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Acute exposure to hand-arm transmitted vibrations (HAVs) may decrease the wall shear stress (WSS) exerted by the blood flow on the arterial endothelium. In the case of chronic exposure to HAVs, these WSS changes can lead to arterial growth and remodeling potentially induced by an intimal hyperplasia phenomenon. Accordingly, we implemented an agent-based model (ABM) that captures the hemodynamics-driven and mechanoregulated cellular mechanisms involved in vibration-induced intimal hyperplasia. Our ABM was combined with flow loop experiments that investigated the WSS-modulated secretion of the platelet-derived growth factor BB (PDGF-BB) by the endothelial cells. The ABM rules parameters were then identified and calibrated using our experimental findings and literature data. The model was able to replicate the basal state (no vibration) as well as predict a 30% stenosis resulting from a chronic drop of WSS values mimicking exposure to vibration during a timeframe of 10 years. The study of the influence of different WSS-modulated phenomena on the model showed that the magnitude of stenosis largely depends on the migratory effects of PDGF-BB and the mitogenic effects of Transforming Growth Factor [Formula: see text] on the Smooth Muscle Cells. The results also proved that the fall in circumferential stress due to arterial layer thickening to a great extent accounts for the degradation of the Extracellular Matrix in the media.

International audience; The aim of this work is to characterize the mechanical parameters governing the in-plane behavior of human skin and, in particular, of a keloid-scar. We consider 2D hyperelastic bi-material model of a keloid and the surrounding healthy skin. The problem of finding the optimal model parameters that minimize the misfit between the model observations and the in vivo experimental measurements is solved using our in-house developed inverse solver that is based on the FEniCS finite element computational platform. The paper focuses on the model parameter sensitivity quantification with respect to the experimental measurements, such as the displacement field and reaction force measurements. The developed tools quantify the significance of different measurements on different model parameters and, in turn, give insight into a given model's ability to capture experimental measurements. Finally, an apriori estimate for the model parameter sensitivity is proposed that is independent of the actual measurements and that is defined in the whole computational domain. This estimate is primarily useful for the design of experiments, specifically, in localizing the optimal displacement field measurement sites for the maximum impact on model parameter inference.

International audience; A sustained exposure to Hand-Arm transmitted-Vibration may cause various vascular pathologies such as the vibration-induced Raynaud’s Syndrome. This disorder is characterized at the tissue level by an arterial growth and remodelling potentially induced by an intimal hyperplasia phenomenon. The proliferation and migration of the Vascular Smooth Muscle Cells (VSMCs) are the keystone of this intimal hyperplasia phenomenon. Wall Shear Stress (WSS) alterations play a key role in inducing such mechanisms. Moreover, finger-transmitted-vibration is likely to be responsible for a WSS decrease (Noel and Settembre 2017). So, the aim of our work is to develop an Agent-Based Model (ABM) of the WSS-modulated arterial growth induced by finger-transmitted vibration. This study is intended for the agent-based migration model.

International audience; In this pre-study, we present the validation of CutiscanVR device on healthy flat skin and its relevant sensitivity to environmental conditions. A primary application on the earlobe is presented as well.

International audience; Keloids are pathologic scars, defined as fibroproliferative diseases resulting from abnormal wound responses, which grow beyond the original wound margins. They develop on specific pro-keloid anatomic sites frequently characterized by high stress states. The initiation and growth mechanisms of keloid are not well-understood. This study relates multimodal investigation of a keloid by using mechanicaltests in vivo and imaging techniques. A single case composed of a keloid, the healthy skin surrounding the keloid, and the contralateral healthy skin on the upper arms of a woman has been investigated in extension and suction by using non-invasive devices dedicated to in vivo skin measurement. The thickness and microstructure of these soft tissues have been observed by echography, tomography and confocal microscopy. Displacement fields have been obtained by using digital image correlation. Unlike healthy skin, keloid is not a well-defined multilayer structure : the frontier between epidermis and dermis disappears. The mechanical behavior of keloid is highly different from healthy skin one. The R-parameters have been deduced from suction curves. Physical parameters as tissue extensibility, initial and final tangent moduli have been identified from the stress-strain curves. The extensibility (respectively, initial rigidity) of keloid is highly lower (respectively, higher) than that of healthy skin. To compare the final rigidity of keloid versus healthy skin, further tests have to be performed with higher strain values.

This work presents a combination of finite element simulations of copper alloy thin sheet blanking and a wear algorithm based on Archard formulation for abrasive wear of the punch. Firstly, a tribometer has been specifically designed to measure wear coefficient, and punch worn profiles have been extracted by means of a double-print method. Secondly, the blanking process has been simulated through the finite element method by using an elasto-plastic constitutive model and the shear failure model. Thirdly, a wear algorithm has been programmed using experimental wear data and mechanical fields computed from blanking simulation. Then, a damage criterion, namely the shear failure model, has been calibrated by an original method based on stress triaxiality analysis and shear height value measured from blanked edge profile. Finally, punch wear predictions have been discussed and compared to experimental results.

International audience; Background/Purpose : This paper aims to present an ultra-light extensometer device dedicated to the mechanical characterization of the human skin in vivo.Methods : The device developed was conceived to be non invasive, to work with-out any stand and to perform various uniaxial tensile tests with either effort or displacement control. We also use specific guarding tabs to make in vivo extension tests analogous to traction tests.Results : Force displacement curves are derived from the data provided by the device's sensors. The latter are converted into stress strain curves thanks to complementary measurements of the skin thickness. We present typical experimental data and results that demonstrate the device ability to built stress strain curves characteristic of the human skin behavior. An additional imaging unit records a sequence of images of the solicited skin area for further calculations of the displacement fields by digital image correlation.Conclusion : The analysis of the displacement and deformation fields validates the guarding tab efficiency and the capacity of the device to characterize the mechanical behavior of the human skin in vivo.

International audience; Background/Purpose : The mechanical properties and behavior of the human skin in vivo are of medical importance, particularly to surgeons who have to consider the skin extension capabilities in the preparation of surgical acts. Variable data can be found in literature that result from diverse kinds of tests (in vivo, ex vivo, post-mortem) performed with different instruments.Methods : This paper presents the results of in vivo measurements performed on a cohort of 20 healthy volunteers with an ultralight homemade uniaxial extensometer. Different anatomical zones were explored under different directions of solicitation in order to document inter- and intra-individual variability as well as skin anisotropy.Results : The experimental data obtained are fitted with a phenomenological exponential model allowing the identification of three parameters characteristic of the tested skin behavior. These parameters can be related to the concept of skin extensibility used by surgeons.Conclusion : The inter- and intra-variability observed on that cohort confirms the need for a patient-specific approach based on the in vivo measurement of the mechanical behavior of the human skin of interest. Even the direction of higher skin stiffness is found to be individual dependent. The capability of the extensometer used in this study to fulfill such measurement needs is also demonstrated.

International audience; Laparoscopic sacrocolpopexy (LSC) is nowadays one of the most common surgery performed forpelvic organ prolapse. Hysterectomy can be associated with this procedure but few data exist about its utility. We aim to compare thebiomechanical efficacy of sacrocolpopexy with and without supra-cervical hysterectomy for pelvic organ prolapse using 3D finite element modeling so as to test the hypothesis that hysterectomy could improve stress and strain on pelvic organs and on apical supportingligaments.

Blanking burr and punch wear are two phenomena closely linked. This leads to consider burr as the best criterion for regrinding or renewing tools. Thus, in order to control the quality and cost in blanking process, it is necessary to measure with the best accuracy the amount of burr and wear punch. To do this, a method for measuring the volume of burr was developed. This method is based on the use of 3D topographical images. On the other hand, punch wear was calculated by combination of a mathematical model to the geometric shape of punch. This model gives the geometry variations of the punch, depending on the number of press storks. At the end, the aim of this study is to identify a relationship between burr and punch wear

Through the study presented here, we want to identify how the simulation of the blanking process could reduce defects of production, improve punches life and assist in the progression and control of the process. This was carried out with using software LS-DYNA. Based on the results obtained by simulation of blanking operation in two dimensions, we can predict the evolution of the gradual wear of active parts of punch according to the number of press strokes; by developing a calculation algorithm based on the Archard law of wear.

International audience; The V-Y advancement flap is a usual technique for the closure of skin defects. A triangular flap is incised adjacent to a skin defect of rectangular shape. As the flap is advanced to close the initial defect, two smaller defects in the shape of a parallelogram are formed with respect to a reflection symmetry. The height of the defects depends on the apex angle of the flap and the closure efforts are related to the defects height. Andrades et al. 2005 have performed a geometrical analysis of the V-Y flap technique in order to reach a compromise between the flap size and the defects width. However, the geometrical approach does not consider the mechanical properties of the skin. The present analysis based on the finite element method is proposed as a complement to the geometrical one. This analysis aims to highlight the major role of the skin elasticity for a full analysis of the V-Y advancement flap. Furthermore, the study of this technique shows that closing at the flap apex seems mechanically the most interesting step. Thus different strategies of defect closure at the flap apex stemming from surgeon’s know-how have been tested by numerical simulations.

International audience; In clinical practice, the V-Y advancement flap is a widely used technique to cover human skin defect, which consists in incising; advancing and suturing a triangular flap adjacent to the base of a rectangular defect (see Figure 1a). A previous geometrical study of the V-Y flap technique allowed us to find a good compromise between the flap size and the defect width [1]. However, the geometrical approach does not consider the mechanical properties of the human skin by assuming rigid-body behaviour of the skin. The aim of the present paper deals with a numerical analysis as a complement to the geometrical one to highlight the major role of the skin elasticity in the V-Y advancement flap. A compromise between the size of the flap and the level of the closure force value has been found when varying the angle at the flap apex, noted . The sensitivity to the mechanical parameters makes the closure force dependent on the size to be covered. At the end, the successive actions of the surgeon are analyzed.

National audience; Il apparaît souvent saugrenu aux mécaniciens que l'un des leurs s'intéresse au tégument humain. Pourtant, la connaissance du comportement et des réponses de ce tissu aux sollicitations extérieures est essentielle dans beaucoup de domaines et pas seulement celui des dermatologues qui à eux seuls constituent déjà un champ large d'intérêt pour développer, par exemple, des tissus de substitution aux propriétés voisines de celles du tissu cutané. Parmi ces domaines, je citerai quelques exemples où la mécanique flirte avec la biomécanique.

International audience; Background : The V–Y advancement flap and, more recently, the keystone flap are commonly used to cover skin defects. Both flaps allow for primary closure after advancement by substituting the initial defect for a narrower defect distributed over a greater length. The first objective of this study was to develop a geometrical analysis of the V–Y advancement flap. The second objective was to explain the benefit of using the keystone flap compared to a single V–Y advancement flap.Material and method : A geometrical analysis is proposed using a two-dimensional analysis in which the flaps are assumed to have a rigid-body behaviour. First, in the case of the V–Y advancement flap, a trigonometric relationship is defined between the distance of closure before and after advancement, thus implying the value of the flap's apex angle. Second, by considering the keystone flap as the association of three V–Y advancement flaps, the trigonometric relationship is applied to the keystone flap.Results : In the case of the V–Y advancement flap, the optimal apex angles are between 20° and 60°. At less than 20°, the length of the flap increases in an exaggerated manner. At greater than 60°, the distance of closure, particularly at the apex of the flap where a corner stitch is performed, is greater than the distance of closure of the initial defect. In the case of the keystone flap, the width of the final defect around the flap is clearly smaller and more regular compared to the final defect around a single V–Y advancement flap.Conclusion : The geometrical analysis of the V–Y advancement flap in our description illustrates the major benefit of the keystone flap over a single V–Y advancement flap.

International audience; This research on punch wear resulting from the blanking of copper alloy thin sheet has been conducted by means of experimental and numerical analyses. Firstly, the experimental method has consisted in measuring punch worn profiles from replicas, and secondly in obtaining the wear coefficient by using a specific tribometer. The numerical modelling of blanking process has been developed with the finite element method to compute the mechanical fields necessary to calculate wear. Thus, the Archard formulation for abrasive wear has been programmed to compute the wear depth and the resulting punch geometry. Finally the simulation results of wear prediction have been compared to experimental ones.

International audience; Keloid scars are benign skin tumours that affect only humanity, especially among the Asian and African populations. Keloids consist in the excessive accumulation of dermal collagen that extends beyond the boundaries of the original wound (Kelly 2009). They are located on specific sites, tend to enlarge over time and pose aesthetic and psychological problems for patients. The physiopathology of keloids is unclear, and there is still no therapeutic consensus. Nevertheless, it appears that keloids result from a combination of genetic, cellular and mechanical factors (Salles et al. 2009).

L’objectif du travail presente est de proposer un outil numerique efficace pour simuler le procede de decoupage et pour determiner les caracteristiques geometriques et mecaniques d’une piece decoupee. Deux strategies distinctes sont proposees pour simuler la propagation de fissures : une methode d’elimination des elements finis et une approche de fissuration discrete. En premier lieu, ces deux methodes ont ete evaluees sur l’exemple-test d’une plaque asymetrique en traction. En second lieu, la capacite de ces deux methodes de propagation a predire un profil de rupture realiste est analysee dans le cadre du decoupage. Les courbes effort-deplacement du poincon obtenues par ces deux methodes de propagation de fissures sont comparees a des courbes experimentales.

Precision blanking process is widely used by electronic and micromechanical industries to produce small and thin components in large quantities. To take account of the influence of strain rate and temperature on precision blanking of thin sheet in copper alloys, we have proposed a thermo‐elasto‐visco‐plastic modelling. In addition, dynamic recrystallization takes place in Cual copper alloy during the blanking process of thin sheet. A new modelling of dynamic recrystallization based on the thermodynamics of irreversible processes is presented. Blanking simulations of Cual copper sheet are carried out in order to analyze the softening effect induced by dynamic recrystallization.

Blanking process is widely used by electronic and micromechanical industries to produce small and thin components in large quantities. To take into consideration the influence of strain rate and temperature on precision blanking of thin sheet in copper alloy, a thermo‐elasto‐visco‐plastic modelling has been developed in [1]. Furthermore the blanking of thin sheet in Cual copper presents dynamic recrystallization. A new modelling of dynamic recrystallization based on the thermodynamics of irreversible processes is proposed. Blanking simulations of Cual copper sheet are performed to analyze the softening effect induced by dynamic recrystallization.

Publisher Summary This chapter presents a micromechanical nonlocal damage model to predict the damage evolution in metal forming processes, especially in the cold forging of small components. The modeling considered in this chapter is based on a Gurson model modified by Bennani, where the nonlocal damage has been defined in the same manner as Pijaudier-Cabot and Bazant. A nonlocal damage modeling based on Gurson's model has been implemented in the large strain finite element framework of POLYFORM code for quasi-static loading conditions. The first results show that nonlocal damage could reduce the problem of mesh dependency. Future works consist in testing this nonlocal formulation on classical tensile tests with axisymmetric notched specimens and then to apply it on metal forming processes—such as blanking or cold forging.

The aim of this study consists in carrying out the V-Y advancement flap, which is a surgery technique for covering wounds with substance loss. In the V-Y advancement flap, a triangular flap is inci...

International audience; The aim of this study consists in carrying out the V-Y advancement flap, which is a surgery technique for covering wounds with substance loss. In the V-Y advancement flap, a triangular flap is incised adjacent to the defect. As the flap is advanced to close the substance loss, two smaller defects in the form of parallelogram are formed and sutured (Pauchot et al. 2010). A numerical modelling is proposed and compared with experimentalmeasurements of closure force.

International audience; Scar is a common visible mark of human tissue healing. Sometimes pathological phenomena lead to abnormal hypertrophic or keloid scars, with evolutions varying depending on different conditions: origin of the tissue barrier disruption, concerned body area, or ethnic origin. Based on these statements, care procedures have been developed to avoid aesthetical or functional impairments: drugs injection, surgery, cryotherapy or mechanical compression. The story will relate the matching of a multi-disciplinary team that focused on covering an unmet need for ear lobe keloid treatment, providing patients an optimal and holistic care. The benefits researched lied in improving the understanding of the disorder, avoiding the recidivism of the scars, diminishing the frequency and duration of care, and in end improving patients’ quality of life. The paper will not only narrate the building of a health innovation, on technological, clinical, user points of view, but will also try to detail the evaluations planned at the different stages of development, as well as the challenges, conditions and prerequisites allowing to produce concrete solution.

This work proposes a tribological analysis of the blanking operation. A better knowledge of the wear mechanisms present on the cutting punches is necessary to allow their reproduction in the laboratory and thus to test new tools materials, to extend their life time and increase the productivity of the process. Firstly, an open-type tribometer is developed in order to recreate the abrasive wear mechanisms present on the press. The innovative characteristics of this tribometer are the possibility of directly installing sheets identical to cutting pieces, and the friction distances can approach five kilometers on new surface. An energy approach of the wear is conducted in order to compare the results obtained with the tribometer and measurements on the press. Secondly, real tests on a cutting press with an instrumented tool are carried out. The measurement of the wear of the punch by replication and thin layer activation are the two "in-situ" techniques put in place during the tests. Differents cutting configurations are tested in order to observe their impact on the cutting force, the appearance of the cut edge and the wear of the punch. The wear of the punch is too low in the cutting test to be measured, but the rates of energy dissipated in the friction can be estimated. Thirdly, a comparison of the dissipated energies of friction on the tribometer and on the press shows significant deviations. To explain them, a finite element simulation of the cutting operation is carried out. A prediction of wear is established to show the potential of the energetic approach. A vibratory analysis of the tool shows that the phase of cracking of the sheet induces sometimes numerous oscillations of the punch which can lead to wear by fatigue.; Ces travaux de thèse proposent une analyse tribologique de l’opération de découpage sur presse. Une meilleure connaissance des mécanismes d’usure présents sur les poinçons de découpage est nécessaire pour permettre leur reproduction en laboratoire et ainsi tester de nouveaux matériaux d’outils, pour allonger leur durée de vie et augmenter la productivité des outillages. Dans un premier temps un tribomètre de type ouvert est développé afin de recréer les mécanismes d’usure par abrasion présents sur presse. Cette configuration ouverte est choisie car lors de la découpe, l’outil vient découper une pièce sur une surface neuve en continue. Les caractéristiques innovantes de ce tribomètre sont la possibilité d’installer directement des tôles identiques à celles découpées, et les distances de frottement qui peuvent approcher cinq kilomètres sur surface neuve. Une approche énergétique de l’usure est mise en place afin de comparer les résultats obtenus avec le tribomètre et les mesures sur presse. En effet, dans un second temps, des essais réels sur presse à découper avec un outil instrumenté sont conduits. La mesure de l’usure du poinçon par réplication et par activation superficielle sont les deux techniques « in-situ » mises en place lors des essais. Différentes configurations de découpe sont testées afin d’observer leur impact sur l’effort de découpage, l’aspect du bord découpé et l’usure du poinçon. L’usure du poinçon est trop faible dans l’essai de découpage pour être mesurée, mais les taux d’énergie dissipée dans le frottement peuvent être estimés. Dans un troisième temps une comparaison des énergies dissipées dans le frottement sur le tribomètre et sur presse montre d’importants écarts. Pour les expliquer, une simulation par éléments finis de l’opération de découpe est conduite. Une prédiction de l’usure est établie afin de montrer le potentiel de la méthode d’approche énergétique. Une analyse vibratoire de l’outil montre que la phase de fissuration de la tôle induit des oscillations parfois nombreuses du poinçon qui peuvent conduire à de l’usure par fatigue. Des essais d’usure par fatigue sont réalisés et montrent que suivant les nuances, le carbure de tungstène usiné par électroérosion à fil est moins résistant à l’écaillage.

From a mechanical point of view, human skin is a complex multilayer structure with viscoelastic, non-linear and anisotropic properties. The work presented in this thesis combines experimentation, modeling and the identification by inverse method, and is characterized by using a new extensometer device suitable for non-invasive mechanical measurements of in vivo skin. Load-displacement responses for different angular configurations, intensities and body locations were obtained in in vivo tests. Ex vivo tests were, however performed for comparison and validation. Particular attention was paid to the initial skin tension. The different experimental tests were simulated using two materials' behavior laws: the first order Ogden’s law, describing the isotropic hyperelastic behavior of the skin and the Holzapfel-Gasser-Ogden’s law (HGO), describing the anisotropic hyperelastic behavior of the material. The latter was implemented in the Ansys® software usermat. The characteristic parameters of the tested skin areas were identified by the inverse method. The influence of the compressibility of the skin on its mechanical behavior was highlighted. Finally, a numerical analysis was performed on the V-Y advancement flap, which is a surgical technique of suture practiced for filling the losses of substance.; D’un point de vue mécanique, la peau est une structure multicouche complexe ayant des propriétés viscoélastique, non-linéaire, quasi-incompressible, anisotrope et en état de précontrainte. Le travail présenté dans cette thèse associe expérimentation, modélisation et identification numérique et se distingue en particulier par l’utilisation d’un dispositif d’extensométrie développé au laboratoire et adapté à des mesures in vivo non invasives. Des tests ex vivo ont cependant été réalisés également à titre de comparaison et de validation. Une attention particulière a été portée à la tension cutanée initiale (ou naturelle). Les essais in vivo ont permis d’obtenir des réponses force – déplacement sous différentes configurations angulaires, d’intensité et pour diverses localisations corporelles. Les essais ex vivo ont quant à eux permis d’estimer l’état de contrainte initiale par la mesure des forces nécessaires à la remise en tension d’explants. Ces différents essais expérimentaux ont été modélisés en utilisant deux lois de comportement : la loi d’Ogden du premier ordre permettant de décrire un comportement hyperélastique isotrope et la loi d’Holzapfel-Gasser-Ogden (HGO) décrivant un comportement hyperélastique anisotrope. Cette dernière a été implémentée sous l’interface utilisateur du logiciel Ansys®. Les paramètres caractéristiques des zones cutanées testées ont été identifiés par méthode inverse. L’influence de la compressibilité de la peau sur son comportement mécanique est mise en évidence. Au final, les travaux de cette thèse ont été appliqués au lambeau d’avancement de type V-Y qui est une technique de suture pratiquée pour combler les pertes de substance.École doctorale : Sciences pour l'ingénieur et microtechniques Spécialité : Mécanique Contribution à l'étude expérimentale et numérique du comportement hyperélastique et anisotrope de la peau humaine par : Djamel REMACHE Thèse co-encadrée par