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To assess the repeatability and kinematic data of Modjaw® recordings from a group of asymptomatic patients.Modjaw® mandibular kinematic data were recorded for 22 asymptomatic volunteers (DC/TMD questionnaire). Sagittal (SCI at 3 and 5 mm) and transversal (TCI at 4 mm) condylar inclination values of the instantaneous center of rotation were measured over two recording sessions. The repeatability of recordings was determined from the intraclass correlation coefficient (ICC), which is based on a one-way random-effects ANOVA.The repeatability of recordings was found to be good to excellent. The mean TCI in mediotrusion was 7.1° ± 5.1, and the mean SCI in protrusion was 51.07° ± 9.43.The Modjaw® device reliably records the patient's real hinge axis kinematics during functional mandibular movements. Data can be transferred with the patient's personal reference plane and digital casts to the CAD/CAM software.

While dental composite long-term aging has already been studied in the past, no data exist about the early aging while it might be detrimental regarding the composites' longevity. This study aims to better understand the effects of early water exposure on dental composites. Dental resin composites with different fillers ratio were subjected to water exposure during 24 h, 1 week, or 1 month. After photopolymerization, the samples were stored at different conditions, whether in wet or dry condition (W, D, respectively) and in wet conditions after a first 24 h storage in dry conditions (DW). Three-point bending tests were performed to measure the flexural modulus. The samples were then subjected to a sorption/desorption protocol. While the matrix alone did not undergo any mechanical degradation with exposure time, the composites matrices presented a decrease in elastic modulus. This decrease was the highest for the matrix with nonsilanized fillers. Interestingly, the DW condition was detrimental for all the samples. Regarding the sample with nonsilanized fillers in DW for 1 month presented an elastic modulus lower than the matrix alone. These results were assigned to the sorption capacity of the polymer matrix, suggesting that the diffusion mechanisms and the nature of water molecules are determinant in the composite degradation. This study showed that dental composite early degradation mechanisms after water exposure are involved in the polymer matrix postpolymerization process as soon as after 24 h. Such mechanisms are detrimental in terms of the dental composite efficiency and have to be understood.

Objective Thermocycling is widely used to age dental composites but with very different results from one study to another, even with apparent similar conditions. This study aims at understanding better the relative damaging speed of matrix and fillers, based on theoretical models. Methods Eight formulations of an experimental dental material were produced. The same organic matrix was used and silanated barium glass particles were added as fillers with different filler ratios. Samples were thermocycled up to 10 000 cycles. Three-point bending tests were carried out at different steps. The yield stress was measured among other mechanical properties. Results Composite properties were degraded by thermocycling. The decrease was slight during the first 5 000 cycles whereas it decreased significantly after 10 000 cycles. The Turcsanyi model asserts that the interface yield stress is slightly affected in the first 5 000 cycles and then falls down, while the decrease of matrix yield stress is linear. Significance Each component of a composite does not age at the same rate. First, the matrix acts as a protector until the water finds its way to the interphase. The filler silanization treatment is highly sensitive to hydrolysis and is damaged rapidly from that moment. Numerical simulations and surface observations confirmed that cracks appear to propagate in the neighbourhood of the interface but not directly within it.

With modern-day technical advances, high sagittal oblique osteotomy (HSOO) of the mandible was recently described as an alternative to bilateral sagittal split osteotomy for the correction of mandibular skeletal deformities. However, neither in vitro nor numerical biomechanical assessments have evaluated the performance of fixation methods in HSOO. The aim of this study was to compare the biomechanical characteristics and stress distribution in bone and osteosynthesis fixations when using different designs and placing configurations, in order to determine a favourable plating method. We established two finite element models of HSOO with advancement (T1) and set-back (T2) movements of the mandible. Six different configurations of fixation of the ramus, progressively loaded by a constant force, were assessed for each model. The von Mises stress distribution in fixations and in bone, and bony segment displacement, were analysed. The lowest mechanical stresses and minimal gradient of displacement between the proximal and distal bony segments were detected in the combined one-third anterior- and posterior-positioned double mini-plate T1 and T2 models. This suggests that the appropriate method to correct mandibular deformities in HSOO surgery is with use of double mini-plates positioned in the anterior one-third and posterior one-third between the bony segments of the ramus.

This study addresses the feasibility of underactuated arm exoskeletons as an alternative solution to the often bulky and heavy exoskeletons which actuate the shoulder with 3 DoF. Specifically, the study investigates how the wrist and elbow joint adapts their kinematics when the shoulder abduction is constrained. Ten healthy participants conducted three different grasping activities of daily living, during natural motion and during constrained shoulder abduction at two fixed angles: the resting position angle and at an angle of 10 ° abduction from the resting position. Motion capture data was collected and used as input for a musculoskeletal computer model adapted to this study. Statistical parametric mapping tools were employed to analyze the joint angles estimated by the model. The results show significant differences within the joint angles when the shoulder abduction is constrained. The wrist flexion angle deviated up to 13.6 ° and the elbow pronation angle decreased by 8.7 ° on average throughout the movement compared to the natural motion during restricted shoulder abduction motion. Thus, the shoulder could be underactuated and the participants could still accomplish the activities of daily living with changes in the wrist and elbow joint kinematic angles.

Introduction This study aims at identifying mechanical characteristics under bi-axial loading conditions of extracted swine pia mater (PM) and dura and arachnoid complex (DAC). Methods 59 porcine spinal samples have been tested on a bi-axial experimental device with a pre-load of 0.01 N and a displacement rate of 0.05 mm.s−1. Post-processing analysis included an elastic modulus, as well as constitutive model identification for Ogden model, reduced Gasser Ogden Holzapfel (GOH) model, anisotropic GOH model, transverse isotropic and anisotropic Gasser models as well as a Mooney-Rivlin model including fiber strengthening for PM. Additionally, micro-structure of the tissue was investigated using a bi-photon microscopy. Results Linear elastic moduli of 108±40 MPa were found for DAC longitudinal direction, 53±32 MPa for DAC circumferential direction, with a significant difference between directions (p Statement of Significance This study is the first to present biaxial tensile test of pia mater as well as constitutive model comparisons for dura and arachnoid complex tissue based on such tests. Collagen structures observed by semi-quantitative analysis of two photon microscopy confirmed the use of anisotropic Gasser model for pia mater and existence of fenestration. While clear identification of fibre population was not possible in DAC, results from anisotropic Gasser model depicted better fitting on experimental data as per this protocol. Bi-axial mechanical testing allows quasi-static characterization under conditions closr to the physiological context and the results presented could be used for further simulations of physiology. Indeed, the inclusion of meningeal tissue in finite element models will allow more accurate and reliable numerical simulations.

Objective: The Evaluation of Clinical Practice (ECP) conducted with a sample of French general dental practitioners aimed to measure the methods used to diagnose and manage bruxism. Methods: The ECP was performed using a declarative online questionnaire-based anonymous survey (SurveyMonkey) of 1388 practitioners. Twenty-two questions were grouped in 5 categories: (1) Sociodemographic characteristics (Q1-6); (2) Knowledge of the prevalence and definition of bruxism (Q7-9); (3) Diagnostic approach (Q10-11) and management (Q12-Q13); (4) The use of occlusal splints (Q14-21); (5) Oral rehabilitation (Q22). Results: The answers obtained (233; 16.8%) revealed a wide disparity and insufficient diagnosis (e.g. only 41% looked for sleep disorders, 22.3% for consumption of stimulants, 3% for upper airway obstruction) and management of bruxism (e.g. only 21.9% of participants proposed cognitive-behavioral therapy). Discussion: The discrepancies detected, such as the use of inappropriate splints (30 to 70%), emphasize the need for more prompt research-to-practice transfer of new knowledge.

The ideal artificial heart valve does not exist yet. Understanding of mechanical and structural properties of natural tissues is necessary to improve the design of biomimetic aortic valve. Besides these properties are needed for the finite element modeling as input parameters. In this study we propose a new method combining biaxial tests and digital image correlation. These tests are carried out on porcine aortic valves. In this work, we use a modified version of the HGO (Holzapfel-Gasser-Ogden) model which is classically used for hyper-elastic and anisotropic soft tissues. This model can include fiber orientation. The identification of HGO model parameters can be determined using experimental data and two different protocols. One protocol is based on the identification of collagen fibers orientation as well as the mechanical parameters. The second one, is based on a complementary experiment to determine orientation (confocal laser scanning microscope). Both lead to determine different sets of material parameters. We show that the model is more likely to reproduce the actual mechanical behavior of the heart valves in the second case and that a minimum of three different loading conditions for the biaxial tensile tests is required to obtain a relevant set of parameters.

Dental decays are one of the most widespread surgeries over the world. But half of the operation’s deals with the repair of a former restoration instead of curing an original decay. To reduce this ...

A composite dental restoration is facing an aggressive environment which may damage the material in vivo. Water thermocycling is frequently used to simulate the ageing of a composite, but its effec...

Objective A costly advantageous approach in composites development process is to limit experimental tests by predicting mechanical properties with respect to their filler ratio. Models exist for other fields than dentistry. They have been compared to 3-point bending test experimental results for yield stress, flexural modulus and flexural strength. Methods Five formulations of the same experimental material were made. They were composed of an organic matrix and different ratios of silanated barium glass particles. The samples were stored in distilled water for 24 h at 37 °C prior to the 3-point bending test. The Turcsanyi model for yield stress was notably investigated, and SEM was used to complete data analysis. Results The yield stress showed reproducible results and a good fit with Turcsanyi model with respect to filler ratio. The flexural modulus data are not scattered but did not fit with the existing models. No trend could emerge for flexural strength and strain because of scattering; these properties are more unpredictable. The SEM observations of fracture areas confirm a good matrix-filler interface quality. Significance SEM pictures validated the numerical parameter obtained from Turcsanyi model. The latter therefore seems to be applicable to dental composites. Firstly, it enables to predict the evolution of the material yield stress without testing all filler ratios. Secondly, this model provides a good way to get micro-information on the matrix-filler interface from macroscopic tests. The discrepancy between flexural modulus results and theory highlighted the necessity to include an “interface quality” parameter in accurate predictive models.

Resume Objectif Determiner une loi de comportement mecanique du placenta afin de l’implementer dans les simulateurs numeriques d’accidents de la route. Patientes et methodes Etude experimentale d’indentation de 80 placentas apres delivrance de femmes enceintes francaises. Utilisation de la methode mathematique d’analyse inverse apres modelisation numerique de l’experience. Optimisation des parametres de la loi obtenue grâce aux donnees experimentales. Resultats Loi d’Ogden type Hyper-Visco-Elastique optimisee pour le placenta par les parametres μ1 = 0,0001881 Mpa, μ2 = −0,000240 Mpa, μ3 = μ4 = 0 Mpa et α1 = 2, α2 = −8, α3 = α4 = 0 en condition quasi statique. Discussion et conclusion La loi obtenue approche plus precisement le comportement mecanique du placenta que les precedentes etudes et pourrait etre utilisee dans les recherches virtuelles de lesions placentaires dans les accidents de la route.

The finite element method is a numerical modeling tool used in various fields in medicine and surgery such as orthopedics, traumatology, and cardiovascular surgery. But this tool also has several applications in maxillofacial surgery. We present the advantages of this method by describing its principles as well as the various fields of application in maxillofacial surgery. This article was intended to help novices understand the results of various studies using this method.

In the water and gas distribution industry, electrofusion is one of the main techniques used for welding polyethylene pipes. In order to help understanding the origin of some defects discovered recently and to optimize and predict the welding quality, we developed a coupled numerical and experimental approach. Our numerical model, that computes a weld quality index based on molecular interdiffusion, is able to reasonably well predict whether welding will occur or not depending on the welding conditions imposed.

International audience; The use of numerical simulation to investigate heart and valvular mechanics is becoming increasingly popular. In particular, finite element analysis is often used to support the operation planning procedure as well as the design of new prostheses with mechanical properties as close as possible to those of natural tissues and an even better biocompatibility. With one of the highest prevalence of cardiovascular degenerative diseases [1], aortic valves (AV) have been widely studied during the last decades.The elastic [2] and time-dependent [3] behaviors of the AV leaflets under physiological biaxial loading states have been previously investigated in the literature over a wide range of loading conditions.. As most soft tissues, AV has an oriented network of collagen fibers embedded in an elastin matrix, which is responsible for their hyperelastic and anisotropic behaviors. Accordingly, non-linear transverse isotropic constitutive equations are often used assuming a macroscopically-identifiable preferred fiber direction.In this study a new method is proposed in order to estimate relevant material and structural properties of AV while reducing at the same time the number of complex and time-consuming experiments. An inverse analysis procedure based on the finite element computation of planar biaxial tensile tests was used to set-up a reduced protocol. This protocol was then experimentally reproduced to identify real material parameters. The obtained material parameters will be later used to model heart valve tissues.

CARS 2005: Computer Assisted Radiology and Surgery; International audience; For the "wet" form of the macular degeneration, macular translocation is a promising treatment modality that offers patients a chance to improve their vision. This involves moving the macula so that the retina lies over a healthier part of the choroid layer beneath it. The aim of this work was to develop a numerical model able to predict this relative displacement between the retina and the choroid as a function of the initial fold depth.

International audience; Trauma during pregnancy especially occurring during car crashes leads to many foetal losses. Numerical modelling is widely used in car occupant safety issue and injury mechanisms analysis and is particularly adapted to the pregnant woman. Material modelling of the gravid uterus tissues is crucial for injury risk evaluation especially for the abruption placentae which is widely assumed as the leading cause of foetal loss. Experimental studies on placenta behaviour in tension are reported in the literature, but none in compression to the authors' knowledge. This lack of data is addressed in this study. To complement the already available experimental literature data on the placenta mechanical behaviour and characterise it in a compression loading condition, 80 indentation tests on fresh placentae are presented. Hyperelastic like mean experimental stress versus strain and corridors are exposed. The results of the experimental placenta indentations compared with the tensile literature results tend to show a quasi-symmetrical behaviour of the tissue. An inverse analysis using simple finite element models has permitted to propose parameters for an Ogden material model for the placenta which exhibits a realistic behaviour in both tension and compression.

International audience

International audience; The aim of this study was to predict stress modification in the temporomandibular joint (TMJ) after symphyseal distraction (SD). The study was performed using three-dimensional finite element analysis using a complete mastication model. Geometric data were obtained from MRI and CT scans of a healthy male patient and each component was meshed as various regions. The distraction was performed with a 10 mm expansion after simulation of a surgical vertical osteotomy line on the model in the mandibular midline region. The geometry and mesh of the bone callus were constructed. The bone callus was modelled as a strengthened region characterized by a Young's modulus corresponding to consolidated bone to predict the long-term biomechanical effect of SD. Boundary conditions for jaw closing simulations were represented by different jaw muscle load directions. The von Mises stress distributions in both joint discs and condyles during closing conditions were analysed and compared before and after SD. Stress distribution was similar in discs and on condylar surfaces in the pre- and post-distraction models. The outcomes of this study suggest that anatomical changes in TMJ structures should not predispose to long-term tissue fatigue and demonstrate the absence of clinical permanent TMJ symptoms after SD. © 2012 International Association of Oral and Maxillofacial Surgeons.

International audience; Purpose: This study aims at analysing the stresses distribution in the temporomandibular joint (TMJ) using a complete high-resolution finite element model (FE Model). This model is used here to analyse the stresses distribution in the discs during a closing jaw cycle. In the end, this model enables the prediction of the stress evolution in the TMJ disc submitted to various loadings induced by mandibular trauma, surgery or parafunction. Materials and methods: The geometric data for the model were obtained from MRI and CT scans images of a healthy male patient. Surface and volume meshes were successively obtained using a 3D image segmentation software (AMIRA®). Bone components of skull and mandible, both of joint discs, temporomandibular capsules and ligaments and dental arches were meshed as separate bodies. The volume meshes were transferred to the FE analysis software (FORGE®). Material properties were assigned for each region. Boundary conditions for closing jaw simulations were represented by different load directions of jaws muscles. The von Mises stresses distribution in both joint discs during closing conditions was analyzed. Results: The pattern of von Mises stresses in the TMJ discs is non-symmetric and changed continuously during jaw movement. Maximal stress is reached on the surface disc in areas in contact with others bodies. Conclusions: The three-dimension finite element model of masticatory system will make it possible to simulate different conditions that appear to be important in the cascade of events leading to joint damage

International audience; Development of a numerical model applicable to clinical practice, and in particular oral implantology, requires knowledge of the mechanical properties of mandibular bone. The wide range of mechanical parameters found in the literature prompted us to develop an inverse analysis method that takes into account the exact geometry of each specimen tested, regardless of its shape. The Young's modulus of 3000. MPa we determined for mandibular bone using this approach is lower than the values reported in the literature. This difference can be explained by numerous experimental factors, related in particular to the bone specimens used. However, the main reason is that, unlike most previously published papers on the subject, the heterogeneity of bone led us to select a specimen size at the upper end of the scale, close to clinical reality.

International audience; Thin membranes subject to multiaxial loadings may exhibit wrinkling phenomena. Modelling this phenomenon can be interesting if one wants to understand the origin of wrinkling and optimise the design of the membrane in order to avoid such kind of defect. The work, presented here aims at predicting wrinkling phenomena in thin hyperelastic membranes undergoing large deformation due to multiaxial loadings -using a finite element modelling tool for 3-D configurations. The constitutive equations used for modelling the membrane behaviour are hyperelastic models (the neo-Hookean model, the Mooney-Rivlin one and a third one with a higher degree of non-linearity). They have been implemented in a finite element code developed in our laboratory FORGE2005®, which is based on a mixed pressure-velocity formulation. The software is then applied to the deformation of a hyperelastic spherical form undergoing internal pressure. We show that the ability of tetrahedral elements to correctly predict wrinkling phenomena strongly depends on the various numerical parameters used (load increment, pressure ratio, mesh size, number of elements ...)

International audience

International audience; New surgical techniques require fine control from the surgeon's point of view. Until recently, the necessary experience was only obtainable through traditional training protocols (using cadavers, animals, etc.). However, numerous training simulators have now been developed for use in this area. We present a new approach based on a three-dimensional finite element software and on different kinds of linear and nonlinear elastic constitutive equations that is able to predict realistic results. To classify these equations in terms of accuracy, we performed ex-vivo experimental measurements on lamb kidneys. The software has been applied to soft tissue deformation, namely lamb kidney and human uterus, and the numerical results have been compared to experimental ones.

International audience; Computer simulations of minimal invasive procedures have been developed for surgery planning or training or for the evaluation of surgical procedure. In order to perform realistic and precise simulations of surgery on soft tissue, one key step consists in introducing accurate tissue-specific mechanical parameters. The goal of this work was to transfer an indentation procedure from the laboratory to the operating room using a new portable indentation device. The numerical simulations with 3D finite element software of the experiments allowed us to identify the characteristic rheological properties which minimize the gap between computed end measured physical quantities. The next step will be to extend this procedure to pathologic uterus and to other solid organs.

We present a new approach for identification of the material electromagnetic parameters that are involved in electrothermal process simulations. We use inverse analysis techniques coupled with an induction heating finite-element model (FEM) and software developed in our laboratory. We describe here the direct induction heating FEM, the physical formulations, and the iterative identification procedure, and then present numerical tests and results.

Distraction osteogenesis (DO) is a surgical process used to reconstruct skeletal deformities and lengthen bones of the body. A corticotomy is used to fracture the bone into two segments which are gradually moved apart during the distraction phase, allowing new bone to form in the gap. When the targeted length is reached, a consolidation phase follows in which the bone is allowed to keep healing. Early results in humans indicated that the process can be applied in maxillofacial surgery. But it is of prime importance that bone movements be carefully planned before a device is implanted, especially in the area of the temporomandibular joint (TMJ) which may be at the origin of chronic pain. Finite element (FE) analysis has been proven to be a suitable tool for approximating the distribution of loads in such structures. Several models of TMJ are already available in literature. But most of them considered symmetrical movements of the mandible and did not account for the asymmetry of both joints. The aim of this work was to propose a high resolution 3D FE model of the masticatory system that enables the investigation of stress distribution in the TMJ disks before, during and after distraction.

As tooth decays are the most widespread pathologies, dental restoration is a global public health problem. Manufacturers of dental composite resins must therefore offer increasingly high performance and lasting materials while meeting health recommendations. The development process is costly but could be improved by a better understanding of their mechanical behaviour and the development of theoretical and numerical predictive models for their properties. In this work, an experimental material is tested before and after accelerated ageing protocols (thermocycling). A detailed experimental protocol has been established so that the results are reproducible and comparable between them. Predictive models of the yield stress and the elastic modulus, initially proposed for other applications, are compared with experimental results and then adapted to the specificities of dental composites, with high filler ratios. The use of a numerical model of a composite material also makes it possible to enrich the experimental database by playing for instance on the modulus of the the components, without having to produce the materials. Despite some limits of this innovative approach, the comparison of experimental, theoretical and numerical results give promising outlooks. They allow to predict essential characteristics of composites in an easier way and to make direct links between macroscopic and microscopic properties. Finally the understanding of the ageing mechanisms was improved.; Les lésions carieuses étant les pathologies les plus répandues, la restauration des tissus lésés est un problème de santé publique mondial. Les fabricants de résines composites de restauration se doivent donc de proposer des matériaux toujours plus performants et durables tout en répondant aux recommandations sanitaires. Ce processus de développement est coûteux et pourrait être amélioré par une meilleure compréhension de leur comportement mécanique et par l’élaboration de modèles théoriques et numériques prédictifs de leurs propriétés. Dans cette thèse, un matériau expérimental est testé avant et après des protocoles de vieillissement accéléré (thermocyclage). Un protocole expérimental détaillé a été établi pour que les résultats soient reproductibles et comparables entre eux. Des modèles prédictifs de la limite élastique et du module élastique, initialement proposés pour d’autres applications, sont confrontés aux résultats de campagnes expérimentales puis adaptés aux spécificités des composites dentaires, fortement chargés. Le recours à un modèle numérique de composite permet en outre d’enrichir la base de données expérimentale en jouant par exemple sur les modules des constituants, sans avoir à produire réellement les matériaux. Malgré certaines limitations de cette approche innovante, la confrontation des résultats expérimentaux, théoriques et numériques offre des perspectives très encourageantes. Ils permettent notamment de prédire plus simplement des caractéristiques essentielles des composites, d’effectuer des liens directs entre des propriétés macroscopiques et microscopiques, et d’améliorer la compréhension des mécanismes de vieillissement de ces matériaux.

This PhD thesis aims to develop experimental and numerical tools for the mechanical characterization and the numerical modeling of natural or artificial aortic valve tissues. These tools are intended to be used for the development of new biomimetic polymeric implants. Nowadays, almost 300 000 prosthetic valves are implanted every year worldwide. Two families of prosthetic valves are currently available~: mechanical and biological prostheses. However, both solutions suffer from major drawbacks. In this context, polymeric prostheses represent a promising alternative but currently suffer from insufficient material properties to be suitable for a long--lasting implantation. In this work, an experimental protocol using biaxial tensile tests together with full--field surface measurement and confocal microscopy is proposed. Since numerical simulation is intended to assist the design phase of new implants by predicting their mechanical behavior, a structure and a fluid solver are developed and coupled. Using experimental results, implemented constitutive models are calibrated through an inverse analysis procedure.; L’objectif de cette thèse de doctorat est de développer des outils expérimentaux et numériques pour la caractérisation mécanique et la modélisation des tissus, naturels ou artificiels, de valve aortique. Ces outils sont destinés à être utilisés pour l'élaboration de nouveaux implants biomimétiques en matériaux polymères. Chaque année, près de 300 000 prothèses de valves sont implantées à travers le monde. Ces implants peuvent être de deux types~: mécaniques ou biologiques. Les deux solutions souffrent cependant d'inconvénients majeurs. Dans ce contexte, les prothèses en matériaux polymères représentent une alternative prometteuse même si elles ne disposent pas encore de propriétés mécaniques suffisantes. Dans ce travail, un protocole expérimental combinant essais de traction biaxiale, mesure de champs et microscopie confocale est proposé. La mise au point de nouveaux implants peut aussi largement bénéficier de la modélisation numérique afin d'étudier leur comportement mécanique. Ainsi, un solveur structure et un solveur fluide ont été implémentés et couplés. À partir des résultats expérimentaux, les modèles de comportements ont été calibrés en utilisant une procédure d'analyse inverse.

This PhD thesis aims to develop experimental and numerical tools for the mechanical characterization and the numerical modeling of natural or artificial aortic valve tissues. These tools are intended to be used for the development of new biomimetic polymeric implants. Nowadays, almost 300 000 prosthetic valves are implanted every year worldwide. Two families of prosthetic valves are currently available~: mechanical and biological prostheses. However, both solutions suffer from major drawbacks. In this context, polymeric prostheses represent a promising alternative but currently suffer from insufficient material properties to be suitable for a long--lasting implantation. In this work, an experimental protocol using biaxial tensile tests together with full--field surface measurement and confocal microscopy is proposed. Since numerical simulation is intended to assist the design phase of new implants by predicting their mechanical behavior, a structure and a fluid solver are developed and coupled. Using experimental results, implemented constitutive models are calibrated through an inverse analysis procedure.; L’objectif de cette thèse de doctorat est de développer des outils expérimentaux et numériques pour la caractérisation mécanique et la modélisation des tissus, naturels ou artificiels, de valve aortique. Ces outils sont destinés à être utilisés pour l'élaboration de nouveaux implants biomimétiques en matériaux polymères. Chaque année, près de 300 000 prothèses de valves sont implantées à travers le monde. Ces implants peuvent être de deux types~: mécaniques ou biologiques. Les deux solutions souffrent cependant d'inconvénients majeurs. Dans ce contexte, les prothèses en matériaux polymères représentent une alternative prometteuse même si elles ne disposent pas encore de propriétés mécaniques suffisantes. Dans ce travail, un protocole expérimental combinant essais de traction biaxiale, mesure de champs et microscopie confocale est proposé. La mise au point de nouveaux implants peut aussi largement bénéficier de la modélisation numérique afin d'étudier leur comportement mécanique. Ainsi, un solveur structure et un solveur fluide ont été implémentés et couplés. À partir des résultats expérimentaux, les modèles de comportements ont été calibrés en utilisant une procédure d'analyse inverse.

The Electrofusion welding process is widely used to join polyethylene components in gas distribution networks. Even trusty as a technique, the field feedback points out some divergences whose influence on the long term performance of the weld. One of the well-known consequences of these divergences is the “sticking” (aka “cold weld”) that is the result of an uncompleted or even inexistent interdiffusion of the macromolecules of the materials to join. Most numerical simulations are two-dimensional whereas the process is usually three-dimensional both in terms of heat transfer and mechanical aspects. The main objective of the work was to develop a 3D finite element model and to validate it by comparing to a real situation the temperature evolution and the thermally affected areas in a simple planar welding geometry with the same dimensional characteristics as a real fitting chosen to make easier the instrumentation. The numerical model takes into account the fitting parameters such as polyethylene thermal and mechanical properties (i.e. melting and crystallization kinetics, phase transition, thermal expansion) and the electrical and geometrical settings. It computes a criterion based on the macromolecular interdiffusion theory able to determine whether a good welding occurred or not at the end of the welding cycle. The computed results (temperature, melted and cold areas and fracture surfaces) were compared with experimental data and gave very good agreement in terms of temperature, liquid phase fraction distribution and fracture surfaces. Finally the numerical model and the experimental process were used to study the influence of welding conditions on the weld itself and to study the welding of complex geometries such as the industrial fittings.; Le soudage par électrofusion est la technique majoritairement utilisée pour assembler les tubes et les accessoires en polyéthylène utilisés sur le réseau gazier. Ses très bons résultats initiaux ont été ternis ces dernières années par un certain nombre de dysfonctionnements relevés tant sur le terrain qu'en laboratoire. Ils se traduisent par des soudures de qualité médiocre du fait de la présence de zones de très faible cohésion. L'objectif de ce travail est de développer des outils experts tant expérimentaux que numériques permettant d'optimiser les conditions de soudage par électrofusion. L'originalité de notre étude a été de développer un modèle éléments finis tridimensionnel prenant en compte les différents mécanismes et phénomènes physiques sous-jacents, responsables de la formation de la soudure. Le modèle permet de calculer le taux de transformation de la matière, de prendre en compte les enthalpies de fusion et de cristallisation, de calculer le taux d'interdiffusion des macromolécules à l'interface entre les différents corps à souder pour finalement prédire la qualité de la soudure en fonction des conditions de chauffage imposées. Pour valider le modèle numérique, tout en facilitant l'accès aux grandeurs expérimentales, nous avons conçu et réalisé un dispositif expérimental se présentant sous la forme d'une géométrie relativement simple et plane mais respectant les caractéristiques d'un accessoire réel. La confrontation entre résultats numériques et expérimentaux a permis de démontrer les capacités du modèle numérique à reproduire fidèlement la réalité. Les différents outils ont alors été utilisés pour étudier l'influence des conditions de soudage sur la soudure et pour étudier le soudage de géométries plus complexes telles que celles rencontrées dans les pièces industrielles.

The Electrofusion welding process is widely used to join polyethylene components in gas distribution networks. Even trusty as a technique, the field feedback points out some divergences whose influence on the long term performance of the weld. One of the well-known consequences of these divergences is the “sticking” (aka “cold weld”) that is the result of an uncompleted or even inexistent interdiffusion of the macromolecules of the materials to join. Most numerical simulations are two-dimensional whereas the process is usually three-dimensional both in terms of heat transfer and mechanical aspects. The main objective of the work was to develop a 3D finite element model and to validate it by comparing to a real situation the temperature evolution and the thermally affected areas in a simple planar welding geometry with the same dimensional characteristics as a real fitting chosen to make easier the instrumentation. The numerical model takes into account the fitting parameters such as polyethylene thermal and mechanical properties (i.e. melting and crystallization kinetics, phase transition, thermal expansion) and the electrical and geometrical settings. It computes a criterion based on the macromolecular interdiffusion theory able to determine whether a good welding occurred or not at the end of the welding cycle. The computed results (temperature, melted and cold areas and fracture surfaces) were compared with experimental data and gave very good agreement in terms of temperature, liquid phase fraction distribution and fracture surfaces. Finally the numerical model and the experimental process were used to study the influence of welding conditions on the weld itself and to study the welding of complex geometries such as the industrial fittings.; Le soudage par électrofusion est la technique majoritairement utilisée pour assembler les tubes et les accessoires en polyéthylène utilisés sur le réseau gazier. Ses très bons résultats initiaux ont été ternis ces dernières années par un certain nombre de dysfonctionnements relevés tant sur le terrain qu'en laboratoire. Ils se traduisent par des soudures de qualité médiocre du fait de la présence de zones de très faible cohésion. L'objectif de ce travail est de développer des outils experts tant expérimentaux que numériques permettant d'optimiser les conditions de soudage par électrofusion. L'originalité de notre étude a été de développer un modèle éléments finis tridimensionnel prenant en compte les différents mécanismes et phénomènes physiques sous-jacents, responsables de la formation de la soudure. Le modèle permet de calculer le taux de transformation de la matière, de prendre en compte les enthalpies de fusion et de cristallisation, de calculer le taux d'interdiffusion des macromolécules à l'interface entre les différents corps à souder pour finalement prédire la qualité de la soudure en fonction des conditions de chauffage imposées. Pour valider le modèle numérique, tout en facilitant l'accès aux grandeurs expérimentales, nous avons conçu et réalisé un dispositif expérimental se présentant sous la forme d'une géométrie relativement simple et plane mais respectant les caractéristiques d'un accessoire réel. La confrontation entre résultats numériques et expérimentaux a permis de démontrer les capacités du modèle numérique à reproduire fidèlement la réalité. Les différents outils ont alors été utilisés pour étudier l'influence des conditions de soudage sur la soudure et pour étudier le soudage de géométries plus complexes telles que celles rencontrées dans les pièces industrielles.

Mandibular surgery such as distraction osteogenesis can generate anatomical modifications in the temporomandibular joint (TMJ) discs. The resulting stress modifications can be at the origin of a temporary or permanent disc dislocation with degeneration and may cause severe oral and facial pain or masticatory dysfunctions. The aim of this work was to predict stress modification in the temporomandibular joint (TMJ) after mandibular symphyseal distraction (SD). This surgical procedure is used to resolve dental crowding on the mandibular dental arch.In order to study the potential impact of such a surgery on TMJ discs a three-dimensional finite element analysis of a complete mastication model was performed. Geometric data were obtained from MRI and CT scans of a healthy male patient and each component was meshed individually. The distraction was performed on the model with a 10 mm expansion after simulation of a surgical vertical osteotomy line in the mandibular midline region. The geometry and mesh of the bone callus were generated. The bone callus was modeled as a strengthened region characterized by a Young's modulus corresponding to consolidated bone to predict the long-term biomechanical effect of SD. Boundary conditions for jaw closing simulations were represented by different jaw muscle load directions. The von Mises stress distributions in both joint discs and condyles during closing conditions were analyzed and compared before and after SD. Contrary to usual analyses, no symmetry was used, and the whole mandible was analyzed in order to exhibit potential asymmetries. Stress distribution was similar in discs and on condylar surfaces in the pre- and post-distraction models. The outcomes of this study suggest that anatomical changes in TMJ structures should not predispose to long-term tissue fatigue and demonstrate the absence of clinical permanent TMJ symptoms after SD.; Les chirurgies de l'os mandibulaire peuvent modifier la position anatomique des disques et des condyles de l'articulation temporo-mandibulaire (ATM). Les modifications de contraintes qui en résultent peuvent être à l'origine d'une dislocation temporaire ou permanente du disque et peuvent provoquer des dysfonctionnements s'exprimant par des douleurs buccales et faciales. L'objectif de ce travail était de prévoir les modifications de contraintes dans l'articulation temporo-mandibulaire (ATM) après un protocole de distraction symphysaire mandibulaire (DS). Ce traitement chirurgical sert à traiter les encombrements dentaires de la mandibule.De manière à étudier l'impact d'une telle intervention au niveau de l'ATM, nous avons fait le choix de réaliser un modèle d'approche numérique de mastication par éléments finis. Les données géométriques ont été obtenues à partir de l'imagerie scanner et IRM d'un patient dont les composants de l'ATM ont été maillés. La chirurgie de distraction symphysaire a été réalisée sur le modèle avec un élargissement de 10 mm dans la région médiane de la mandibule. La géométrie et le maillage du cal osseux ont été reconstruits. Le cal osseux a été caractérisé par un module d'élasticité correspondant à l'os consolidé pour prédire l'effet biomécanique à long terme de la DS. Pour simuler une fermeture de la mâchoire, les conditions aux limites ont été appliquées au modèle sous la forme de vecteurs de force. Les champs de contraintes de von Mises dans les deux disques et condyles ont été analysés et comparés avant et après la DS. Contrairement aux approches habituellement menées, le modèle proposé est complet et ne contient pas de symétrie, de manière à mettre en évidence d'éventuelles asymétries dans la répartition des contraintes. La répartition des contraintes était proche dans les disques et sur les surfaces condyliennes dans les modèles avant et après distraction. Les résultats de cette étude suggèrent que les changements anatomiques des structures de l'ATM ne prédisposent pas à une fatigue des tissus. La DS n'exposerait donc pas au risque de dysfonction des ATM et de symptômes cliniques.

Mandibular surgery such as distraction osteogenesis can generate anatomical modifications in the temporomandibular joint (TMJ) discs. The resulting stress modifications can be at the origin of a temporary or permanent disc dislocation with degeneration and may cause severe oral and facial pain or masticatory dysfunctions. The aim of this work was to predict stress modification in the temporomandibular joint (TMJ) after mandibular symphyseal distraction (SD). This surgical procedure is used to resolve dental crowding on the mandibular dental arch.In order to study the potential impact of such a surgery on TMJ discs a three-dimensional finite element analysis of a complete mastication model was performed. Geometric data were obtained from MRI and CT scans of a healthy male patient and each component was meshed individually. The distraction was performed on the model with a 10 mm expansion after simulation of a surgical vertical osteotomy line in the mandibular midline region. The geometry and mesh of the bone callus were generated. The bone callus was modeled as a strengthened region characterized by a Young's modulus corresponding to consolidated bone to predict the long-term biomechanical effect of SD. Boundary conditions for jaw closing simulations were represented by different jaw muscle load directions. The von Mises stress distributions in both joint discs and condyles during closing conditions were analyzed and compared before and after SD. Contrary to usual analyses, no symmetry was used, and the whole mandible was analyzed in order to exhibit potential asymmetries. Stress distribution was similar in discs and on condylar surfaces in the pre- and post-distraction models. The outcomes of this study suggest that anatomical changes in TMJ structures should not predispose to long-term tissue fatigue and demonstrate the absence of clinical permanent TMJ symptoms after SD.; Les chirurgies de l'os mandibulaire peuvent modifier la position anatomique des disques et des condyles de l'articulation temporo-mandibulaire (ATM). Les modifications de contraintes qui en résultent peuvent être à l'origine d'une dislocation temporaire ou permanente du disque et peuvent provoquer des dysfonctionnements s'exprimant par des douleurs buccales et faciales. L'objectif de ce travail était de prévoir les modifications de contraintes dans l'articulation temporo-mandibulaire (ATM) après un protocole de distraction symphysaire mandibulaire (DS). Ce traitement chirurgical sert à traiter les encombrements dentaires de la mandibule.De manière à étudier l'impact d'une telle intervention au niveau de l'ATM, nous avons fait le choix de réaliser un modèle d'approche numérique de mastication par éléments finis. Les données géométriques ont été obtenues à partir de l'imagerie scanner et IRM d'un patient dont les composants de l'ATM ont été maillés. La chirurgie de distraction symphysaire a été réalisée sur le modèle avec un élargissement de 10 mm dans la région médiane de la mandibule. La géométrie et le maillage du cal osseux ont été reconstruits. Le cal osseux a été caractérisé par un module d'élasticité correspondant à l'os consolidé pour prédire l'effet biomécanique à long terme de la DS. Pour simuler une fermeture de la mâchoire, les conditions aux limites ont été appliquées au modèle sous la forme de vecteurs de force. Les champs de contraintes de von Mises dans les deux disques et condyles ont été analysés et comparés avant et après la DS. Contrairement aux approches habituellement menées, le modèle proposé est complet et ne contient pas de symétrie, de manière à mettre en évidence d'éventuelles asymétries dans la répartition des contraintes. La répartition des contraintes était proche dans les disques et sur les surfaces condyliennes dans les modèles avant et après distraction. Les résultats de cette étude suggèrent que les changements anatomiques des structures de l'ATM ne prédisposent pas à une fatigue des tissus. La DS n'exposerait donc pas au risque de dysfonction des ATM et de symptômes cliniques.

Software to simulate the mechanical behaviour of hyperelastic materials (representative of soft tissue), with at least two deformable bodies in large deformations has been developed. From a mechanical point of view, the breast implant which has been the object of our study is a complex structure composed primarily of two bodies: an envelope and a silicone gel. A literature review has allowed us to determine the appropriate methods to characterize the mechanical behaviour of each component according to its nature (solid or gel). From a numerical point of view, two hyperelastic models (Neo-Hookeen and Mooney-Rivlin) were selected on the basis of a literature review. They have been implemented in a finite element code developed CEMEF, based on a mixed formulation velocity-pressure. Hyperelastic models selected can not be included as such in their energy formulation. They must first be adapted to the specific formalism of constitutive laws. Numerical developments achieved were validated by comparing numerical solutions with analytical ones when they were available or experimental results. The code was then used to model the global behaviour of a prosthesis subjected to simple loadings such as a simple compression test or indentation, or solicitations which are more complex (fatigue test, modelling surgical operation). Buckling phenomena are likely to occur in certain conditions and materialize in the form of wrinkles. We conducted a comprehensive study on the modelling of this phenomenon, including by seeking numerical conditions it is necessary to respect (load increment, pressure ratio, quality and size of the mesh) to highlight in the case a thin membrane discretized with tetrahedral elements of type P1+/ P1.; Un logiciel permettant la simulation du comportement mécanique des matériaux hyperélastiques (représentatif des tissus mous), avec au moins deux corps déformables en grandes déformations a été développé. D’un point de vue mécanique, l’implant mammaire qui a fait l’objet de notre étude est une structure complexe composée principalement de deux corps : une enveloppe et un gel en silicone. Une étude bibliographique nous a permis de déterminer les méthodes adéquates pour caractériser le comportement mécanique de chaque constituant selon sa nature (gel ou solide). D’un point de vue numérique, deux modèles hyperélastiques (Néo-Hookéen et Mooney-Rivlin) ont été choisis sur la base d’une étude bibliographique. Ils ont été implémentés dans un code élément finis développé au CEMEF, basé sur une formulation mixte vitesse pression. Les modèles hyperélastiques choisis ne peuvent être intégrés tels quels sous leur formulation énergétique. Ils doivent être préalablement adaptés au formalisme spécifique des lois de comportement. Les développements numériques réalisés ont été validés en confrontant les résultats des calculs à des solutions analytiques lorsque celles-ci étaient disponibles ou à des résultats expérimentaux. Le code a ensuite été utilisé pour modéliser le comportement global d’une prothèse soumise à des sollicitations simples comme un essai de compression ou d’indentation, ou encore à des sollicitations plus complexes (essai de fatigue, modélisation de la pose de la prothèse). Des phénomènes de flambement sont susceptibles d’apparaître dans certaines conditions et se matérialisent sous la forme de plis. Nous avons réalisé une étude approfondie sur la modélisation de ce phénomène, en cherchant notamment les conditions numériques qu’il est nécessaire de respecter (pas de temps, différence de pression, qualité et taille du maillage) pour les mettre en évidence dans le cas d’une membrane fine discrétisée à l’aide d’éléments tétraédriques de type P1+/P1.

Software to simulate the mechanical behaviour of hyperelastic materials (representative of soft tissue), with at least two deformable bodies in large deformations has been developed. From a mechanical point of view, the breast implant which has been the object of our study is a complex structure composed primarily of two bodies: an envelope and a silicone gel. A literature review has allowed us to determine the appropriate methods to characterize the mechanical behaviour of each component according to its nature (solid or gel). From a numerical point of view, two hyperelastic models (Neo-Hookeen and Mooney-Rivlin) were selected on the basis of a literature review. They have been implemented in a finite element code developed CEMEF, based on a mixed formulation velocity-pressure. Hyperelastic models selected can not be included as such in their energy formulation. They must first be adapted to the specific formalism of constitutive laws. Numerical developments achieved were validated by comparing numerical solutions with analytical ones when they were available or experimental results. The code was then used to model the global behaviour of a prosthesis subjected to simple loadings such as a simple compression test or indentation, or solicitations which are more complex (fatigue test, modelling surgical operation). Buckling phenomena are likely to occur in certain conditions and materialize in the form of wrinkles. We conducted a comprehensive study on the modelling of this phenomenon, including by seeking numerical conditions it is necessary to respect (load increment, pressure ratio, quality and size of the mesh) to highlight in the case a thin membrane discretized with tetrahedral elements of type P1+/ P1.; Un logiciel permettant la simulation du comportement mécanique des matériaux hyperélastiques (représentatif des tissus mous), avec au moins deux corps déformables en grandes déformations a été développé. D’un point de vue mécanique, l’implant mammaire qui a fait l’objet de notre étude est une structure complexe composée principalement de deux corps : une enveloppe et un gel en silicone. Une étude bibliographique nous a permis de déterminer les méthodes adéquates pour caractériser le comportement mécanique de chaque constituant selon sa nature (gel ou solide). D’un point de vue numérique, deux modèles hyperélastiques (Néo-Hookéen et Mooney-Rivlin) ont été choisis sur la base d’une étude bibliographique. Ils ont été implémentés dans un code élément finis développé au CEMEF, basé sur une formulation mixte vitesse pression. Les modèles hyperélastiques choisis ne peuvent être intégrés tels quels sous leur formulation énergétique. Ils doivent être préalablement adaptés au formalisme spécifique des lois de comportement. Les développements numériques réalisés ont été validés en confrontant les résultats des calculs à des solutions analytiques lorsque celles-ci étaient disponibles ou à des résultats expérimentaux. Le code a ensuite été utilisé pour modéliser le comportement global d’une prothèse soumise à des sollicitations simples comme un essai de compression ou d’indentation, ou encore à des sollicitations plus complexes (essai de fatigue, modélisation de la pose de la prothèse). Des phénomènes de flambement sont susceptibles d’apparaître dans certaines conditions et se matérialisent sous la forme de plis. Nous avons réalisé une étude approfondie sur la modélisation de ce phénomène, en cherchant notamment les conditions numériques qu’il est nécessaire de respecter (pas de temps, différence de pression, qualité et taille du maillage) pour les mettre en évidence dans le cas d’une membrane fine discrétisée à l’aide d’éléments tétraédriques de type P1+/P1.

There is a growing need in surgical simulation, especially with the development of complex surgical methods. Nevertheless, surgical simulators must be accurate in order to be efficient. In this context, we have developed a software code, with the collaboration of the university hospital Archet II, based on a finite element method and using hyperelasticity constitutive equations, which are more suitable for describing large deformation of soft tissues. However, this software has led to numerical instabilities which have been eliminated using a visco-elastic model. The added viscosity component has been defined in order to avoid any modification of the elastic behaviour of the organs. This means that it must be low enough to be negligible comparing to the elastic behaviour but high enough to avoid or postpone instabilities. An inverse analysis procedure, for which mechanical tests have been developed, allowed us to identify the uterus and fallopian tube rheological parameters. The experimental data have been recorded just after hysterectomy has taken place in order to be as close as possible to the in-vivo conditions. Moreover, a numerical cutting method, based on the "kill element" one, allowed us to qualitatively simulate elementary gestures of a fallopian tube section: clamping to avoid any displacement and cutting.; Devant la complexité croissante des pratiques chirurgicales et les préoccupations éthiques et médico-légales, les simulateurs chirurgicaux ont su montrer a priori leur utilité. Mais pour être vraiment efficaces, ils doivent être précis. Nous nous sommes intéressés dans le cadre de cette thèse, menée en étroite collaboration avec le service de gynécologie obstétrique de l'hôpital L'archet II de Nice, au développement d'un logiciel de simulation d'opérations chirurgicales réaliste. Basé sur la méthode des éléments finis, il prend en compte des lois de comportement hyperélastiques, supposées être parmi les mieux adaptées pour décrire le comportement mécanique des tissus mous. Après avoir mis en évidence des instabilités numériques de notre code éléments finis du fait de l'utilisation de ces lois, nous nous sommes intéressés à un modèle visco-hyperélastique. Ne cherchant pas en première approximation à rendre compte du comportement visqueux des organes, la part visqueuse de la loi de comportement a été déterminée de façon à être suffisamment faible pour ne pas modifier le comportement global des tissus mais suffisamment grande pour éliminer les instabilités. Une méthodologie d'identification par analyse inverse qui a nécessité, outre la mise au point de notre code éléments finis, le développement d'essais mécaniques appropriés, a été appliquée à l'identification des paramètres rhéologiques d'un corps utérin et d'une trompe de Fallope. De façon à identifier le comportement des organes au plus près de qu'il est in vivo, les essais expérimentaux ont été réalisés juste après leur ablation, dans une salle contiguë au bloc opératoire. Le développement d'un module de découpe, basé sur la méthode du "kill-element" nous a par ailleurs permis de simuler une suite d'opérations chirurgicales élémentaires allant de la stabilisation des organes, à l'aide de pinces chirurgicales, à leur découpe à l'aide de ciseaux chirurgicaux, pour lesquels nous avons observé de bons résultats qualitatifs.