An analytical model of an elementary elliptical cell forming an alveolar elastic material under plane stress

This paper analyzes the static behavior of alveoled materials that is about to be developed for dynamic optimization of structural panels. It deals precisely with materials made of elliptical thin cells, filled with polymer material. The main contribution of the paperconsists in elaborating an analytical approach describing the material. The considered problem represents an unidirectional stress, the goal being to calculate the elastic energy and strain globally obtained in the material. The wall of the elementary cell is represented in accordance with the classical BRESSE's theory of thin beams, with specific adaptation for elliptical shape. The polymer material filling the cell is modelized with ABSI!s method of equivalence, which allows a direct approximation of various continuous media by equivalent spring segments. This method is presented and discussed for the present configuration, with its specific adaptation. The final result obtained by these analytical approaches is then compared to results from a finite element model. In spite of local differences between the analytical results and numerical computation, it appears clearly that the precision obtained by the proposed analytical approach is better than 95%, which is sufficient for this kind of material. Thus, the proposed analytical calculation and methodology allows robust and quick determination of material characteristics for elementary cells of such alveoled materials. The resulting laws can then be introduced into global models of a grid of cells

Applications de la dynamique explicite à l’ENSICA : atterrissage et amerrissage des spationefs et problèmes d’absorption d’énergie

L’absorption dynamique d’énergie au sein des structures minces a donné lieu à plusieurs développements liés aux matériaux et à leurs comportements spécifiques au sein des structures aérospatiales. La problématique du flambage dynamique en cisaillement a permis, dans une première phase, de réaliser des essais et modèles à petite échelle, fortement dynamiques et non-linéaires. Ils ont été appliqués à la qualification à l’atterrissage des équipements de véhicules spatiaux, à l’aide d’essais en similitude et de simulations explicites. Au cours d’une deuxième phase, les matériaux expansés écrasables ont fait l’objet d’essais destructifs dans le cadre de la conception des interfaces véhicule-astronaute assurant la sécurité au choc. Enfin, au cours de la troisième phase, certains matériaux structuraux (alliages légers et carbone-epoxy), polymères ou fibres textiles sont testés dynamiquement en flexion sous vide et en cisaillement pour extraire leurs amortissements dynamiques intrinsèques. Ces phénomènes et modélisations sont porteurs d’applications industrielles liées à la sécurité, mais aussi de démonstrations et d’illustrations pédagogiques riches et variées

Development of a dynamic virtual reality model of the inner ear sensory system as a learning and demonstrating tool

In order to keep track of the position and motion of our body in space, nature has given us a fascinating and very ingenious organ, the inner ear. Each inner ear includes five biological sensors - three angular and two linear accelerometers - which provide the body with the ability to sense angular and linear motion of the head with respect to inertial space. The aim of this paper is to present a dynamic virtual reality model of these sensors. This model, implemented in Matlab/Simulink, simulates the rotary chair testing which is one of the tests carried out during a diagnosis of the vestibular system. High-quality 3D-animations linked to the Simulink model are created using the export of CAD models into Virtual Reality Modeling Language (VRML) files. This virtual environment shows not only the test but also the state of each sensor (excited or inhibited) in real time. Virtual reality is used as a tool of integrated learning of the dynamic behavior of the inner ear using ergonomic paradigm of user interactivity (zoom, rotation, mouse interaction,…). It can be used as a learning and demonstrating tool either in the medicine field - to understand the behavior of the sensors during any kind of motion - or in the aeronautical field to relate the inner ear functioning to some sensory illusions

The aerocrew mission : training space Session at Ny Aalesund Arctic base

The Aerocrew mission has been realized in December 2007, in the frame of the International Polar Year, and in cooperation with the Polar Institut Paul-Émile Victor. The team has realized an original5 days training experience at Ny-Aalesund Arctic Base (79°N) the. The 11 crew members constituted a space crew, including physicians, aerospace crew trainers and engineers, and were implied in a seminar with 4 sessions, dealing with the training capabilities of Arctic Bases. The goal was on one hand to show that this kind of base constitutes a pertinent and affordable facility for space and aerospace teams, and on the other hand that the specific aerospace crew training techniques, could be fruitful for the scientists in artcic bases (glaciologists, geologists, specialists of the atmosphere). The 4 sessions, given by professionals of aerospace, robotics and medicine, covered the training methods for crews, robotics for outdoor and indoor activities, engineering of embedded systems, and the internal arrangement of crafts. The experience has shown the efficiency of a transverse visiting multidisciplinary team for training, and possible synergies with the resident scientists. In addition, the sessions were enriched by demonstrations such as mini-robot for observation, micro-helicopter for special sites, and also the comparison between EVA Russian glove and Polar Suits. After this mission, it was possible to conclude that this kind of cooperation could certainly open perspectives with crossed benefits either for space training and arctic research

Damage monitoring in sandwich beams by modal parameter shifts: a comparative study of burst random and sine dwell vibration testing

This paper presents an experimental study on the effects of multi-site damage on the vibration response of honeycomb sandwich beams, damaged by two different ways i.e., impact damage and core-only damage simulating damage due to bird or stone impact or due to mishandling during assembly and maintenance. The variation of the modal parameters with different levels of impact energy and density of damage is studied. Vibration tests have been carried out with both burst random and sine dwell testing in order to evaluate the damping estimation efficiency of these methods in the presence of damage. Sine dwell testing is done in both up and down frequency directions in order to detect structural non-linearities. Results show that damping ratio is a more sensitive parameter for damage detection than the natural frequency. Design of experiments (DOE) highlighted density of damage as the factor having a more significant effect on the modal parameters and also proved that sine dwell testing is more suitable for damping estimation in the presence of damage as compared to burst random testing

Wood wasp inspired space and earth drill

In this chapter, we explain why the low gravity encountered on Mars or on the Moon and the low mass of the probes, landers and rovers that carry drilling devices limit classical drilling techniques. Novel boring solutions optimised in mass and power consumption are thus needed for space applications. Biologists have identified the wood wasp, an insect that is capable of "drilling" into wood to lay its eggs. A low mass and low power system, like an insect, capable of drilling into wood is of the highest interest for planetary drilling and terrestrial drilling alike. The general working principle of the wood wasp drill ("dual reciprocating drilling") will be exposed and the potential benefits of imitating the wood wasp for planetary drilling will be highlighted. Since the nature of wood is highly fibrous but the nature of extraterrestrial and terrestrial soils are not, it is necessary to adapt the wood wasp ovipositor to our target soils. A test bench to evaluate the influence of the different geometries and operational parameters was produced and is presented here. The dual reciprocating drilling experimental results obtained on this test bench are also highlighted. They should lead to a new and enhanced model and comprehension of dual-reciprocating-drilling

Damage localization using experimental modal parameters and topology optimization

This work focuses on the developement of a damage detection and localization tool using the Topology Optimization feature of MSC.Nastran. This approach is based on the correlation of a local stiness loss and the change in modal parameters due to damages in structures. The loss in stiness is accounted by the Topology Optimization approach for updating undamaged numerical models towards similar models with embedded damages. Hereby, only a mass penalization and the changes in experimentally obtained modal parameters are used as objectives. The theoretical background for the implementation of this method is derived and programmed in a Nastran input file and the general feasibility of the approach is validated numerically, as well as experimentally by updating a model of an experimentally tested composite laminate specimen. The damages have been introduced to the specimen by controlled low energy impacts and high quality vibration tests have been conducted on the specimen for dierent levels of damage. These supervised experiments allow to test the numerical diagnosis tool by comparing the result with both NDT technics and results of previous works (concerning shifts in modal parameters due to damage). Good results have finally been archieved for the localization of the damages by the Topology Optimization

Harmonic response of the organ of corti: results for wave dispersion

Inner ear is a remarkable multiphysical system and its modelling is a great challenge. The approach used in this paper aims to reproduce physic with a realistic description of the radial cross section of the cochlea. A 2D‐section of the organ of Corti is fully described. Wavenumbers and corresponding modes of propagation are calculated taking into account passive structural responses. The study is extended to six cross sections of the organ of Corti and a large frequency bandwidth from 100 Hz to 3 kHz. Dispersion curves reveal the influence of fluid structure interactions with a dispersive behavior at high frequencies. Longitudinal mechanical coupling provides new interacting modes of propagation

Correlating low energy impact damage with changes in modal parameters: diagnosis tools and FE validation

This paper presents a basic experimental technique and simplified FE based models for the detection, localization and quantification of impact damage in composite beams around the BVID level. Detection of damage is carried out by shift in modal parameters. Localization of damage is done by a topology optimization tool which showed that correct damage locations can be found rather efficiently for low-level damage. The novelty of this paper is that we develop an All In One (AIO) package dedicated to impact identification by modal analysis. The damaged zones in the FE models are updated by reducing the most sensitive material property in order to improve the experimental/numerical correlation of the frequency response functions. These approximate damage models(in term of equivalent rigidity) give us a simple degradation factor that can serve as a warning regarding structure safety

L’amortissement dynamique non-destructif au sein des matériaux structuraux

Les déformations - même légères - au sein des structures donnent lieu à des irréversibilités opérant une absorption d’énergie mécanique au cours du mouvement. Celle-ci peut être appréhendée sur des phénomènes répétitifs (de type vibratoire) ou transitoires (de type onde de choc). Le comportement élastique réversible du matériau est représenté par sa rigidité, reliant statiquement les contraintes aux déformations. Quant à son comportement dissipatif, la “viscosité” du matériau le modélise convenablement, reliant cinétiquement les contraintes aux variations de déformations dans le temps. La rigidité peut être constante ou non, selon que le matériau est linéaire ou non. De même, la viscosité peut être variable selon la non-linéarité de la dissipation. Pour évaluer correctement l’amortissement intrinsèque aux matériaux de constructions et à leurs assemblages, il est nécessaire de procéder à des essais sous vide, afin d’éliminer toute dissipation fluide d’origine externe (aérodynamique). Cela permet de mieux connaître le comportement dynamique des matériaux structuraux, notamment pour les véhicules aérospatiaux dans lesquels la dissipation peut être utile pour amortir les phénomènes vibratoires ou pour minimiser la transmission des chocs