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International audience; Lower back pain is a major public health problem. Despite claims that lumbar belts change spinal posture due to applied pressure on the trunk, no mechanical model has yet been published to prove this treatment. This paper describes a first model for belt design, based on the one hand on the mechanical properties of the fabrics and the belt geometry, and on the other hand on the trunk geometrical and mechanical description. The model provides the estimation of the pressure applied to the trunk, and a unique indicator of the belt mechanical efficiency is proposed: pressure is integrated into a bending moment characterizing the belt delordosing action on the spine. A first in-silico clinical study of belt efficiency for 15 patients with 2 different belts was conducted. Results are very dependent on the body shape: in the case of high BMI patients, the belt effect is significantly decreased, and can be even inverted, increasing the lordosis. The belt stiffness proportionally increases the pressure applied to the trunk, but the influence of the design itself on the bending moment is clearly outlined. Moreover, the belt/trunk interaction, modeled as sticking contact and the specific way patients lock their belts, dramatically modifies the belt action. Finally, even if further developments and tests are still necessary, the model presented in this paper seems suitable for in-silico pre-clinical trials on real body shapes at a design stage.

International audience; Numerical simulation for resin transfer moulding manufacturing process is attempted using the extended finite element method combined with the level set method. The level set method is used to transport the resin flow front at each time step during the mould filling. Extended finite element method allows to obtaining a good numerical precision of the resin pressure near the resin flow front, where the gradient of the pressure could be discontinuous. The enriched shape functions of extended finite element method are derived using the level set values so as to correctly describe these shape functions with the resin flow front. In addition, the position of the resin flow front at each time step is calculated by an implicit characteristic Galerkin finite element method. Some examples are presented to validate our study in comparison with analytical or experimental results and to illustrate its industrial applications.

International audience; Knee degradation and pain when developing osteoarthritis are strongly related not only to the pressure on the cartilage, but also to the knee stability and to the subsequent loadings on the ligaments. Authors proposed the knee models without any flexion. Knee flexion had been introduced by controlling actively muscular groups or by using a full displacement-controlled model. But in both cases, the pressure applied on the articulation has been questioned, the forces used to achieve the flexion being far from the physiology in the former and the bone positioning uncertainties leading to high variations in the cartilage pressure and ligament loads in the latter. Here, we propose a mixed approach, both using medical imaging (MRI, EOS X-ray system) and force platform in conjunction with a finite element model. A healthy volunteer underwent a MRI and an EOS imaging of the knee. EOS images gave the exact position of the bones for five flex-ion angles of the knee, ranging from 0° to 85°. The subject's knee was loaded with a specific force on his foot during all acquisitions to keep consistent boundary conditions on the knee. A 3D geometrical model of the bones and cartilages was segmented from the MRI stacks; this model was meshed and smoothed for Finite Element

International audience; The main goal of this study is to optimize the structural thickness distribution for improving the mechanical performance of composite structures manufactured by compression molding processes. During the preliminary preparation for optimization, a processing simulation program was developed to predict the fiber volume fraction and orientation using a Control Volume/Finite Element method. To verify the effects of the processing conditions on the mechanical properties, a few simple geometries and loading conditions were investigated. Considering the fiber state changes, the optimal thickness distributions of a plate in one- and two-dimension have been searched. Box's complex method was applied to solve the non-linear inequality constrained problem. (C) 2009 Elsevier Ltd. All rights reserved.

A multi-objective optimization methodology is proposed which simultaneously considers the mechanical performance and the manufacturing cost from the early stage of design of composite laminated plates. Resin transfer molding process is chosen as the manufacturing process for its wide acceptance among industries. Interrelations between the structural parameters and the process parameters are identified. With proper assumptions, the multi-objective problem is formulated into a problem with a single objective function. As design variables, the stacking sequence of layers is investigated which minimizes the maximum displacement and the mold filling time. Injection gate location is also considered in order to minimize the mold filling time for a given structure geometry, material properties and loading condition. The genetic algorithm is adopted as the optimization scheme. The results from the sample problems illustrate usefulness of the developed methodology.

A multi-constraint optimization methodology for the design of composite laminated plates manufactured by Resin Transfer Molding (RTM) process is presented. As design constraints, both the manufacturing process requirement and the structural requirement were considered. The stacking sequence of layers and the thickness of the structure were optimized for a preassigned geometry of the structure, constituent materials and loading condition. As a structural requirement, either the stiffness constraint or strength constraint was selected. Such constraint was used as basis in the enhancement for the specific mechanical performance of composite structures. Maximum allowable mold filling time was assigned as a process requirement in the effort to increase productivity. The objective function was newly defined without introduction of any auxiliary parameters, such as scaling parameters, weighting coefficients and penalty parameters which are usually involved in multi-constraint or multi-objective optimization problems. As an optimization method, the genetic algorithm was used. The results for a sample problem show the validity of the proposed optimization methodology.

This paper presents and illustrates a straightforward method to determinate the concentration of the humidity in non steady and transient states in the core of the resin matrix composite panel exposed to cyclic temperature and moisture environmental conditions during a long time. In order to complete the previous studies, an analytical solution in transient state is proposed. Several examples are presented to demonstrate the assessment and performance in this method compared to the classical step-by-step integration.

An integrated optimisation methodology is proposed to optimise the manufacturing cost as well as the structural performance and the weight of composite laminated plates manufactured by the resin transfer moulding (RTM) process. In the present approach, the fibre type, the number of fabrics, the layer stacking sequence and the fibre volume fraction are optimised to minimise the structural weight and the material cost of composite structure under the stiffness constraint and the mould filling time constraint which is a part of process cycle time. With the results obtained, it is investigated how the weight and the material cost are traded-off. The optimisation methodology suggests a guide to cost-effective material selection in the preliminary conceptual design stage.

International audience; A simultaneous optimization methodology is proposed considering both the structural and the process requirements for the weight minimization of laminated plates manufactured by the Resin Transfer Molding (RTM) process. The coupling between the structural performance and the process cost is considered through the investigation of state parameters in the RTM process. As the structural constraint, maximum allowable displacement or maximum allowable failure index of the structure under load is assigned. For the process constraint, maximum allowable mold filling time is given. A new approach to deal with design constraints without having to concern about the penalty parameters is suggested. The influence of design constraints on the optimal design configuration is investigated through parametric studies. As the optimization scheme, Genetic Algorithm (GA) is employed. To take into account the layer number variation, genetic operators such as the crossover and the mutation are modified.