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Lecompte T.,University of Southern Brittany | Arbab-Chirani S.,Brest National School of Engineering | Calloch S.,LBMS | Pilvin P.,University of Southern Brittany
Topics in Dynamics of Civil Structures - Proceedings of the 31st IMAC, A Conference on Structural Dynamics, 2013 | Year: 2013

Most of civil engineering cable structures are subjected to potential damages mainly due to dynamic oscillations induced by wind, rain or traffic. If vibration amplitudes of bridge cables for example are too high, it may cause a fatigue phenomenon. Recently, researches had been conducted dealing with the use of damping devices in order to reduce vibration amplitudes of cables. Thin shape memory alloy (SMA) NiTi (Nickel-Titanium) wires were used as a simplified damping device on a realistic full scale 50 m long cable specimen in Ifsttar (Nantes - France) laboratory facility, and its efficiency was shown. It has been done using finite element simulations, as well as experimental test methods. The aim of this work is to link the wire material behavior with the local damping induced along the cable qualitatively. Indeed, thermomechanical energy dissipation of the NiTi-based wires enables their damping power. The hysteretic behavior in NiTi-based alloys demonstrates a consequent dissipation because of an exothermic martensitic transformation and then an endothermic reverse transformation. © The Society for Experimental Mechanics, Inc. 2013.

Le Duigou A.,University of Southern Brittany | Baley C.,University of Southern Brittany | Grohens Y.,University of Southern Brittany | Davies P.,French Research Institute for Exploitation of the Sea | And 3 more authors.
Composites Part A: Applied Science and Manufacturing | Year: 2014

A significant recent development in the composite field is the appearance of biocomposites (biopolymers reinforced by plant fibres) which combine mechanical performance and low environmental impacts. However, to replace conventional composites a significant effort is needed to understand their mechanical behaviour under complex loading (both in-plane and out-of-plane). The interfacial behaviour (fibre/matrix) of these materials also requires particular attention in order to optimize mechanical properties. With this aim modified Arcan, transverse tension and microdroplet debonding tests have been performed on flax reinforced PLLA biocomposites, as very few data of this type are available. The out-of-plane tensile and tensile-shear properties of these biocomposites are lower than those measured in shear. Manufacturing parameters, and particularly consolidation pressure, are critical for these materials. Out-of plane apparent shear strengths are similar to those from debonding tests. A common feature of the tests performed at the three scales is the appearance of fibre peeling. © 2014 Elsevier Ltd. All rights reserved.

Alarcon E.,LBMS | Alarcon E.,ASCR Institute of Physics Prague | Heller L.,ASCR Institute of Physics Prague | Chirani S.A.,LBMS | And 3 more authors.
MATEC Web of Conferences | Year: 2015

Tensile fatigue of superelastic medical graded NiTi wires was analysed in stress control regime with special attention paid to the deformation/transformation processes involved. Concave shaped samples were machined from NiTi wires allowing us to confine deformation processes into the centre of the sample. The localization of phase transformations within the centre was confirmed using in-situ infrared imaging. Characteristic stress-displacement responses for amplitudes inducing either R-phase only or both R-phase and martensite were identified for these samples. A limited number of pull-pull fatigue tests in force-control regime were performed. The obtained S-N curve and associated stress-displacement responses allowed for identification of three fatigue regimes differing in the fatigue life-time by orders of magnitude. Particularly, fatigue life-time deteriorating effect of R-phase transformation was identified. © Owned by the authors, published by EDP Sciences, 2015.

Legrand V.,ENSTA Bretagne | Moyne S.,ENSTA Bretagne | Pino L.,LBMS | Arbab Chirani S.,ENSTA Bretagne | And 3 more authors.
Materials Science Forum | Year: 2013

Superelastic NiTi shape memory alloys (SMA) are the base of endodontic files. The flexibility of these instruments permits the preparation of root canals. Unfortunately the intracanal file separation can occur. To have a good idea of the mechanical behavior of these instruments, we propose in this study the finite elements simulations taking into account the real shape of root canals. This has been possible by using a well adapted model describing all the particularities of superelastic SMA and by using representative limit conditions. © (2013) Trans Tech Publications, Switzerland.

Tual N.,ENSTA Bretagne | Tual N.,French Research Institute for Exploitation of the Sea | Carrere N.,ENSTA Bretagne | Davies P.,French Research Institute for Exploitation of the Sea | And 2 more authors.
16th European Conference on Composite Materials, ECCM 2014 | Year: 2014

The renewable marine energies represent a major economic and political development. Among these new sources of energy, tidal turbines offer considerable potential. Most of the tidal turbine blades developed by industry so far are manufactured using thick carbon fibre composites. To ensure the life of the blades, it is necessary to develop a damage model taking into account the water absorption and its effects on behavior. Moreover, the multi-scale nature of these materials leads to complex, coupled failure mechanisms, whose thresholds and evolution are dependent on the layup and ply thickness. The purpose of this paper is to propose an experimental approach to characterize the long term behavior of different carbon/epoxy composites for tidal turbine blades.

Sameallah S.,Isfahan University of Technology | Kadkhodaei M.,Isfahan University of Technology | Legrand V.,LBMS | Legrand V.,ENSTA Bretagne | And 2 more authors.
Journal of Intelligent Material Systems and Structures | Year: 2015

When shape memory alloys are subjected to cyclic loadings, the stabilized dissipated energy is an effective parameter in studying their performance, for instance, the fatigue life. However, thermomechanical coupling in the behavior of shape memory alloys under cyclic loadings causes the amount of stabilized dissipated energy to be obtainable once the responses of all transient cycles are determined. In this article, direct formulae are proposed to numerically evaluate stabilized dissipated energy of a shape memory alloy under cyclic tensile loadings as a function of maximum and minimum applied stresses as well as the loading frequency. A one-dimensional fully coupled thermomechanical constitutive model with a cycle-dependent phase diagram is utilized to be able to directly predict the uniaxial stress-strain response of a shape memory alloy in a specified cycle with no need of solving the previous cycles. The results are experimentally assessed for NiTi and CuAlBe specimens. Since the backward transformation in CuAlBe is realized to more gradually occur than that in NiTi, an enhanced phase diagram is proposed in which different slopes are considered for the start and finish of backward transformation strip. The numerical predictions of the present approach are shown to be in a good agreement with the experimental findings for cyclic tensile loadings. © SAGE Publications.

Sameallah S.,Isfahan University of Technology | Legrand V.,LBMS | Saint-Sulpice L.,LBMS | Kadkhodaei M.,Isfahan University of Technology | Arbab Chirani S.,LBMS
Smart Materials and Structures | Year: 2015

Stabilized dissipated energy is an effective parameter on the fatigue life of shape memory alloys (SMAs). In this study, a formula is proposed to directly evaluate the stabilized dissipated energy for different values of the maximum and minimum applied stresses, as well as the loading frequency, under cyclic tensile loadings. To this aim, a one-dimensional fully coupled thermomechanical constitutive model and a cycle-dependent phase diagram are employed to predict the uniaxial stress-strain response of an SMA in a specified cycle, including the stabilized one, with no need of obtaining the responses of the previous cycles. An enhanced phase diagram in which different slopes are defined for the start and finish of a backward transformation strip is also proposed to enable the capture of gradual transformations in a CuAlBe shape memory alloy. It is shown that the present approach is capable of reproducing the experimental responses of CuAlBe specimens under cyclic tensile loadings. An explicit formula is further presented to predict the fatigue life of CuAlBe as a function of the maximum and minimum applied stresses as well as the loading frequency. Fatigue tests are also carried out, and this formula is verified against the empirically predicted number of cycles for failure. © 2015 IOP Publishing Ltd.

Choqueuse V.,LBMS | Marazin M.,University of Western Brittany | Collin L.,University of Western Brittany | Yao K.C.,University of Western Brittany | Burel G.,University of Western Brittany
IEEE Transactions on Signal Processing | Year: 2010

Blind recognition of communication parameters is a research topic of high importance for both military and civilian communication systems. Numerous studies about carrier frequency estimation, modulation recognition as well as channel identification are available in literature. This paper deals with the blind recognition of the space-time block coding (STBC) scheme used in multiple-input-multiple-output (MIMO) communication systems. Assuming there is perfect synchronization at the receiver side, this paper proposes three maximum-likelihood (ML)-based approaches for STBC classification: the optimal classifier, the second-order statistic (SOS) classifier, and the code parameter (CP) classifier. While the optimal and the SOS approaches require ideal conditions, the CP classifier is well suited for the blind context where the communication parameters are unknown at the receiver side. Our simulations show that this blind classifier is more easily implemented and yields better performance than those available in literature. © 2010 IEEE.

Florin P.,LBMS | Florin P.,PSA Peugeot Citroën | Doudard C.,LBMS | Facchinetti M.L.,PSA Peugeot Citroën | Calloch S.,LBMS
Procedia Engineering | Year: 2015

The determination of welded steel sheet assemblies high cycle fatigue properties is a prior concern of the automotive industry. Such assemblies are designed as high-safety parts, for which any fatigue failure is supposed to be prevented. Thus, the determination of complex structures stress field is necessary to design them. Even though finite element models are more and more accurate, experimental methods for the stress field tensors measurement under cyclic loadings are useful to validate those models. The purpose of this work is the experimental determination of the first stress tensor invariant amplitude at the surface of a complex structure under cyclic loading, a car wishbone, with a method based on thermal measurements, the Thermoelastic Stress Analysis (TSA). Parameters which have an influence on the measured temperature at the surface of the structure are studied, including the non-adiabatic behaviour of specimens due to a heterogeneous stress field and the influence of the paint used to measure the temperature with an infra-red camera. All these parameters are taken into account to determine successfully the wishbone stress tensor amplitude during a cyclic test. © 2015 Published by Elsevier Ltd.

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