Staff members at Los Alamos National Laboratory (LANL) produced a summary of the structural health monitoring literature in 1995. This presentation will summarize the outcome of an updated review covering the years 1996 2001. The updated review follows the LANL statistical pattern recognition paradigm for SHM, which addresses four topics: 1. Operational Evaluation; 2. Data Acquisition and Cleansing; 3. Feature Extraction; and 4. Statistical Modeling for Feature Discrimination. The literature has been reviewed based on how a particular study addresses these four topics. A significant observation from this review is that although there are many more SHM studies being reported, the investigators, in general, have not yet fully embraced the well-developed tools from statistical pattern recognition. As such, the discrimination procedures employed are often lacking the appropriate rigor necessary for this technology to evolve beyond demonstration problems carried out in laboratory setting.

A review of structural health monitoring literature 1996-2001

A critical review of the intrinsic nature of vortex-induced vibrations

This article reviews the development of the original modal assurance criterion (MAC) together with other related assurance criteria that have been proposed over the last twenty years. Some of the other assurance criteria that will be discussed include the coordinate modal assurance criterion (COMAC), the frequency response assurance criterion (FRAC), coordinate orthogonality check (CORTHOG), frequency scaled modal assurance criterion (FMAC), partial modal assurance criterion (PMAC), scaled modal assurance criterion (SMAC), and modal assurance criterion using reciprocal modal vectors (MACRV). In particular, the thought process that relates the original MAC development to ordinary coherence and to orthogonality computations will be explained. Several uses of MAC that may not be obvious to the casual observer (modal parameter estimation consistency diagrams and model updating are two examples) will be identified. The common problems with the implementation and use of modal assurance criterion computations will also be identified. The development of the modal assurance criterion 1-2 over twenty years ago has led to a number of similar assurance criteria used in the area of experimental and analytical structural dynamics. It is important to recognize the mathematical similarity of these varied criteria in order to be certain that conclusions be correctly drawn from what is essentially a squared, linear regression correlation coefficient. The modal assurance criterion is a statistical indicator, just like ordinary coherence, which can be very powerful when used correctly but very misleading when used incorrectly. This article will first review the historical development of the modal assurance criterion. Other similar assurance criteria will then be identified although the list is not intended to be comprehensive. Typical uses of the modal assurance criterion will be discussed and finally, typical abuses will be identified.

The modal assurance criterion–twenty years of use and abuse

Past, present and future of nonlinear system identification in structural dynamics

Introduction. 1. Nonlinear theories of elasticity of plates and shells 2. Nonlinear theories of doubly curved shells for conventional and advanced materials 3. Introduction to nonlinear dynamics 4. Vibrations of rectangular plates 5. Vibrations of empty and fluid-filled circular cylindrical 6. Reduced order models: proper orthogonal decomposition and nonlinear normal modes 7. Comparison of different shell theories for nonlinear vibrations and stability of circular cylindrical shells 8. Effect of boundary conditions on a large-amplitude vibrations of circular cylindrical shells 9. Vibrations of circular cylindrical panels with different boundary conditions 10. Nonlinear vibrations and stability of doubly-curved shallow-shells: isotropic and laminated materials 11. Meshless discretization of plates and shells of complex shapes by using the R-functions 12. Vibrations of circular plates and rotating disks 13. Nonlinear stability of circular cylindrical shells under static and dynamic axial loads 14. Nonlinear stability and vibrations of circular shells conveying flow 15. Nonlinear supersonic flutter of circular cylindrical shells with imperfections.

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Nonlinear Vibrations and Stability of Shells and Plates

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.

Influence of the elasto-plastic adhesive contact on Micro-Switches

The aim of this paper is to deal with multi-physics simulation of micro-electro-mechanical systems (MEMS) based on an advanced numerical methodology. MEMS are very small devices in which electric as well as mechanical and fluid phenomena appear and interact. Because of their microscopic scale, strong coupling effects arise between the different physical fields, and some forces, which were negligible at macroscopic scale, have to be taken into account. In order to accurately design such micro-electro-mechanical systems, it is of primary importance to be able to handle the strong coupling between the electric and the mechanical fields. In this paper, the finite element method (FEM) is used to model the strong coupled electro-mechanical interactions and to perform static and transient analyses taking into account large mesh displacements. These analyses will be used to study the behaviour of electrostatically actuated micro-mirrors.

Model of Electrostatic Actuated Deformable Mirror Using Strongly Coupled Electro-Mechanical Finite Element

During their lifetime, street lighting devices (or luminaires) are subject to environmental excitations induced by the traffic and the wind. Fatigue effects due to ambient vibrations of long duration are the main cause of structural failures in outdoor pole mounted luminaires. Street lighting manufacturers are very much concerned with vibration testing of luminaire prototypes in order to determine if they can support the vibration environment expected during their lifetime without being damaged. Up to now, qualification tests are performed according to different standards which are not specific to street lighting devices. These standards do not have the same severity so that the choice of one standard rather than another is not obvious. The aim of the research presented here is to propose a new methodology to quantify the severity of different vibration environments. To this end, different severity criteria are first defined : these are based on the maximax response spectrum, the fatigue damage spectrum or the dissipative damage spectrum. Based on these criteria, the severity of different standards such as IEC 68-2-6, ANSI C 136-31, … may be estimated and compared. To choose the most appropriate criterion, the identification and the knowledge of failure processes are of prime importance. As an example, the methodology is applied to the simple case of a base excited beam. Vibration testing is performed on an electro-dynamic shaker to validate the theoretical approach. Resume Au cours de leur vie, les appareils d'eclairage routier (ou luminaires) sont soumis a des excitations environnementales induites par le trafic et le vent. Les phenomenes de fatigue engendres par les vibrations ambiantes de longue duree sont la cause principale des ruptures dans les luminaires montes sur poteau. Les fabricants d'appareils d'eclairage routier sont concernes au plus haut point par les tests de vibration de leurs prototypes afin de determiner s'ils peuvent supporter, sans etre endommages, l'environnement vibratoire auquel ils sont soumis durant leur vie. Jusqu'a present, les tests de qualification sont realises selon differentes normes qui ne sont pas specifiques aux appareils d'eclairage routier. Ces normes n'ont pas la meme severite de sorte que le choix de l'une plutot qu'une autre n'est pas bien defini. L'objectif de la recherche presentee ici est de proposer une nouvelle methode pour quantifier la severite de differents environnements vibratoires. Pour cela, differents criteres de severite sont d'abord definis : ils sont bases sur le spectre de robustesse, le spectre de dommage par fatigue et le spectre d'energie dissipee. Grâce a ces criteres, la severite de differentes normes comme IEC 68-2-6, ANSI C 136-31, … peut etre estimee et comparee. Afin de choisir le critere le plus approprie, l'identification et la connaissance des processus de rupture sont de premiere importance. Comme illustration, la methode est appliquee au cas simple d'une poutre excitee par la base. Les tests de vibration sont realises au moyen d'un excitateur electrodynamique dans le but de valider l'approche theorique.

Comparison of the severity of standards used for the vibration testing of luminaires Comparaison de la sévérité de normes utilisées pour les tests de vibration de luminaires

This paper presents the advantages of a strong coupled formulation to model the electro-mechanical coupling appearing in MEMS. Usually the classical softwares use a staggered methodology iterating between two different codes to obtain the solution of the coupled problem. In this research a strong coupled formulation is proposed and a tangent stiffness matrix of the whole problem is computed. Using this matrix, nonlinear algorithms such as the Riks-Crisfield algorithm may be applied to solve the static nonlinear problem and determine accurately the static pull-in voltage. Moreover, the natural frequencies may be computed around each equilibrium positions. The dynamic behaviour of the structure may also be studied and two new parameters are defined: the dynamic pull-in voltage and the dynamic pull-in time. This strong coupled methodology deriving from variational principle may also be used for topology optimisation and extended finite elements.

On the Advantages of Using a Strong Coupling Variational Formulation to Model Electro-Mechanical Problem

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 (Schreder).

Jean-Claude Golinval

Papers

Influence of the elasto-plastic adhesive contact on Micro-Switches

Model of Electrostatic Actuated Deformable Mirror Using Strongly Coupled Electro-Mechanical Finite Element

Comparison of the severity of standards used for the vibration testing of luminaires Comparaison de la sévérité de normes utilisées pour les tests de vibration de luminaires

On the Advantages of Using a Strong Coupling Variational Formulation to Model Electro-Mechanical Problem

Qualification procedure of luminaires in the event of an impact to the pole