Suivi vibratoire des transmissions à engrenages en régime variable

Cet article s’inscrit dans le cadre du diagnostic des transmissions par engrenages en régime variable. L’objectif de ce travail est la recherche d’un indicateur pertinent sur l’état des engrenages défectueux à partir des signaux de vibrations simulés. L’approche que nous voulons présenter est de permettre l’extraction des fréquences spectrales en se basant sur le spectrogramme obtenu par la transformation de Fourier rapide à court terme. Le résultat obtenu est comparée à celui obtenu par le calcul de la fréquence instantanée directe obtenue par la transformée de Hilbert dans le cas où la vitesse de rotation est constante puis le cas où cette dernière varie selon un profil retenu. Après modélisation dynamique de la transmission, les réponses sont calculées en utilisant le schéma d’intégration de Runge Kutta Pour simuler le signal à analyser, nous avons introduit volontairement des défauts d’excentricités sur les roues dentées

Structure and photophysics of indigoids for singlet fission: Cibalackrot

We report an investigation of structure and photophysics of thin layers of cibalackrot, a sturdy dye derived from indigo by double annulation at the central double bond. Evaporated layers contain up to three phases, two crystalline and one amorphous. Relative amounts of all three have been determined by a combination of X-ray diffraction and FT-IR reflectance spectroscopy. Initially, excited singlet state rapidly produces a high yield of a transient intermediate whose spectral properties are compatible with charge-transfer nature. This intermediate more slowly converts to a significant yield of triplet, which, however, does not exceed 100% and may well be produced by intersystem crossing rather than singlet fission. The yields were determined by transient absorption spectroscopy and corrected for effects of partial sample alignment by a simple generally applicable procedure. Formation of excimers was also observed. In order to obtain guidance for improving molecular packing by a minor structural modification, calculations by a simplified frontier orbital method were used to find all local maxima of singlet fission rate as a function of geometry of a molecular pair. The method was tested at 48 maxima by comparison with the ab initio Frenkel-Davydov exciton model. Published under license by AIP Publishing

Une approche méthodologique numérique et expérimentale d'aide à la détection et au suivi vibratoire de défauts d'écaillage de roulements à billes

Cette étude est consacrée à la maintenance conditionnelle par analyse vibratoire, domaine d activité qui constitue une part toujours plus importante des dispositions permettant de rentabiliser l instrument de production industriel. Elle propose une méthodologie numérique et expérimentale d aide à la détection et au suivi vibratoire des défauts d écaillage sur les roulements à billes. L objectif de ce travail est d utiliser un point de mesure situé sur le carter d une machine tournante permettant de réaliser une surveillance vibratoire efficace. Il s est orienté dans deux directions. D abord en ajoutant un composant structurel optimisé sur le carter de la machine, appelé résonateur, dont le rôle est de canaliser les vibrations. Ensuite en déterminant numériquement le point de mesure optimum de détection des défauts, qui peut également servir au suivi de l évolution de la sévérité de l écaillageThis study deals with conditional maintenance by vibratory analysis. This activity constitutes an increasingly important part of the tools used to keep industrial plants in continuous service. This work proposes a numerical and experimental methodology of assistance to the detection and the vibratory follow-up of spalling defects in ball bearings. The objective of this work is to use a measurement point located on the casing of a revolving machine to carry out an effective vibratory monitoring. Two steps can be distinguished in this work. The first one consists in the conception of an optimized structural component, called resonator, to channel the vibrations if placed on the casing of the machine. The second step is a numerical determination of the optimum measurement point for defects detection, which can also be used for the follow-up of the evolution of severity of the spallingREIMS-BU Sciences (514542101) / SudocSudocFranceF

Maintenance Evaluation and Optimization of a Multi-State System Based on a Dynamic Bayesian Network

Nowadays, the main challenge in maintenance is to establish a dynamic maintenance strategy to significantly track and improve the performance measures of multi-state systems in terms of production, quality, security and even the environment. This paper presents a quantitative approach based on Dynamic Bayesian Network (DBN) to model and evaluate the maintenance of multi-state system and their functional dependencies. According to transition relationships between the system states modeled by the Markov process, a DBN model is established. The objective is to evaluate the reliability and the availability of the system with taking into account the impact of maintenance strategies (perfect repair and imperfect repair). Using the proposed approach, the dynamic probabilities of system states can be determined and the subsystems contributing to system failure can also be identified. A practical application is demonstrated by a case study of a blower system. Through the result of the diagnostic inference, to improve the performances of the blower, the critical components C, F, W, and P should be given more attention. The results indicate also that the perfect repair strategy can improve significantly the performances of the blower, while the imperfect repair strategy cannot degrade the performances in comparison to the perfect repair strategy. These results show the effectiveness of this approach in the context of a predictive evaluation process and in providing the opportunity to evaluate the impact of the choices made on the future measurement of systems performances. Finally, through diagnostic analysis, intervention management and maintenance planning are managed efficiently and optimally

Following the growth of a rolling fatigue spalling for predictive maintenance

The bearing is one of the most important components of rotating machines. Nevertheless, in normal conditions of use, it is subject to fatigue which creates a defect called a rolling fatigue spalling. In this work, we present a follow-up of the thrust bearing fatigue on a test bench. Vibration analysis is a method used to characterize the defect. In order to obtain the fatigue curve more adjusted, we have studied the vibration level according to statistical indicators: the Root Mean Square value (RMS value), which is one of the best indicators to show the evolution of the bearing degradation. The approach follows the working of the bearing until the degradation with an on line acquisition of vibration statements in form of time signals. With the signal treatment, we obtain the values of the vibration amplitudes which characterize the vibration state of the bearing. Consequently, these values allow us to plot the fatigue curves. During our experimental work, this operation is applied for a batch of thrust bearings for which we have obtained similar fatigue curves where the evolution trend follows a regression model from the detection of the onset of the first spall. The result of this work will contribute to predict the working residual time before failure

Localisation et restitution des sources vibratoires: une approche numérique et expérimentale

L'analyse vibratoire permet d'appréhender l'état de fonctionnement de machines tournantes. Le signal, enregistré par des accéléromètres, peut contenir, simultanément, des informations de plusieurs composants rendant difficile l'interprétation de l'état de l'un d'entre eux. Dans ce cadre les problèmes inverses s'avèrent être un outil intéressant. Ils permettent de revenir à l'information originale à partir d'observations. Leurs instabilités nécessitent un grand nombre d'observations face au nombre de sources, et demandent l'emploi de méthodes dites de régularisation. Cependant une régularisation signifie une perte d'information, et l'emploi d'un système surdéterminé entraîne une qualité de l'information moindre. Cet article propose de pallier à ces problèmes en optimisant la position des capteurs de vibration afin de rendre l'inversion la plus exacte possible. Cette optimisation sera obtenue d'une part par une approche numérique, qui nécessite un recalage du modèle, et d'autre part par une approche expérimentale, grâce à l'analyse modale

Mise en place d’une procédure de surveillance vibratoire des défauts, sur une presse transfert dans le secteur automobile, dans le cadre d'une maintenance conditionnelle.

Le sujet s’inscrit dans un contrat de recherche dont le but est d’établir une procédure de surveillance par analyse vibratoire des roulements sur l’arbre transfert d’une presse d’emboutissage de 5000 tonnes, du secteur automobile. Cette presse fonctionne à faible vitesse et génère un choc d’amplitude très importante. Ainsi, les signaux vibratoires sont fortement pollués dû à la frappe. Il est donc capital d’isoler certaines phases du signal avant de pouvoir le traiter

Following the growth of a rolling fatigue spalling for predictive maintenance = Suivi de la croissance d'un écaillage de fatigue de roulement d'une butée a billes dans le cadre d'une maintenance prédictive

The bearing is one of the most important components of rotating machines. Nevertheless, in normal conditions of use, it is subject to fatigue which creates a defect called a rolling fatigue spalling. In this work, we present a follow-up of the thrust bearing fatigue on a test bench. Vibration analysis is a method used to characterize the defect. In order to obtain the fatigue curve more adjusted, we have studied the vibration level according to statistical indicators: the Root Mean Square value (RMS value), which is one of the best indicators to show the evolution of the bearing degradation. The approach follows the working of the bearing until the degradation with an on line acquisition of vibration statements in form of time signals. With the signal treatment, we obtain the values of the vibration amplitudes which characterize the vibration state of the bearing. Consequently, these values allow us to plot the fatigue curves. During our experimental work, this operation is applied for a batch of thrust bearings for which we have obtained similar fatigue curves where the evolution trend follows a regression model from the detection of the onset of the first spall. The result of this work will contribute to predict the working residual time before failur

Vibratory monitoring of a spalling bearing defect in variable speed regime

Rotating machines monitoring in a non-stationary regime, characterized by the operating parameters (speed, load) variation, presents a particular challenge. The speed variation has an impact on the vibratory response given by the accelerometers and therefore masks any defect that may be detected by classical indicators (for example RMS value). To overcome this problem, a new indicator is proposed. For this, a signal accelerometer and a signal from an optical encoder are acquired simultaneously. An algorithm to estimate the instantaneous speed from the signal delivered by the optical encoder is applied. Then, each sample of the accelerometer signal is divided by its corresponding instantaneous speed sample. The RMS value is then applied to the resulting signal. A model simulation signal is used to test the proposed method. A test rig is performed to extract signals of different degradation states of thrust bearings in variable speed regime. The results show a correlation between the proposed RMS value and the thrust bearings state in variable regime