Because the timber market is more and more competitive, the particleboard manufacturers are looking for new sources of plant raw material. In the same time, the use of healthier, safer and more environmentally friendly materials becomes a priority in the building sector. In this context, using bio-based adhesives to bond the particles instead of the synthetic ones is an interesting alternative. In the same time agricultural byproducts as annual plant stems can be a sustainable alternative raw material. These resources are abundant, renewable and safe raw material. Moreover, their porous structure gives them interesting properties for building materials such as lightness and thermal insulation capacity. Two agricultural byproducts abundant in France have been studied: flax shives and sunflower bark. Particleboards were made at laboratory scale by thermocompression of the plant raw particles to a target density of 500 kg m- 3. The plant particles were bond by different methods: - * without addition of any adhesive. In that case water was sprayed on the plant particles before the forming process and was evaporated during the thermocompression. It leads to extraction of soluble and lignocellulosic compounds from the agroresources that can act as adhesives. - * with addition of a biobased adhesive based on casein, the protein from bovine milk, or based on a commercial caseinate, added at different ratios to the plant particles. - The effect of the type of agroresources, the particle size, the formulation of the biosourced adhesive, and its application are evaluated testing the physico-chemical properties of the particleboards: mechanical properties (bending test and internal bond), thermal properties, and behavior towards water and fire. Using a biobased adhesive improves the mechanical properties of the particleboards significantly compared to the version without added adhesive. Panels made with flax shives generally showed better properties than with sunflower bark, so flax shives seem more suitable for particleboard manufacturing. But after optimization of the formulation and the process, both raw materials could be used with casein-based adhesive yielding efficient and fully biobased particleboards for applications such as furniture or door panels.

The objective of the present paper is to predict numerically the effect of low velocity impact on the composite epoxy reinforced with quasi-unidirectional flax fabrics. The composite circular plate is meshed with a solid shell finite element (SS). Only one element in the thickness direction is adopted. This SS element is implemented into the user element (UEL) interface of ABAQUS in order to overcome numerical locking problems that may occurred when using the ABAQUS solid and shell elements. The epoxy/flax composite is characterized by a elasto-visco-plastic behavior. The Hill’s anisotropic criterion of plasticity with isotropic hardening and the Johnson-Cook viscoplastic model are applied. The simulations are accomplished via ABAQUS/Standard. The obtained results present the efficiency of the developed model using one solid shell element in the thickness direction from a computational point of view.

The main objective of this work is to develop an hexahedral solid shell finite element in order to resolve the numerical locking effects that may have occurred when employing the conventional solid and shell finite elements. The developed formulation relay on the coupling between the Assumed Natural Strain (ANS) and Enhanced Assumed Strain (EAS) methods. The FE model was implemented into the user element (UEL) interface of the FE commercial code ABAQUS by using the UEL FORTRAN subroutine. The robustness and performance of this element are proven using dynamic contact metal sheet behavior at low velocity impact. The obtained results are validated with finding from the literature. The developed solid shell element is efficient from a computational view point as the thickness direction is discretized adopting only single element layer.

This study is focusing on the finite element simulation of low velocity impact applied to glass fiber-reinforced composites. Elasto-visco-plasticity is adopted taking into account strain rate effect, with isotropic hardening. To avoid numerical locking, hexahedral solid shell finite element SS is developed. The formulation is based on the mixed Assumed Natural Strain (ANS) and the Enhanced Assumed Strain (EAS) methods. A geometrical non linear condition is applied. The finite element is implemented in UEL subroutine via the commercial software ABAQUS/Standard. The numerical element proved its efficiency comparing to conventional element and previous experimental results in (Mars et al. 2018). Numerical simulations with solid element are conducted using Abaqus/standard via user material UMAT subroutine. In terms of computation time, the solid shell element is less time consuming when comparing to conventional solid element. This is due to the fact that a single element through the thickness direction is adopted. Element efficiency is assessed for various fibers contents.

The main objective of this paper is to develop a numerical model susceptible to solve the numerical locking problems that may appear when applying the conventional solid and shell finite elements of ABAQUS. This model is based on a hexahedral solid shell element. The formulation of this element relays on the combination of the enhanced assumed strain (EAS) and assumed natural strain (ANS) methods with modified First Shear Deformation Theory (FSDT). The developed element is implemented into the ABAQUS user element (UEL) interface. The performance of this element is demonstrated by different benchmark tests from the literature. Our contribution consists on applying a single solid shell element through the thickness direction to predict the low velocity impact behavior on functionally graded material (FGM) circular plates.

The future industrial implementation of membranes for oxygen transport requires new designs to increase oxygen semi-permeation, together with robust performance under operating conditions. This work describes the development of innovative membrane designs based on perovskite foams with a very large porosity (above 90%) supporting thin dense perovskite membranes (thickness of 50-100 mu m). The preparation of such foam-supported membranes is described in this paper. The performances in terms of oxygen semi-permeation are also measured and compared with the best results reported in the literature up to date.

In the past decades, research was directed towards the use of plant fibres instead of synthetic fibres as reinforcement of composites. Due to their high specific mechanical properties coupled with low cost and their wide availability at the European scale, flax fibres could be considered as the most interesting plant fibres. Experimental tests carried out on flax fibre-reinforced composites have shown that these latter are characterized by a nonlinear viscoelastic–viscoplastic behaviour. In this paper, our work was focused on modelling the elastic–viscoplastic behaviour of a quasi-unidirectional flax fibre-reinforced composites. First of all, we developed a three-dimensional elastic–viscoplastic model taking into account the orthotropic elasticity and the anisotropic viscoplastic behaviour of quasi-unidirectional flax/epoxy composites. Then, based on tensile tests at different strain rates, we identified the isotropic hardening using an optimized exponential Johnson–Cook law. The model was validated against experimental data. Finally, we implemented the behaviour model in a UMAT procedure of the finite element code ABAQUS/Implicit and simulated low-velocity impact behaviour of a flax/epoxy circular plate. Simulation has shown that the impact velocity has a great influence on the behaviour of flax fibre-reinforced epoxy composite plate.

The paper deals with an automated and double-scale finite element (FE) model to evaluate the effective elastic properties of 3D overlapping random fibre composites. An efficient and perfectly reliable approach to generate meshes in the context of random heterogeneous media for which some difficulties are encountered, is proposed. The basic idea is to attain an approximation of the geometry relative to a grid of regular hexahedral elements. The concept called voxelisation is tremendously sped up using an adaptive mesh refinement (AMR) which enables one to locally and efficiently smooth each heterogeneity. Thus, a fast, reliable and fully automated generation of representative volume elements (RVE) is possible whatever the complexity of the geometry is. In the present work, algorithms to generate RVE according to the concept of voxelisation are provided. In addition, numerical tests are performed to evaluate both the efficiency of the model and the reliability of the results in the framework of linear elasticity and random fibre composites.

La1−xSrxFe1−yGayO3−δ perovskite membranes are promising candidates for catalytic membrane reactors applications due to their potential high oxygen semi-permeation fluxes and good chemical stability in working conditions. The oxygen flux through La1−xSrxFe1−yGayO3−δ perovskite membranes is mainly governed by oxygen exchanges at the membrane surface. This work shows how to strongly increase such an oxygen flux while developing a dedicated ultra-divided surface coating. Such a coating is obtained by following a route derived from sol–gel and allowing an elementary grain diameter control in the 5–10nm range. In this way, the oxygen fluxes through the coated membrane can be increased of more than an order of magnitude in comparison to uncoated membranes. This paper clearly shows that the oxygen flux through the uncoated membrane is governed by oxygen surface exchange, while for coated membranes it is governed by a balance between surface exchange and bulk diffusion. Our surface-modified dense La1−xSrxFe1−yGayO3−δ membranes show good performance in long term in working conditions (high temperature and large oxygen partial pressure gradients).

This paper reports new evidence that oxygen surface exchange and bulk diffusion in a mixed conductor can be simultaneously determined via the oxygen semi-permeation method. Herein, we report the use of an original apparatus for oxygen activity measurements at both membrane surfaces to evaluate the oxygen surface exchange and bulk diffusion coefficients. Oxygen surface exchange and bulk diffusion in the La1-xSrxFe1-yGayO3-delta perovskite series are also determined and compared with the results from three different methods: isotopic exchange, conductivity relaxation, and oxygen semi-permeation. Although the thermodynamic conditions for these methods are not exactly the same, the values obtained for the oxygen surface exchange and bulk diffusion coefficients are in good agreement. (C) 2013 The Electrochemical Society. All rights reserved.

BaTiO3‐based materials are currently used for the fabrication of multilayer ceramic capacitors (MLCC) because of their high dielectric properties. The inkjet printing (IJP) process can be used to fabricate MLCC of complex configurations by integrating internal electrodes and dielectric layers in a single step using a multi printing‐head system. Stabilized aqueous suspensions of BaTiO3‐based powders are required to obtain dielectric inks adapted to IJP. This study investigates the influence of BaTiO3 powder hydrolysis in water on the surface chemistry and stability in relationship with the milling step used to adjust the powder grain size to IJP. Optimum parameters for a good stability of BaTiO3 suspensions are identified. The selected dispersant is a polyacrylate (PAA) for which the content is adjusted to minimize the sedimentation rates as required by IJP. Moreover, the addition of ethylene glycol is shown to be necessary to avoid the formation of a gel structure which could result from the interaction of borates ions leached from the surface of BaTiO3 with the PAA dispersant. A mechanism of gel formation is proposed.

Many recent studies have focused on the development of perovskite membranes with high oxygen semi-permeation performance. However, the usual experimental setups used to measure oxygen semi-permeation values may lead to significant errors in the actual performance of the membrane materials. In this paper, special attention is paid to the experimental conditions and the associated impacts on oxygen semi-permeation measurements collected from the membrane. Furthermore, the experimental setups described in the literature do not allow the direct identification of the limiting step for oxygen transport through the membrane, i.e., either through bulk oxygen diffusion or oxygen surface exchange on both membrane surfaces. In this work, a specific experimental setup is proposed for the discrimination of oxygen bulk diffusion and surface exchange phenomena.

This paper reports new evidence that oxygen surface exchange and bulk diffusion in a mixed conductor can be simultaneously determined via the oxygen semi-permeation method. Herein, we report the use of an original apparatus for oxygen activity measurements at both membrane surfaces to evaluate the oxygen surface exchange and bulk diffusion coefficients. Oxygen surface exchange and bulk diffusion in the La1-xSrxFe1-yGayO3-δ perovskite series are also determined and compared with the results from three different methods: isotopic exchange, conductivity relaxation, and oxygen semi-permeation. Although the thermodynamic conditions for these methods are not exactly the same, the values obtained for the oxygen surface exchange and bulk diffusion coefficients are in good agreement.

The decrease of the dense layer thickness can lead to increase the internal stresses in the membrane due to the chemical expansion of membrane material under a large gradient of oxygen partial pressure. This chemical expansion due to pO2 gradient through the membrane leads to important mechanical stresses in the membrane and commonly to the membrane rupture under large range of pO2, i.e. air/methane atmosphere. The solution suggested in this paper is the elaboration by tape casting and co-firing process of multilayer membranes with a specific design in order to decrease stresses due to the chemical expansion in working conditions.

The paper deals with the assessment of the influence of morphological parameters of a 2D random short fibre composite on its effective elastic properties. A double-scale 2D finite element approach is used and periodic representative volume elements are generated according to the model with an n-order approximate geometry. This one is a recent and powerful tool to generate meshes in the context of complex microstructures such as random fibre composites. Impact of three morphological features namely, aspect ratio, tortuosity of fibres and width of the interphase area, is investigated. Numerical results are provided for several contrasts of properties and volume fractions of fibres.

This paper focuses on a stochastic and multi-scale finite element (FE) model to estimate the effective properties of 2D overlapping random fibre composites. We describe a new and efficient geometric approximation to solve different problems encountered when building the mesh in which the overlapping phenomenon between two or more fibres arises. The basic idea is to attain an approximation of the fibre geometry relative to quadrangular grid elements and an adaptive mesh refinement (AMR). Thus, the model allows one to obtain a fast, reliable and totally automated generation of a large number of representative volume elements (RVEs) of random fibre composites. Several numerical tests are performed to evaluate both the efficiency of the model and the reliability of the results. It can be noted that, here we only consider the mechanical response of the material in the framework of linear continuum mechanics.

The La(1−x)SrxFe(1−y)GayO3−δ perovskites are one of the most promising materials for catalytic membrane reactor because of their excellent oxygen semi-permeation, low thermal expansion coefficient and good chemical stability at high temperature (700–1000°C) under a wide range of oxygen partial pressure (from 0.21 to 10−19atm). In this paper, the thermal expansion coefficient (TEC) and the oxygen semi-permeation of La(1−x)SrxFe(1−y)GayO3−δ perovskite in relation with Sr and Ga substitutions have been measured and discussed. The chemical stability of La(1−x)SrxFe(1−y)GayO3−δ perovskite formulations under diluted methane atmosphere is tested and discussed.This study leads to identify the Sr and Ga substitution ratios presenting the best compromise between high oxygen semi-permeation, low thermal expansion coefficient and good chemical stability in working conditions. In this way, one of the best compromises between good oxygen permeation fluxes, dimensional and chemical stabilities are La0.6Sr0.4Fe0.6Ga0.4O3−δ and La0.6Sr0.4Fe0.7Ga0.3O3−δ.