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Brest, France

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.

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.

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.

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.

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.

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