Different experimental ways to minimize the preforming defects of multi-layered interlock dry fabric

International audienceThis study presents a strategy to improve the quality of a dry fabric’s preforms. Preforming tests were realized with one and two-layers of interlock carbone fabric at different configurations. Initial results led to preforms with several defects. For one-layer preforming, a new blank holder geometry and an increase of the pressure applied on the fabric allowed to improve the quality of the preforms. On the other hand, for two-layer preforming, the insertion of a mat fabric in the interface of the two preformed layers allowed to decrease the friction and to improve the preforms quality, significantly

Experimental analysis of the contact between layers of dry fabrics

International audienceA better apprehension of the behaviour of the interface between sheets of woven reinforcement during the forming of dry fabrics is necessary for a better optimization of the LCM processes. Even if numerical studies are carried out to simulate multi-layer forming, the contact between the layers is very roughly modelled using an approximate friction coefficient. To knowledge, only few preliminary results can be found concerning the contact fabric/fabric. In order to understand and characterize the contact between layers of different fabrics, a specific friction device has been designed in our lab. This machine was designed with the aim of carrying out tests as well on fabric/ fabric, fabric/metal but also fibre/fibre friction. After a short presentation of the device, results concerning steel/steel friction will be presented in order to validate the device. Then first results obtained about fabric/fabric contact will be given, in order to point out the contacts mechanism involved

Experimental Tool of woven Reinforcement Forming

International audienceThis paper concerns the development of an experimental device which is able to form very complex double curved geometry. Objectives are to analyze the evolution of the woven preform during the forming process. This device contains one mechanical module containing the classical tools in forming process, (punch, blank holder, and open-die), and one optical module to measure the 3D-deformed shape and the distribution of local deformations, like shear angles of the woven reinforcement during all the process. Experimental results are obtained with an interlock carbon woven fabric, used in aeronautical applications. Wrinkling and buckling will be analyzed at the global scale of the piece. The evolution of the shear angle will be presented at local scale (on face, or edges of the geometry)

Extragonadal mixed germ cell tumor of the right arm: description of the first case in the literature

<p>Abstract</p> <p>Background</p> <p>Extragonadal localization of germ cell tumors (GCTs) is rare; to the best of our knowledge, a location in the soft tissue of the arm has never been previously reported in the literature.</p> <p>Case presentation</p> <p>We report the case of a 37-year-old man who presented with a primary malignant mixed non-seminomatous GCT (teratocarcinoma variety) in the right arm, treated by a combination of cisplatin-based chemotherapy and surgery. After 18 months of close follow-up, no locoregional recurrence or distant metastases have been detected.</p> <p>Conclusions</p> <p>A combination of chemotherapy and surgery is the most appropriate treatment strategy for extragonadal GCTs, to ensure both local and systemic control.</p

Virtual mechanical testing of a complex 3D woven fabric: a unified simulation methodology for deformation mechanics of textile structures during tension, shear and draping

The most common method of modelling the behaviour of fibrous materials such as yarns and woven fabrics, is to treat them as continuous solids. The fibrous behaviour is then taken into account by appropriate constitutive laws. These constitutive laws are however very difficult to develop due to the complex behaviour (non-linearity, large displacements, anisotropy, crushing, …). Here, we show a more viable simulation methodology which allows for the virtual testing of fibrous materials. In this method, yarns are modelled as a bundle of (virtual) fibres which can realign themselves. Hence, the fibrous behaviour is taken into account in a very natural manner. The methodology is applied to study the mechanical behaviour of a complex 3D woven fabric under tensile and shear loadings. This allows for the virtual determination of tensile and shearing properties of the fabric without the need to produce or test the actual fabric. Especially in the case of 3D woven fabrics, where production and testing can be costly and time-consuming, virtual testing can result in large cost-savings. Furthermore, the proposed method is very versatile and we show that it can also be used for weaving, stitching and draping simulations when high detail is required

EFFECT OF INTER-PLY SLIDING ON THE APPEARANCE OF DEFECTS FOR MULTILAYERED COMPOSITE SHAPING

International audienceThe transport sector is one of the fastest growing consumer of energy and producer of greenhouse gases in the world. Consequently, transportation means with a low energy consumption, and thus global warming, are more and more demanding as being a major concern again the protection of the environment and hence respect a durable development. This aim can be achieved by reducing the mass of the transportation means and this by replacing metallic materials by composites ones on structural parts subjected to severe mechanical solicitations and this with equal mechanical performances. Indeed, composite materials are able to propose credible answers to the optimization of the thick structural parts with significant size through their good ratio strength/weight and especially their anisotropy which can be adapted to the mechanical solicitation of the structure. To manufacture the composites pieces, the RTM is the more interesting process because it offers the best compromise in terms of repeatability, production rates and low final cost [ une référence]. The first step of the process consists in draping a dry preform before injection of the liquid resin. This stage is a delicate phase and the mechanisms taking place are complex and different than the ones occurring during the stamping of metallic sheets. These mechanisms are far from being fully understood [1] which hampers the mastery of the manufacturing process and development of composite materials. In addition, the increasing use of materials with low environmental effect (biomaterials ...) and complex weaving architectures (interlock, 3D fabrics), makes it more difficult. Many methods have been proposed recently to achieve representative sheet forming simulations of dry fabric, with different approaches [2-4]. These studies need several key entries such as the dry fabric mechanical properties and the fabric/tool friction coefficient, which have been widely studied [5-8]. When dealing with the multiply forming of composite thick parts, a significant relative sliding of the layers occurs [9]. This sliding generates fabric/fabric friction that has been recently studied [10, 11] and where the effect of woven meso-structure on the behavior has been highlighted. However, this relative sliding coupled with the phenomena that occur during the friction [11] can leads to the defects apparition or their amplification. The aim of this study is then to investigate experimentally the effect of fabric/fabric friction behavior on defects apparition when dealing with multilayered shaping of composite dry fabric. For this purpose, forming tests of interlock fabric (G1151) with prismatic punch were carried out on a specific device [12]. Tests conditions allowing defects apparition, such as wrinkles, in the useful areas of the shapes are used. Tests were realized with one layer and several layers of dry fabric with the same test conditions. Defects and shear angles were quantified in the useful shape areas (fig. 1) for each test then quantitative and qualitative comparisons were made between the different configurations. These comparisons showed that the shear angles on different areas of interest are almost identical between the multilayered shapes and single-ply ones. For defects, the locations of areas on which they appear are the same (fig. 1). However, the importance of each defect and the extent of the affected areas are more significant in the case of multilayered shapes. Additional defects, such as fiber breakage, were also observed in the same areas for this configuration. These measures and observations carried out in this study highlight the effect of the fabric/fabric friction behavior and relative sliding between layers on the defects and their appearance

inter-ply friction effect on the forming result of multi-layered composite

International audienceDuring forming, defects can occur and have to be taken into account because they can significantly affect the mechanical performance of the part. This experimental study shows the type and number of defects is a function of the punch geometry, the process parameters, the orientation of the fabric with respect to the punch and the inter-ply friction. Inter-ply friction has a huge effect on the quality of the preform when inter-ply sliding occurs. This inter-ply Friction leads to several overhanging yarn shocks that generate high tangential forces, which inhibit the relative sliding of plies

prediction of proximal femur fracture (finite element modeling based on mechanical damage and experimental validation)

Les fractures causées par l'ostéoporose de l extrémité supérieure du fémur sont devenues un problème majeur de santé publique. Par conséquent, ce sujet devient un axe de recherche de plus en plus important pour les cliniciens et les chercheurs biomédicaux. Le but de cette étude est de développer une nouvelle approche pour prédire la fracture du col du fémur. Cette étude propose de développer et valider des modèles par éléments finis (EF) en 2D et 3D, basés sur le concept de l endommagement mécanique des milieux continus, permettant de simuler la fracture de la partie proximale du fémur en tenant compte de l initiation progressive de fissures et leur progression. Deux configurations ont été utilisées: appui monopodal et chute. L ensemble des lois de comportements quasi fragile couplées à une loi d endommagement sont implémentées en langage FORTRAN dans ABAQUS/Standard (sous-programme de type UMAT). La densité minérale osseuse (BMD) a été mesurée par l absorptiométrie à rayon X en double énergie DXA pour la région d'intérêt. Les modèles ont été développés dans deux variantes (l une isotrope et l autre orthotrope) puis validés avec des résultats expérimentaux obtenus sur des essais en appui monopodale réalisés sur des fémurs humain. Durant ces essais, des mesures optiques basées sur la méthode de corrélation d'images numériques (DIC) ont été réalisées afin d acquérir les différents champs de déplacement et de déformation. Le modèle numérique 3D a réussi à prédire l ensemble de la courbe force-déplacement ainsi que l'emplacement et l'amorce de la rupture des fémurs. Par ailleurs, Malgré sa robustesse, la variante 3D du modèle numérique reste difficilement exploitable dans l état pour réaliser un diagnostic préventif dans des délais acceptables pour des cliniciens, car très consommatrice en temps de calcul. Pour pallier à cela, le modèle simplifié en 2D a été préliminairement validé sous les mêmes conditions aux limites et les résultats ont montré une bonne corrélation avec l expérience. Ces travaux ont souligné le potentiel de la modélisation par éléments finis basée sur l endommagement quasi-fragile à devenir un outil complémentaire de prédiction du risque de la fracture osseuse.Femoral fractures caused by the osteoporosis become major problem of public health, and therefore, this subject becomes an increasingly important goal for both clinicians and biomedical researchers. The purpose of this study is to develop a new coupled approach to predict the fracture of neck femoral. The current study proposes a validated 2D and 3D finite element (FE) models based on continuum damage mechanics in order to simulate human proximal femur fracture considering the progressive cracks initiation and propagation. These models are applied and validated under single limb stance and sideways fall configuration. Quasi brittle behavior laws coupled to damage are implemented in FORTRAN and fed into ABAQUS/Standard codes to describe the constitutive behavior (subroutine UMAT). Bone mineral density (BMD) is measured using dual energy X-ray absorptiometry (DXA) for the region of interest. The models have been developed within two variants (one isotropic, the other anisotropic) and validated with experimental results of tests performed on human femur samples under single limb stance configuration. During these tests, optical measurements based on the method of digital image correlation (DIC) were conducted to acquire the various fields of displacement and deformation. To calculate the fracture risk of the femoral head, it is necessary to assign correctly the bone material properties. The 3D FE models were able to predict the overall force-displacement curve, location and initiation of femur fractures. Moreover, despite its robustness, this 3D FE model is still limited to be used, within clinically acceptable time, for diagnostic purposes. To overcome this, the model was simplified into 2D model which has been preliminarily validated under identical boundary conditions and the results showed a good correlation with experiments. These studies have highlighted the potential of the finite element model based on quasi-brittle damage to become a complementary tool for predicting the risk of bone fracture.ORLEANS-SCD-Bib. electronique (452349901) / SudocSudocFranceF

Effect of inter-ply sliding on the quality of multilayer interlock dry fabric preforms

International audienceForming thick, complex shapes with several layers is needed in high technology fields. During forming, defects can occur and have to be taken into account because they can significantly affect the mechanical performance of the part. This experimental study shows that, when working with dry fabric forming, the type and number of defects is a function of the punch geometry, the process parameters, the orientation of the fabric with respect to the punch and the inter-ply friction. Inter-ply friction has a huge effect on the quality of the preform when inter-ply sliding occurs. This inter-ply friction leads to several overhanging yarn shocks that generate high tangential forces, which inhibit the relative sliding of plies. In addition, to reduce the number and amplitude of defects, the layers subjected to severe defects can be placed in the inner position where they are subjected to the compression applied by the upper layers