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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; 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; 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.

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; 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.

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.

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.

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.

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.