EXPERIMENTAL AND NUMERICAL STUDY OF NITI HOLEY PLATES LOADED IN TENSION

International audienceWe present results of experiments and numerical modeling of superelastic deformation of NiTi holey plates

Etude expérimentale du comportement d'une tôle perforée aléatoirement en NiTi superélastique

Nous étudions expérimentalement la réponse complexe observée lors de la traction d'une plaque mince perforée superélastique NiTi. La présentation du travail abordera ainsi les aspects de conception, réalisation et validation du dispositif expérimental permettant le maintien de la planéité de l'éprouvette et des mesures de champs. Pour comparer le comportement pseudo-élastique d'un NiTi en phase superélastique, à une plasticité classique, les essais sont également effectués sur un acier inox

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

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

A stress concentration-free bonded Arcan tensile compression shear test specimen for the evaluation of adhesive mechanical response

International audienceAdhesively bonded structures are increasingly used in the industry: aerospace, aeronautics, automotive and nautical fields. It is thus necessary to characterize the behavior of an adhesive in an assembly from an experimental point of view to a modeling one. The development of reliable models needs very good tests to define the performances of the adhesive used. The modified Arcan test developed by Cognard et al. is an interesting test. However it is difficult to use. The work presented in this paper deals with an evolution of this test called the Arcan Tensile/Compression–Shear Test (Arcan TCS). It simplifies the previous approach taking also into account the influence of the edge effects with the development of a new geometry of the beaks close to the adhesive. It is suited to apply tensile/compression–shear loadings to the adhesive. The test specimen proposed was designed and manufactured to improve the modified Arcan test without reducing the efficiency of the results also including an improvement of the bonding procedure. This new specimen is validated with finite element simulations and tested with an epoxy adhesive to determine the load–displacement behavior and the envelopes at failure

Proposal of a test loading a four point bending specimen thanks to an experimental Arcan device

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Proposal of a test loading a four point bending specimen thanks to an experimental Arcan device

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A 3D model to analyze the behavior of composite laminates subjected to out-of-plane loadings

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Laser shock peening of Ti-17 titanium alloy: Influence of process parameters

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