Application of a Combined Active Control and Fault Detection Scheme to an Active Composite Flexible Structure.

In this paper, the problem of increasing reliability of active control procedure is considered. Indeed, a design method of rejection perturbation in presence of potentially faults, on a flexible structure with integrated piezo-ceramics, is presented. The piezo-ceramics are used as actuators and sensors. A single unit based solution, which handles both control action and fault diagnosis is proposed. The algorithm uses H∞ optimization techniques. A full order model of the structure is first obtained via both finite-element (FE) approach and identification procedure. This model is then reduced in order to be used in our robust approach. By a suitable choice of weightings functions, the provided method is able to reject disturbance robustly and to estimate occurred faults. The case of sensors and actuators faults is discussed. The choice of weightings for diagnosis and control systems is also tackled. Finally, the effectiveness of this integrated method is confirmed by both simulation and experimental results

Simulation of a finishing operation : milling of a turbine blade and influence of damping

Milling is used to create very complex geometries and thin parts, such as turbine blades. Irreversible geometric defects may appear during finishing operations when a high surface quality is expected. Relative vibrations between the tool and the workpiece must be as small as possible, while tool/workpiece interactions can be highly non-linear. A general virtual machining approach is presented and illustrated. It takes into account the relative motion and vibrations of the tool and the workpiece. Both deformations of the tool and the workpiece are taken into account. This allows predictive simulations in the time domain. As an example the effect of damping on the behavior during machining of one of the 56 blades of a turbine disk is analysed in order to illustrate the approach potential

Optimal Sensors Placement to Enhance Damage Detection in Composite Plates

This paper examines an important challenge in ultrasonic structural health monitoring (SHM), which is the problem of the optimal placement of sensors in order to accurately detect and localize damages. The goal of this study is to enhance damage detection through an optimal sensor placement (OSP) algorithm. The problem is formulated as a global optimization problem, where the objective function to be maximized is evaluated by a ray tracing approach, which approximately models Lamb waves propagation. A genetic algorithm (GA) is then used to solve this optimization problem. Simulations and experiments were conducted to validate the proposed method on a carbon epoxy composite plate. Results show the effectiveness and the advantages of the proposed method as a tool for OSP with reasonable computation time.Projet AIRCELLE (EPICE/CORALIE

Application of a Combined Active Control and Fault Detection Scheme to an Active Composite Flexible Structure.

In this paper, the problem of increasing reliability of active control procedure is considered. Indeed, a design method of rejection perturbation in presence of potentially faults, on a flexible structure with integrated piezo-ceramics, is presented. The piezo-ceramics are used as actuators and sensors. A single unit based solution, which handles both control action and fault diagnosis is proposed. The algorithm uses H∞ optimization techniques. A full order model of the structure is first obtained via both finite-element (FE) approach and identification procedure. This model is then reduced in order to be used in our robust approach. By a suitable choice of weightings functions, the provided method is able to reject disturbance robustly and to estimate occurred faults. The case of sensors and actuators faults is discussed. The choice of weightings for diagnosis and control systems is also tackled. Finally, the effectiveness of this integrated method is confirmed by both simulation and experimental results

A general method to accurately simulate material removal in virtual machining of flexible workpieces

Multi-axis milling and other computer numerical control machining processes allow us to create very complex geometries and thin parts. In this context, virtual machining is a powerful tool, but the simultaneous vibrations of the tool and workpiece are not easy to define and take into account. This paper presents a general method with which to simulate material removal when both the workpiece and tool are assumed to be non-rigid. We consider that they both vibrate when we define the Boolean chip. This is not usually considered with the aim of predicting the machined surface vibrations and the resulting geometric defects including roughness. By extending the material frame associated with the non-rigid workpiece, our method precisely defines the material removal for any tool or workpiece. It then allows us to establish a method of deriving efficient numerical approximations with which to simulate a succession of machining operations from roughening to finishing. Two kinds of finite element approximations are linked. One is a classical elastic finite element model including damping. The second, which is kinematically linked to the first, accurately describes the relative motion of each part of the tool with respect to the workpiece, and ensures the description of material removal and related forces. Two industrial examples show the potential of the method

A data-driven temperature compensation approach for Structural Health Monitoring using Lamb waves

This paper presents a temperature compensation method for Lamb wave structural health monitoring. The proposed approach considers a representation of the piezo-sensor signal through its Hilbert transform that allows one to extract the amplitude factor and the phase shift in signals caused by temperature changes. An ordinary least square (OLS) algorithm is used to estimate these unknown parameters. After estimating these parameters at each temperature in the operating range, linear functional relationships between the temperature and the estimated parameters are derived using the least squares method. A temperature compensation model is developed based on this linear relationship that allows one to reconstruct sensor signals at any arbitrary temperature. The proposed approach is validated numerically and experimentally for an anisotropic composite plate at different temperatures ranging from Formula to Formula . A close match is found between the measured signals and the reconstructed ones. This approach is interesting as it needs only a limited set of piezo-sensor signals at different temperatures for model training and temperature compensation at any arbitrary temperature. Damage localization results after temperature compensation demonstrate its robustness and effectiveness.Projet AIRCELLE/CORALIE

Simulation numérique de l'usinage par outil coupant à l'échelle macroscopique (contribution à la définition géométrique de la surface usinée)

PARIS-Arts et Métiers (751132303) / SudocSudocFranceF

APPROCHE PROBABILISTE POUR LA PRISE EN COMPTE DE LA DISPERSION DE PARAMETRES MECANIQUES APPLICATION A LA FATIGUE VIBRATOIRE DE RESEAUX DE TUYAUTERIES

L'APPROCHE PROBABILISTE PERMET D'INCORPORER LA VARIABILITE ET LES INCERTITUDES PARAMETRIQUES DANS LES MODELES MECANIQUES. CETTE APPROCHE CONSISTE GENERALEMENT A DECRIRE LES PARAMETRES INCERTAINS DES MODELES PAR DES VARIABLES ALEATOIRES ET A SE RAMENER AU CALCUL D'UNE INTEGRALE MULTIPLE. CEPENDANT, LES METHODES CLASSIQUES PERMETTANT CE CALCUL, TELLES QUE LES METHODES FORM/SORM ET LES METHODES DE MONTE-CARLO, PEUVENT S'AVERER ETRE IMPRECISES OU TRES COUTEUSES EN CALCULS, EN PARTICULIER POUR CERTAINES APPLICATIONS INDUSTRIELLES DE DYNAMIQUE VIBRATOIRE. UNE NOUVELLE METHODE EFFICACE D'ECHANTILLONNAGE D'IMPORTANCE EST DONC PROPOSEE. LA METHODE EST BASEE SUR UNE APPROXIMATION ASYMPTOTIQUE DU SECOND DEGRE COMBINEE AVEC LA METHODE DE L'HYPERCUBE LATIN ET ASSURE UNE VARIANCE FINIE DES ESTIMATEURS. UN ALGORITHME SPECIFIQUE D'OPTIMISATION GLOBALE EST DEVELOPPE AFIN DE RESOUDRE UNE ETAPE PREALABLE NECESSAIRE QUI CONSISTE A TROUVER LES POINTS DE MAXIMUM DE VRAISEMBLABLE. L'EFFICACITE DE LA METHODE COMPAREE AUX METHODES CLASSIQUES EST ILLUSTREE AVEC PLUSIEURS EXEMPLES NUMERIQUES. UNE AMELIORATION CONSIDERABLE DE LA VITESSE DE CONVERGENCE DES ESTIMATEURS PEUT ETRE REALISEE. UN PROBLEME INDUSTRIEL MONTRE EGALEMENT L'INTERET PRATIQUE DE LA METHODE PROPOSEE. IL S'AGIT DE PREDIRE LE COMPORTEMENT VIBRATOIRE DE TUYAUTERIES, POUR LESQUELLES ON OBSERVE QUE LA DISPERSION SUR DES PARAMETRES ENTRE DES SYSTEMES THEORIQUEMENT IDENTIQUES PEUT ENGENDRER DES COMPORTEMENTS VIBRATOIRES TRES DIFFERENTS.PARIS-Arts et Métiers (751132303) / SudocSudocFranceF

Simulation numérique de l'usinage à l'échelle macroscopique (prise en compte d'une pièce déformable)

L'idée de mettre en place un simulateur relativement général de la partie mécanique de l'usinage à l'échelle macroscopique est à l'origine de ce travail. Le principal apport de ce travail est la prise en compte de pièces dont la zone concernée par l'usinage est flexible. Cette présence de déformations dans la pièce a nécessité une définition précise de l'enlèvement de matière. Cette définition se fonde sur une configuration dite matérielle, où la réalisation pratique de la simulation de l'usinage est effectuée. Par ailleurs, les pièces flexibles étant généralement très minces, l'enlèvement de matière peut modifier de façon significative le comportement dynamique de la pièce (perte de masse et de raideur). Pour être fidèle, une simulation doit alors prendre en compte cette modification de façon régulière en cours d'usinage. Nous montrons que cette prise en compte ne peut dans certains cas être évitée, et nous proposons une stratégie limitant les coûts numériques induits par cette prise en compte. Un autre apport du travail réalisé est l'utilisation d'un modèle géométrique différent de celui des approches précédentes du LMSP, pour représenter le volume occupé par la pièce. Avec le modèle géométrique de la pièce retenu dans les travaux précédents du LMSP (modèle B-Rep analogue aux modèles utilisés en CAO), de très nombreuses intersections de polyèdres conduisent à des facettes "dégénérées". La nouvelle technique adoptée est celle des Z-buffer où la pièce est modélisée par des dexels (ensemble de " bâtonnets " disposés sur une matrice régulière). Cette description permet de simplifier sensiblement les algorithmes d'intersection tout en les rendant plus robustes. Cette nouvelle description nous a conduit à revoir la démarche de modélisation de l'interaction outil/pièce et notamment la démarche de calcul des efforts de coupe. Cette modélisation s'intègre dans le logiciel Nessy du LMSP.PARIS-Arts et Métiers (751132303) / SudocMETZ-Arts et Métiers (574632301) / SudocSudocFranceF

Modélisation des poutres sandwich elasto-piézo-électriques (élément fini raffiné)

PARIS-Arts et Métiers (751132303) / SudocSudocFranceF