Reduced joint models for damping design of multi-jointed structures

− Design of damping in multi-jointed structures is studied here. − Dissipation sources are viscoelastic behavior and contact/friction at joints interfaces. − Reduction on meta-models of nonlinear joints models is investigated. − Experimental characterization of nonlinear forces

A General Bayesian Framework for Ellipse-based and Hyperbola-based Damage Localisation in Anisotropic Composite Plates

This paper focuses on Bayesian Lamb wave-based damage localization in structural health monitoring of anisotropic composite materials. A Bayesian framework is applied to take account for uncertainties from experimental time-of-flight measurements and angular dependent group velocity within the composite material. An original parametric analytical expression of the direction dependence of group velocity is proposed and validated numerically and experimentally for anisotropic composite and sandwich plates. This expression is incorporated into time-of-arrival (ToA: ellipse-based) and time-difference-of-arrival (TDoA: hyperbola-based) Bayesian damage localization algorithms. This way, the damage location as well as the group velocity profile are estimated jointly and a priori information taken into consideration. The proposed algorithm is general as it allows to take into account for uncertainties within a Bayesian framework, and to model effects of anisotropy on group velocity. Numerical and experimental results obtained with different damage sizes or locations and for different degrees of anisotropy validate the ability of the proposed algorithm to estimate both the damage location and the group velocity profile as well as the associated confidence intervals. Results highlight the need to consider for anisotropy in order to increase localization accuracy, and to use Bayesian analysis to quantify uncertainties in damage localization.Projet CORALI

Effects of temperature on the impedance of piezoelectric actuators used for SHM

— FEM modeling of piezoelectric patches used as actuators and sensors for SHM applications. — Test/analysis correlation of temperature effects in piezoelectric materials and glue — Numerical methods associated with the prediction of electric transfers.Projet AIRCELLE (EPICE/CORALIE

Harmonic Balance-Based Approach for Quasi-Periodic Motions and Stability Analysis

Quasi-periodic motions and their stability are addressed from the point of view of different harmonic balance-based approaches. Two numerical methods are used: a generalized multidimensional version of harmonic balance and a modification of a classical solution by harmonic balance. The application to the case of a nonlinear response of a Duffing oscillator under a bi-periodic excitation has allowed a comparison of computational costs and stability evaluation results. The solutions issued from both methods are close to one another and time marching tests showing a good agreement with the harmonic balance results confirm these nonlinear responses. Besides the overall adequacy verification, the observation comparisons would underline the fact that while the 2D approach features better performance in resolution cost, the stability computation turns out to be of more interest to be conducted by the modified 1D approach

Harmonic Balance-Based Approach for Quasi-Periodic Motions and Stability Analysis

Quasi-periodic motions and their stability are addressed from the point of view of different harmonic balance-based approaches. Two numerical methods are used: a generalized multidimensional version of harmonic balance and a modification of a classical solution by harmonic balance. The application to the case of a nonlinear response of a Duffing oscillator under a bi-periodic excitation has allowed a comparison of computational costs and stability evaluation results. The solutions issued from both methods are close to one another and time marching tests showing a good agreement with the harmonic balance results confirm these nonlinear responses. Besides the overall adequacy verification, the observation comparisons would underline the fact that while the 2D approach features better performance in resolution cost, the stability computation turns out to be of more interest to be conducted by the modified 1D approach

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

Sensor validation of a Structural Health Monitoring Process for Aircraft Nacelle

This paper details the implementation process of an embedded structural health monitoring (SHM) system enabling condition-based maintenance of aircraft nacelles. One critical issue before being able to make use of such system is to ensure the effective bonding of the chosen actuators and sensors with their host structure, especially as the latter will be exposed to harsh environments and wide operational variability. In this work, we are concerned with the composite components of the nacelle and we use piezoelectric elements as both sensors and actuators. We propose an integrated approach that allows to validate a combination “Substrate—Glue—Piezoelectric” (SGP) and thus provides criteria to choose and size these assemblies. This validation scheme is based on the observation of the variations of the static capacity of the piezoelectric element after enduring various temperature and stress conditions when bonded to its host structure. Based on those SGP combinations, an active SHM strategy interrogating the structure by means of elastic wave propagation is currently being developed and preliminary results on samples representative of the nacelle are presented and discussed.Projet AIRCELLE (EPICE/CORALIE

Conception et validation d’une liaison boulonnée dissipative

On présente ici une méthodologie de conception d’une liaison boulonnée dissipative ainsi que sa validation par une étude expérimentale. Un premier calcul statique permet de caractériser la zone de compression induite à l’interface par le serrage. Cette zone contribue seule à la tenue statique de la liaison et est conservée en liaison métallique. On justifie ensuite l’intérêt d’introduire une couche de matériau viscoélastique dans le reste de la surface de contact. La réalisation expérimentale permet de montrer des augmentations d’amortissement d’un facteur supérieur à trois pour les modes globaux et illustre les difficulités liées aux défauts de forme des surface de contact. On montre enfin comment les performances peuvent être optimisées numériquement

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

Influence of flank face on the condition of chatter self-excitation during turning

This paper addresses a modelling approach for cutting tool and workpiece material interaction with ploughing taken into account. In the proposed model the distributed contact on the flank face is replaced by a concentrated additional cutting edge characterised by two physical parameters and bringing about a new delay term into the dynamical system. It is shown that under monoharmonic excitation of the tool on the direction orthogonal to the cutting velocity, it is possible to isolate the effect of the flank face and observe experimentally its parameters. The influence of the ploughing on the instability boundaries of continuous cutting is investigated. An analytical expression is obtained for the effective linear damping coefficient due to ploughing and depending on the cutting velocit