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Nantes, France

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

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. Source

Ghribi D.,INSA Lyon | Bruyere J.,INSA Lyon | Velex Ph.,INSA Lyon | Octrue M.,CETIM | Haddar M.,University of Sfax
Journal of Mechanical Design, Transactions of the ASME

This paper addresses the definition of robust profile modifications in spur and helical gears. An original methodology is introduced which relies on closed-form analytical results on transmission errors combined with a gradient descent algorithm and a Gauss quadrature (GQ) based full factorial method. The results compare very well with those delivered by using classic Monte Carlo simulations with a considerable gain in computational time. The influence of the probability distribution law for the design parameters (depth and extent of modification) is analyzed along with the contribution of gear quality grade and load variation. Some optimum robust linear relief is presented which minimizes transmission error fluctuations over a broad range of loads even in the presence of significant geometrical tolerances. © 2012 American Society of Mechanical Engineers. Source

Jollivet T.,CETIM | Greenhalgh E.,Imperial College London
Procedia Engineering

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. Source

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

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. Source

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. Source

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