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International audience; The paper presents the results of dynamic crushing of sandwich tubes that had skins made of carbon or glass fibres-with epoxy resin-and an I214 poplar ply core. By increasing the number of poplar plies from two to six, the absorbed energy is doubled, showing the significant contribution of the wood. The Specific Energy Absorption of sandwiches with carbon fibre skins oscillated between 49.4 and 60 J/g while that with glass fibre skins varied from 35.4 to 43.3 J/g.

International audience; The quasi-static behavior of innovative wood based sandwich structures with plywood core and skins made either of aluminum or of fiber reinforced polymer (carbon, glass or flax composite skins) was investigated. The wood based sandwich structures were subjected to three point static bending tests to determine their strength and failure mechanisms. Two different manufacturing processes, namely vacuum bag molding and thermo-compression, were used to manufacture the structures. The influence of some aspects of the different manufacturing processes on the flexural behavior of wood based sandwich structures are discussed. It is shown that manufacturing processes influence strongly the static responses. Failure modes and strengths are investigated during quasi-static bending tests. Bending tests showed that the mechanical characteristics were very high compared to those of a reference sandwich that is currently used for civil aircraft floors. This new kind of structure is environmentally friendly and very cheap, and seems promising for the transportation industry in general.

International audience; The development and certification of aeronautical composite structures is still largely based on the pyramid of tests. This approach is extremely costly in terms of number of tests and design loops. Moreover, it is based on uniaxial tests whereas the real structures are mostly subjected to combined loadings. The aim of the collaborative research program “VERTEX” is to progress towards Predictive Virtual Testing and to significantly reduce the development costs of aeronautical and space programs. In this first part, the specific methodology for multiaxial tests of aeronautical structures is presented. The concept of the technological specimen and its size are justified. Then, the development of a specific test rig is presented, on which compression/tension, shear, internal pressure and combinations are possible. Since structural tests are complex to instrument, a specific full-field measurement technique is developed. It is based on a multi-camera instrumentation and an original Finite Element approach to Stereo Digital Image Correlation (FE-SDIC). Within such a framework, given that the very same mesh can be used for the simulation and the measurement, the corresponding displacements can be compared directly. In addition, a mechanical regularization of the FE-SDIC measurements allows mechanically consistent fields to be evaluated, such as displacement and rotation fields that could be used as boundary conditions in the simulations. The experimental procedure, the measurement methodologies and the calculation/test dialogue are validated on isotropic metal plates in this paper.

International audience; Our on-going research focusses upon composite structural parts such as stiffened panels with co-bonded stringers. This study is aiming to developing a numerical tool based on commercial softwares (e.g. Abaqus ® and Fortran ®) enabling after-cure deformations to be predicted for co-bonded composite parts. Several simulations moduli were developed to describe i the thermochemical, ii the thermomechanical behaviours of prepreg plies and structural adhesive film and iii the mould/part interaction. An experimental work was conducted in parallel in order to get firstly simulation input parameters (i.e. material behaviour laws) and secondly experimental deformations on co-bonded composite specimen. The materials used were the Hexcel U.D. prepreg tape M21EV/IMA and the Cytec FM300M structural adhesive film. During a first step (first cure cycle), the process-induced strains of the laminated panel that will be stiffened with stringers were computed and compared to experimental ones. During the second step (second cure cycle) the process-induced strains and deformation were computed on the cured laminate but also on the stringer foot and on the structural adhesive as shown in Fig. 1. Lastly comparing experimental results to simulations shows clearly the interest of considering a 2 steps manufacturing process with 2 cure cycles instead of a single one in which all the components (i.e. panel, adhesive and stringer foot) are cured together.

International audience; Context: Raised grain occurs on wood surfaces after the application of a waterborne varnish and forces manufacturers to sand the surfaces between coats. Actually, little research has characterised this phenomenon and no techniques have been discovered to avoid its occurrence.Aims: This study aims to identify the topographic parameters that explain the visuo-tactile sensation of raised grain and to define a finished surface quality acceptable to consumers and industry.Methods: Oak (Quercus robur L.) and beech (Fagus sylvatica L.) wood surfaces were planed and sanded in order to have various levels of raised grain. Visuo-tactile analyses were carried out on surfaces having received one coat of varnish to characterise raised grain and having two coats to characterise the acceptable finished surface quality without sanding. Topographic parameters were measured on each type of varnished surface and correlated with the visuo-tactile scores.Results: Raised grain was characterised by the visuo-tactile sensation of protruding peaks and a certain amount of material in the core of the roughness profile for both wood species. Industrials overestimated the surface quality required by consumers. Thresholds of topographic parameters were determined to define acceptable finished surface quality.Conclusion: These findings allowed objective criteria to be defined for describing raised grain and to help industries to optimise their wood machining and finishing processes.

This paper focuses on the study of the effect of rectification by grinding on the mechanical behavior in quasi-static tests (compression and inter-laminar shear) of two long fiber composite materials machined by two cutting processes: tool machining (edge cutting) and abrasive diamond cutting (ADS). Two sets of specimens of different surface roughness are generated by varying the cutting conditions for each material. One set is rectified. First, the results of compression and inter laminar shear tests show that the mechanical behavior is highly affected by the surface roughness. Secondly it is shown that the operation of rectification improves the mechanical behavior. However this improvement is highly affected by the surface roughness of the specimen before rectification and is dependent on the long fiber composite material.

International audience; The hole wall defects created during drilling of carbon fiber reinforced polymer laminates are analyzed. First, an analysis of the location of the defects on the wall is performed. It is shown that, using results of orthogonal cutting, it is possible to predict the location of the main defects. Then refined scanning electron microscopic observation shows the different patterns of the defects. These observations raise the question of the quantification and measurement of the quality of holes drilled in composite laminates. Two roughness parameters, Ra and the bearing surface are compared and significant differences are found. This study is a contribution to a better definition of quality indicators for machined surfaces in composite structures, which should help to limit overquality and production costs.

International audience; The main focus of this paper is to investigate the defects generated by different machining processes (namely burr tool machining, abrasive water jet machining \textquoteleftAWJM\textquoteright and abrasive diamond cutter \textquoteleftADS\textquoteright) and their impact on the mechanical behavior of CFRP in quasi-static (compression and inter-laminar shear) and tensile\textendashtensile fatigue tests. The cutting conditions are selected so that different levels of degradation can be obtained. The machined surface is characterized using roughness measuring devices with and without contact and SEM observations. The results show that the defects generated during the trimming process with a cutting tool are fibers pull-out and resin degradation. These defects are mainly located in the layers with the fibers oriented at -45° and 90°. However, when using abrasive water jet and abrasive diamond processes, the defects generated have the form of streaks and are not dependent on the fiber orientation. Furthermore, the results of quasi-static tests performed on specimens machined by cutting tools show that AWJ specimens offer a better resistance in compression but the ADS samples offer higher inter-laminar-shear strengths. Moreover, the results of fatigue tests show that specimens machined with a burr tool offer higher endurance limit. Finally, it is concluded that the type and the mode of the mechanical loading (quasi-static fatigue) affect the mechanical response of CFRP and favor a given machining process.

International audience; An experimental study was lead in order to identify the impact of cutting parameters over the machining quality and cutting forces when drilling an interlock composite 3D woven with a diamond coated drill with lubrication. Two approaches were studied: design of experiments and standardized tool/material method derived from metal machining. For both approaches, feed rate has been identified as the most influent parameter, while cutting speed was not influent. Then wear tests were carried on in order to quantify the impact of cutting parameters over tool wear. Wear tests have proven that tool wear is mainly dependent on the machined length and that it does not impact much the machining quality.

In this chapter the influence of tool geometry and cutting conditions on cutting forces, surface defects and the percetage of dust generated durring trimming and reaching the pulmonary alveoli is investigated. The surface defects were analysed using a scanning electron microscope and diferent surface roughness measurement devices. It was observed that these leters were highly depend on the cutting condition and the tool geometry, and more important that the effect of cutting parameters can be completely diferent from a tool to an other or even when considering different ranges of cutting parameters (standard cutting speed and high cutting speed). The compressive strenght after machining is also investigated. It is observed that whatever tool geometry, cutting conditions, surface roughnesses (defects) are, the response still the same for all the composite samples except for those machined at cutting temperatures higher than the glass fiber transition.

In this work, high speed trimming of a multi directional carbon fiber reinforced plastic using a tungsten carbide burr tool is studied. The influence of the machining parameters on both the dust size and surface quality is investigated. A high percentage of dust is found under the theoretical chip size and the surface quality is found to be affected by the cutting parameters. The percentage of inhaled dust reaching the pulmonary alveoli is quantified and found to be very high, it is also found that this percentage is affected by the cutting conditions.

International audience; The general context of the development of out-of-autoclave processes in the aeronautics industry raises the question of the possible links between these new processes and impact behaviour. In this study, a Taguchi table was used in a design of experiment approach to establish possible links. The study focused on the liquid resin infusion process applied to laminates made with stitched or unstitched quadri-axial carbon Non-Crimp Fabric(NCF). On the basis of previous studies and an analysis of the literature, five process parameters were selected (stitching, curing temperature, preform position, number of highly porous media, vacuum level). The impact energy was set at 35 J in order to obtain enough residual dent depth. The parameters analysed during and after impact were: maximum displacement of the impactor, energy absorbed, permanent indentation depth, and delaminated surface. Then, compression after impact tests were performed and the corresponding average stress was measured. The interactions found by statistical analysis show a very high sensitivity to stitching, which was, of course, expected. A very significant influence of curing temperature and a significant influence of preform position were also found on the permanent indentation depth and a physical explanation is provided. Globally, it was demonstrated that the resin infusion process itself did not influence the impact behaviour.

In the framework of the E-U program ALCAS (Advanced Low-Cost Aircraft Structure), a new Z-pinning technique was developed by EADS Innovation Works. This technology was used to manufacture low-cost Z-pinned junction demonstrators (L and T shaped specimens) typical of aeronautical structures. In order to understand load transfer mechanisms in this kind of assembly, a multi-level analysis was performed. In the first part of this study, tension and shear pin behaviour was investigated as well as pin pull-out from neat resin or laminate. An analytical model was proposed to predict the maximum load capability of a single pin for an insertion depth of less than 8 mm which correspond to the usual technology. Now, in this second part, we demonstrate that the behaviour of the junction under pull-out, shear and unfolding is globally homothetic to the mechanical behaviour of a pin. This study provides the basis for a pre-sizing methodology for Z-pinned junctions under complex loading.

Sandwich structures are widely used in the aerospace field, also for primary parts. However, due to the low strength of core properties, the failure behavior under high stress concentration such as joining position is hard to evaluate. This study is, at present, a key task to enable future exploitation of the joint for structural sandwich consisted of Carbon Fiber Reinforced Polymer (CFRP) face and a Honeycomb core made of phenolic impregnated NomexTM paper. Previous experimental investigations provided the failure mechanism of sandwich plates with hard points in the form of inserts, and special attention is focused on the problem of sandwich panels with inserts of the fully potted types. Numerical simulations are achieved in this work with good correlation based on experimental test.

The paper proposes first to study the behavior of honeycomb alone under uniform cyclic compression-relaxation loading. It is found that the behavior is linear until it reaches the maximum force following by a sudden drop of force and at the end following by a constant force during the compression. This force-displacement behavior is observed to be similar for all material of honeycomb such as; Nomex (with different densities and cell dimensions), fiber-glass and aluminum. From experimental study, the behavior becomes significantly non-linear in the area of constant force (flat zone) especially the spring-back behavior. A mathematical model is proposed to simulate completely compression-spring-back behavior of honeycomb. This mathematical model describes the behavior of honeycomb in compression and spring-back loading only in function of the maximum depth due to impact. The proposed mathematical model is then integrated to FEA model to simulate the spring-back behavior of sandwich structure with metallic skins and honeycomb core. After integrating the influence of skin-honeycomb interaction, a complete mathematical model which includes non-linearity of compression-spring-back behavior and rotation due to skin-honeycomb interaction is proposed to simulate the behavior of sandwich structure subjected to low energy/ low velocity impact (indentation) loading using spherical impactor. Some simulations of indentation and relaxation on sandwich structure with nomex honeycomb using different diameters of spherical indenter and different thickness of metallic skin are obtained with a good comparison with experimental results.

In this study, failure modes occurring during Filled hole compression (FHC) tests were analysed using post-mortem analysis for failure pattern identification and high-speed cameras for failure scenario (damage initiation and progress). Two different failure scenario were experienced depending upon the stacking sequence: ∗ Net compression failure for high 0° oriented lay-ups. The crack initiation is observed near the bolt but the location differs with bolt tightening or not, enabling future validation of finite element models. ∗ Off-set compression failure for low oriented lay-ups. This failure mode was attributed to bearing by-pass loads in the literature. Nevertheless, this study demonstrates that a different scenario can occur linked to a specimen effect: first a delamination appears at the free edges of the specimens. Then, as the delamination area grows, a local buckling occurs creating a net failure at the tip of the wave. The results obtained in this study are the basis for developing more robust sizing methods for bolted joints based on physical understanding of failure mechanism and associated sensitivity parameters.

International audience; A multi-level analysis of skin/stiffener debonding is used for the fuselage design of future aircraft during postbuckling. The specimens composed of a laminate (the skin) to which an over-thickness (the flange) had been added were subjected to four-point bending, which led to interface failure between the flange and the skin. These tests were performed with several configurations and parameters, such as the orientation of the plies located at the interface, temperature (-50°C, 20°C and 70°C), ageing and manufacturing mode: co-cured or co-bonded. The flange shape (tapered or not) and thickness were also considered. Test data are presented and analyzed and critical configurations are identified. Finite element models were developed and the flange debonding loads computed, firstly by use of cohesive models and then through a fracture mechanics approach (Virtual Crack Closure Technique). In both cases, the Benzeg-gagh-Kenane criterion was selected and proved its efficiency but the fracture mechanics approach was an order of magnitude less time consuming, which will enable future modelling to include larger sizes.

International audience; A model enabling the detection of damages developing during a low velocity/low energy impact test on laminate composite panels has been elaborated. The ply model is composed of interface type elements to describe matrix cracks and volumic finite elements. This mesh device allows to respect the material orthotropy of the ply and accounts for the discontinuity experimentally observed. Afterwards delaminations are described with interfaces similar to the ones observed with matrix cracks and the coupling between these two damages are established. In the first step, simple stress criteria are used to drive these interface type elements in order to assess the relevance of model principle. Nevertheless, the well known problem of mesh sensitivity of these criteria prevents the use of this model for now as a predictive tool but rather as a qualitative tool. An experimental validation is carried out thanks to impact experimental tests performed by Aboissiere (2003) and a very good match has been found. However, this model could predictivelly be used and would allow to foresee an original method to detect delaminations during anexperimental test. This modelling has been successfully tested experimentally and compared to a C-Scan ultrasonic investigation.

A finite element model is proposed to determine the residual print of sandwich structures with Nomex honeycomb core and metallic skins indented by a spherical indenter and to simulate its behavior when this indented structure is subjected to lateral compressive loading (known as CAI/ Compression after impact). The particularities of this model rely on representing the honeycomb with a grid of non-linear springs which its behavior law calibrated from uniform compression test. This simple model, after integrating the cycle behavior law of honeycomb, allows predicting the geometry of residual print with a good precision. This model is then developed to propose a complete computation from indentation, residual print geometry to lateral compressive loading after indentation (CAI). This model also allows predicting numerically the residual strength of structure in CAI and the elliptical evolution of residual print geometry during CAI loading. A good correlation with test results is obtained except for the very small residual print depth.

Omega stringers offer interesting structural capabilities and are expected on future aircraft fuselages. In postbuckling mode, the final failure of these structures may occur by stringer debonding between stringer flanges and the skin of the fuselage. In this study, it is demonstrated that the use of fracture mechanics allows to predict skin/omega stringer separation under multiple load cases. Three different load cases and experiments are presented allowing a debonding to start at different locations: at free flange edges or at the inner radius of the omega. Firstly, a skin/stringer configuration subjected to three point bending following the longitudinal axis of the stringer was tested. For this configuration, a numerical study was made and shows the influence of a refined mesh taking into account resin fillets. Secondly, new specimens were obtained by cutting into slices the longitudinal specimen. Those specimens were subjected to four points bending. It has been shown that the upper rolls position of the test jig could modify the debonding location. Numerical models have allowed to determine accurately the debonding location and the associated load level. For some specimens, resin fillets were removed from the flange tips and their effect were assessed numerically and experimentally.

A finite element model is proposed to determine the residual strength and the evolution of damage area of indented sandwiches structures with Nomex honeycomb core and metallic skins indented by a spherical indenter under longitudinal compression load (CAI). The honeycomb is represented by a grid of non-linear springs which its behavior law is obtained by performing simple transverse uniform compression test on a block of honeycomb alone.The comparisons between computation and test result show that the model can simulate accurately the form of damage geometry during indentation, its residual print when the load is relieved (relaxation) and the residual strength and the evolution of damage geometry during CAI.

Dans le domaine aeronautique les impacts, meme de faible energie, sur des structures sandwichs a âme nid d'abeille posent des problemes majeurs en terme de resistance residuelle. La modelisation de l'endommagement du a l'impact necessite la connaissance preliminaire du comportement du nid d'abeille en compression. Des essais realises en compression quasi-statique uniforme sur des pains de nids d'abeille en differents materiaux (Nomex, Aluminium et Canson) permettent de decomposer la sequence de formation du pli et les facteurs influents. Ces essais tendent a montrer que la force de compression transite essentiellement par les aretes verticales du nida. Des essais complementaires sur un motif d'arete confirme cette analyse. La modelisation issue de cette analyse propose, pour connaitre la reponse d'une structure nid d'abeille en compression ou indentation, de determiner la reponse individuelle d'une arete verticale par un essai de compression uniforme. A partir de la loi experimentale obtenue, la reponse a l'indentation de la structure sandwich est la superposition de la reponse des aretes pour la forme d'indenteur et la profondeur d'indentation consideree. Une bonne correlation essais/calcul est obtenue lors d'essais de validation sur nids Nomex avec diverses formes d'indenteurs. La methode proposee est generale et peut etre etendue a divers materiaux cellulaires.

Cet article propose un socle de connaissances des structures composites stratifiees. Les principaux materiaux d'usage sont presentes, ainsi que leurs declinaisons commerciales et les principaux moyens de mise en oeuvre. Les methodes de predimensionnement usuelles se basant sur la theorie des stratifies classiques sont developpees : calcul des contraintes dans les plis, criteres de rupture associes, flambement, calcul d'assemblages. Les questionnements plus avances comme l'impact, la fatigue, les endommagements ou le vieillissement sont aussi abordes.

Preface Hydroelastic Impacts of DeformableWedges Riccardo Panciroli Blast Loading of Sandwich Structures and Composite Tubes H. Arora, P. Hooper, and John P. Dear Interaction of Underwater Blasts and Submerged Structures S. Abrate Compressively Pre-stressed Navy Relevant Laminated and Sandwich Composites Subjected to Ballistic Impact Eric Kerr-Anderson, Selvum Pillay, Basir Shafiq, and Uday K. Vaidya Development of a Test to Simulate Wave Impact on Composite Sandwich Marine Structure Peter Davies, Benoit Bigourdan, Dominique Choqueuse, Nicolas Lacotte, and Bertrand Forest Damage Mechanisms and Energy Absorption in Composite Laminates Under Low Velocity Impact Loads V. Lopresto and G. Caprino Perforation of Composite Laminate Subjected to Dynamic Loads Shirley Kalamis Garcia-Castillo, Sonia Sanchez-Saez, Carlos Santiuste, Carlos Navarro, and Enrique Barbero Discrete Impact Modeling of Inter- and Intra-laminar Failure in Composites Christophe Bouvet, N. Hongkarnjanakul, S. Rivallant, and J.J. Barrau High Velocity Hail Impact on Composite Laminates - Modelling and Testing Robin Olsson, Rickard Juntikka, and Leif Asp Discrete Modeling of the Crushing of Nomex Honeycomb Core and Application to Impact and Post-impact Behavior of Sandwich Structures Bruno Castanie, Yulfian Aminanda, Jean-Jacques Barrau, and Pascal Thevenet Foldcore Sandwich Structures and Their Impact Behaviour: An Overview Sebastian Heimbs Experimental and Numerical Study of Normal and Oblique Impacts on Helicopter Blades J. Aubry, P. Navarro, I. Tawk, S. Marguet, J.F. Ferrero, S. Lemaire, and P. Rauch Energy Absorbing Sacrificial Structures Made of Composite Material for Vehicle Crash Design G. Belingardi, S. Boria, and J. Obradovic Composites and Dynamic Failures: Experimental and Numerical Solving Strategies and Solutions Daniel Coutellier J. Aubry, P. Navarro, I. Tawk, S. Marguet, J.F. Ferrero, S. Lemaire, and P. Rauch Energy Absorbing Sacrificial Structures Made of Composite Material for Vehicle Crash Design G. Belingardi, S. Boria, and J. Obradovic Composites and Dynamic Failures: Experimental and Numerical Solving Strategies and Solutions Daniel Coutellier J. Aubry, P. Navarro, I. Tawk, S. Marguet, J.F. Ferrero, S. Lemaire, and P. Rauch Energy Absorbing Sacrificial Structures Made of Composite Material for Vehicle Crash Design G. Belingardi, S. Boria, and J. Obradovic Composites and Dynamic Failures: Experimental and Numerical Solving Strategies and Solutions Daniel Coutellier

The design of some modern ultra-light weight aicraft or helicopter structures uses the dissymmetrical sandwich technology. In this kind of design, stresses are taken by the thick skin of the sandwich known as working skin and made of multilayered carbon. The behaviour with global buckling is fulfilled by the core and a thin skin known as stabilizing skin made of two carbon or Kevlar layers. The certification of such structures rests partly on monoaxial tests in compression or shear with deformable square of representative test plates, or on tests under complex stresses of complete substructures. The purpose of this study is on one hand to build an original way of testing which would be able to test representative plates under uniaxial compression, shear and combined compression/shear loading, and on the other hand to build a specific non-linear theory with the associated program able to describe the behaviour of the real plates.

International audience; In this paper, high speed trimming of a multidirectional CFRP using unused and used burr tools is considered in order to investigate the influence of the machining parameters (e.g., feed speed, cutting speed and cutting distance) on the cutting forces, machining temperature, and the machined surface quality. To estimate the effect of the tools’ wear and cutting parameters on the cutting forces and surface roughness, a statistical method (ANOVA) has been used. When considering an unused tool, the recorded temperatures were below the glass transition temperature of the composite material (Tg). In the case of used tools, these temperatures were mostly higher than the Tg. Furthermore, SEM observations of the machined surface showed damaged areas. These areas were wider when the cutting distance increased. Statistical analyses have shown that the machining parameters have a significant influence on the variation of the machined surface quality and the cutting forces.

International audience; Process induced distortions prediction is a major issue for structural parts like self-reinforced panels. They may cause important displacements for parts of large dimension and compromise the quality of the assembly. Development of numerical process models is necessary to avoid the expensive and time-consuming trial-and-error approach. Various numerical models exist to predict those distortions. However, regarding co-bonded integrated structures, the influence of the adhesive film on final distortions is often ignored. The aim of this study is to simulate process induced distortions for co-bonded integrated structures and to understand the contribution of the adhesive film on those distortions. To do that, Finite Element Analysis (FEA) simulations are used. To be able to set up the FEA, thermal and mechanical properties are characterized for the epoxy-carbon fiber prepreg M21EV/IMA and the epoxy adhesive film FM300-M. Various models and parameters associated are determined and used to describe thermal and mechanical behaviour of both materials. Those models and properties are then employed to implement a FEA on ABAQUS using FORTRAN subroutines. The numerical model simulates process induced distortions during an autoclave cycle for co-bonded parts. Using this model, we aim to define stringer foot specimen geometry and lay-up to enable an experimental/numerical comparison.

International audience; no abstract

International audience; no abstract

International audience; Low carbon emission is a shared goal of all transportation industry. One way to match this expectation consists in the introduction of lightweight materials with high specific properties such as composites materials. Wood based materials combined with fibre-reinforcedpolymerappear to be good candidates if we introduce environmental aspects, safety considerations,and energy absorption capabilities. Thus, several sandwich configurations with plywood cores has been characterized to impact tests in order to quantify the energy absorption capability of such materials. A comparison of these results is proposed with the sandwich materials currently used in the aeronautics industry to be able to identify the potentiality of these new wood-based structures. We analyzed their post impact strength through compression after impact test. Finally, several structures were identified as good compromise solutions between residual strength and stiffness to replace actual sandwich structures. Regarding to their impact behaviour, and based on numerical models developed, manufacturing and testing of a crash box using wood based sandwich structures should be carried out in the future.; Limiter les émissions de carbone est un objectif commun à toutes les industries du transport. Une façon de répondre à cette attente consiste à introduire des matériaux de plus en plus légers avec des propriétés spécifiques élevées tels que les matériaux composites. Les structures composites à base de bois semblent être de bons candidats si l’on considère à la fois les aspects environnementaux, les notions de sécurité,et les capacités d'absorption d'énergie. Ainsi, plusieurs configurations de sandwichs avec âme en contreplaqué ont été caractérisées à l’impact afin de quantifier leur capacité d’absorption d’énergie. Une comparaison de ces résultats est proposée avec les structures sandwichs utilisées actuellement dans l’industrie aéronautique de manière à pouvoir identifier le potentiel de ces nouvelles structures à base de bois. Nous avons analysé leurs propriétés résiduelles via un essai de compression après impact. Au final, plusieurs structures présentant un bon compromis entre résistance résiduelle et rigidité ont été identifiées pour remplacer les structures sandwichs actuelles. Sur la base de leur comportement à l'impact et des modèles numériques développés, la fabrication d’une crash box utilisant des matériaux sandwich à base de bois devrait être envisagée dans les années à venir.

International audience; no abstract

International audience; no abstract

International audience; Insert in composite sandwich structures sizing relies on simplified formulas based on beam theory. In reality, the failure scenario of inserts subjected to pull-out loading implies shear bucking and tears in Nomex honeycomb, debonding between metallic inserts and potting, debonding between potting and sandwich skins, static failure in the potting and skins and sometimes skins failures. An enhanced model (by comparison to the models developed by Bunyawanichakul et al. taking into account all the failure mode is developed. Cyclic shear tests are done to capture the shear bucking of the walls of a Nomex honeycomb cell (which is reversible) and the beginning of tearing (winch is irreversible). A technological test is also performed to model the debonding between a metallic insert and the potting. After validation with pull-out tests, the model is used to make failure mode maps useful for rapid sizing by engineers.

International audience; no abstract

The research objective is to model the low velocity/low energy impact on sandwich structures with metallic skins. A progressive approach is carried out by considering first the honeycomb core alone, then static indentation on sandwich structures and finally a dynamic analysis. During the first step, a phenomenological study of the behavior of honeycomb subjected to crushing is completed. It appears that local rotations and cell edges plays an important role in the crushing phenomenon. It is then possible to propose a simple analytical model able to represent the indentation of honeycomb alone for various indenter geometries by modelling only the cell edges behavior. The compression law of the cell edges is identified by a basic uniform compression test. This key-idea is then used to create a finite element model using a grid of nonlinear springs to represent the honeycomb structure. The contact law of static indentation tests of metal-skins Nomex™ honeycomb sandwich structures can thus be found numerically and agree well with the experiments. Finally, this contact law can be used to model dynamic impacts which demonstrates the static/dynamic equivalence for this range of impact and structures.Copyright © 2006 by ASME

International audience

International audience; no abstract

International audience; no abstract

International audience; This work presents the results of 21 shear tests on three types of honeycomb cores: the HRH-78-3/16-3.0, HRH-10-3/16-6.0 and an aluminium honeycomb core made of 5052 alloy with 3/8" cells. First, a benchmark of the different designs for shear testing of the honeycomb cores is made. Then, several double lap specimens were fabricated and tested while a 3D image correlation system was used to record the tests. An experimental analysis of the post-buckling phenomena of the HRH-78 W is presented. An artificial neural network is developed and used to visually identify the buckles of the test specimens. Finally, a detailed description of the behaviour of the structure including the postbuckling scenario is presented.

International audience; The constraints related to structures design in the field of transportation are increasingly complex in order to comply with safety standards. Composite materials being increasingly widespread within these structures, their behavior must therefore be more accurately mastered. Current numerical tools can now permit an accurate simulation in the static field, but concerning fast transient problems, the available numerical methods are not optimal yet. Starting from concrete cases, this chapter introduces problem solving strategies. A procedure is then presented to improve numerical simulations in the field of rapid dynamics. It includes the establishment of experimental protocols to assist in a thorough understanding of materials behavior. These experimental studies can then provide models, laws and methodologies to better simulate the behavior of composite structures under dynamic load. However experimentation is sometimes complicated by the size of structures. The similitude techniques can then provide a solution. Similitude techniques are used to study composite materials subjected to impact. We propose here an approach allowing modeling and numerical simulation validated on an industrial case.