Página 1 dos resultados de 67 itens digitais encontrados em 0.050 segundos

Modèle de comportement des structures bobinées : étude des fonds

EL MOUSSAID, Mohammed; PERRY, Nicolas; WAHL, Jean Christophe; BOIS, Christophe
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
FR
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76.23%
L’utilisation de matériaux composites sur des réservoirs permet le développement d’applications de stockage haute pression. En effet, dans ce domaine les composites sont très compétitifs par rapport aux matériaux métalliques classiquement utilisés. Sur les structures épaisses, l’utilisation de composites permet d’obtenir des pressions à rupture très élevées (de l’ordre de 2000 bar), qui ne sont pas atteignables en utilisant des réservoirs métalliques. Toutefois, cela conduit à utiliser de fortes épaisseurs de composites, et le comportement de ce type de structure reste mal maitrisé. En particulier, le comportement des fonds doit être étudié avec précision. Il faut en effet intégrer la géométrie complexe liée au procédé de mise en œuvre.

Comportement à l'impact des composites fibres de verre/Epoxy modifié copolymère à bloc.

BOUMBIMBA, Rodrigue Matadi; VIOT, Philippe; FROUSTEY, Catherine; LEONARDI, Fréderic; GERARD, Pierre; INOUBLI, Raja
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
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116.05%
Epoxy resins are widely used in the design of fibre composite materials. This increasing use finds its reason in the fact that these materials have excellent mechanical and thermal properties. Playing on its chemical composition and curing speed, it’s possible to vary the mechanical properties from the extreme flexibility to high rigidity. However, the inherent toughness of a highly crosslinked epoxy is relatively low. It therefore seems desirable for high impact resistance applications, to improve the toughness, without affecting the other usual properties of this polymer. Recent studies have shown a significant improvement in impact resistance of epoxy in the presence of block copolymers. Our work aims to investigate the effect of triblock copolymer-based acrylate (Nanostrength) on the impact resistance of glass / epoxy composite. An experimental device, called "drop tower" is used to perform impact tests on composites with or without Nanostrength. Dynamic mechanical analyses (DMA) were conducted, first to characterize the effect of addition of Nanostrength on the thermomechanical properties, but also to establish a correlation between thermomechanical properties and impact resistance. Different observation tools, such as optical observation...

Reliability approach on impacted composite materials for railways

DAU, Frédéric; GUILLAUMAT, Laurent; COCHETEU X, Francis; CHAUVIN, Thomas
Fonte: Revue des Composites et matériaux avancés Publicador: Revue des Composites et matériaux avancés
EN
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66.24%
This paper deals with a reliability approach applied on composite plates which should be used in railway structures under low velocity impact loading.Impacted composite plates in bending configuration are considered as an application of the reliability approach to composite materials. Mass of projectile, height of fall and distance between supports are the three variables considered. A limit state function G is defined by the impact force compared to a critical one. Using reliability approach, the reliability indexallows to estimate the probability of failurePf. It is then assessed for several values of the critical force using Monte Carlo direct method and First Order Reliability Method (FORM) approximated method. For FORM method, genetic algorithms are investigated to obtain the best reliability index. Results obtained by the approximated FORM method are finally discussed and compared to Monte Carlo simulations considered as a reference .

An expert system to characterise the surfaces morphological properties according to their tribological functionalities: The relevance of a pair of roughness parameters

BIGERELLE, M.; NAJJAR, D.; MATHIA, T.; IOST, Alain; COOREVITS, Thierry; ANSELME, K.
Fonte: Elsevier Publicador: Elsevier
EN
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95.81%
Knowing that a surface or profile can be characterized by numerous roughness parameters, the objective of this investigation was to present a methodology which aims to determine quantitatively and without preconceived opinion the most relevant pair of roughness parameters that describe an abraded surface. The methodology was firstly validated on simulated fractal profiles having different amplitudes and Hölder exponents and it was secondly applied to characterise different worn regions of a retrieved metallic femoral head articulated against an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup containing an embedded metallic fibber into its surface. The methodology consists in combining the recent Bootstrap method with the usual discriminant analysis. It was validated on simulated fractal profiles showing that, among more than 3000 pairs tested, the total amplitude Rt and the fractal dimension Δ is the most relevant pair of roughness parameters; parameters corresponding to the variables modulated in the analytical expression of the fractal function. The application of this methodology on a retrieved metallic femoral head shows that the most relevant pair of parameters for discriminating the different investigated worn regions is the arithmetic roughness parameter Ra paired with the mean peak height Rpm. This methodology finally helps in a better understanding of the scratch mechanism of this orthopedic bearing component.

Prediction of the Spindle and Tool Receptance : Industrial Application in Reaming Process

SELMI, Jaouher; COSTES, Jean-Philippe; LORONG, Philippe; POULACHON, Gérard; CARRAS, Patrice
Fonte: MM Science Journal Publicador: MM Science Journal
EN
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96.04%
It is proposed to apply a methodology in order to evaluate the ability of different machining systems (Spindle/Tool) to run a reaming process in a stable way.The methodology is based on an experimental measurement of the dynamic behavior for the system including the spindle and the tool holder. Then, by coupling frequencies response functions, a new system (Spindle/Tool) FRF is predicted at the tool tip. Finally, the critical depth of cut is analytically calculated from the eigenvalues of the characteristic equation of the dynamic reaming process.; Programme CIFRE

Approche multi-échelle de l’hétérogénéité de déformation du dioxyde d’uranium

SOULACROIX, Julian; MICHEL, Bruno; GATT, Jean-Marie; KUBLER, Régis; BARRALLIER, Laurent
Fonte: CSMA Publicador: CSMA
FR
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66.2%
Le dioxyde d’uranium est le combustible nucléaire de référence pour la filière des réacteurs à eau pressurisée en France. Une étude expérimentale du comportement mécanique de ce matériau montre qu’il est le lieu d’une déformation hétérogène, c’est-à-dire d’une déformation plastique localisée, à l’échelle macroscopique. Des simulations numériques montrent que l’apparition et la forme de la localisation dépendent du comportement local du matériau, de la sollicitation appliquée, des conditions aux limites, mais aussi de la description initiale de la microstructure, et notamment la prise en compte d’une hétérogénéité initiale du matériau.

Semi phenomenological modelling of the behavior of TRIP steels

KUBLER, Régis; BERVEILLER, Marcel; BUESSLER, Pascal
Fonte: International Journal of Plasticity Publicador: International Journal of Plasticity
EN_US
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96.11%
The authors are grateful to ArcelorMittal R&D for supporting this research.; A new semi-phenomenological model is developed based on a mean-field description of the TRIP behavior for the simulation of multiaxial loads. This model intends to reduce the number of internal variables of crystalline models that cannot be used for the moment in metal forming simulations. Starting from local and crystallographic approaches, the mean-field approach is obtained at the phase level with the concept of Mean Instantaneous Transformation Strain (MITS) accompanying martensitic transformation. Within the framework of the thermodynamics of irreversible processes, driving forces, martensitic volume fraction evolution and an expression of the TRIP effect are determined for this new model. A classical self-consistent scheme is used to model the behavior of multiphased TRIP steels. The model is tested for cooling at constant loads and for multiaxial loadings at constant temperatures. The predictions reproduce the increase in ductility, the dynamic softening effect and the multiaxial behavior of a multiphased TRIP steel

Geometrical Specification Model for Gear - Expression, Metrology and Analysis

DANTAN, Jean-Yves; BRUYERE, Julien; BAUDOUIN, Cyrille; MATHIEU, Luc
Fonte: Elsevier Publicador: Elsevier
EN
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95.95%
To ensure the gear precision, industries need a coherent model to express, to analyse and to check geometrical specifications. Most gear tolerance representations are directly driven by the convenience of dimensional metrology and not by the convenience of the set of activities of the tolerancing process. Therefore, to ensure the coherence of all tolerancing process activities, there is a necessity to develop a complete gear tolerance model which should: represent standard tolerance practices; be integrated in the Computer-Aided systems of design, manufacturing and metrology; be controlled by CMM; and support automated tolerance analysis. The proposed model extends capabilities of a vectorial dimensioning & tolerancing model in order to satisfy the four requirements. This model is based on GeoSpelling [1]. Its coherence is illustrated by two applications: gear tolerance analysis and gear tolerance verification by CMM.

Formability prediction of thin metal sheets using various localization criteria

ALTMEYER, Guillaume; ABED-MERAIM, Farid; BALAN, Tudor
Fonte: Springer Link Publicador: Springer Link
EN_US
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95.81%
The aim of this paper is to give an overview of the theoretical basis of the most significant and commonly used localization criteria reformulated into a unified framework, and to apply these criteria to different materials in order to determine their formability domains. After giving a general material description based on a phenomenological approach, theoretical foundations of localization criteria are presented together with their advantages and drawbacks. These criteria rely on diverse theories: maximum load principle, bifurcation analysis, Marciniak-Kuczynski analysis, and stability analysis by a linear perturbation method. They are then applied to a brass and a Dual Phase steel and the predicted Forming Limit Diagrams (FLD) are discussed.

Numerical and analytical modeling of orthogonal cutting : The link between local variables and global contact characteristics

MOLINARI, Alain; CHERIGUENE, Rachid; MIGUELEZ, Henar
Fonte: Elsevier Publicador: Elsevier
EN_US
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95.81%
The response of the tool–chip interface is characterized in the orthogonal cutting process by numerical and analytical means and compared to experimental results. We study the link between local parameters (chip temperature, sliding friction coefficient, tool geometry) and overall friction characteristics depicting the global response of the tool–chip interface. Sticking and sliding contact regimes are described. The overall friction characteristics of the tool are represented by two quantities: (i) the mean friction coefficient qualifies the global response of the tool rake face (tool edge excluded) and (ii) the apparent friction coefficient reflects the overall response of the entire tool face, the effect of the edge radius being included. When sticking contact is dominant the mean friction coefficient is shown to be essentially the ratio of the average shear flow stress along the sticking zone by the average normal stress along the contact zone. The dependence of overall friction characteristics is analyzed with respect to tool geometry and cutting conditions. The differences between mean friction and apparent friction are quantified. It is demonstrated that the evolutions of the apparent and of the mean friction coefficients are essentially controlled by thermal effects. Constitutive relationships are proposed which depict the overall friction characteristics as functions of the maximum chip temperature along the rake face. This approach offers a simple way for describing the effect of cutting conditions on the tool–chip interface response. Finally...

Thermo-mechanical behaviour of TRIP 1000 steel sheets subjected to low velocity perforation by conical projectiles at different temperatures

RODRIGUEZ MARTINEZ, José Antonio; PESCI, Raphaël; RUSINEK, Alexis; ARIAS, Angel; ZAERA, Ramon; PEDROCHE, David Arias
Fonte: Elsevier Publicador: Elsevier
EN_US
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95.81%
This paper presents and analyzes the behaviour of TRIP 1000 steel sheets subjected to low velocity perforation by conical projectiles. The relevance of this material resides in the potential transformation of retained austenite to martensite during impact loading. This process leads to an increase in strength and ductility of the material. However, this transformation takes place only under certain loading conditions strongly dependent on the initial temperature and deformation rate. In order to study the material behaviour under impact loading, perforation tests have been performed using a drop weight tower. Experiments were carried out at two different initial temperatures T0 213 K and T0 288 K, and within the range of impact velocities 2.5 m/s 6 V0 6 4.5 m/s. The experimental setup enabled the measuring of impact velocity, residual velocity, load time history and failure mode. In addition, dry and lubricated contacts between the striker and the plate have been investigated. Finally, by using X ray diffraction it has been shown that no martensitic transformation takes place during the perforation process. The causes involving the none appearance of martensite are examined.

Caractérisation thermique d’une couche mince de Ge2Sb2Te5 en fonction de la température dans une expérience pompe-sonde résolue en temps

SCHICK, Vincent; BATTAGLIA, Jean-Luc; KUSIAK, Andrzej; ROSSIGNOL, Clément
Fonte: Société Française de Thermique / Congrès Français de Thermique - Energies et transports durables, 25 - 28 mai 2010, Le Touquet Publicador: Société Française de Thermique / Congrès Français de Thermique - Energies et transports durables, 25 - 28 mai 2010, Le Touquet
FR
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75.8%
Les PCM (Phase Change Memory) développés par l’industrie microélectronique utilisent des verres chalcogénures des systèmes Ge-Sb-Te pour assurer le stockage de données informatiques par changement de structures cristallines. Il est fondamental, afin de maîtriser ces phénomènes de changement de phase pour le stockage des données, de connaître les propriétés thermiques de ces matériaux. On mesure ainsi l'effusivité thermique de couche mince de 210 nm d'épaisseur sur une plage de température de 25°C à 250°C. Les mesures sont réalisées par thermo-réflectométrie résolue en temps. On étudie ainsi la réponse d'un échantillon à une impulsion de 100 fs sur une durée de 6 ns. L’estimation des propriétés thermiques se fait en utilisant un modèle basé sur la loi de Fourier.

High cycle multiaxial fatigue crack initiation : experimental observations and microstructure simulations

AGBESSI, Komlan; SAINTIER, Nicolas; PALIN-LUC, Thierry
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
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106.04%
This study provides an analysis of high cycle multiaxial fatigue crack initiation modes based on SEM observations.The statistical study of crack initiation preferential sites shows that grains with multiple slip have a high probability of crack initiation. The application of Dang Van criterion at the grain scale using finite element analysis (cubic elasticity with / or without crystal plasticity) on 3D synthetic semi-periodic microstructures shows a strong heterogeneity of both the hydrostatic stress and shear. The evolution of this heterogeneity introduced by the material behavior is discussed. Finally, a method based on the extreme values statistics is proposed and applied to the fatigue indicative parameter associated to the Dang Van criterion. The effects of free surface and constitutive material model were analyzed.

Micromechanical behavior of UO2: crystalline anisotropy and associated internal stressezs in polycrystals

SOULACROIX, Julian; MICHEL, Bruno; GATT, Jean-Marie; KUBLER, Régis; BARRALLIER, Laurent
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
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106.14%
Uranium dioxide is the standard nuclear fuel for pressurized water reactors in France. This ceramic is manufactured by sintering. The standard shape for use in nuclear reactor is a small cylinder, also called “pellet”, which measures about 8mm in diameter and 12mm in height. These pellets are then stacked into a zirconium alloy cladding, forming a rod. The fuel rods are then assembled together and these assemblies are put in the nuclear core. The mechanical behavior of the nuclear fuel during operation depends on the mechanical state of the rod (pellet and cladding), which can be related to other phenomena taking place during irradiation. A first step in the modeling approach is to study the mechanical behavior of non irradiated uranium oxide. For a temperature higher than about 1000°C and for a strain rate higher than about 1.10

Nonlinear structural damage detection based on cascade of Hammerstein models

REBILLAT, Marc; HAJRYA, Rafik; MECHBAL, Nazih
Fonte: Elsevier Publicador: Elsevier
EN
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106.01%
Structural damages can result in nonlinear dynamical signatures that can significantly enhance their detection. An original nonlinear damage detection approach is proposed that is based on a cascade of Hammerstein models representation of the structure. This model is estimated by means of the Exponential Sine Sweep Method from only one measurement. On the basis of this estimated model, the linear and nonlinear parts of the output are estimated, and two damage indexes (DIs) are proposed. The first DI is built as the ratio of the energy contained in the nonlinear part of an output versus the energy contained in its linear part. The second DI is the angle between the subspaces obtained from the nonlinear parts of two set of outputs after a principal component analysis. The sensitivity of the proposed DIs to the presence of damages as well as their robustness to noise are assessed numerically on spring-mass-damper structures and experimentally on actual composite plates with surface-mounted PZT-elements. Results demonstrate the effectiveness of the proposed method to detect a damage in nonlinear structures and in the presence of noise.

Damage tolerance of impacted curved panels

BALLERE, Ludovic; VIOT, Philippe; LATAILLADE, Jean-Luc; GUILLAUMAT, Laurent; CLOUTET, S
Fonte: Elsevier Publicador: Elsevier
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96.02%
The final aim of this study is to evaluate the influence of impact damage on the residual strength of carbon/epoxy vessels stressed by internal pressure. An intermediate stage determined the residual behaviour of pre-impacted curved panels loaded in tension. Curved panels were impacted, reproducing the damage types observed in impacted vessels filled with propellant. Delamination damage was assessed by ultrasonics and optical microscopy used to observe intra-laminar mechanisms. Tension after impact (TAI) tests quantified the residual behaviour. An experimental design was used as an alternative to the complex analytical modelling of dynamic damage mechanisms. With this original technique, empirical relationships were established, linking impact parameters to residual properties. The force to failure was found to vary in a bi-linear manner with impact energy. Below a specific level of impact energy corresponding to failure in 4/7 of the plies, there is no significant reduction in the residual strength. The composite Young’s modulus decreased linearly with impact energy.

Étude micromécanique de l’influence de défauts sur la tenue en fatigue à grand nombre de cycles

GUERCHAIS, Raphael; SAINTIER, Nicolas; MOREL, Franck; ROBERT, Camille
Fonte: Congrès Français de mécanique Publicador: Congrès Français de mécanique
FR
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66.27%
The aim of this study is to analyse the influence of micro-notches on the fatigue behaviour of an electrolytic copper using finite element simulations of polycrystalline aggregates. In these simulations, in which the grains are explicitly modelled, the anisotropic behavior of each FCC crystal is described by the generalized Hooke’s law with a cubic elasticity tensor and by a single crystal visco-plastic model. The numerical analysis is done using several smooth and notched microstructures. The cyclic mechanical responses of the grains are then studied for different defect sizes and the ability of three fatigue criteria to predict the defect size effect on the fatigue strength is evaluated thanks to the comparison with experimental data.

A mechanistic approach to the Kitagawa-Takahashi diagram using a multiaxial probabilistic framework

PESSARD, Etienne; BELLETT, Daniel; MOREL, Franck; KOUTIRI, Imade
Fonte: ELSEVIER Publicador: ELSEVIER
EN_US
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96.09%
The aim of this paper is to propose a flexible multiaxial modelling framework that is capable of combining two fatigue damage mechanisms so as to continuously describe the Kitagawa-Takahashi diagram. It is proposed that this diagram represents two distinct fatigue damage mechanisms: one associated with crack initiation (or microstructurally small cracks) and the other with crack propagation (or long cracks). It is further postulated that these damage mechanisms are more appropriately modelled using di erent fatigue criteria. A probabilistic modelling framework is proposed in which any two suitable fatigue criteria can be combined in order to simultaneously model both damage mechanisms and the transition between them. This framework is based on the weakest link hypothesis and results in a probabilistic Kitagawa-Takahashi type diagram.

Proposal for a smart pressurised ring test to study thick composite produced by filament winding

BOIS, Christophe; PILATO, Aurélie; WAHL, Jean-Christophe; PERRY, Nicolas
Fonte: Elsevier Publicador: Elsevier
EN
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95.81%
This work was supported by OSEO agency. The authors would like to thank Air Liquide and EADS Composites Aquitaine for their technical support in the H2E project.; Improvements in the characterisation of materials used in pipes, tubes or vessels rely on the development of tests on cylindrical samples in order to be consistent with the real manufacturing process. Existing devices are unable to reach the pressure limits required to test high pressure hydrogen storage tanks. We therefore propose an original test device based on a conical fitting system. First, the operational principle and the pressure measurement technique are presented. Next, the choice of apparatus design parameters according to test requirements is discussed. In addition, the device’s capabilities are illustrated on a 39 mm thick CFRP ring test including Digital Image Correlation measurements.

DEMARCHE DE CONCEPTION D’UN ESSAI DE CARACTERISATION MECANIQUE MULTI-INSTRUMENTE : CAS D'UN TEST DE MISE SOUS PRESSION D’ANNEAU COMPOSITE

PILATO, Aurélie; PERRY, Nicolas; BOIS, Christophe; WAHL, Jean-Christophe
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
FR
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76.18%
Les auteurs tiennent à remercier l’entreprise Composite Aquitaine qui a réalisé et fournis des structures composites bobinées épaisses pour la réalisation des essais. Ils tiennent aussi à remercie P.Loeuillet pour son implication dans la mise en œuvre et la réalisation de cet essais.; le stockage de l'hydrogène sous forme gazeuse nécessite de développer les modèles de comportement des réservoirs composites (carbone époxy) réalisés en utilisant le procédé d'enroulement filamentaire. Ces réservoirs doivent supporter des hautes pressions de timbrage (jusqu’à 2100bars) ce qui conduit à des structures bobinées épaisses. Les modèles théoriques de comportements ne sont donc plus applicables, car régis par des hypothèses liés aux structures composites fines. Un test d’anneau sous pression a été développé pour représenter les sollicitations réelles de la structure et valider les propositions de modèles de comportements de structures épaisses. Cet essai est multi instrumenté pour observer des variations dans l’épaisseur des propriétés du matériau. Le but de cet article est de présenter la démarche de conception du dispositif de test adapté à l'utilisation d'une machine d'essai de traction. Cette conception a nécessité une étape d’itération avec les résultats d’analyse des premiers échantillons testés...