Página 1 dos resultados de 262 itens digitais encontrados em 0.040 segundos

Limitations of simple flow models for the simulation of nanoimprint

TEYSSEDRE, Hubert; GILORMINI, Pierre; REGNIER, Gilles
Fonte: Carl Hanser Verlag Publicador: Carl Hanser Verlag
EN
Relevância na Pesquisa
75.95%
A quick evaluation of the forces involved in nanoimprint would be very helpful in the prevention of mold deflection. Unfortunately, it is shown here that assuming simplified flows may lead to quite incorrect evaluations of these forces, even for simple periodic patterns and a Newtonian behavior. The mere use of the classical result of the lubrica- tion theory does not account for the range of thickness-to-width ratios that may be involved, especially at the beginning of the process. An improved squeeze model includes this effect, but still underestimates the imprint force. Moreover, finite element simulations demonstrate limitations of two more elaborate models that are found in the literature. These simulations also show that two flow modes can be defined, according to whether or not the polymer touches the mold sidewalls. A deeper analysis of these two modes may help the definition of a more appropriate simplified model in the future.; Projet ANR SINCRONE

Springback of thick sheet AHSS subject to bending under tension

CHALAL, Hocine; RACZ, Sever-Gabriel; BALAN, Tudor
Fonte: ELSEVIER Publicador: ELSEVIER
EN_US
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76.18%
Lien vers la version éditeur : http://www.sciencedirect.com/science/article/pii/S0020740312000677; The springback behavior of four advanced high-strength sheet steels (Dual-Phase, TRIP, ferrite-bainite) with thicknesses ranging from 1.2 to 4 mm was investigated by means of the bending-under-tension (BUT) test. The applicability of several guidelines from the literature was investigated experimentally and numerically. The monotonic decrease of springback as back force increased was confirmed for this category of sheet steels, and a general trend for the non-linear influence of the tool radius was observed. The influence of numerical factors on the predicted values of springback was investigated, and conclusions and simple guidelines were drawn from the analysis with industrial sheet forming applications in mind.

Application of the continuum shell finite element SHB8PS to sheet forming simulation using an extended large strain anisotropic elastic–plastic formulation

SALAHOUELHADJ, Abdellah; ABED-MERAIM, Farid; CHALAL, Hocine; BALAN, Tudor
Fonte: Springer Publicador: Springer
EN_US
Relevância na Pesquisa
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http://link.springer.com/article/10.1007%2Fs00419-012-0620-x; This paper proposes an extension of the SHB8PS solid–shell finite element to large strain anisotropic elasto-plasticity, with application to several non-linear benchmark tests including sheet metal forming simulations. This hexahedral linear element has an arbitrary number of integration points distributed along a single line, defining the "thickness" direction; and to control the hourglass modes inherent to this reduced integration, a physical stabilization technique is used. In addition, the assumed strain method is adopted for the elimination of locking. The implementation of the element in Abaqus/Standard via the UEL user subroutine has been assessed through a variety of benchmark problems involving geometric non-linearities, anisotropic plasticity, large deformation and contact. Initially designed for the efficient simulation of elastic–plastic thin structures, the SHB8PS exhibits interesting potentialities for sheet metal forming applications – both in terms of efficiency and accuracy. The element shows good performance on the selected tests, including springback and earing predictions for Numisheet benchmark problems.

A space–time approach in digital image correlation: Movie-DIC

BESNARD, Gilles; GUERARD, Sandra; ROUX, Stéphane; HILD, François
Fonte: elsevier Publicador: elsevier
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76.14%
A new method is proposed to estimate arbitrary velocity fields from a time series of images acquired by a single camera. This approach, here focused on a single spatial plus a time dimension, is specialized to the decomposition of the velocity field over rectangular shaped (finite-element) bilinear shape functions. It is therefore assumed that the velocity field is essentially aligned along one direction. The use of a time sequence over which the velocity is assumed to have a smooth temporal change allows one to use elements whose spatial extension is much smaller than in traditional digital image correlation based on successive image pairs. This method is first qualified by using synthetic numerical test cases, and then applied to a dynamic tensile test performed on a tantalum specimen. Improvements with respect to classical digital image correlation techniques are observed in terms of spatial resolution.

Influence of the microstructure and defects on the high cycle fatigue strength of 316L stainless steel under multiaxial loading

GUERCHAIS, Raphaël; MOREL, Franck; SAINTIER, Nicolas; ROBERT, Camille
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
EN
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75.95%
In the present study, the effects of both the microstructure and defects on the high cycle fatigue behavior of the 316L austenitic stainless steel are investigated thanks to finite element simulations of polycrystalline aggregates. The numerical analysis relies on a metallurgical and mechanical characterization. To complete the experimental study, load-controlled fatigue tests are also carried out to determine the fatigue limits at 2.106 cycles under uniaxial and multiaxial loading conditions using both smooth specimens and specimens containing an artificial hemispherical surface defect. In the finite element models, where the grain morphologies are explicitly modeled, the anisotropic behavior of each crystal is described by the generalized Hooke’s law and by a single crystal visco-plastic model. From the simulations carried out with different defect sizes and orientation sets, statistical informations regarding mesoscopic mechanical fields are analyzed. Then, using the FE results, the ability of a probabilistic fatigue criterion to predict the influence of defects and biaxiality on the average fatigue limits is evaluated thanks to a comparison with the experimental data.

Direct experimental evidence of time-temperature superposition at finite strain for an amorphous polymer network

DIANI, Julie; GILORMINI, Pierre; ARRIETA, Juan Sebastain
Fonte: Elsevier Publicador: Elsevier
EN
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75.95%
The time-temperature superposition property of an amorphous polymer acrylate network is characterized at infinitesimal strain by standard dynamic mechanical analysis tests. Comparison of the shift factors determined in uniaxial tension and in torsion shows that both tests provide equivalent time-temperature superposition properties. More interestingly, finite strain uniaxial tension tests run until break at constant strain rate show that the acrylate network exhibits the same time-temperature superposition property at finite strain as at infinitesimal strain. Such original experimental evidence provides new insight for finite strain constitutive modelling of polymer amorphous networks.; ANR REFORM 10-JCJC-0917

Characterising the impact of surface integrity on the fatigue behaviour of forged components

GERIN, Benjamin; PESSARD, Etienne; MOREL, Franck; VERDU, Catherine
Fonte: Société Française de Métallurgie et de Matériaux Publicador: Société Française de Métallurgie et de Matériaux
EN
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86.27%
The present study focusses on analysing and modelling the influence on fatigue behaviour of the surface of a hot-forged C70 connecting rod which undergoes a shot-blasting treatment. The shot-blasting heavily affects the surface and thus the fatigue properties. In addition, the forging process introduces large defects which also have an effect on the fatigue strength. So as to be able to determine which aspects of the surface integrity are the most influential in fatigue, various surface states were thoroughly characterised and then tested in high cycle fatigue in bending. The various aspects studied are the surface roughness and large defects, residual stresses, microstructure and hardness.

Characterising the impact of surface integrity on the fatigue behaviour of a shot-peened connecting rod

GERIN, Benjamin; PESSARD, Etienne; MOREL, Franck; VERDU, Catherine
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
EN
Relevância na Pesquisa
76.18%
The present study focuses on analysing and modelling the influence on fatigue behaviour of the surface of a hot-forged C70 connecting rod which undergoes a shot-blasting treatment. The shot-blasting heavily affects the surface and thus the fatigue properties. In addition, the forging process introduces large defects which also have an effect on the fatigue strength. So as to be able to determine which aspects of the surface integrity are the most influential in fatigue, additional surface states were generated by shot-peening the as-forged surface. The various surface states were thoroughly characterised and then tested in high cycle fatigue in bending. The various aspects studied are the surface roughness and large defects, residual stresses, and microstructure.

Statistical assessment of multiaxial HCF criteria at the grain scale

MOREL, Franck; HOR, Anis; PALIN-LUC, Thierry; SAINTIER, Nicolas; ROBERT, Camille
Fonte: Elsevier Publicador: Elsevier
EN
Relevância na Pesquisa
76.18%
Multiaxial high cycle fatigue modeling of materials is an issue that concerns many industrial domains (automotive, aerospace, nuclear, etc.) and in which many progress still remains to be achieved. Several approaches exist in the literature: invariants, energy, integral and critical plane approaches all of them having their advantages and drawbacks. These different formulations are usually based on mechanical quantities at the micro or mesoscales using localization schemes and strong assumptions to propose simple analytical forms. This study aims to revisit these formulations using a numerical approach based on crystal plasticity modeling coupled with explicit description of microstructure (morphology and texture) and proposes a statistical procedure for the analyses of numerical results in the HCF context. This work has three steps: First, 2.5D periodic digital microstructures based on a random grain sizes distribution are generated. Second, multiaxial cyclic loading conditions corresponding to the fatigue strength at 106 cycles are applied to these microstructures. Third, the mesoscopic Fatigue Indicator Parameters (FIPs), formulated from the different criteria existing in the literature, are identified using the finite element calculations of the mechanical fields. These mesoscopic FIP show the limits of the original criteria when it comes to applying them at the grain scale. A statistical method based on extreme value probability is used to redefine the thresholds of these criteria. These new thresholds contain the sensitivity of the HCF behavior to microstructure attributes. Finally...

Thermal characterization of the SiO2-Ge2Sb2Te5 interface from room temperature up to 400 °C

BATTAGLIA, Jean-Luc; KUSIAK, Andrzej; SCHICK, Vincent; CAPPELLA, Andrea; WIEMER, Claudia; LONGO, Massimo; VARESI, Enrico
Fonte: American Institute of Physics Publicador: American Institute of Physics
EN
Relevância na Pesquisa
76.02%
The thermal conductivity of Ge2Sb2Te5 (GST) layers, as well as the thermal boundary resistance at the interface between the GST and amorphous SiO2, was measured using a photothermal radiometry experiment. The two phase changes in the Ge2Sb2Te5 were retrieved, starting from the amorphous and sweeping to the face centered cubic (fcc) crystalline state at 130 °C and then to the hexagonal crystalline phase (hcp) at 310 °C. The thermal conductivity resulted to be constant in the amorphous phase, whereas it evolved between the two crystalline states. The thermal boundary resistance at the GST-SiO2 interface was estimated to be higher for the hcp phase than for the amorphous and fcc ones.

On modeling shape memory polymers as elastic two-phase composite materials

GILORMINI, Pierre; DIANI, Julie
Fonte: Elsevier Publicador: Elsevier
EN
Relevância na Pesquisa
75.96%
A model has been proposed recently, which describes the experimentally observed mechanical behavior of some shape memory polymers. It considers a purely thermoelastic behavior, without strain rate effects, and assumes essentially that the polymer can be considered as a two-phase composite, with glassy and rubbery phases having volume fractions that depend on temperature only. Since a uniform stress hypothesis was used in the original formulation, with an inconsistency when thermal expansion was considered, this model is revisited here by taking advantage of the many results that have been established in the theory of composite materials. It is shown, especially, that a uniform strain hypothesis is more appropriate than assuming a uniform stress.; Projet ANR jeunes chercheurs REFORM 10-JCJC-0917.

Predicting thermal shape recovery of crosslinked polymer networks from linear viscoelasticity

DIANI, Julie; GILORMINI, Pierre; FREDY, Carole; ROUSSEAU, Ingrid
Fonte: Elsevier Publicador: Elsevier
EN
Relevância na Pesquisa
75.96%
The viscoelastic behavior of an amorphous shape-memory polymer network and its dependence on time and temperature were measured by dynamic mechanical analysis. The resulting thermomechanical behavior was modeled and implemented in a commercial finite element code. The ability of the resulting thermomechanical model to simulate and, eventually, predict the shape storage and shape recovery of the material was evaluated by comparison with experimental shape memory thermomechanical torsion data in a large deformation regimen. The simulations showed excellent agreement with experimental shape memory thermomechanical cycle data. This demonstrates the dependence of the shape recovery on time and temperature. The results suggest that accurate predictions of the shape recovery of any amorphous polymer networks under any thermomechanical conditions combination solely depends on considering the material viscoelasticity and its timetemperature dependence.; Projet ANR jeunes chercheurs REFORM 10-JCJC-0917.

A torsion test for the study of the large deformation recovery of shape memory polymers

DIANI, Julie; FREDY, Carole; GILORMINI, Pierre; MERCKEL, Yannick; REGNIER, Gilles; ROUSSEAU, Ingrid
Fonte: Elsevier Publicador: Elsevier
EN
Relevância na Pesquisa
75.96%
A torsion device was designed and built for testing the shape fixity and shape recovery of shape memory polymers at large deformation. A simple thermal chamber was used to regulate the thermal environment during testing and a CCD camera was used for recording the deformation. Such a torsion testing system provided a quantitative estimate of the kinematics and kinetics of shape recovery for samples submitted to large deformations at moderate strains that are more likely expected in actual shape memory applications. In addition, such measurements are complementary to those obtained from large strain uniaxial tension tests usually run for during traditional shape memory effect characterization. As a result, the torsional shape memory testing device and testing method described is expected to contribute building complementary data for the thermomechanical modeling of shape memory polymers.; Projet ANR jeunes chercheurs REFORM 10-JCJC-0917.

Investigation of advanced strain-path dependent material models for sheet metal forming simulations

HADDAG, Badis; BALAN, Tudor; ABED-MERAIM, Farid
Fonte: Elsevier Publicador: Elsevier
EN_US
Relevância na Pesquisa
76.15%
Sheet metal forming processes often involve complex loading sequences. To improve the prediction of some undesirable phenomena, such as springback, physical behavior models should be considered. This paper investigates springback behavior predicted by advanced elastoplastic hardening models which combine isotropic and kinematic hardening and take strain-path changes into account. A dislocation-based microstructural hardening model formulated from physical observations and the more classical cyclic model of Chaboche have been considered in this work. Numerical implementation was carried out in the ABAQUS software using a return mapping algorithm with a combined backward Euler and semi-analytical integration scheme of the constitutive equations. The capability of each model to reproduce transient hardening phenomena at abrupt strain-path changes has been shown via simulations of sequential rheological tests. A springback analysis of strip drawing tests was performed in order to emphasize the impact of several influential parameters, namely: process, numerical and behavior parameters. The effect of the two hardening models with respect to the process parameters has been specifically highlighted.

Analyse de la congélation de tissus biologiques à l’échelle cellulaire par Thermographie InfraRouge

PRADERE, Christophe; TOUTAIN, Jean; BAMFORD, Matthieu; BATSALE, Jean-Christophe
Fonte: Société Française de Thermique / Congrès Français de Thermique, 29 mai - 1 juin 2007, Île des Embiez Publicador: Société Française de Thermique / Congrès Français de Thermique, 29 mai - 1 juin 2007, Île des Embiez
FR
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76.19%
Ce travail concerne l'étude de la congélation de tissus biologiques avec des premiers résultats d’analyse de champs de température obtenus par thermographie infrarouge. On montre plusieurs configurations expérimentales allant d’un milieu modèle (cristallisation d’eau pure en microcanal) à un milieu biologique hétérogène réel (épiderme d’oignon). Le fait de disposer d'un champ de température 2D transitoire offre de nombreuses et nouvelles possibilités de traitements et d’analyses de cartographies de propriétés thermophysiques.

Caractérisation thermique des matériaux pour mémoires à changement de phase à haute température et échelle submicrométrique.

SCHICK, Vincent; CAPPELLA, Andrea; BATTAGLIA, Jean-Luc; KUSIAK, Andrzej
Fonte: Société Française de Thermique / Congrès Français de Thermique, 2009, Golfe du Morbihan Publicador: Société Française de Thermique / Congrès Français de Thermique, 2009, Golfe du Morbihan
FR
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76.36%
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. Le principe de stockage de l'information repose sur la différence de résistivité électrique entre l’état amorphe et l’état cristallin de ces verres, le passage entre ces différents états s’effectuant par chauffage (effet Joule). 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 la conductivité thermique de couche mince de faible épaisseur (100 nm – 800 nm) sur une plage de température de 25°C à 400°C. La résistance d’interface entre le GST et le diélectrique utilisé dans les PCM (ici du SiO2) est aussi estimée.

Fatigue analysis of catenary contact wires for high speed trains

MASSAT, Jean-Pierre; NGUYEN TAJAN, T.M.L.; MAITOURNAM, Habibou; BALMES, Etienne
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
EN_US
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76.11%
The fatigue fracture is one of the most critical failures which may occur on the high speed network because it is undetectable and it has a huge impact on traffic disruption. The contact wire lifespan of a high speed line is estimated at more than 50 years and thus it is necessary to consider the risk of fatigue. The Railway Technical Research Institute in Japan studied this phenomenon for a long time and performed experimental tests. Using these results and by comparing with failures occurred in France, a preliminary analysis is carried out to identify parameters which significantly influence the fatigue phenomenon. This analysis consists in using the numerical software OSCAR© to evaluate the loads, perform a fatigue assessment of the contact wire. The procedure, using a one-dimensional and a three-dimensional model, is described in this article.

Évaluation de la dispersion des propriétés mécaniques d’un matériau composite par sous-échantillonnage

DAU, Frédéric; PINEAU, Pierre
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
FR
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86%
This article presents a subsampling and homogenization technique developed to depict behaviour variability at mesoscopic scale in composite materials. This variability is intended to feed multiscale modelling at mesoscale. The technique presented here is meant to characterize the transverse behaviour of unidirectional plies in a stratified Polymer Matrix Composite. A Finite Element Method simulation is performed at microscopic scale considering the heterogeneous media, the mesh being constructed from a transverse micrograph. A part of the ply entitled the sample and supposed to be representative of the material is studied under plane strain hypothesis. A unique loading simulation, reduced to three basic load cases, is applied. Subsamples taken into the simulation cell are homogenized at post-processing level of strain and stress fields. A standard mechanics approach was considered. Various subsampling schemes are performed with various size and spatial distribution to generate statistical distributions of effective elastic properties. Some statistical aspects are highlighted and discussed.

Simulation du comportement de la silice sous indentation Vickers par la méthode des elements discrets: densification et mécanismes de fissuration; Congrès français de mécanique (21; 2013; Bordeaux (Gironde))

JEBAHI, Mohamed; ANDRE, Damien; DAU, Frédéric; CHARLES, Jean-Luc; IORDANOFF, Ivan
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
FR
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86.05%
The indentation response of glasses can be classified into three classes : normal, anomalous and intermediate depending on the deformation mechanism and the cracking response. Silica glass, as a typical anomalous glass, deforms primarily by densification and has a strong tendency to form cone cracks that can accompany median, radial and lateral cracks when indented with a Vickers tip. This is due to its propensity to deform elastically by resisting plastic flow. Several investigations of this anomalous behavior can be found in the literature. The present paper serves to corroborate these results numerically using the discrete element method. A new pressure-densification model involving the discrete element method (DEM) is developed that allows for a quantitative estimate of the densification under very high pressure. This model is then used to simulate the Vickers indentation response of silica glass under various indentation forces. The numerical results obtained compare favorably with past experimental results.

Influence of a pulsed laser regime on surface finish induced by thedirect metal deposition process on a Ti64 alloy

GHARBI, Myriam; PEYRE, Patrice; GORNY, Cyril; MORVILLE, Simon; LE MASSON, Philippe; CARRON, Denis; FABBRO, Rémy; CARIN, Muriel
Fonte: ELSEVIER Publicador: ELSEVIER
EN
Relevância na Pesquisa
76.18%
tThe direct metal deposition (DMD) laser technique is a free-form metal deposition process, which allowsgenerating a prototype or small series of near net-shape structures. Despite numerous advantages, oneof the most critical issues of the technique is that produced pieces have a deleterious surface finish whichrequires post machining steps. Following recent investigations where the use of laser pulses instead of acontinuous regime was successful to obtain smoother DMD structures, this paper relates investigationson the influence of a pulsed laser regime on the surface finish induced by DMD on a widely used titaniumalloy (Ti64). Findings confirm that using high mean powers improves surface finish but also indicate aspecific effect of the laser operating mode: using a quasi-continuous pulsed mode instead of fully-cw laserheating is an efficient way for surface finish improvement. For similar average powers, the use of a pulsedmode with large duty cycles is clearly shown to provide smoothening effects. The formation of larger andstable melt pools having less pronounced lateral curvatures, and the reduction of thermal gradients andMarangoni flow in the external side of the fusion zone were assumed to be the main reasons for surfacefinish improvement. Additional results indicate that combining the benefits from a pulsed regime and auniform laser irradiation does not provide further reduction of surface roughness.