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The present article investigates the melting process of aluminum foam/paraffin composite with low porosity by using experimental and numerical methods. Three composites with porosities 67%, 75%, an...

International audience; Phase change material (PCM) is a promising candidate for application to thermal energy storage. However, low thermal conductivity hinders its wide application. In this paper, a porous metal structure (PMS) with cubic cell is used to enhance the thermal performance of PCM, in which additive manufacturing (AM) as advanced manufacturing technology enables the fast and precise fabrication of PMS with a controlled structure and material. A visualized experiment setup is built to investigate the thermal performance of PCM with and without PMS, including solid-liquid interface, temperature variation, and total melting time. To examine the heat transfer characteristics and clarify the role of PMS in the melting process, a three-dimensional numerical model is developed based on the pore-scale numerical simulation method. The experimental results illustrate that embedding PMS can significantly improve the thermal performance of PCM, e.g., the total melting time can be shortened by 38% compared with that for PCM without PMS. The numerical results are in good agreement with experimental results, which indicates that heat transfer characteristics can be predicted using pore-scale numerical simulation. The numerical results show that the temperature field of PCM with PMS is more uniform and heat transfer mechanics is different for PCM with and without PMS. In addition, PMS made of highly thermally conductive materials significantly enhances the thermal performance of PCM. Due to structure and material controllability of porous material fabricated by AM, this study highlights the capacity and potential of PMS as a heat transfer enhancer.

International audience; The hybrid solution of natural-synthetic fibres can be an effective option to enhance the moisture resistance of natural fibre reinforced polymer composites. This work aims at studying the effect of long-term water immersion of hybrid composites on their mechanical and damping properties. These properties were investigated using free vibrations from samples composed of quasi-unidirectional flax and glass layers and epoxy resin. The results showed that the saturation mass uptake and the diffusion coefficient of the composites were strongly dependent on the stacking sequence between the flax and glass layers. For instance, less than 25 days were necessary to reach the water saturation when flax fibre reinforcements were in the outer layers, whereas it took over 10 months when these reinforcements were in the inner layers. Compared to the flax fibre reinforced composite, the flax-glass hybrid laminate with two inner flax layers and two outer glass layers was the most efficient for a specification where damping and bending modulus are the main criteria. This one enabled a significant increase in bending and specific bending moduli (+38 % and +79 % respectively compared to the unaged flax laminate), a considerable slowing down of the diffusion phenomenon, while limiting the decrease in damping property with ageing (−20 %).

International audience; In this paper, a comprehensive experimental and numerical investigation is conducted to study the thermal behavior of phase change material (PCM) infiltrated in low porosity metal foam (LPMF). A visible experiment is designed to trace the temperature field and solid-liquid melting evolvement of PCM with and without metal foam. The experimental method and pore-scale numerical simulation are employed to extract temperature histories at different location during the melting process. Besides, the effective thermal conductivity of composite PCM is calculated by numerical simulation and compared with the theoretical models. Experimental results indicate that the thermal behavior of PCM can be visibly enhanced by embedding LPMF, e.g., by comparing with pure paraffin, the melting time of composite PCM is reduced by 45% and the maximum temperature difference is decreased by 83.3%. The porosity has influences on the thermal characteristics of composite PCMs. Numerical results exhibit good agreement with experimental data, which indicates that modified Kelvin model can be employed to predict the thermal performance of composite PCM. Also it can be found from numerical results that effective thermal conductivities of composite PCMs are distinctly heightened, e.g., the effective thermal conductivities of composite PCM with 67% porosity is about 108 times as much as that of paraffin. Numerical model is of great significance for study and design of thermal management system using composite PCM.

International audience; Pore-scale numerical simulation is conducted to study the thermal performance of composite change phase material (PCM). The low melting point paraffin wax R56 is selected as PCM. Aluminum foam with cubic periodic cell structure is designed, which not only possesses high thermal conductivity, high porous structure and low relative density but also can be rapidly manufactured by the new manufacturing technology. Hence it is an excellent candidate used as metal matrix of composites. The pore-scale numerical method is used to calculate the temperature variation and trace the melting evolution of composite PCM. The effects of geometrical parameters of metal foam such as porosities and pore densities on the thermal behavior of composite PCM are numerically investigated. It is observed from numerical results that the effects of aluminum foam on the thermal performance of composite PCM are very pronounced. Compared with the pure paraffin, the melting time for composite PCM is greatly shortened to 24.1% of that of pure paraffin. Also the effective thermal conductivity of composite PCM is drastically improved, e.g., the effective thermal conductivity can be enhanced about 123 times as much as that of pure paraffin. By comparing with the different porosities and pore densities composite PCMs, the geometrical parameters of aluminum foam have the distinct effects on the thermal performance of composite PCMs, e.g., the melting rate for composite PCMs with the low porosity or high pore density is higher as compared to the composite PCMs with the high porosity or low pore density. By analyzing the temperature-time history, it is demonstrated that there is local thermal non-equilibrium phenomenon between aluminum skeleton and paraffin during the melting process and local thermal non-equilibrium gradually weakens as the reduction of temperature difference between aluminum skeleton and paraffin.

International audience; The aim of this study is to show the interest of the mechanical and dynamical properties of glass-flax hybrid composites. Therefore, various staking sequences of glass-flax hybrid composites were manufactured and tested in free vibrations. The damping coefficients were identified by fitting the experimental responses of free-free bending vibrations. The obtained results show that the staking sequences and the position of flax fiber layers in the hybrid composites changed the properties, so a classification of different stacking sequences was established. In fact, the hybrid laminate made of two glass external layers placed on both sides of four flax layers is very interesting in term of its mechanical and damping properties. Indeed, it showed better specific bending modulus and loss factor than glass composites with proportions of 31 and 39%, respectively. A study of a structure of this composite has been made to validate the obtained results.

International audience; Since the past five decades, the study of new materials has become attractive in both scientific research and industrial applications. For purpose of enhancing mechanical properties of metallic foam, a new composite entitled “Metal-Porous-Polymer-Composite (MPPC)” consisting of open-cell metallic foam and filling polymers was developed by infiltrating the filling polymers throughout the connected pores in open-cell metallic foam. Based on a three-dimensional (3D) structural modeling, microscopic structural models of Al metallic foam and MPPCs with spherical pores and Kelvin’s pores are established in the finite element code. Introducing the elastoplastic mechanical properties, the polymer–metal interfacial behaviors and the proper loads and boundary conditions on these structural models of Al metallic foam and MPPCs, the numerical compressive behaviors of Al metallic foam and PA6/Al & LDPE/Al MPPCs are successfully performed. The results show that the mechanical properties of PA6/Al & LDPE/Al MPPCs are mainly influenced by the filling polymers, the kind of pores, the pore size, the polymer–metal interface, the polymer volume fraction and the distribution of pores, respectively. It means that a good understanding can be provided concerning the deformation mechanism and engineering applications of both Al metallic foam and MPPCs.

International audience; Phase change material (PCM) saturated in metal foam is a promising candidate for thermal energy storage (TES). However, there are some potential factors affecting the thermal charging performance of composite PCM, such as heating and contact conditions. In this paper, paraffin and copper foam are selected as PCM and metal matrix, respectively. Heating conditions are top, left and bottom heating. The contact gaps are set to 0, 0.4 and 0.8 mm to represent different contact conditions. The numerical investigation on thermal charging performance of composite PCM under different heating and contact conditions is performed. Based on volume-averaged method, the numerical model is developed to study the thermal characteristics of composite PCM including solid-liquid interface, liquid fraction, velocity, total melting time and average heat storage rate. Results show that there are the comprehensive effects of heating and contact conditions on thermal performance. The heating condition can affect phase change heat transfer mode, and thus has a significant influence on thermal charging performance. The contact conditions have the different effects on thermal behavior of composite under different heating conditions, e.g., under top heating condition, the total melting time of composite with 0 mm and 0.8 mm contact gaps is almost the same. Whereas, under left heating condition, the total melting time of composite with 0.8 mm contact gap is 2.6 times that of composite with 0 mm contact gap. The study of the effect mechanism of heating and contact conditions is of great significance for practical application of composite PCM in TES system.

This study focuses on the thermal analysis and comparing a lattice model and an optimized model of open-cell metal foams manufactured thanks to a metal casting process. The topological optimization defines the complex geometry through thermal criteria and a plaster mold reproduces it in 3D printing to be used in casting. The study of the thermal behavior conducted on the two open foam metal structures is performed based on several measurements, as well as numerical simulations. It is observed that the optimized metal foam presented less and non-homogenous local temperature than the lattice model with the gap of about 10 °C between both models. The pore size and porosity significantly affect the heat transfer through the metal foam. The comparison between numerical simulations and experimental results regarding the temperature fields shows a good agreement allowing the validation of the developed three-dimensional model based on the finite element method.

International audience; In order to measure the residual stress components in an elastic thin plate, the hole-drilling strain-gage method has been used. This method enables to determine the relation between the magnitudes and directions of the principal stresses and the strain relaxation about the hole. In the existing analytical models based on stress field, the formulations associated with the hole-drilling method are based on the assumption of an infinite plate, this may cause some errors for a finite plate and it’s difficult to validate these solutions by FE methods. Furthermore, in the composite, the displacement field is continuous but the stress field is not necessarily continuous, the displacement field based method has to be used. In the present paper an analyt-ical model based on a displacement field described by a function with coefficients to determine for a finite round thin plate is presented. The coefficients used in the displacement field are independent on the three residual stress components, and they are determined by minimization of the internal strain energy during the hole-drilling process. Once the coefficients in the dis-placement field are determined, three strains measured in three radial directions are utilized to determine the three residual stress components. The proposed analytical model can be also adapted to infinite plate by assuming that the diameter of the round plate tends to infinite.

International audience; The metal foam/phase change material (PCM) composite is a promising material in the thermal energy storage system. In the present study, a modified structure of metal foam, finned metal foam with graded porosity (FFGP), is proposed to further accelerate the melting process of the composite. The finite volume method and two equations model are applied in the modeling of FFGP. The average power of energy storage is defined to evaluate the energy storage efficiency of the composite. The effects of the structural parameters of FFGP on the average power of energy storage are investigated, including thickness of metal fin, porosity gradient of metal foam and pore per inch (PPI). The results indicate that FFGP structure could reduce the total melting time and enhance greatly the energy storage performance. This is because the metal fin changes the melting sequence of PCM and the gradient metal foam contributes to the heat transfer between the heat source and the composite. Besides, the value of PPI has a great impact on natural convection in the composite. Through combining the proper metal fin, gradient metal foam and PPI, the FFGP structure with the good performance could be obtained.

International audience; This study focuses on the methodology of periodic open-cell composite foams manufacturing by rapid tooling as well as the thermal analysis of the obtained structure. A bimaterial is prepared by introducing a phase change material (paraffin wax) into metal foam. The aim is to provide a structural bimaterial to study its thermal behavior for energy storage and achieve an adapted geometry with the help of rapid tooling by three-dimensional printing (3DP). Concretely, the bimaterial melting process is experimentally studied in order to determine thermal behavior. The temperature variations and distributions of the bimaterial are analyzed and compared with the results of pure paraffin. Moreover, the effect of natural convection is analyzed and discussed. The results show that the periodic open-cell metal foam could be a potential solution to the problem of storage and recovery of energy.

International audience

The tribological performances of in-situ (TiB + TiC) / Ti1100 composites prepared by casting and the matrix alloy were tested by pin-on disc mode. The worn surface and wear debris were investigated by SEM. The models of the composites during the wear process were simulated by ABAQUS FEA software. The analysis shows the stress distributions inside the composites under the different shear stress. The wear mechanism of the composites is probed.

International audience; Three methods to further enhance thermal performance of the metal foam/phase change material (PCM) composite are investigated and compared. These three methods include changing the pores per inch (PPI) of metal foam, modifying the shape of the cold wall and using the discrete heat sources. In this study, the composite consists of two materials: aluminum foam with 90% porosity as metal foam and paraffin wax as PCM. The numerical model based on finite volume method is developed, and the non-equilibrium equation is applied to study the melting process of the paraffin embedded in aluminum foam. The heat loss, the liquid average velocity and the efficiency of latent heat storage are analyzed and discussed. The results show that adopting the aluminum foam with high PPI value or modifying the shape of the cold wall could improve the thermal response of composite. Besides, the discrete heat sources could lead to a large average velocity in the liquid region. Combining the advantages of these methods, an optimization method is also proposed, which could improve the efficiency to 83.32% comparing with the pure paraffin.

International audience; The aim of this work is to study the effect of water ageing of quasi-Unidirectional Flax fibre Reinforced Epoxy (UFRE) composites on their mechanical and damping properties. The studied composites were manufactured by press platen process and subjected to water immersion at room temperature. Mechanical and damping properties of unaged and aged materials were investigated using free vibrations. Next, they were dried and tested to study the reversibility of the variation of those properties caused by water ageing. The results showed that water uptake induces a decrease in the bending moduli and an increase in loss factors compared in term of ageing time. It was also proven that those variations are practically reversible in the case of loss factors but irreversible in the case of bending moduli.

The cooling conditions used in the forming process of composite materials play an important role in the creation ofresidual stress. In this study, a new method for measuring residual stress in composite laminates is presented. Three cooling conditions were used to produce different residual stress levels. Residual stresses in [02/902]s and [08] laminate have been measured by the incremental holedrilling method combined with 3-D finite element modelling. A software which quickly calculates all the coefficients for each increment was developed. The automatic procedure can be used to calculate the calibration coefficient for any type oflaminate (ply number, mechanic characteristics,...) and whatever the number of increments and their depths. The different results show that this method provides access to the in-depth distribution and through thickness ofresidual stress in the laminate with a good accuracy and practicality.

In this article, an eco-friendly and cost effective surface treatment method is proposed for hemp fiber, enabling fabrication of hemp fiber/polypropylene (PP) composites, which show better mechanical properties than the PP composites containing untreated or alkali treated hemp fiber. Various techniques, such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), moisture analysis, and differential scanning calorimetry (DSC), are employed for the characterization of hemp fiber and polymer composites interface. Based on these results, the conventional alkali treatment of hemp fiber results in the damage of elementary fiber by eliminating parts of lignin and hemicellulose, which could be the reason for the decline of mechanical properties for the resulted polymer composites. On the contrary, water treatment cleans the fiber surface by effectively removing the water-soluble polysaccharides while ensures minimum degradation on elementary fiber structure, which contributes to the improved mechanical properties of final polymer composites: the Young's modulus, fracture stress and fracture strain were enhanced by 3.66, 7.86, and 14.6%, respectively, when compared with untreated fiber reinforced composites. POLYM. COMPOS., 2014. © 2014 Society of Plastics Engineers

International audience; The acoustic properties of an air-saturated macroscopically inhomogeneous aluminum foam in the equivalent fluid approximation are studied. A reference sample built by forcing a highly compressible melamine foam with conical shape inside a constant diameter rigid tube is studied first. In this process, a radial compression varying with depth is applied. With the help of an assumption on the compressed pore geometry, properties of the reference sample can be modelled everywhere in the thickness and it is possible to use the classical transfer matrix method as theoretical reference. In the mixture approach, the material is viewed as a mixture of two known materials placed in a patchwork configuration and with proportions of each varying with depth. The properties are derived from the use of a mixing law. For the reference sample, the classical transfer matrix method is used to validate the experimental results. These results are used to validate the mixture approach. The mixture approach is then used to characterize a porous aluminium for which only the properties of the external faces are known. A porosity profile is needed and is obtained from the simulated annealing optimization process.

Hierarchical porous wood-templated ZnO has been successfully synthesized using Lauan and Fir woods as template through a simple hydrothermal bioinspired approach. The template type and calcination temperature in the preparation process have a large effect on the morphologies and porous structures of ZnO according to FESEM, TEM, mercury porosimetry and N 2 adsorption investigations. The gas sensing performances of wood-templated and non-templated ZnO were investigated using H 2 , CO, H 2 S, NH 3 , Formaldehyde, Methanol, Ethanol, Acetone, and Isobutene. The article studies the effects of wood template, calcination temperature, and working temperature of gas flow on the gas sensitivity and selectivity in detail. It is revealed that wood-templated ZnO has excellent sensitivity and selectivity to H 2 S due to inheritance of wood's hierarchical porous structure. The sensing response to H 2 S of Fir-templated ZnO is about 5.1 times higher than that of non-templated ZnO. Fir-templated ZnO calcined at 600 °C, has the best sensing properties including the highest gas sensing response, the highest selectivity coefficients of H 2 S and the shortest response and recovery time. The selective sensing mechanism has been discussed from some key aspects, such as gas properties, gas–solid reactions, grain size and hierarchical porous microstructures.

Porous iron with woodlike microstructures was prepared from two kinds of wood templates through a developed biotemplating method in the present work. The biomorphic iron oxide was first produced through infiltration and sintering procedures, and was then reduced to the biomorphic iron in a hydrogen atmosphere at high temperatures (600C and 1000C). The morphologies of iron and iron oxide products were observed using SEM and FESEM, and their crystal structures were identified using X-ray diffraction. The results indicate that the pure iron phase can be obtained after the reduction process and the products faithfully retained the microstructures of the corresponding wood templates. [doi:10.2320/matertrans.48.878]

This work investigates the effect of residual stresses on the damage of composite laminate. The incremental hole-drilling method is applied to determine residual stresses in composite laminates [02/θ2]s and then acoustic emission technique is used for the identification of damage appearance during the tensile testing. The samples with different residual stress distribution are prepared through curing and post curing in order to study the role of residual stress on the damage of composite laminates. Besides the experimental method, the theoretical approach is applied to illustrate the role of residual stress on the damage of composite laminates.

This work aims to numerically analyze the mechanical properties of thermoplastic composite laminates with the [0°/90°]4s, [±25°]s4 and [0°/±45°/90°]2s stacking sequences under three-point bending loading. Three-dimensional multilayer structural models of composite laminates are established and then orthotropic elastics, Hill yield criterion and isotropic hardening rule are applied on these structural models of composite laminates to conduct the bending mechanical deformation. Fine enough meshes and reasonable loads and boundary conditions can efficiently reduce the computing cost. Afterwards, three-dimensional fiber–matrix structural models with disordered fiber arrangements of 0°/90°, 25°/−25° and 0°/45° interlaminates at the free edges of composite laminates are also created, in which the boundary conditions are transferred step by step using a three-step structural submodeling. Once more, orthotropic elastics and isotropic hardening are applied on these fiber–matrix structural models. This work provides a good way to understand the bending mechanical behavior of thermoplastic composite laminates with different stacking sequences.

International audience; The present work aims to determine the residual stresses in carbon fiber/epoxy composite laminates, by means of the incremental hole-drilling method. Based on mechanical theories of composite laminates and an elastic plate with a circular hole, the relationship between the relaxed strains on the surface of laminates and the residual stresses in laminates was established. This newly deduced theoretical formula was adapted into the incremental hole-drilling method and allowed us to further study the residual stresses in the through-thickness direction for various composite laminates. Related numerical modeling of composite laminate with a hole was built to calibrate the coefficients within the formula. Experiments were conducted and the residual stresses in composite laminates [02/θ2]s are presented. The proposed approach was validated with the consistence between our results for cross-ply laminates and those in literature.

The compression characteristics of open-cell aluminum foams were experimentally and numerically investigated. It is found that the mechanical parameters, such as collapse stress and absorbed energy, are dependent on the porosity of aluminum foams material. During simulation of metal foam compression, the finite elements distort severely at the local regions with high gradient of physical field. The procedure integrates Explicit solver of Abaqus FEA, 3D Optiformmesher and Python script program transfer to execute step by step the incremental deformation of deformable body.

This work studies the behavior of a multidirectional laminate under Mode II loading. We describe the process of delamination in a reinforced composite of glass/epoxy. The stacking sequence (plies orientation [± θ] was selected to minimize the coupling effects. The Mode II interlaminar test under three-point bending and cantilever flexure using ENF (End Notch Flexure) and ELS (End Load Split) specimens, respectively, was performed and analyzed. The test procedures and the results of strain-energy-release rate study for crack initiation are presented. The fracture process and the mechanical behavior of the two types of specimens are analyzed. The analysis clearly shows a close link between the angle θ, the ratio a/L, and the thickness h of the specimen. Fracture by delamination can be obtained only with an optimal choice of these parameters. The analysis of the states of stresses at the tip of crack allows us to explain the phenomenon of bifurcation between plies and is confirmed by the experimental results.

International audience; In this work, polypropylene composites reinforced by woven hemp fiber were fabricated using compression molding. The effects of compression temperature, ranging from 160 °C to 200 oC, on the tensile properties of the resulted composites were studied. The tensile tests of neat woven hemp fiber heated under different temperatures (160-280 oC) were also performed. The scanning electron microscopy (SEM) was employed to observe the fiber surface. The results showed that the tensile properties of the reinforced composites decreased with the increase of compression temperature, but a rise up to 40.31 MPa at 190 oC occurred. The tensile properties of the woven fibers decreased as the temperature increased, even a marked reduction at 220 oC. The SEM presents the fiber surface indicating the degradation of pectin or lignin on the fiber surface.

International audience; Due to their remarkable mechanical properties, carbon nanotube (CNT) reinforced aluminum (Al) matrix composites have attracted a wide range of research interests. This work attempts to experimentally and numerically investigate the relationship between the micro-structures and mechanical behavior of CNT/Al composites. Three-dimensional (3D) computational structural modeling of CNT/Al composites is performed, in which the size, morphology, orientation, location and volume fraction of CNTs are reproduced to be similar to those of the actual micro-structures of CNT/Al composites. The strengthening of the mechanical properties of the constituent materials of CNT/Al composites and reasonable load and boundary conditions are studied based on the models of CNT/Al composites developed. The tensile mechanical behavior of CNT/Al composites is numerically evaluated and experimentally verified. Results show that the enhanced mechanical properties of CNT/Al composites can be attributed to three factors: CNT reinforcements, matrix grain refinement and layered architectures. Through the microscopic structural modeling methods presented herein, the effects of model size, interfacial behavior, volume fraction of CNTs and layered structures on the mechanical behaviors of CNT/Al composites can be reproduced to understand the strengthening and deformation mechanisms of CNT/Al composites.

In this work, the residual stresses for composite laminates [02/θ2]S determined by means of the incremental hole-drilling method with a formula to express the relationship between the residual stresses and the relaxed strains around the drilled hole. Then the ageing tests related to hydrothermal condition are carried out to analyze the influence on the residual stress redistributions and also on the mechanical behaviors of the carbon/epoxy laminates.

International audience; Pressure infiltration casting technique is widely used to manufacture open-cell metal foam and it has been well performed in manufacture practice in our research group. In the present study, an attempt is made to highlight the influence of the infiltration casting process on the physical structure of metal foam. According to the production practice, several parameters: the pressure difference, the temperature condition, the particle size and the mould dimension, need to be well considered. A 2D model coupling porous zone and multiphase is created with a fixed grid. The cooling and solidifying process of molten metal are as well carried out with enthalpy method. Reasonable convergence rules are used to proceed high quality calculations. This work provides excellent experimental and numerical comprehension of pressure infiltration casing process to manufacture open-cell metal foam. These understandings can well guide and optimize the product manufacture, the physical structure and the mechanical behaviors of open-cell metal foams within their industrial application.

International audience; The literature concerning ± laminates under mode II (propagation mode) loading encounters a difficulty in calculation of the structural dimensions. Indeed, it is rare to have a specimen geometry which fully satisfies the conditions for application of the Linear Elastic Fracture Mechanics (LEFM). Thus, the aim of this work is the optimisation of the specimen geometry which allows the characterisation of mode II by the approach of the LEFM concept. The results obtained show an interaction between the geometrical characteristics of the specimen (thickness h), the angle of orientation of the plies () and the characterisation of delamination. The experimental results are in good agreement with the analytical predictions. The use of the acoustic emission allows us to observe that delamination is only one final stage in a process of damage which starts well before.

International audience; Polypropylene reinforced by hemp fibers composites were prepared by injection method. An aging chamber was used to simulate and accelerate the natural ageing process. The influence of moisture and UV aging on the mechanical properties of the composites is studied in this paper. A modified law of mixtures applying to polypropylene/hemp fibers composites is proposed. The microstructures of the composites during aging treatment were analyzed by means of digital microscope. We can see that the moisture and UV aging reduced the mechanical properties of the composites. The UV aging is more penalizing on the mechanical properties of composites, compared to the moisture aging after 4 weeks of exposure.

International audience; Dynamic response of open-cell metal foam under low-velocity impact loading is important in applications involving impact resistance and energy absorption, etc. Assuming that metal foam is a conceptually continuous material, the macroscopic mechanical behaviors, both static and dynamic, must be studied. Within the dynamic mechanical properties of metal foam, impact response becomes the renewed interest to understand the characteristics of impact deformation. The present work aims to experimentally and numerically analyze the low-velocity impact response of open-cell metal foam. A series of low-velocity drop impact tests are realized on the open-cell metal foam samples with different relative densities and at different impact velocity. Afterwards, a well compiled program in Python controls the whole multiple drop impact process on each sample of metal foam. Corresponding numerical modeling and the simulation for single impact analysis are continuously carried out with the finite element (FE) program ABAQUS/Explicit. Proper meshing technique, loading and boundary conditions are conducted on all the foam models, and at the same time, the required mechanical properties: elastic module, Poisson's ratio, uniaxial stress-strain response and strain-rate dependence are utilized. In conclusion, the simulated results provide the good agreements with the experimental results in the case of low-velocity impact testing of open-cell metal foam. Experimental procedure and numerical simulation offer good approaches to improve the impact resistance and energy absorption of the open-cell metal foam.

International audience; In this work, we demonstrated a novel surface-enhanced Raman scattering (SERS) substrate inspired by natural nanostructures of butterfly wing scales. By facile and low-cost procedures, we synthesized the substrate composed of tin dioxide (SnO2) and silver (Ag) nanoparticles (NPs). Micrographs and composition analyses exhibited the morphologies of Ag-Biomorphic SnO2 which inherited the natural three-dimension (3D) periodic nanostructures, and characterized the elemental information of the nanocomposites. SERS spectra were measured by using rhodamine 6G (R6G) as analyte molecules. The satisfying sensibility (with the enhancement factor about 106) and good reproducibility of this SERS-active substrate revealed the effectiveness of our work. It is expected that this substrate would be a potential candidate for relative applications.

International audience; The weathering of hemp fiber influences their appearance and mechanical properties. The aim of this study is to better understand the mechanism of aging of hemp fiber exposed to different conditions (moisture, heat and UV aging). A xenon aging test machine was used to simulate and accelerate the natural ageing. The influence of each aging condition on the mechanical properties of hemp fiber is investigated by micro tensile tests. The microstructures and water absorption of these natural fibers were analyzed by means of SEM and gravimetric methods. Humidity absorption of hemp fibers depends on the relative humidity, not concerning the temperature. Temperature accelerates the saturation of fibers. All aging process reduced the mechanical properties of hemp fibers. After 4 weeks exposure, fibers aged by UV has the worst mechanical properties compared to humidity and temperature aging.

A novel porous ZnFe2O4/SiO2 composite product has been generated with a template-directed assembly method from porous diatomite under different synthesis conditions, such as precursor concentrations (metallic nitrates), calcination temperature and diatomite type. The phase composition and morphology of all the materials were examined by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results indicated that an inherited hierarchical porous structure from the diatomite template can be obtained, and the synthesis conditions were found to have clear effects on the formation of the ZnFe2O4/SiO2 composite. The ideal composite of ZnFe2O4/SiO2 can be obtained through optimization of diatomite template type, precursor solution and calcination temperature. Furthermore, the adsorption abilities of two types of diatomites were analyzed in detail using FTIR spectra and nitrogen adsorption measurements etc, which proved that A-diatomite (Shengzhou-diatomite) is better than B-diatomite (Changbai-diatomite) on the aspect of adsorbing Zn and Fe ions, and of forming the ZnFe2O4.

International audience; The objective of this paper is to study the influence of residual stresses due to fabrication conditions on the thermomechanical behavior of carbon/epoxy laminate structures (cross ply). These studied laminates have undergone various cycles of thermal aging. The addition of a post-cure cycle after the end of the initial cycle makes it possible to reduce the residual stresses level. The incremental hole-drilling method is used to measure the residual strain in the laminates. These measured strains and the numerical calibration coefficients obtained by the finite element method allow to calculating the residual stress distribution in composite depth. The obtained results show that heat treatments of composite structures do not lead to an important reduction the initial residual stress due the fabrication conditions.

International audience; Residual stresses occur during most manufacturing processes (from shrinkage of the resin, difference of thermal expansion coefficients, etc.). Residual stresses may cause local yielding and damage initiation and propagation, and can severely affect performances of a composite structure component. The aim of this work is to investigate the influence of residual stresses on the mechanical behavior of carbon/epoxy cross-ply laminates under tensile and torsion loading. The residual stresses field was determined using the incremental blind-hole drilling technique combined with the finite element analysis. The effect of various cure cycles on the residual stress level is analysed. The quantitative effect of the residual stresses on the mechanical behaviour and the damage initiation and growth is studied by using acoustic emission technique.

International audience; The incremental hole-drilling method is an effective semi-destructive technique for determining the profile and magnitude of residual stresses in composite laminates. This method provides access to the residual stress profile of the intra and inter plies in the through thickness of the laminate. Correct application of the method requires optimisation of the relevant experimental parameters. Tests were performed to investigate the influence of two experimental parameters—the depth of each drilled increment and the influence of the relative position of the strain gages compared with the radius of the hole drilled. The development of a rapid automatic method for numerical calculation of the calibration coefficients enhanced the interest of the method while extending the experimental data range being investigated. The results clearly show that these parameters have an appreciable effect on determination of the residual stress gradient, and especially the magnitude and stability of the residual stress.

Residual stresses play an important role on the mechanical behavior of composite laminate. The development of new methods to determine the residual stresses gradient within the laminates is necessary. This article presents the adaptation of the compliance method in the case of composite laminates carbon/epoxy [02/902]s. The incremental drilling of a constant width groove allows for each increment to measure the strains (using strain gages) and displacements (using an optical device) of particularly points of the structure surface. These experimental data are compared with results given by a finite elements simulation. This comparison allows to raise the residual stresses in the composite laminate.

High-performance composite are fabricated by hot isostatic pressing of matrix and fibers. The cooling conditions in the forming process (Resin Transfer Molding, Structural Resin Injection Molding, Laying-up) play an important part in the thermal residual stress distribution. The existence of residual stresses, combined with mechanical loads, could considerably decrease the durability of laminate structures by leading matrix cracking, fibres breaking and interface delamination initiation. The objective of this study is to investigate the influence of residual stresses on the mechanical behavior of composite laminates. Incremental hole-drilling method combined with 3D FE analysis is used to performed the internal strains in laminate plates [0 2 /90 2 ] s polymerized with different cooling conditions (fast, normal and slow). The emission acoustic events system was used during static tensile tests and the signal interpretations are given by a schematic classification in order to estimated the damage initiation between interfaces. The results of this study show that the general level of the residual stresses changes appreciably with the conditions processing and prove that this new method gives a new prospect for the study of the residual stresses distribution in advanced composites parts.

International audience; The cooling condition in the forming process (resin transfer molding (RTM), structural resin injection molding (SRIM), laying-up) plays an important part in residual stress distribution in the advanced composite pieces. The residual stresses, which are induced during the cool-down process following high temperature consolidation, result from the coefficient of thermal expansion (CTE) mismatch between plies. This paper describes the development of a finite element method to simulate the prediction of residual stresses and strains fields induced by cool-down process. In this research we used incremental hole drilling method combined with acoustic emission to understand the chronology of damage events, the development of damage modes (matrix cracks, laminate delamination and fibers fractures). The laminate plates [02/902]s was polymerized with three different cooling conditions (fast, normal and slow). Specimens cut from these plates were tested to measure their tensile strength and to investigate the influence of residual stresses on the mechanical behavior of laminate structures.