Prediction of the dynamic response of a plate treated by particle impact damper

International audienceIn this paper, an experimental characterisation of a particle impact damper (PID) under periodic excitation is investigated. The developed method allows the measurement of damping properties of PID without the supplementary use of a primary structure. The passive damping of PID varies with the excitation frequency and its design parameters. The nonlinear damping of PID is then interpreted as an equivalent viscous damping to be introduced in a finite element model of a structure to predict its dynamic response. The results of numerical simulations are in good agreement with those of experiment and show the relevance of the developed method to predict the dynamic behaviour of a structure treated by PID's

Robust design of spacecraft structures under lack of knowledge

International audienceIn robust design, lacks of knowledge are rarely taken into account explicitly, but this is the case in the RRDO-IG. This paper summarises the ongoing developments and perspectives for the use of the RRDO-IG methodology in a spatial industrial context, where non-linearities have to be treated. After shortly describing the RRDO-IG methodology and the actual encountered problems, we will construct an improvement strategy based on a state of the art in metamodelisation and failure probability computation

Identification of Admittance Coefficients from in-situ Measurements in Acoustic Cavities

International audienceIn recent decades, sound intensity and quality is taking an increasingly important place in the design process of products like cars or aircrafts. Different types of absorbing materials have therefore been developed and used in such products to achieve this purpose. Acoustical calculations are quite heavy and industries generally have to use numerical tools to predict the influence of absorbing materials on the sound propagation inside cavities. In these ones, the acoustical properties of absorbing materials are described by the admittance (or impedance) coefficient, which is a simplification of the physical model. However, the limits of applicability of this model are not well known and the conditions in which its parameters are measured can differ significantly from the ones in which the materials are really used. In this paper, a model updating technique process is used to identify the parameters required to describe admittance coefficients from sound pressure measurements inside a closed cavity. Updating techniques have been used for many years to improve numerical models, and consist in minimizing an error between the numerical solutions and a set of experimental results. The technique based on the Constitutive Relation Error (CRE), initially proposed by Ladevèze [1] for structural dynamics problems, is an indirect method in which the cost function, called the CRE, is based on an energy norm. The main advantages of this method are that the updated parameters keep a physical meaning, that it allows taking into account the measurement error and that it allows locally evaluating the modeling and measurement errors [2]. In this paper the CRE-based updating technique is applied to the acoustical problem ([3], [4]) in order to identify the admittance coefficients and the local estimators are developed. The method is applied on real 2D (Kundt's tube) and 3D (concrete box) experimental data

Nonlinear techniques for wide-bandwidth resonant energy harvesting

International audienceEnergy harvesting from motion is presently receiving great worldwide attention as a means to power autonomous systems. Conventional linear vibration energy harvesters are usually designed to be resonantly tuned to the ambient dominant frequency. They have a narrow operating bandwidth that limits their application in real-world environments where the ambient vibrations have their energy distributed over a wide spectrum of frequencies, with significant predominance of low frequency components and frequency tuning is not always possible due to geometrical/dynamical constraints

Wideband frequency characterization of a shape memory polymer

International audienceThis study is an experimental evaluation of the mechanical properties of shape memory polymer Veriflex R under different tests conditions. Veriflex R was chosen because of its easy accessibility and its properties similar to epoxy resins which make it very suitable for use in a wide variety of technical applications. Dynamic mechanical analysis (DMA) has been used to determine the evolution of the viscoelastic properties versus temperature and frequency under harmonic loading. The time-temperature superposition principle has been found to be valid for this material. This is illustrated here through the use of the master curves. Furthermore a modal analysis on a Veriflex R rectangular plate has been performed in order to reach higher frequencies than the DMA, and a finite element model was employed to find the viscoelastic properties of the material. A correlation between these two experimental methods allowed to highlight a disparity of results explained by the deterioration of the Veriflex R over time

Numerical simulation and experimental validation of gap supported tube subjected to fluid-elastic coupling forces for hybrid characterization tests

International audienceIn steam generators, the primary loop tubes are subjected to fluid coupling forces and impacts. Understanding the behavior of these tubes is crucial when designing steam generators. In fact, it can afford an optimization of produced energy and a long average life of the structure. Up to now, the effect of the coupling forces on structural behavior was identified on reduced scale structures. Thus, the aim of our research is to give a better understanding of stabilizing effects of shock and coupling with fluid elastic forces. In order to validate numerical investigations, since fluid elastic forces are difficult simulate and expensive to reproduce experimentally, the fluid coupling forces will be assumed to be represented using velocity dependant (fluid and structure) damping and stiffness matrices, and experimentally reproduced using active vibration control into hybrid experimental tests to simplify big structure characterization. In this paper, a method for modeling the structure behavior in order to estimate the effects of the coupling between the fluid elastic forces and impacts is presented. This strategy implies lower costs and avoids difficulties associated to the case of fluid in the experiments. This model will be implemented in the active control loop in the next step of the study

Identification of system matrices based on experimental modal analysis and its application in structural health monitoring

This paper presents a system matrices identification approach directly from the real-time measured structural responses. Based on the experimental modal analysis, the identified system matrices are expected to represent the system behaviours as same as the experimentally measured ones. Due to the fact that the system matrices, i.e. the mass, stiffness, and damping matrices, are the direct reflection of the inherent properties of the structure, they can be naturally served as the indicator of structural damages. The identification approach utilizes the state space representation for the equation development to construct the system matrices using the complex modes (i.e. the complex eigenvalues and eigenvectors). The complex modes, however, requires a calibration process to enforce the so-called properness condition, which is not generally fulfilled by the modes because of the inevitable experimental noise. An efficient method based on the Riccati equation is proposed to calibrate the complex eigenvectors so that they can be safely used to construct the system matrices. A scalar quantity based on the norm of the matrices is defined as the indicator for structural health monitoring. The overall approach is performed on a numerical model of a structure with controllable modifications (i.e. artificial damages). The difference between the identified matrices of the original and modified structures clearly demonstrates the approachs feasibility in structural health monitoring

Static and Dynamic Thermo Mechanical Characterization of a Bio-Compatible Shape Memory Polymer

International audienceShape memory polymers encounter a growing interest over the past ten years particularly because their eventual bio-compatibility leads to many bio-medical applications. They also present many benefits for the design of micro-adaptive systems for deployment or controlled damping materials. Indeed, the SMPs are polymeric smart materials which have the remarkable ability to recover their primary shape from a temporary one when submitted to an external stimulus. The present study deals with the synthesis and the thermo-mechanical characterization of a thermally-actuated SMP. The polymer considered hereafter is a chemically cross-linked thermoset. It is synthesized via photo polymerization (UV curing) of the monomer tert-butyl acrylate (tBA) with the crosslinking agent poly(ethylene glycol) dimethacrylate (PEGDMA) and the photoinitiator 2,2-dimethoxy-2-phenylacetophenone (DMPA). A mechanical characterization has been performed using three kinds of tests: quasi-static tensile tests, tensile dynamic mechanical analysis (DMA) and modal tests. The Young's modulus and the Poisson ratio are determined at ambient temperature using the first technique. The DMA is used to determine the evolution of viscoelastic properties as a function of the temperature and the frequency under harmonic loading. The modal analysis is employed to identify the viscoelastic properties of the material at higher frequency. A comparison of the results obtained by these three experimental methods highlights their complementarity

Récupération d'énergie vibratoire par voie électromagnétique sous excitation aléatoire

Ce travail porte sur l'étude d'un récupérateur d'énergie vibratoire électromagnétique soumis à une excitation aléatoire de type bruit-blanc. On utilise un modèle éprouvé pour extraire une règle de dimensionnement du récupérateur optimal soumis à une source vibratoire bruit-blanc et l'expression de la puissance maximale récupérable