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Evaluation of Tribo-Mechanical Properties of Thin Films Using Atomic Force Microscope Pustan, Marius ; Rochus, Véronique ; Wu, Ling et al in First European Conference on Nanofilm ECNF2010 (2010) Experimental investigations of mechanical and tribological properties of thin films using an atomic force microscope and its combination with nanoidentation are presented in this paper. The normal mode of ... [more ▼] Experimental investigations of mechanical and tribological properties of thin films using an atomic force microscope and its combination with nanoidentation are presented in this paper. The normal mode of an atomic force microscope is used to measure the stiffness and hardness of thin films which are tribologically characterized by roughness, nano-scale adhesion forces and friction forces. The friction forces are measured using the lateral force mode of atomic force microscope. In order to measure the adhesion forces of thin films, spectroscopy in point with atomic force microscope was performed. Direct measurement of tribological and mechanical behaviour of thin films is important to increase the lifetime of microstructures which use thin films for friction and stiction reduction of microsystems. [less ▲] Detailed reference viewed: 89 (24 ULg)Design of Microswitch Systems Avoiding Stiction due to Surface Contact Wu, Ling ; Noels, Ludovic ; Rochus, Véronique et al in SEM 2010 Annual Conference & Exposition on Experimental and Applied Mechanics (2010) Stiction which results from contact between surfaces is a major failure mode in micro electro-mechanical systems (MEMS). Increasing restoring forces using high spring constant allows avoiding stiction but ... [more ▼] Stiction which results from contact between surfaces is a major failure mode in micro electro-mechanical systems (MEMS). Increasing restoring forces using high spring constant allows avoiding stiction but leads to an increase of the actuation voltage so that the switch’s efficiency is threatened. A statistical rough surfaces interaction model, based on Maugis’ and Kim’s formulations is applied to estimate the adhesive forces in MEMS switches. Based on the knowledge of these forces, the proper design range of the equivalent spring constant, which is the main factor of restoring force in MEMS switches, can be determined. The upper limit of equivalent spring constant depends mainly on the expected actuator voltage and on the geometric parameters, such as initial gap size and ,thickness of dielectric layer. The lower limit is assessed on the value of adhesive forces between the two contacting rough surfaces. It mainly depends on the adhesive work of contact surfaces and on the surfaces’ roughness. In order to study more complicated structures, this framework will be used in a multiscale model: resulting unloading micro adhesive contact-distance curves of two rough surfaces will be used as contact forces in a finite-element model. In this paper the extraction of these curves for the particular case of gold to gold micro-switches is pursued. [less ▲] Detailed reference viewed: 160 (43 ULg)Subspace-based Methods for Machinery Analysis and Monitoring Nguyen, Viet Ha ; Rutten, Christophe ; Golinval, Jean-Claude Conference (2010) The objective of this presentation is to address the problem of structural damage detection or fault diagnosis in mechanical systems using subspace-based methods. Different methods are reviewed starting ... [more ▼] The objective of this presentation is to address the problem of structural damage detection or fault diagnosis in mechanical systems using subspace-based methods. Different methods are reviewed starting from Principal Component Analysis (PCA) also known as Proper Orthogonal Decomposition (POD) of time responses. PCA is known as an efficient method for extracting modal features of linear structures from output-only measurements. Those features define a subspace which characterizes the dynamical behavior of the structure. It becomes than possible to detect structural damage by comparing a reference subspace (obtained from the healthy structure) with current subspaces on the basis of the concept of angles between subspaces. Other damage indexes based on statistics may also be used. One of the drawbacks of PCA is the need of several sensors. If the number of sensors is too small, modal identification and/or damage detection may not be performed in good conditions using PCA. An alternative PCA-based method named Null Subspace Analysis (NSA) may then be used. The NSA method generates data by means of block Hankel matrices and is proven to be efficient when the number of available sensors is small or even reduced to one sensor only. However, when damage activates nonlinearity, the detection problem may necessitate methods which are more sensitive to nonlinear behaviors. To this purpose, Kernel Principal Component Analysis (KPCA) is a nonlinear extension of PCA built to authorize features with nonlinear dependence between variables. The method is “flexible” in the sense that different kernel functions may be used to better fit the testing data. Industrial applications are presented to illustrate the proposed methods. [less ▲] Detailed reference viewed: 39 (0 ULg)Effects of the geometrical dimensions on stress and strain of electrostatically actuated MEMS resonators at pull-in and stiction positions Pustan, Marius ; Golinval, Jean-Claude ; Rochus, Véronique in EuroSimE 2010 (2010) Detailed reference viewed: 18 (12 ULg)Damage Diagnosis of Beam-like Structures Based on Sensitivities of Principal Component Analysis Results Nguyen, Viet Ha ; Golinval, Jean-Claude in IMAC-XXVIII A Conference on Structural Dynamics (2010) This paper addresses the problem of damage detection and localization in linear-form structures. Principal Component Analysis (PCA) is a popular technique for dynamic system investigation. The aim of the ... [more ▼] This paper addresses the problem of damage detection and localization in linear-form structures. Principal Component Analysis (PCA) is a popular technique for dynamic system investigation. The aim of the paper is to present a damage diagnosis method based on sensitivities of PCA results in the frequency domain. Starting from Frequency Response Functions (FRFs) measured at different locations on the beam, PCA is performed to determine the main features of the signals. Sensitivities of principal directions obtained from PCA to beam parameters are then computed and inspected according to the location of sensors; their variation from the healthy state to the damaged state indicates damage locations. It is worth noting that damage localization is performed without the need of modal identification. Once the damage has been localized, its evaluation may be quantified if a structural model is available. This evaluation is based on a model updating procedure using previously estimated sensitivities. The efficiency and limitations of the proposed method are illustrated using numerical and experimental examples. [less ▲] Detailed reference viewed: 80 (26 ULg)Simulation of Particle Levitation due to Dielectrophoresis Rochus, Véronique ; ; Golinval, Jean-Claude et al in EuroSimE 2010 (2010) The aim of the research is to model accurately dielectrophoresis using different numerical tools and compare them to experimental results. The dielectrophoresis phenomenon consists in the creation of ... [more ▼] The aim of the research is to model accurately dielectrophoresis using different numerical tools and compare them to experimental results. The dielectrophoresis phenomenon consists in the creation of electrostatic forces on nano or micro particles due to a gradient of electric field. The aim of such a setup is to control the motion of micro or nano particles for MEMS applications, for instance, for bioanalysis devices. To validate the numerical results, some prototypes have been fabricated at TU Delft. Using these simulations, a design of microstructure has been chosen to levitate Silica micro-particles. Experimental measurements have been performed and some characteristic behaviours of particle depending on the amplitude and the frequency of the applied voltage have been identified. The measurements are compared to the numerical simulation. [less ▲] Detailed reference viewed: 41 (3 ULg)Damage localization in Linear-Form Structures Based on Sensitivity Investigation for Principal Component Analysis Nguyen, Viet Ha ; Golinval, Jean-Claude in Journal of Sound & Vibration (2010), 329 This paper addresses the problem of damage detection and localization in linear-form structures. Principal Component Analysis (PCA) is a popular technique for dynamic system investigation. The aim of the ... [more ▼] This paper addresses the problem of damage detection and localization in linear-form structures. Principal Component Analysis (PCA) is a popular technique for dynamic system investigation. The aim of the paper is to present a damage diagnosis method based on sensitivities of PCA results in the frequency domain. Starting from Frequency Response Functions (FRFs) measured at different locations on the structure; PCA is performed to determine the main features of the signals. Sensitivities of principal directions obtained from PCA to structural parameters are then computed and inspected according to the location of sensors; their variation from the healthy state to the damaged state indicates damage locations. It is worth noting that damage localization is performed without the need of modal identification. Influences of some features as noise, choice of parameter and number of sensors are discussed. The efficiency and limitations of the proposed method are illustrated using numerical and real-world examples. [less ▲] Detailed reference viewed: 44 (10 ULg)Experimental modal analysis of nonlinear vibrating structures using nonlinear normal modes Peeters, Maxime ; Kerschen, Gaëtan ; Golinval, Jean-Claude in IV European Conference on Computational Mechanics, Paris, 2010 (2010) Detailed reference viewed: 40 (14 ULg)Influence of Adhesive Rough Surface Contact on Micro-Switches Wu, Ling ; Rochus, Véronique ; Noels, Ludovic et al in Journal of Applied Physics (2009), 106(11), 113502 Stiction is a major failure mode in micro electro-mechanical systems (MEMS). Undesirable stiction, which results from contact between surfaces, threatens the reliability of MEMS severely as it breaks the ... [more ▼] Stiction is a major failure mode in micro electro-mechanical systems (MEMS). Undesirable stiction, which results from contact between surfaces, threatens the reliability of MEMS severely as it breaks the actuation function of MEMS switches for example. Although it may be possible to avoid stiction by increasing restoring forces using high spring constants, it follows that the actuation voltage has also to be increased significantly, which reduces the efficiency. In our research, an electrostatic-structural analysis is performed to estimate the proper design range of the equivalent spring constant which is the main factor of restoring force in MEMS switches. The upper limit of equivalent spring constant is evaluated based on the initial gap width, the dielectric thickness, and the expected actuation voltage. The lower limit is assessed on the value of adhesive forces between the two contacting 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. A statistical model is used to simulate the rough surface, and the Maugis’s model is combined with Kim’s expansion to calculate adhesive forces. In the resulting model, the critical value of the spring stiffness depends on the material and surface properties, such as the elastic modulus, surface energy and surface roughness. The aim of this research is to propose simple rules for design purposes. [less ▲] Detailed reference viewed: 138 (53 ULg)Qualification Procedure of Luminaires in the Event of an Impact to the Pole ; ; Golinval, Jean-Claude Conference given outside the academic context (2009) The objective of the study is to develop a testing specification on an electrodynamic shaker which ensures the qualification of a parking lighting device, whose pole is impacted by a car. The methodology ... [more ▼] The objective of the study is to develop a testing specification on an electrodynamic shaker which ensures the qualification of a parking lighting device, whose pole is impacted by a car. The methodology is based on both a numerical approach and an experimental approach using an electrodynamic shaker. The first step of the analysis consists in modeling the structure and the excitation by means of a finite element approach. The calculation of the dynamic response of the "pole/lighting device" system to impact loading is repeated for different geometries of the pole. The second step is to consider each dynamic response at the fixing point of the lighting device on the pole as input for a base-excited single degree of freedom system. The theory developed for such a system allows to define severity criteria like the Shock Response Spectrum (SRS) which is the most representative criterion in the case of an impact. The severity of the vibration environment of the lighting device is then obtained by considering the envelope of the different computed SRS. Finally, different test specifications leading to equivalent SRS are proposed and the device is tested on an electrodynamic shaker. The developed methodology was applied to the NEMO lighting device (Schréder). [less ▲] Detailed reference viewed: 64 (8 ULg)Damage Detection of Mechanical Components Using Null Subspace Analysis Rutten, Christophe ; ; Golinval, Jean-Claude Conference given outside the academic context (2009) This paper presents two original applications of the Null Subspace Analysis (NSA) method for fault diagnosis in mechanical components. The method is first applied to the case-study of electro-mechanical ... [more ▼] This paper presents two original applications of the Null Subspace Analysis (NSA) method for fault diagnosis in mechanical components. The method is first applied to the case-study of electro-mechanical devices at the end of the assembly line with the aim of assessing their overall quality. The advantages of the proposed method rely in its rapidity of use and its reliability. At first, a set of five good (i.e. healthy) devices and four damaged devices was considered. The components were instrumented with one triaxial accelerometer on the flank and one monoaxial accelerometer on the top. Based on the NSA method, a mapping of the space [ active components, system order ] up to a system order of 100, was realized in order to select the appropriate order and number of active components. Eventually, thanks to this mapping, the method was able to successfully detect all the faulty components using the signal from only one accelerometer in one direction. The second application is related to the quality assessment of welded joints between stripes in a steel processing plan. Six welded joints with nominal welding parameters and twenty-seven welded joints with out-of-range parameters were realized. Again, the NSA method was able to diagnose successfully the welded joints using a single signal from one accelerometer. [less ▲] Detailed reference viewed: 105 (10 ULg)Damping material characterization and modeling: an industrial case-study Poncelet, Fabien ; ; Kerschen, Gaëtan et al in International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE 2009), San Diego, 2009 (2009, August) Turbojet engines contain potential nonlinearity sources such as geometric nonlinearities due to the slenderness and the length of modern blades, contacts between the blades and the shrouds, friction in ... [more ▼] Turbojet engines contain potential nonlinearity sources such as geometric nonlinearities due to the slenderness and the length of modern blades, contacts between the blades and the shrouds, friction in the connections, and material nonlinearities. This paper focuses on the damping material which can be found in some stator stages of low-pressure compression parts. This material makes the shroud and all the blades of the stage interdependent, providing damping and fluid vein airtightness. The objective is to propose a characterization and a numerical modeling methodology that could easily be integrated within an industrial process. Nonlinearity characterization tests, based on the Restoring Force Surface method, are presented as well as viscoelastic characterization. Finally the proposed viscoelastic modeling, based on the Modal Strain Energy method, is validated against experimental data. [less ▲] Detailed reference viewed: 70 (7 ULg)Energy Transfer and Dissipation in a Duffing Oscillator Coupled to a Nonlinear Attachment Viguié, Régis ; Peeters, Maxime ; Kerschen, Gaëtan et al in Journal of Computational and Nonlinear Dynamics (2009), 4(4), The dynamics of a two-degree-of-freedom nonlinear system consisting of a grounded Duffing oscillator coupled to an essentially nonlinear attachment is examined in the present study. The underlying ... [more ▼] The dynamics of a two-degree-of-freedom nonlinear system consisting of a grounded Duffing oscillator coupled to an essentially nonlinear attachment is examined in the present study. The underlying Hamiltonian system is first considered, and its nonlinear normal modes are computed using numerical continuation and gathered in a frequency-energy plot. Based on these results, the damped system is then considered, and the basic mechanisms for energy transfer and dissipation are analyzed. [DOI: 10.1115/1.3192130] [less ▲] Detailed reference viewed: 38 (11 ULg)Nonlinear normal modes, Part 1: Useful framework for the structural dynamicist Kerschen, Gaëtan ; Peeters, Maxime ; Golinval, Jean-Claude et al in Mechanical Systems & Signal Processing (2009), 23 The conceptofnonlinearnormalmodes(NNMs)isdiscussedinthepresentpaperandits companion,PartII.BecausethereisvirtuallynoapplicationoftheNNMstolarge-scale engineeringstructures ... [more ▼] The conceptofnonlinearnormalmodes(NNMs)isdiscussedinthepresentpaperandits companion,PartII.BecausethereisvirtuallynoapplicationoftheNNMstolarge-scale engineeringstructures,thesepapersareanattempttohighlightseveralaspectsthat mightdrivetheirdevelopmentinthefuture.Specifically,wesupportthat(i)numerical methodsforthecontinuationofperiodicsolutionspavethewayforaneffectiveand practical computationofNNMs,and(ii)time–frequencyanalysisisparticularlysuitable fortheanalysisoftheresultingdynamics.Anotherobjectiveofthepresentpaperisto describe,insimpleterms,andtoillustratethefundamentalpropertiesofNNMs.Thisis achievedtoconvincethestructuraldynamicistnotnecessarilyacquaintedwiththemthat theyareausefulframeworkfortheanalysisofnonlinearvibratingstructures. & 2008ElsevierLtd.Allrightsreserved [less ▲] Detailed reference viewed: 144 (28 ULg)Modal Analysis of a Nonlinear Periodic Structure with Cyclic Symmetry ; Peeters, Maxime ; Kerschen, Gaëtan et al in AIAA Journal (2009), 47 The objective of this paper is to examine nonlinear normal modes and their bifurcations in cyclic periodic structures. The nonlinear normal modes are computed using a numerical technique that combines ... [more ▼] The objective of this paper is to examine nonlinear normal modes and their bifurcations in cyclic periodic structures. The nonlinear normal modes are computed using a numerical technique that combines shooting and pseudoarclength continuation. Unlike perturbation techniques, the resulting algorithm can investigate strongly nonlinear regimes of motion. This study reveals that modal interactions may occur without necessarily having commensurate natural frequencies in the underlying linear system. In addition, a countable infinity of such modal Q2 interactions are shown to exist in the system. [less ▲] Detailed reference viewed: 50 (3 ULg)Nonlinear normal modes, Part 2: Toward a pratical computation using numerical continuation techniques Peeters, Maxime ; Viguié, Régis ; Sérandour, Guillaume et al in Mechanical Systems & Signal Processing (2009), 23 The conceptofnonlinearnormalmodes(NNMs)isdiscussedinthepresentpaperandits companion,PartI.OnereasonofthestilllimiteduseofNNMsinstructuraldynamicsis that theircomputationisoftenregardedasimpractical ... [more ▼] The conceptofnonlinearnormalmodes(NNMs)isdiscussedinthepresentpaperandits companion,PartI.OnereasonofthestilllimiteduseofNNMsinstructuraldynamicsis that theircomputationisoftenregardedasimpractical.However,whenresortingto numericalalgorithms,weshowthattheNNMcomputationispossiblewithlimited implementationeffort,whichpavesthewaytoapracticalmethodfordeterminingthe NNMsofnonlinearmechanicalsystems.Theproposedalgorithmreliesontwomain techniques,namelyashootingprocedureandamethodforthecontinuationofNNM motions. Thealgorithmisdemonstratedusingfourdifferentmechanicalsystems,a weakly andastronglynonlineartwo-degree-of-freedomsystem,asimplifieddiscrete modelofanonlinearbladeddiskandanonlinearcantileverbeamdiscretizedbythefinite elementmethod. [less ▲] Detailed reference viewed: 67 (20 ULg)Influence of Adhesive Rough Surface Contact on Micro-Switches Wu, Ling ; Rochus, Véronique ; Noels, Ludovic et al Scientific conference (2009) Detailed reference viewed: 52 (21 ULg)Using passive nonlinear targeted energy transfer to stabilize drill-stringsystems Viguié, Régis ; Kerschen, Gaëtan ; Golinval, Jean-Claude et al in Mechanical Systems & Signal Processing (2009), 23 Torsional vibrations of drill strings used in drilling oil and gas wells arises from a complex interaction of the dynamics of the drilling structure with speed-dependent effective rock-cutting forces ... [more ▼] Torsional vibrations of drill strings used in drilling oil and gas wells arises from a complex interaction of the dynamics of the drilling structure with speed-dependent effective rock-cutting forces. These forces are often difficult to model, and contribute substantially to the instability problems of controlling the drilling operation so as to produce steady cutting. In this work we show how nonlinear passive targeted energy transfer to a lightweight attachment can be used to passively control these instabilities. This is performed by means of a nonlinear energy sink (NES), a lightweight attachment which has been shown to be effective in reducing or even completely eliminating self-excited motions in aeroelastic and other systems. The NES is a completely passive, inherently broadband vibration absorber capable of attracting and dissipating vibrational energy from the primary structure to which it is attached, in this case a nonlinear discontinuous model of a drill-string system. In this paper we describe a prototypical drill string-NES system, briefly discuss some of the analytical and computational tools suitable for its analysis, and then concentrate on mathematical results on the efficacy of the NES in this application and their physical interpretation. [less ▲] Detailed reference viewed: 91 (6 ULg)Parameter estimation and structural model updating using modal methods in the presence of nonlinearity Golinval, Jean-Claude Conference given outside the academic context (2009) Detailed reference viewed: 45 (8 ULg)Detection of nonlinearity in a dynamic system using deformation modes obtained from the Wavelet Transfrom of measured responses Nguyen, Viet Ha ; Peeters, Maxime ; Golinval, Jean-Claude Conference given outside the academic context (2009) An efficient approach to Structural Health Monitoring of dynamical systems based on the Wavelet Transform (WT) and the concept of subspace angle is presented. The objective is to propose a detection ... [more ▼] An efficient approach to Structural Health Monitoring of dynamical systems based on the Wavelet Transform (WT) and the concept of subspace angle is presented. The objective is to propose a detection method that is sensitive to the onset of nonlinear behaviour in a dynamic system. For this purpose, instantaneous frequencies are identified first from output-only vibration signals using the Wavelet Transform. Time varying deformation shapes are then extracted by analyzing the whole measurement data set on the structure. From this information, different dynamic states of the structure may be detected by inspecting time variations of ‘modal’ features. The experimental structure considered here as application example is a clamped beam with a geometric nonlinearity. Detection of nonlinearity is carried out by means of the concept of subspace angles between instantaneous deformation modes extracted from measurement data using the continuous Wavelet Transform. The method consists in controlling the angular coherence between active subspaces of the current and reference states respectively. The proposed technique, which shows a good sensitivity to small changes in the dynamic behaviour of the structure, may also be used for damage detection. [less ▲] Detailed reference viewed: 108 (29 ULg) |
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