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Helbert G.,IFSTTAR | Saint-Sulpice L.,CNRS Brest Laboratory of Mechanics and Systems Laboratory | Arbab Chirani S.,CNRS Brest Laboratory of Mechanics and Systems Laboratory | Dieng L.,IFSTTAR | And 3 more authors.
Mechanics of Materials | Year: 2014

NiTi shape memory alloys (SMAs) wires exhibit R-phase frequently. This intermediate phase has interesting properties under cyclic loadings and fatigue. These wires have a good potential in civil engineering applications for their damping capacity. In accordance with these applications, in this study, a complete characterisation of NiTi wires is proposed. First the pseudo phase diagram concerning R-phase and its existence comparing to austenite or to martensite is obtained by realising tensile tests at different temperatures and strain amplitudes. Then, the cyclic behaviour under tension at various amplitudes is studied. Based on these loadings, the significant observations are: a small residual strain, the decrease of transformation yield stresses and the evolution of the hysteresis size with the number of cycles. To consider the real use conditions, the effect of strain rate has been studied at two temperatures. The obtained results show that, due to thermo-mechanical coupling, the mechanical behaviour is affected by the evolution of strain rate. Eventually, the damping effect of the studied wires has been evaluated. All the obtained results confirm the potential use of NiTi wires exhibiting R-phase in civil engineering applications. They also constitute an interesting reference for models development describing R-phase occurrence and ease their identification and validation procedures. © 2014 Elsevier Ltd. All rights reserved.

Rombaut N.,Compiègne University of Technology | Rombaut N.,French National Center for Scientific Research | Savoire R.,Compiègne University of Technology | Savoire R.,French National Center for Scientific Research | And 4 more authors.
Industrial Crops and Products | Year: 2015

Grape seed oil being industrially obtained by solvent extraction, in this study we investigate oil extraction from grape seeds by cold screw pressing, as an alternative extraction process.Effect of raw material and process parameters were evaluated using a 12 experiments Taguchi experimental design. Variables were (1) type of grape seeds, (2) preheating temperature (90 and 120. °C), (3) screw rotation speed (40 and 70. rpm) and (4) die diameter (10 and 15. mm). The type of grape seed was the most influencing parameter on the studied responses. Screw rotation speed and die diameter only affected the oil yield. Maximum oil yield was observed for type 1 grape seeds (64.3%, o/o). Total oil polyphenol content was also maximal for type 1 seeds with up to 121. mg. GAE/kg of oil. Maximum oil yield was 57.3% and 58.8% (o/o) for type 2 and type 3 grape seed respectively and total polyphenol oil content was below 90. mg. GAE/kg for these two types of seeds. Additional experiments were carried out on type 1 seeds to enhance oil yield and oil polyphenol content. Maximal oil yield achieved was 73% (o/o) and total oil polyphenol content was increased up to 26% (153. mg/kg of oil) on the maximum yield obtained with Taguchi design. © 2014 Elsevier B.V.

Gueguen Y.,French National Center for Scientific Research | Rouxel T.,French National Center for Scientific Research | Gadaud P.,CNRS Physics Laboratory | Bernard C.,French National Center for Scientific Research | And 4 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The viscous-flow behavior and temperature dependence of the elastic moduli of chalcogenide glasses from the germanium-selenium system were studied by means of homemade high-temperature indentation setup and resonant-frequency technique (1-10 kHz), respectively, for temperatures between 0.8 and 1.2×T g. The softening rates, both in the elastic and in the viscous-flow regimes, were correlated to network destructuration or reorganization events in the light of previously reported high-temperature neutron-scattering data. The concomitant change of Poisson's ratio (ν) and the thermodynamic parameters of the thermally activated viscous-flow process were characterized and provide a new basis for the understanding of the sources for the softening in the transition range. The temperature dependence of ν suggests weak changes of the network cross-linking degree at large Ge contents. On the contrary, in the case of a-Se, a steep fragmentation of the structural units is inferred from the ν(T) data, and the flow process is accompanied by a huge entropy change (activation entropy at saddle point). The entropy contribution at Tg (Tg×ΔSa) represents more than 50% of the activation enthalpy for flow (ΔHa) and increases with the selenium content. Hence the free activation energy (ΔGa) is much smaller than apparent activation energy as derived from viscosity data. © 2011 American Physical Society.

Brest J.S.,CNRS Laboratory of Materials Engineering of Brittany | Brest J.S.,Higher Institute of Aeronautics and Space | Keryvin V.,CNRS Laboratory of Materials Engineering of Brittany | Longere P.,Higher Institute of Aeronautics and Space | Yokoyama Y.,Tohoku University
Journal of Alloys and Compounds | Year: 2014

Multiaxial and heterogeneous mechanical experiments, by means of the diametral compression test (Brazilian test), were carried out on Zr-based Bulk Metallic Glass. Attention was notably focused on obtaining the displacement field in the area of interest (large strains) employing a Digital Image Correlation device, in addition to the measurement of the usual global load-displacement curve. In order to reproduce the behaviour of the BMG at stake, several constitutive equations were considered with growing complexity: von Mises, Drucker-Prager (pressure dependence), free volume based model as well as a viscoplastic Coulomb-Mohr type model. The two latter were implemented as user-material in a Finite Element computation code. The results of these investigations including experiments and computational simulations are discussed. © 2012 Elsevier B.V. All rights reserved.

Durin A.,MINES ParisTech | De Micheli P.,MINES ParisTech | Ville J.,POLYTECHS SA | Ville J.,CNRS Laboratory of Materials Engineering of Brittany | And 3 more authors.
Composites Part A: Applied Science and Manufacturing | Year: 2013

Limiting fibre breakage during composite processing is a crucial issue. The purpose of this paper is to predict the evolution of the fibre-length distribution along a twin-screw extruder. This approach relies on using a fragmentation matrix to describe changes in the fibre-length distribution. The flow parameters in the screw elements are obtained using the simulation software Ludovic®. Evolution of an initial fibre-length distribution for several processing conditions was computed and the results were compared with experimental values. The computation gives satisfying results, even though more comparisons with experiments would be necessary. © 2013 Elsevier Ltd. All rights reserved.

Longere P.,CNRS Clement Ader Institute | Longere P.,CNRS Laboratory of Materials Engineering of Brittany | Geffroy A.-G.,CNRS Laboratory of Materials Engineering of Brittany | Geffroy A.-G.,DCNS S.A. | And 2 more authors.
International Journal of Damage Mechanics | Year: 2012

This article presents a physically motivated approach, which has been developed in order to describe the transition of behavior between dense metal plasticity and microporous metal plasticity in the context of dynamic plasticity and adiabatic conditions. Considering that void germination requires a certain amount of plastic deformation, a 'primary' hole nucleation criterion as well as a statistical law governing the 'secondary' hole formation kinetics has been proposed. In a consistent way, the hole nucleation criterion accounts for the accelerating effects of stress triaxiality and the delaying effects of temperature and strain rate. In addition, a modification of the GTN model was proposed, allowing for describing cavity growth under shear loading. The 3D constitutive equations were implemented as user material in the engineering finite element computation code Abaqus®. Numerical simulations were conducted considering a single finite element under uniaxial tensile loading and simple shear then notched cylindrical samples under remote uniaxial tensile loading. The numerical results clearly show the influence of the hole nucleation criteria on the ductile damage and failure. © The Author(s), 2011.

Abou Nader C.,Saint - Joseph University | Abou Nader C.,Institut Universitaire de France | Pellen F.,Institut Universitaire de France | Roquefort P.,CNRS Laboratory of Materials Engineering of Brittany | And 4 more authors.
Optics Letters | Year: 2016

The noninvasive detection of a material's viscoelasticity is of great importance in the medical field. In fact, certain diseases cause changes in tissue structure and biological fluid viscosity; tracking those changes allows for detection of these diseases. Rheological measurements are also imperative in the industrial field, where it is necessary to characterize a material's viscoelasticity for manufacturing purposes. In this Letter, we present a noncontact, noninvasive, and low cost method for determining low viscosity values and variations in fluids. Laser speckle and viscometric measurements are performed on test samples having low scattering coefficients and low viscosities. The speckle spatial analysis proved to be as accurate as the speckle temporal correlation method reported in previous studies. Very low viscosities of the order of 1 mPa.s were retrieved for the first time using speckle images with either a frame rate of 1950 fps or a single acquired image. © 2016 Optical Society of America.

Crete J.P.,CNRS Clement Ader Institute | Crete J.P.,CNRS Laboratory of Materials Engineering of Brittany | Longere P.,CNRS Clement Ader Institute | Cadou J.M.,CNRS Laboratory of Materials Engineering of Brittany
ECCOMAS 2012 - European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers | Year: 2012

The present work is devoted to the numerical simulation of crack propagation in engineering materials whose failure results from void initiation, growth and coalescence. The behavior of the plate material is described via a Gurson type model accounting for the combined effects of strain hardening, thermal softening, viscoplasticity and void growth induced damage. The eXtended Finite Element Method has been retained to describe the kinematic consequences of the crack propagation across the mesh. The crack is assumed to propagate as soon as the stored energy around the crack tip reaches a critical value. The related crack length is estimated from the crack velocity considering the current time increment. The constitutive model and the extended finite elements were both implemented in the engineering FE computation code Abaqus as user subroutines. The numerical simulation of a notched plate under tension loading has been conducted. While making some simplifications, the present work reproduces numerically the 2D propagation of a crack resulting from void growth induced damage.

Pham C.-H.,CNRS Laboratory of Materials Engineering of Brittany | Thuillier S.,CNRS Laboratory of Materials Engineering of Brittany | Manach P.-Y.,CNRS Laboratory of Materials Engineering of Brittany
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2015

The objective of this paper is to characterize the mechanical behavior of an ultra-thin stainless steel, of 0.15-mm thickness, that is commonly used in the manufacturing of miniature connectors. The main focus is the relationship between some microstructural features, like grain size and surface roughness, and the macroscopic mechanical behavior investigated in uniaxial tension and simple shear. In tension, adaptations to the very small sheet thickness, in order to hold the specimen under the grips, are presented. Yield stress, initial elastic modulus, and evolution of the loading–unloading slope with plastic deformation were evaluated. Moreover, the kinematic contribution to the hardening was characterized by monotonic and cyclic simple shear test and reproduced by a mixed hardening law implemented in Abaqus finite element code. Then, the evolution of surface roughness with plastic strain, both in tension and simple shear, was analyzed. It was shown that in the case of an ultra-thin sheet, the stress levels, calculated either from an average thickness or when considering the effect of the surface roughness, exhibit a significant difference. Finally, the influence of surface roughness on the fracture of a tensile specimen was also investigated. © 2015, The Minerals, Metals & Materials Society and ASM International.

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