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Clausse B.,CEA Saclay Nuclear Research Center | Lhemery A.,CEA Saclay Nuclear Research Center | Walaszek H.,CETIM
Journal of Physics: Conference Series | Year: 2017

An Electro-Magnetic Acoustic Transducer (EMAT) is a non-contact source used in Ultrasonic Testing (UT) which generates three types of dynamic excitations into a ferromagnetic part: Lorentz force, magnetisation force, and magnetostrictive effect. This latter excitation is a strain resulting from a magnetoelastic interaction between the external magnetic field and the mechanical part. Here, a tensor model is developed to transform this effect into an equivalent body force. It assumes weak magnetoelastic coupling and a dynamic magnetic field much smaller than the static one. This approach rigorously formulates the longitudinal Joule's magnetostriction, and makes it possible to deal with arbitrary material geometries and EMAT configurations. Transduction processes induced by an EMAT in ferromagnetic media are then modelled as equivalent body forces. But many models developed for efficiently predicting ultrasonic field radiation in solids assume source terms given as surface distributions of stress. To use these models, a mathematical method able to accurately transform these body forces into equivalent surface stresses has been developed. By combining these formalisms, the magnetostrictive strain is transformed into equivalent surface stresses, and the ultrasonic field radiated by magnetostrictive effects induced by an EMAT can be both accurately and efficiently predicted. Numerical examples are given for illustration. © Published under licence by IOP Publishing Ltd.

Antoni J.,University Claude Bernard Lyon 1 | Eltabach M.,CETIM
Mechanical Systems and Signal Processing | Year: 2013

A keep-it-simple (KIS) solution is introduced that interpolates a signal up to an arbitrary accuracy. It consists of interpolating the complex envelopes at the output of a perfect-reconstruction filter-bank: if K subbands are used, the proposed interpolation scheme is shown to have a similar figure of merit as if the signal was initially oversampled by factor K at the acquisition stage, yet without the storage burden implied by the latter method. © 2012 Elsevier Ltd. All rights reserved.

Omnes B.,Cetim | Heuillet P.,LRCCP
Constitutive Models for Rubber IX - Proceedings of the 9th European Conference on Constitutive Models for Rubbers, ECCMR | Year: 2015

This paper presents the recently studies carried out to improve the knowledge on the tightness of the rubber seal at low temperature, around −50°C. The thermomechanical behaviour, the evolution of the leakage through the temperature glass transition (Tg) and the study of different constitutive equations implemented in the finite element code, are the major items covered by this study. The experimental results obtained on the samples and the O-rings, have been compared to the numerical results. A hyper viscoelastic model with the Prony cells and Time-Temperature dependences has been chosen. The material parameters have been identified on a thermomechanical database. © 2015 Taylor and Francis Group.

Geringer J.,Ecole Nationale Superieure des Mines de Saint - Etienne CMP | Tatkiewicz W.,Ecole Nationale Superieure des Mines de Saint - Etienne CMP | Rouchouse G.,CETIM
Wear | Year: 2011

This study is focused on performing tribological tests on new materials for orthopaedic implants applications, PAEK (poly aryl ether ketone) polymer group. The experiments were performed in physiological liquid, at 37°C, for simulating the human body fluid. PAEK's tribological properties that are wear rate of polymers and wear mechanisms on common metallic alloys used as orthopaedic implants: Co-Cr, 316L SS and Ti-6Al-4V are compared to the gold standard used for hip joint prosthesis, the UHMWPE (ultra high molecular weight polyethylene) on the same metal alloys. PEEK (poly ether ether ketone) and PEKK (poly ether ketone ketone)/CF (carbon fibers) show the lowest wear rate on every counter metallic material; the system UHMWPE on any metal alloys exhibit the highest wear rate although having the lowest friction coefficient. From microscopic images and the evolution of the friction coefficient, a wear mechanism was suggested for each polymeric material. © 2011 Elsevier B.V.

Chapuis B.,ONERA | Terrien N.,CETIM | Royer D.,Laue Langevin Institute
Journal of Physics: Conference Series | Year: 2011

The phenomenon of Lamb waves focusing in anisotropic plates is theoretically and experimentally investigated. An analysis based on a far field approximation of the Green's function shows that Lamb waves focusing is analog to the phonon focusing effect. In highly anisotropic structures like composite plates the focusing of A0 and S0 mode is strong; the energy propagates preferentially in the fibre directions, which are minima of the slowness. This has to be taken into account when developing, for example, a transducer array for structural health monitoring systems based on Lamb waves in order to avoid dead zones. © Published under licence by IOP Publishing Ltd.

The control of sound fields radiated by vibrating structures in a passenger compartment, (especially structures connected to different organs like the engine powertrain, the fan motor unit, seats, the steering column, electrical motors more and more, etc.) is among the functions of the automotive manufacturers. The absence of physical prototypes in the development phase systems led OEMs1 to use tests results obtained on benches following technical specifications from manufacturers. The transition "bench to vehicle"for vibro- acoustic behaviour sets many challenges that this standard intends to clear up. This standard specifies the experimental method to transpose the dynamic forces generated by the global movements of an active component between the vehicle and a test bench. The efforts are first measured on test benches and then transposed from test bench towards the vehicle. The standard is now a French standard (XP R 19-701) and is submitted to ISO process [1]. Copyright © 2016 SAE International.

Chapuis B.,ONERA | Terrien N.,CETIM | Royer D.,University Paris Diderot
Journal of the Acoustical Society of America | Year: 2010

The radiation of Lamb waves by an axisymmetric source on the surface of an anisotropic plate is investigated. An analytical expression of the Green's function, valid in the far field domain, is derived. This approximation shows that the anisotropy of the propagation medium induces a focusing of Lamb modes in some directions, which correspond to minima of the slowness. Numerical simulations and experiments demonstrate that for the fundamental A 0 and S 0 modes, this phenomenon, analog to the phonon focusing effect, can be very strong in materials such as composite fiber-reinforced polymers. This effect due to the plate anisotropy must be correctly taken into account, for example, in order to develop systems for in situ structural health monitoring. The choice of the most appropriate Lamb mode, the excitation frequency, and the design of the array of piezoelectric disks used as transmitters and receivers depends on such considerations. © 2010 Acoustical Society of America.

Bennebach M.,CETIM | Palin-Luc T.,Arts et Metiers ParisTech
Procedia Engineering | Year: 2015

In power transmission machinery or crane industries, shafts are designed using specific standards that may not correctly cover the large panel of materials and loadings involved in these sectors, making it necessary to use safety factors leading to over-conservative life predictions and non-optimized designs. Shafts are key components, usually experiencing alternated normal stresses combined with static or fluctuating (intermittent) shear stresses. In high cycle multiaxial fatigue, it is admitted that mean shear stress has no significant effect on the fatigue strength of smooth specimens if the maximum shear stress does not exceed about 80% of the material shear yield limit. Under combined rotating bending and torsion the situation is unclear, especially in presence of notches. In this paper the effect of a static and intermittent shear stress on the fatigue strength of two quenched and tempered steel grades, 30NiCrMo8 and 42CrMo4, is studied on notched specimens with bending theoretical stress concentration factors Kt = 1.7 and Kt=2.7. It is shown that mean shear stress has little effect on the median rotating bending endurance limit at 3×106 cycles, the maximum decrease is about 5%, whereas this decrease is more pronounced for intermittent shear stress (varying in blocks), reaching up to 30% for the sharpest notch. © 2015 Published by Elsevier Ltd.

Boisseau A.,CETIM | Peyrac C.,CETIM
Procedia Engineering | Year: 2015

For marine applications, composite materials offer many advantages over metallic structures, with respect to ease of fabrication of complex profiles or light weight for installation and maintenance. Nevertheless, material selection is critical. In the case of a composite material, the choice of reinforcement is important if stress corrosion is to be avoided, while resin chemistry must be optimized to limit matrix damage. Fiber/matrix interface properties are also critical when composites are immersed for long periods. The main objective of this study is to identify and quantify the influence of the specific environmental marine conditions on composite material behavior, especially in cyclic loading. In order to perform a comparative study of fatigue behavior, three composite materials have been tested and analyzed. Fatigue tests have been carried out in bending on composite materials at initial state and after sea water ageing. The fatigue life and the evolution of the damage have been compared for each material. These experimental data allow us to identify and compare the fatigue behavior of several composite materials in a marine environment.

Jollivet T.,Cetim | Greenhalgh E.,Imperial College London
Procedia Engineering | Year: 2015

Fractography is a tool widely used in the academic world but a little-known technique in the industrial world. This tool can be useful at most stages of the development of composite parts: prototyping characterization, industrialization, production quality problems,. Finally when a composite part is broken during service, fractographic analysis is one of the most efficient tools for the determination of the root causes of failure. Fractography is useful for the engineer who has to determine if the failure results of a mechanical overload or of a fatigue phenomenon. The implementation of a fractographic investigation requires to follow a methodology with different steps: The first step is to determine the direction of propagation in the different zones of the rupture by recognition of features on the broken surface. From these results, the initiation area can often be identified. Then a long part of the work consists in seeking features of static or fatigue damage. Fractography also allows to determine what type of mechanical loading has caused the micro-damage in the initiation area. This information can be compared with the expected loading. Sometimes, the fatigue fractographic features are localized just along manufacturing defects. In this case, a specific study is required to establish the harmfulness of these defects. The defect acceptance criteria after manufacturing are then sometimes amended. Article will discuss these aspects through industrial examples. © 2015 Published by Elsevier Ltd.

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