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International audience; This paper deals with the numerical investigation of the unilateral contact-induced dynamics of a turbomachine blade rotating within a perfectly rigid yet distorted casing. This investigation is motivated by unelucidated vibratory behaviours observed experimentally. The simulations are based on an in-house time-marching strategy incorporating Lagrange multipliers for the unilateral contact treatment, as well as centrifugal stiffening and abradable coating removal. Significant extensions are proposed through the implementation of (1) aerodynamic loading on the blade and (2) post-processing techniques involving the empirical mode decomposition which provides fruitful insights on important transient phenomena. A thorough bifurcation analysis with and without aerodynamic loading highlights the existence of flip bifurcations with period-doubling and period-halving sequences over a broad angular speed range. Numerical simulations with external aerodynamic loading yield quasi-periodic and likely to be chaotic motions that could not be observed under vacuum. The proposed numerical investigations underline the key role of the aerodynamic loading in the blade dynamics and suggest that unexplained experimental vibratory behaviours are related to the vacuum conditions of the experiment.; Cet article porte sur des investigations numériques relativement à la réponse vibratoire d’une aube de turbomachine, suite à des contacts structuraux. Le carter environnant est déformé mais supposé infiniment rigide. Ces travaux sont motivés par l’observation expérimentale de plusieurs phénomènes vibratoires qui restent inexpliqués. Les simulations effectuées reposent sur l’utilisation d’un outil numérique développé au laboratoire combinant un algorithme de calcul de multiplicateurs de Lagrange pour le traitement du contact et la prise en compte des effets centrifuges et de l’arrachement du revêtement abradable. Des ajouts majeurs à cet outil sont proposés avec l’implémentation de: (1) la prise en compte d’un chargement aérodynamique sur l’aube et (2) le post-traitement des résultats par l’intermédiaire de méthodes de décomposition en modes empiriques qui permettent de mieux analyser les phénomènes transitoires. Une analyse de stabilité avec et sans chargement aérodynamique met en évidence l’existence de points de bifurcation sur une large plage de vitesses de rotation. Les simulations numériques prenant en compte le chargement aérodynamique permettent d’observer des mouvements quasi-périodiques et d’autres probablement chaotiques qui n’ont jamais été observé sous vide.

Large cohort studies suggest that high convective volumes associated with online hemodiafiltration may reduce the risk of mortality/morbidity compared to optimal high-flux hemodialysis. By contrast, intradialytic tolerance is not well studied. The aim of the FRENCHIE (French Convective versus Hemodialysis in Elderly) study was to compare high-flux hemodialysis and online hemodiafiltration in terms of intradialytic tolerance. In this prospective, open-label randomized controlled trial, 381 elderly chronic hemodialysis patients (over age 65) were randomly assigned in a one-to-one ratio to either high-flux hemodialysis or online hemodiafiltration. The primary outcome was intradialytic tolerance (day 30-day 120). Secondary outcomes included health-related quality of life, cardiovascular risk biomarkers, morbidity, and mortality. During the observational period for intradialytic tolerance, 85% and 84% of patients in high-flux hemodialysis and online hemodiafiltration arms, respectively, experienced at least one adverse event without significant difference between groups. As exploratory analysis, intradialytic tolerance was also studied, considering the sessions as a statistical unit according to treatment actually received. Over a total of 11,981 sessions, 2,935 were complicated by the occurrence of at least one adverse event, with a significantly lower occurrence in online hemodiafiltration with fewer episodes of intradialytic symptomatic hypotension and muscle cramps. By contrast, health-related quality of life, morbidity, and mortality were not different in both groups. An improvement in the control of metabolic bone disease biomarkers and β2-microglobulin level without change in serum albumin concentration was observed with online hemodiafiltration. Thus, overall outcomes favor online hemodiafiltration over high-flux hemodialysis in the elderly.

International audience; The main purpose of this paper is to present an experimental setup dedicated to the study of high speed interactions such as those occurring between the rotating blade and the casing of an aircraft engine compressor. A simplified approach of rotor/stator interaction was experimentally simulated for ranges of velocities and interaction depths varying from 60 m/s to 270 m/s and from 0.13 mm to 0.35 mm respectively. Only high speed orthogonal contact were studied. The device was made up of a ballistic bench projecting a sample of abradable material (M601) against an instrumented tool (Steel 42CrMo4) representing the simplified blade shape. In order to increase significantly the measurement system bandwidth and to measure accurately the high speed interaction forces, a correction method based on the principle of modal analysis was developed and successfully employed. This work provides new experimental data regarding the material behavior of M601 in high speed orthogonal cutting conditions. They were in good agreement with those already observed in the literature for velocities up to 100 m/s. These new results showed the non-linear increase of the mean interaction force with the velocity and incursion depth for the large range of velocities considered in this present work. Post-experiment observations gave evidence of two wear mechanisms: cutting and plastic deformation.

International audience; Aircraft engine manufacturers are developping a new generation of turbojet engines featuring a lower impact on the environment, increased performances as well as reduced gas consumption. The efficiency of an engine is mostly driven by the operating clearance between the rotating parts and the stator. Accordingly, modern designs focus on the minimization of these clearances. In this context, unavoidable rotor imbalances or mistuning stemming from manufacturing processes as well as distortions resulting from thermal expansion or assembly conditions may generate blade-tip/casing contacts that are now considered as non-accidental operating conditions. In order to minimize the consequences of such events, an abradable coating is sprayed along the inner surface of the casing and acts as a fuse when the blade and the casing are in contact. However, even when an abradable coating is used, significant structural damages and wear as well as blade failures have been witnessed experimentally. The understanding of the physical phenomena at play called, on one hand, for throrough experimental investigations of rotor/stator contacts on full-scale stages of compressors and underlined that blade failure is mainly due to vibratory fatigue although the abradable coating is worn. On the other hand, numerical simulations have been performed to better understand the blade dynamics: over the last decade Snecma and its academic partners jointly developed a code for the simulation of COntacts between ROtor and Stator: COROS. This code allows for the simulation of contacts—with a Lagrange multiplier contact treatment procedure—between full 3D models of engine components and accounts for abradable coating material removal. In particular, the simulation of experimental setups with COROS highlighted the correlation between the blade vibratory response and the abradable material removal. Yet still an experimental code, this paper addresses the integration of COROS within the design process of aircraft engine blades at Snecma. The paper focuses on ongoing research for the identification of critical parameters in the arising of interactions as early as the design stage of components. A particular attention is paid to the mechanical properties of the abradable coating for which both experimental and numerical investigations are detailed.

International audience; Recent studies focused on the numerical prediction of structural instabilities that may arise in rotating components of an aircraft engine. These instabilities are commonly classified into two categories: those induced by aerodynamic phenomena (such as the pressure applied on the blade by the incoming air flow) and those related to structural phenomena (such as potential blade/casing contacts). Based on an existing numerical strategy for the analysis of rotor/stator interactions induced by unilateral contacts between rotating and static components, this paper aims at combining both types of instabilities and provides a qualitative analysis of structural interactions that may arise within the high-pressure compressor of an aircraft engine. The aerodynamic pressure on the blade is simplified as a sinusoidal external load whose frequency depends on the number of upstream guide vanes. Results are presented both in time and frequency domains. Detailed bifurcation diagrams and Poincaré maps underline the fundamental differences in the nature of the witnessed interactions with and without aerodynamic loading on the blade.; Plusieurs etudes récentes ont eu pour objet la simulation numérique des instabilités structurelles pouvant survenir dans des machines tournantes telles que des moteurs d'avion. Typiquement, ces instabilités sont séparées en deux catégories : celles relatives aux phénom enes aérodynamiques (liés par exemplè a la pression imposée sur l'aube par le flux d'air) et celles relatives a des phénom enes uniquement structurels (comme le contact aube/carter). En se basant sur l'utilisation d'une méthode numérique dédiéè a l'analyse d'interactions aube/carter initiées par des contacts entre parties tournante et fixe, les travaux présentés dans cet article ont pour objectif d'analyser conjointement les deux types d'instabilité précédemment citées et de fournir une analyse qualitative des types de régimes d'interactions pouvant survenir dans un moteur d'avion. La pression aérodynamique est modéliséè a l'aide d'un chargement externe d'amplitude sinuso¨dale et dont la fréquence dépend du nombre de redresseurs en aval. Les résultats sont donnés dans les espace temporel et fréquentiel. Les différences fondamentales de nature entre les différentes interactions simulées avec et sans pression aérodynamique sont mises en evidence par des diagrammes de bifurcation détaillés et des cartes de Poincaré.

Recent numerical developments dedicated to the simulation of rotor/stator interaction involving direct structural contacts have been integrated within the Snecma industrial environment. This paper presents the first attempt to benefit from these developments and account for structural blade/casing contacts at the design stage of a high-pressure compressor blade. The blade of interest underwent structural divergence after blade/abradable coating contact occurrences on a rig test. The design improvements were carried out in several steps with significant modifications of the blade stacking law while maintaining aerodynamic performance of the original blade design. After a brief presentation of the proposed design strategy, basic concepts associated with the design variations are recalled. The iterated profiles are then numerically investigated and compared with respect to key structural criteria such as: (1) their mass, (2) the residual stresses stemming from centrifugal stiffening, (3) the vibratory level under aerodynamic forced response and (4) the vibratory levels when unilateral contact occurs. Significant improvements of the final blade design are found: the need for an early integration of nonlinear structural interactions criteria in the design stage of modern aircraft engines components is highlighted.Copyright © 2014 by ASME

A new poly(paraphenylene) recently obtained by electropolymerization of dihalobenzene is described in terms of infra-red and UV-visible absorptions, electron paramagnetic resonance, DC conductivity of the pristine material. The first data on ASF5 doping are given. The properties of the electropolymer are compared to those of other poly(paraphenylene) synthesized by chemical methods.

The fibrous morphology and the crystalline structure of the fibres polyparaphenylene (PPP) are observed by electron microscopy and a comparison is made between the undoped and the doped material.

Polyparaphenylene, PPP, has been polymerized from benzene, as described by Kovacic, and heavily doped in ASF5 vapour. The spin susceptibilities were about 10−6 emu/mole carbon for the Pauli part, plus one Curie spin per 1000 carbon atoms. The asymmetry of the EPR signal of pellets was found to be in good agreement with Dyson's theoretical predictions for slowly diffusive spins in the case of aged samples. On the other hand, the occurence of exchange interactions gave rise in freshly doped samples to enhanced magnetization diffusion rates, and then to more asymmetrical EPR lines.

Amorphous silicon based thin film transistors for the driving of liquid crystal displays have been fabricated in a very simple way with only 2 photolithographic steps. The process for TFT and matrix elaboration are explained. The transistor electrical characteristics are shown to be compatible with LCD working conditions.