size and number. The evolution of damage showed that the presence of notches plays an unfavorable role in the integrity of the structure.

International audience; One of the most applications of stiffened composite panels is the marine application. In this study, a new sandwich structure consists of long E-glass fibers reinforced Balsa composites is evaluated. The use of this material in marine applications for long periods and under different environmental conditions leads to degradation of mechanical properties of structures and the adhesive. Therefore, in order to guarantee the best functioning of structures for long time periods, an experimental characterization procedure is required. For this purpose, the dynamic mechanical behavior of top-hat bonded stiffened composite panels used in marine applications is studied. A special fixture was designed and fabricated for the impact testing of stiffened structures. Manufactured specimens were tested until finale failure and the effect of impact velocities on the load-displacement and strain-displacement behaviors are compared. We have also interested to the effect of impact velocity on the dynamic behavior and damage kinetics.

International audience; The deformable composite structures subjected to water-entry impact can be caused a phenomenon called hydroelastic effect, which can modified the fluid flow and estimated hydrodynamic loads comparing with rigid body. This is considered very important for ship design engineers to predict the global and the local hydrodynamic loads. This paper presents a numerical model to simulate the slamming water impact of flexible composite panels using an explicit finite element method. In order to better describe the hydroelastic influence and mechanical properties, composite materials panels with different stiffness and under different impact velocities with deadrise angle of 100 have been studied. In the other hand, the inertia effect was observed in the early stage of the impact that relative to the loading rate. Simulation results have been indicated that the lower stiffness panel has a higher hydroelastic effect and becomes more important when decreasing of the deadrise angle and increasing the impact velocity. Finally, the simulation results were compared with the experimental data and the analytical approaches of the rigid body to describe the behavior of the hydroelastic influence.

International audience; In this investigation, a new experimental technique in which the deformation, damage mode, and the temperature are measured simultaneously during a high strain rate on laminated composites materials. The composites consist of unidirectional E-glass fibers reinforced epoxy polymer composites used in industrial applications. The experimental setup consists of a compression Split Hopkinson Pressure Bar (SHPB), a high-speed infrared camera and a high-speed Fastcam rapid camera. Specimens, with cubic like a shape, are impacted at different strain rates ranging from 200 to 2000 s(-1). During impact test, the specimen surface is controlled and monitored with the infrared camera which provides thermal images in time sequence and with high-speed camera which acquires the damage progressive in specimens. Experimental results show that the damage throughout specimens differs and the temperature change depending on the damage mode and their maximum exceed 219 degrees C.

International audience; In this study, the impact response of polymer composites containing a random distribution of carbon nanotubes (CNTs) has been investigated by considering energy profile diagrams and associated force time curves. The composite consists of CNTs initially filled Epon 862 Epoxy resin and implanted between plies of T300 6k Carbon fiber with 5HS (satin) weave. Different mass fractions of CNTs were used: 0% as reference, 0.5%, 1%, 2% and 4%. Taylor impact test was used to obtain the impact response of specimens. Projectile manufactured from a high strength and hardened steel with a diameter of 20 mm and 1.5 kg of mass was launched by a compressed gas gun within the velocity of 7 m/s. Deformation histories and damage modes of specimens were recorded during impact using high-speed camera. The effect of CNTs amount on dynamic properties and damage process was discussed.

International audience; The present paper investigates an experimental approach concerning the determination of dynamic behavior and damage kinetics of composite materials based on multiwalled carbon nanotubes (MWCNTs), embedded in electrospun reactive nanofibers in the Taylor impact test. Different impact energies have been considered namely; 21J and 39J to investigate the composite response. Projectiles are manufactured from a commercial steel 2071 with a nominal diameter of 50 mm and 1600 g of weight. The projectile was fired against a composite specimen initially hooked on a cell effort by a compressed gas gun within the velocity of 5 m/s and 7 m/s. Three types of specimens are considered: (1) MAT1 (carbon fiber reinforced epoxy polymer composite), MAT2 (consists of MAT1 and electrospun Polybenzmideazole-Bismaleimide (PBI-BMI) nanofibermats between carbon fiber layers) and MAT3 (consists of MAT2, where PBI-BMI nanofibermats are reinforced with multiwalled carbon nanotubes (MWCNTs)). The effect of the MWCNTs on the dynamic properties of the composite structures was studied. Microscope observations reveal damage progressive, buckling and crush-front propagation during tests. Application of the PBI-BMI reactive nanofibermats reinforced with MWCNTs leads to damage prevention, reducing damage area in composite samples.

International audience; The use of composite materials begin to normalize in various sectors, however, these structures are very susceptible to degradation of their properties and consequently a catastrophic failure. The response of deformable composite subjected to water-entry impact can cause a phenomenon called hydro-elastic effect due to water-flexible laminate interaction. This phenomenon may be large enough to cause the damage in composite panels. This paper employs the finite element method to simulate the behavior of composite wedges under slamming impact with presence of damage. To investigate this situation, the hydro-elastic influence has been analysis as both kinematic effect due to deflection of the composite panel and dynamic effect caused by the interaction between the water and the structure. On the other hand, damage modeling was formulated based on continuum damage mechanics for intra-laminar damage. A user-defined material subroutine VUMAT has been incorporated into explicit Abaqus FE software to enhance the damage simulation, which includes Hashin criteria for degradation of the panel stiffness with failure onset criteria and fracture mechanics. To reinforce the methodology adopted, numerical results are compared with the previous experimental data. A good agreement was observed. Effects of impact velocity and the panels flexibility on the damage have been investigated.

International audience; The microstructure studied in this paper is a Composite made up of Randomly oriented Short Fibers (RSFC) and a computational homogenization is performed to investigate its effective properties. The area fraction is also varied to study its effect on the size of the Deterministic Representative Volume Element (DRVE). It appeared that at certain area fractions, the RSFC does not respect the convergence of the apparent properties calculated under different boundary conditions. This indicates that it does not adhere to the definition of the DRVE in the studied range of scale. The concerned area fraction is found to be around the percolation threshold. The present work consists primarily in investigating the causes of this problem by studying an extreme example of a percolating medium which is a Composite made up of Randomly oriented Long Fibers (RLFC). By identifying the contributing factors, the calculability of the DRVE of a random composite can be predicted by simple verification of the microstructure morphology.

International audience; In this paper, instrumented indentation testing was used to determine the elastic mechanical properties of multiwall carbon nanotubes (CNTs) reinforced polymer composites. A finite element analysis model for simulating micro-indentation test was developed using ABAQUS software and confronted to experimental tests. It seems that CNTs reinforced polymer composites shows an improved of mechanical properties. The microstructure of indentation mark has been evaluated using scanning electronic microscopes and compared with the microstructure of numerical models. It results that adding small amount of CNTs improves the fracture interfacial rigidity and can stop micro-cracks evolution.

International audience; The purpose of this work was to study the influence of microstructure on effective transverse elastic behavior of fiber reinforced composites. Two microstructures were taken into account, hexagonal periodic and random arrangements of fibers. Unlike classical results at low fiber volume fractions and low Young’s modulus contrast between fibers and matrices, results provided by finite elements simulations have shown that microstructure strongly affect the effective properties of composite for both high volume fractions and Young’s modulus contrast. Results were compared to most common analytical models for composites elasticity.

International audience; Homogenization of effective elastic properties of fiber reinforced composites frequently supposed periodic arrangement of fibers because such microstructures allow analytical or low computational cost integrations. Hexagonal frame was often preferred than square one which is strongly anisotropic. In practical situations those periodical microstructures are not realistic. Real microstructures are often random or if they are periodic their boundaries don't fit with the periodic scheme. We studied with the help of finite elements samples that exhibit hexagonal arrangement of fibers embedded in a random distribution. Characteristic length scales of hexagonal area were extracted from observation of stress maps. Principal results are a short scale in which bulk and shear stresses become structured. On the other hand we nether reached a size large enough to observe local stress maps similar to those produced by a periodic model.

International audience; The objective of this paper was to understand the effect of carbon nanotubes (CNT) additives on the elastic behaviors of textile based composites. The materials consist of three phases namely, carbon fibers fabric, Epoxy matrix and carbon nanotubes. Different volume fractions of CNTs were used (0% as reference, 0.5%, 1%, 2% and 4%). A set of mechanical tests as Open Hole Tension, shear Beam Test and Flatwise Tension tests were performed. A damage initiation and cracks propagation in composite specimens were controlled. The experimental results show an increase the mechanical performance of the composite up to 2% of CNT additives. However, beyond this value, the material strength shows a significant decay.

International audience; The morphology characterization and computational methods favored numerical simulation and design of microstructures. Indeed, the multiscale approaches enable us to determine the elastic properties of materials. In this paper, the objective is to develop a three-dimensional microstructure of biocomposites containing natural particles. The biocomposite is made of polypropylene matrix mixed with natural fillers. The image is obtained using the microscope. We describe a serial sectioning process and finite element simulations to reproduce, visualize and model these microstructures. Statistical methods are introduced to study the representativity of specimen. The statistical representative volume element is introduced to determine the minimum volume which provides the representativeness. This statistical volume is compared with experimental and numerical ones.