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Damage detection and local resonances model in CFRP composite material by vibrothermography Demy, Philippe ; Golinval, Jean-Claude ; Scientific conference (2012, September) Vibrothermography (VT) is an active non destructive technique able to detect singularities like delamination, even if the defect internal faces are in contact. Under sonic or ultrasonic mechanical ... [more ▼] Vibrothermography (VT) is an active non destructive technique able to detect singularities like delamination, even if the defect internal faces are in contact. Under sonic or ultrasonic mechanical vibrations, a delamination may behave like a heat source principally due to friction between the rubbing faces and/or stress concentration in the area. The present article focuses on the understanding of the underlying phenomenon so-called "local resonances" and its correlation with the presence of temperature peaks observed at certain frequencies. For this purpose, a simplified finite element modal analysis of the delamination model is compared with the heating rate vs. frequency data's acquired by an infrared camera. Then, some conclusive results of sine sweep and chirp testing will be presented and discussed in regards to this theory. [less ▲] Detailed reference viewed: 72 (12 ULg)Modal identification of time-varying systems using simulated responses on wind turbines Bertha, Mathieu ; Mayorga Rios, Jorge Patricio ; Golinval, Jean-Claude in Sas, P; Moens, D; Jonckheere, S (Eds.) Proceedings of ISMA2012-USD2012 (2012, September) Wind turbines are good examples of time-varying systems as their modal properties depend on their instantaneous configuration. To catch the variations of modal parameters in time-varying systems ... [more ▼] Wind turbines are good examples of time-varying systems as their modal properties depend on their instantaneous configuration. To catch the variations of modal parameters in time-varying systems, classical identification methods have to be adapted to the non-stationary nature of the recorded signals. In this paper, it is proposed to study the dynamic behavior of an offshore five-megawatt wind turbine. First, a numerical model of the wind turbine is created to serve as reference. Then, the time-varying behavior of the system is evaluated by simulating a large number of possible configurations. To this purpose, time responses are generated from the numerical model submitted to different environmental conditions. The wind is considered as the main non-measured external excitation force on the structure and the responses are recorded at several locations to simulate a real measurement process. Special care is brought to the accessibility of the measurement locations and to the limited number of available sensors in practice. Using these simulated measurements, output-only identification methods are used to extract varying dynamic properties of the structure. The final objective of this work is to pave the way to online condition monitoring of wind turbines. [less ▲] Detailed reference viewed: 55 (15 ULg)Étalonnage dynamique des capteurs piézoélectriques pour la mesure de haute pression balistique Elkarous, Lamine ; ; Golinval, Jean-Claude in 4ème Conférence Internationale de métrologie - CAFMET2012 (2012, April 24) Detailed reference viewed: 79 (13 ULg)Damage Detection on the Champangshiehl Bridge using Blind Source Separation ; ; Golinval, Jean-Claude et al in Strauss, Alfred; Frangopol, Dan M.; Bergmeister, Konrad (Eds.) Life-Cycle and Sustainability of Civil Infrastructure Systems (2012) This paper addresses the problem of damage detection in civil engineering structures using characteristic subspaces obtained from principal component analysis (PCA) of output-only measurements. Damage ... [more ▼] This paper addresses the problem of damage detection in civil engineering structures using characteristic subspaces obtained from principal component analysis (PCA) of output-only measurements. Damage detection is performed by comparing subspace features between a reference (healthy) state and a current (possibly damaged) state. The damage indicator used in this study is the angular coherence between sub-spaces. The considered damage detection procedure is illustrated on the Champangshiehl Bridge which is a two span concrete box girder bridge located in Luxembourg. Before its destruction, multiple damage levels were inten-tionally created by cutting a growing number of prestressed tendons. Vibration data were acquired by the University of Luxembourg for each damaged state at many locations on the bridge. As previous studies dem-onstrated the large importance of environmental factors on modal identification, special care was taken to evaluate this influence during the test campaign. [less ▲] Detailed reference viewed: 101 (8 ULg)Fault Diagnosis in Industrial Systems Based on Blind Source Separation Techniques Using One Single Vibration Sensor ; ; Golinval, Jean-Claude in Shock & Vibration (2012), 19(5), 795-801 In the field of structural health monitoring or machine condition monitoring, most vibration based methods reported in the literature require to measure responses at several locations on the structure. In ... [more ▼] In the field of structural health monitoring or machine condition monitoring, most vibration based methods reported in the literature require to measure responses at several locations on the structure. In machine condition monitoring, the number of available vibration sensors is often small and it is not unusual that only one single sensor is used to monitor a machine. The aim of this paper is to propose an extension of fault detection techniques that may be used when a reduced set of sensors or even one single sensor is available. Fault detection techniques considered here are based on output-only methods coming from the Blind Source Separation (BSS) family, namely Principal Component Analysis (PCA) and Second Order Blind Identification (SOBI). The advantages of PCA or SOBI rely on their rapidity of use and their reliability. Based on these methods, subspace identification may be performed by using the concept of block Hankel matrices which make possible the use of only one single measurement signal. Thus, the problem of fault detection in mechanical systems can be solved by using subspaces built from active principal components or modal vectors. It consists in comparing subspace features between the reference (undamaged) state and a current state. The angular coherence between subspaces is a good indicator of a dynamic change in the system due to the occurrence of faults or damages. The robustness of the methods is illustrated on industrial examples. [less ▲] Detailed reference viewed: 52 (3 ULg)Nanomechanical and nanotribological characterization of microelectromechanical system ; ; Golinval, Jean-Claude in Journal of Optoelectronics and Advanced Materials [= JOAM] (2012), 14(3-4), 401-412 Investigations of the mechanical and tribological properties of microelectromechanical system (MEMS) components on nanoscale can provide insights into failure mechanism of material. The main goal of this ... [more ▼] Investigations of the mechanical and tribological properties of microelectromechanical system (MEMS) components on nanoscale can provide insights into failure mechanism of material. The main goal of this paper is focused on the mechanical and tribological characterizations of MEMS mechanical components in order to improve their reliability design. The mechanical properties of interests are stiffness, modulus of elasticity, stress, strain. Dynamical investigations are performed to analyze the resonant frequency response, velocity and amplitude of oscillations of electrostatically actuated microcomponents and to estimate the quality factor. Finite element analysis is used to validate the experimental results of mechanical properties and to simulate the dynamical behaviour of investigated microcomponents. Tribological investigations are developed to estimate the stiction and friction. Testing and the individual characterization of MEMS materials and structures, performed using advanced equipments such as atomic force microscope and optical vibrometer analyzer are presented. [less ▲] Detailed reference viewed: 176 (1 ULg)Stiction failure in microswitches due to elasto-plastic adhesive contact Wu, Ling ; Golinval, Jean-Claude ; Noels, Ludovic in Proceedings of the XII SEM International Conference & Exposition on Experimental and Applied Mechanics (2012) Undesirable stiction, which results from contact between surfaces, is a major failure mode in micro-switches. Indeed the adhesive forces can become so important that the two surfaces remain permanently ... [more ▼] Undesirable stiction, which results from contact between surfaces, is a major failure mode in micro-switches. Indeed the adhesive forces can become so important that the two surfaces remain permanently glued, limiting the life-time of the MEMS. This is especially true when contact happens between surfaces where elasto-plastic asperities deform permanently until the surfaces reach plastic accommodation, increasing the surface forces. To predict this behavior, a micro adhesive-contact model is developed, which accounts for the surfaces topography evolutions during elasto-plastic contacts. This model can be used at a higher scale to study the MEMS behavior, and thus its life-time. The MEMS devices studied here are assumed to work in a dry environment. In these operating conditions only the Van der Waals forces have to be considered for adhesion. For illustration purpose, an electrostatic-structural analysis is performed on a micro-switch. To determine the degree of plasticity involved, the impact energy of the movable electrode at pull-in is estimated. Thus the maximal adhesive force is predicted using the developed model. [less ▲] Detailed reference viewed: 56 (8 ULg)Mechanical and tribological characterization of a thermally actuated MEMS cantilever ; ; Golinval, Jean-Claude in Microsystem Technologies (2012) The temperature effect on the mechanical and tribological behaviors of a microelectromechanical systems cantilever is experimentally investigated using an atomic force microscope. A nonlinear variation of ... [more ▼] The temperature effect on the mechanical and tribological behaviors of a microelectromechanical systems cantilever is experimentally investigated using an atomic force microscope. A nonlinear variation of the bending stiffness of microcantilevers as a function of temperature is determined. The variation of the adhesion force between the tip of atomic force microscope (AFM) probe (Si3N4) and the microcantilever fabricated in gold is monitored at different temperatures. Using the lateral mode operation of atomic force microscope, the influence of temperature on friction coefficient between the tip of AFM probe and microcantilever is presented. Finite element analysis is used to estimate the thermal field distribution in microcantilever and the axial expansion. [less ▲] Detailed reference viewed: 19 (2 ULg)Détection d'endommagement de structures en matériaux composites CFRP par vibrothermographie Demy, Philippe ; Golinval, Jean-Claude ; in Desse, Jean-Michel; Picart, Pascal; Tankam, Patrice (Eds.) Actes du 12ème colloque international francophone sur les méthodes et techniques optiques pour l'industrie (2011, November 21) La vibrothermographie (VT) est une technique de thermographie active basée sur le fait que, sous l’action de vibrations mécaniques induites dans une structure, les défauts peuvent se comporter comme des ... [more ▼] La vibrothermographie (VT) est une technique de thermographie active basée sur le fait que, sous l’action de vibrations mécaniques induites dans une structure, les défauts peuvent se comporter comme des sources de chaleur internes suite à leur interaction avec les ondes élastiques. Ces vibrations peuvent être générées notamment par un excitateur piézoélectrique. La dissipation d’énergie au niveau des singularités liées à la présence de défauts est détectable par une caméra thermique infrarouge. Parmi les mécanismes physiques sous-jacents du phénomène, on relève essentiellement les pertes par friction et hystérésis plastique [1,2]. Des recherches plus approfondies prenant en compte divers facteurs comme les non linéarités de couplage font actuellement l'objet de divers travaux afin de mieux comprendre le phénomène et d'améliorer la fiabilité de la méthode [3,4]. L'objectif de cet article est l'évaluation des potentialités de la vibrothermographie, menée sur différents échantillons en matériaux composites CFRP (Carbon Fiber Reinforced Plastic) utilisés en aéronautique. La technique est prometteuse dans le domaine des essais non destructifs (CND), et apporte une complémentarité aux méthodes conventionnelles utilisables sur ce type de matériaux, comme la radiographie X, les ultrasons ou encore l'interférométrie de speckle [5]. En effet, avec la VT, la détection de défauts est indépendante de leurs orientations dans le spécimen. De plus, des défauts internes relativement profonds peuvent être détectés, y compris sur des échantillons de géométries complexes. C'est pourquoi la VT est particulièrement utile pour la détection de fissures et de délaminations dans les CFRP [6]. Une comparaison expérimentale avec des résultats obtenus par thermographie pulsée optique (stimulation thermique par lampes chauffantes) est également présentée. [less ▲] Detailed reference viewed: 119 (8 ULg)Influence of the elasto-plastic adhesive contact on Micro-Switches Wu, Ling ; Golinval, Jean-Claude ; Noels, Ludovic in Hogge, Michel; Van Keer, Roger; Dick, Erik (Eds.) et al Proceedings of the 5th International Conference on Advanded COmputational Methods in Engineering (ACOMEN2011) (2011, November) Undesirable stiction, which results from contact between surfaces, is a major failure mode in micro,electro-mechanical systems (MEMS). In previous works, a statistical rough surfaces interaction,model ... [more ▼] Undesirable stiction, which results from contact between surfaces, is a major failure mode in micro,electro-mechanical systems (MEMS). In previous works, a statistical rough surfaces interaction,model, based on Maugis and Kim formulations has been presented to estimate the adhesive forces in MEMS switches. In this model, only elastic adhesive contact has been considered. However, during the impact between rough surfaces, at pull-in process for example, plastic deformations of the rough surfaces cannot be always neglected especially for the MEMS with metallic contact surfaces. In the present work, a new micro-model predicting the adhesive-contact force on a single elasticplastic asperity interacting with a rigid plane is presented. This model will be used later on for the interaction between two elastic-plastic rough surfaces. The MEMS devices studied here are assumed to work in a dry environment. In these operating conditions only the Van der Waals forces have to be considered for adhesion. [less ▲] Detailed reference viewed: 52 (5 ULg)A Micro-Macroapproach to Predict Stiction due to Surface Contact in Microelectromechanical Systems Wu, Ling ; Noels, Ludovic ; et al in IEEE/ASME Journal of Microelectromechanical Systems (2011), 20(4), 976-990 Stiction, which results from contact between surfaces, is a major failure mode in micro electro-mechanical systems (MEMS). Indeed microscopic structures tend to adhere to each other when their surfaces ... [more ▼] Stiction, which results from contact between surfaces, is a major failure mode in micro electro-mechanical systems (MEMS). Indeed microscopic structures tend to adhere to each other when their surfaces enter into contact and when the restoring forces are unable to overcome the interfacial forces. Since incidental contacts cannot be completely excluded and since contacts between moving parts can be part of the normal operation of some types of MEMS, stiction prediction is an important consideration when designing micro and nano-devices. In this paper a micro-macro multi-scale approach is developed in order to predict possible stiction. At the lower scale, the unloading adhesive contact-distance curves of two interacting rough surfaces are established based on a previously presented model [L. Wu et al., J. Appl. Phys. 106, 113502, 2009]. In this model, dry conditions are assumed and only the van der Waals forces as adhesion source are accounted for. The resulting unloading adhesive contact-distance curves are dependant on the material and on surface properties, such as, elastic modulus, surface energy and on the rough surfaces topography parameters; the standard deviation of asperity heights and the asperities density. At the higher scale, a finite element analysis is considered to determine the residual cantilever beam configuration due to the adhesive forces once contact happened. Toward this end, the adhesive contact-distance curve computed previously is integrated on the surface of the finite elements as a contact law. Effects of design parameters can then be studied for given material and surface properties. [less ▲] Detailed reference viewed: 206 (94 ULg)Modeling and finite element analysis of mechanical behavior of flexible MEMS components Pustan, Marius ; ; et al in Microsystem Technologies (2011), 17(4), 553-562 This paper describes the studies of the mechanical characteristics of flexible MEMS components including theoretical approaches, finite element analysis and experimental investigations. Modeling and ... [more ▼] This paper describes the studies of the mechanical characteristics of flexible MEMS components including theoretical approaches, finite element analysis and experimental investigations. Modeling and finite element analyses together with theoretical and experimental investigations are performed to estimate the elastic behavior of MEMS components as microcantilevers, microbridges and micromembranes. Finite element analysis of microcomponents deflections under different loading and the stress distribution in beams are determined and compared with the experimental measurements performed using an atomic force microscope. The modeling of a micromembrane supported by four hinges that enable out-of-plane motion is presented. Finite element analysis and experimental investigations are performed to visualize the deflection of the mobile part of the micromembrane under an applied force and the stress distribution in hinges. In additional, this paper provides analytical relations to compute the stiffness and the stress of the investigated flexible MEMS components. [less ▲] Detailed reference viewed: 36 (7 ULg)Effects of the electrode positions on the dynamical behaviour of electrostatically actuated MEMS resonators Pustan, Marius ; ; et al (2011, April 18) The influence of the lower electrode positions on the dynamic response of polysilicon MEMS resonators is studied and presented in this paper. The change in the frequency response of investigated MEMS ... [more ▼] The influence of the lower electrode positions on the dynamic response of polysilicon MEMS resonators is studied and presented in this paper. The change in the frequency response of investigated MEMS resonators as function of the lower electrode positions is measured using a vibrometer analyzer. The decrease in the amplitude and velocity of oscillations if the lower electrode is moved from the beam free-end toward to the beam anchor is experimental monitored. The measurements are performed in ambient conditions in order to characterize the forced-response Q-factor of samples. A decrease of the Q- factor if the lower electrode is moved toward to the beam anchor is experimental determined. Different responses of MEMS resonators may be obtained if the position of the lower electrode is modified. Indeed the resonator stiffness, velocity and amplitude of oscillations are changed. [less ▲] Detailed reference viewed: 39 (5 ULg)Investigation on gas pressure measurement inside small caliber weapons with piezoelectric transducers Elkarous, Lamine ; ; Golinval, Jean-Claude et al in Measurement Science Conference 2012 (2011, March 20) Detailed reference viewed: 33 (6 ULg)Diagnostic de l’état mécanique de structures par analyse de vibrations Golinval, Jean-Claude Scientific conference (2011, January 06) La détection d'un endommagement structural par voie expérimentale et non destructive est un problème dont la complexité dépend non seulement des conditions opérationnelles dans lesquelles les mesures ... [more ▼] La détection d'un endommagement structural par voie expérimentale et non destructive est un problème dont la complexité dépend non seulement des conditions opérationnelles dans lesquelles les mesures peuvent s'effectuer (machine ou structure en fonctionnement ou à l'arrêt), mais aussi du niveau de connaissance souhaité pour la caractérisation du défaut. Quatre niveaux sont généralement distingués, à savoir, dans le sens d’une complexité croissante : - niveau 1 : le problème de détection (dépistage), - niveau 2 : le problème de la localisation, - niveau 3 : la quantification du degré de sévérité du défaut, - niveau 4 : l’estimation de la durée de vie résiduelle de la structure endommagée. L’objectif de cet exposé est de présenter un ensemble de méthodes basées sur la mesure de vibrations et qui ont été développées récemment pour la détection de défauts mécaniques ou d’endommagements structuraux. Ces méthodes de diagnostic sont basées sur la comparaison entre l’état initial (supposé sain) de la structure et un état courant. Elles peuvent également s’avérer utiles pour le suivi en temps réel de l’état de santé mécanique d’une machine. [less ▲] Detailed reference viewed: 137 (5 ULg)Comparison of output-only methods for condition monitoring of industrials systems Rutten, Christophe ; ; Golinval, Jean-Claude in Journal of Physics: Conference Series (2011), 305 In the field of structural health monitoring or machine condition monitoring, the activation of nonlinear dynamic behavior complicates the procedure of damage or fault detection. Blind source separation ... [more ▼] In the field of structural health monitoring or machine condition monitoring, the activation of nonlinear dynamic behavior complicates the procedure of damage or fault detection. Blind source separation (BSS) techniques are known as efficient methods for damage diagnosis. However, most of BSS techniques repose on the assumption of the linearity of the system and the need of many sensors. This article presents some possible extensions of those techniques that may improve the damage detection, e.g. Enhanced-Principal Component Analysis (EPCA), Kernel PCA (KPCA) and Blind Modal Identification (BMID). The advantages of EPCA rely on its rapidity of use and its reliability. The KPCA method, through the use of nonlinear kernel functions, allows to introduce nonlinear dependences between variables. BMID is adequate to identify and to detect damage for generally damped systems. In this paper, damage is firstly examined by Stochastic Subspace Identification (SSI); then the detection is achieved by comparing subspace features between the reference and a current state through statistics and the concept of subspace angle. Industrial data are used as illustration of the methods. [less ▲] Detailed reference viewed: 37 (5 ULg)Nonlinear modal analysis of aerospace structures Peeters, Maxime ; Kerschen, Gaëtan ; Golinval, Jean-Claude et al in Proceedings of the 3rd International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (2011) The dynamic systems theory is well-established for linear systems and can rely on mature tools such as the theories of linear operators and linear integral transforms. This is why theoretical and ... [more ▼] The dynamic systems theory is well-established for linear systems and can rely on mature tools such as the theories of linear operators and linear integral transforms. This is why theoretical and experimental modal analysis, i.e., the computation of vibration modes from a mathematical model and from experimental data, respectively, is really quite sophisticated and advanced. Even though linear modal analysis served, and is still serving, the structural dynamics community for applications ranging from bridges to satellites, it is commonly accepted that nonlinearity is a frequent occurrence in engineering structures. Because linear modal analysis fails in the presence of nonlinear dynamical phenomena, the development of a practical nonlinear analog of modal analysis would be an extremely timely contribution; it is clearly missing in the structural dynamics literature. A new framework for nonlinear modal analysis of real-world structures, which includes the computation of nonlinear modes from finite element models, is introduced in this paper. This framework will permit a rigorous, yet understandable by the practicing engineer, analysis of nonlinear dynamical phenomena. It will also provide solid theoretical foundations for extending finite element model validation to nonlinear aerospace structures. [less ▲] Detailed reference viewed: 46 (1 ULg)Nonlinear normal modes of real-world structures: application to a full-scale aircraft Peeters, Maxime ; Kerschen, Gaëtan ; Golinval, Jean-Claude et al in Proceedings of the ASME International Design Engineering Technical Conferences (2011) The objective of this paper is to demonstrate that the numerical computation of the nonlinear normal modes (NNMs) of complex real-world structures is now within reach. The application considered in this ... [more ▼] The objective of this paper is to demonstrate that the numerical computation of the nonlinear normal modes (NNMs) of complex real-world structures is now within reach. The application considered in this study is the airframe of the Morane-Saulnier Paris aircraft, whose ground vibration tests have exhibited some nonlinear structural behaviors. The finite element model of this aircraft, elaborated from drawings, has more than 80000 degrees of freedom, and softening nonlinearities exist in the connection between the external fuel tanks and the wing tips. From this model, a reduced-order model, which is accurate in the [0-100Hz] range, is constructed using the Craig- Bampton technique. The NNMs of the reduced model are then computed using a numerical algorithm combining shooting and pseudo-arclength continuation. The results show that the NNMs of this full-scale structure can be computed accurately even in strongly nonlinear regimes and with a reasonable computational burden. Nonlinear modal interactions are also highlighted by the algorithm and are discussed. [less ▲] Detailed reference viewed: 26 (2 ULg)Computation of nonlinear normal modes of large structures: application to a full-scale aircraft Peeters, Maxime ; Renson, Ludovic ; Kerschen, Gaëtan et al in Proceedings of the 7th European Nonlinear Dynamics Conference (ENOC 2011) (2011) The objective of this paper is to demonstrate that the numerical computation of the nonlinear normal modes (NNMs) of complex real-world structures is now within reach. The application considered in this ... [more ▼] The objective of this paper is to demonstrate that the numerical computation of the nonlinear normal modes (NNMs) of complex real-world structures is now within reach. The application considered in this study is the airframe of the Morane-Saulnier Paris aircraft, whose ground vibration tests exhibited some nonlinear structural behaviors. The NNMs are computed using a numerical algorithm combining shooting and pseudo-arclength continuation. [less ▲] Detailed reference viewed: 67 (5 ULg)Phase resonance testing of nonlinear vibrating structures Peeters, Maxime ; Kerschen, Gaëtan ; Golinval, Jean-Claude in 28th International Modal Analysis Conference, Jacksonville, 2010 (2011) Detailed reference viewed: 36 (13 ULg) |
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