Interfacial adhesion between the iron fillers and the silicone matrix in magneto-rheological elastomers at high deformations

11International audienceThis work investigates the interfacial adhesion between the iron fillers and the silicone matrix in magneto-rheological elastomers at high deformations. Carbonyl iron powder, composed of mechanically soft spherical particles with a median size of 3.5 μm and a volume concentration of 3.5%, was mixed in a soft silicone matrix (Shore 00-20); the compound was then degassed and cured under temperature. The presence of a homogeneous magnetic field of 0.3 T during the curing process allowed the formation of particle chains. Tensile tests of these samples under scanning electron microscope showed interfacial slipping and debonding between the two phases. To improve interfacial adhesion, a silane primer was applied to the iron particles, following two different procedures, before the mixing and crosslinking process, thus giving two additional types of samples. In tensile testing lengthwise to the particle alignment, with engineering strains up to 150%, the structural responses of the different types of samples were compared. An enhanced adhesion of the iron fillers to the silicone matrix resulting in a reinforced matrix and increased tensile strength during the first loading path could be observed. Furthermore, scanning electron microscope images show that a more elaborated particle-matrix interface was obtained with the primer additive

Influence of interfacial adhesion on the mechanical response of magneto‑rheological elastomers at high strain

International audiencemacroscopic behavior of the composite only after 80 % deformation in the case of the 30 % volume fraction Mre

Optimal dual-PZT sizing and network design for baseline-free SHM of complex anisotropic composite structures

Structural health monitoring (SHM) processes for aeronautic composite structures are generally based on the comparison of healthy and unknown databases. The need for prior baseline signals is one of the barriers to industrial deployment and can be avoided with baseline-free SHM (BF-SHM) methods, based on the attenuations and reflections of symmetric and antisymmetric Lamb wave modes attributable to damage. A promising mode decomposition method is based on the use of dual-PZTs (concentric disc and ring electrodes lying on a single piezoelectric transducer of lead zirconate titanate). However, the performance of such methods highly depends on the Lamb wave mode properties (propagation speed and attenuation , which vary with material orientation and inter-PZT distance), the number and the sensitivity of the dual-PZT to each mode (which depends on the frequency and element size). Considering these constraints, an original three-step process able to design a full dual-PZT network and the optimal range of excitation frequencies to consider on a highly anisotropic and arbitrarily complex aeronautic structure is presented. First, the dispersion curves of Lamb waves in the investigated material together with the minimal size of the damage to detect are used to estimate the size of the dual-PZT, as well as convenient excitation frequencies. A local finite element model representative of the full-scale structure is then used to estimate the optimal distance and orientation between neighboring PZT elements. Finally, a network optimization solver applies these parameters to place dual-PZTs on the fan cowl of an aircraft nacelle and provides a candidate network covering the whole structure

Dual PZT sizing for mode decomposition on a composite anisotropic plate

Structural Health Monitoring is a multidisciplinary field whose aim is to monitor damages within structures. Damages are detected by means of features - Damage Index (DI) - obtained by comparing measurements obtained from an unknown state with data obtained from a reference state stored in a baseline. Most DIs are calculated using Lamb wave signals generated and received by surface-mounted piezoceramic transducers (PZT) excited around a predefined central frequency. Usually, only the faster mode (S0) is considered on composite structures. However, the symmetric and antisymmetric Lamb wave modes tend to highlight different kinds of damages and are both interesting for SHM purpose. For example, a delamination in a composite plate attenuates the antisymmetric mode and reflects the symmetric one. Using two concentric PZTs (a disc and a ring defining a dual PZT) allows the decomposition of both mode contributions in the received signal. The current work presents a method based on Lamb Wave dispersion curves able to size the dual PZT and to determine the excitation frequencies to use for SHM application. This approach is based on three main observations: (i) Only the first symmetric and antisymmetric modes S0 and A0 must be generated, (ii) the dual PZT used as actuator and the excitation frequencies of the signal used must guarantee the actuation of S0 and/or A0 modes with wave length small enough to interact with the targeted minimal damage size, and (iii) the dual PZT used as sensor must be sensitive to both S0 and A0 modes on the selected range of excitation frequency. This method is applied for the sizing of dual PZT bounded to a highly anisotropic composite plate (CFRP [0,90]16) with a thickness of 2 mm and a minimal targeted damage size of 20 mm. Optimal dimensions of the PZT disk and ring are found and results of mode decomposition method on the optimal range of excitation frequencies obtained on a finite element model are presented. This simple method provides an efficient way for dual-PZT sizing in a SHM context where both S0 and A0 modes are investigated

Spatial integration of baseline-free damage detection algorithms based on dual-PZT for the structural health monitoring of anisotropic composite aeronautic structures

The focus is put here on the Structural Health Monitoring (SHM) of composite aeronautic structure using Lamb waves emitted and recorded with piezoelectric transducers (PZT). Conventional algorithms perform Lamb waves acquisition in the healthy state of the structure (referred to as the “baseline”) and then compare incoming data from an unknown state with this one to detect, locate, classify and quantify any potential damage. The acquisition, storage, and update of the initially recorded baseline database constitute a severe drawback of such algorithms. Indeed, the structure under study as well as the environment may vary during its operational life without the appearance of any damage and thus the initial baseline may not be relevant at any instant where damage monitoring is needed. In order to circumvent this drawback, “baselinefree” method (such as the instantaneous baseline [BI] and rupture of reciprocity [RR]) have been developed. Moreover, the use of dual-PZT, i.e. concentric PZT made of a ring and a disk lying on the same ceramic, has been shown as attractive for baselinefree purposes. However, now that several algorithms based on dual-PZT are available, no study dealing with the spatial integration of the results provided by these algorithms have been reported in the literature. It is thus proposed in this paper to investigate strategies for the spatial integration of common baseline-free methods (namely BI and RR) on an experimental case of damage on a highly anisotropic composite plate. Results illustrate the decomposition of Lamb wave modes in signals measured via dual PZTs as well as the proposed spatial integration strategies for these methods

Active flow control systems architectures for civil transport aircraft

Copyright @ 2010 American Institute of Aeronautics and AstronauticsThis paper considers the effect of choice of actuator technology and associated power systems architecture on the mass cost and power consumption of implementing active flow control systems on civil transport aircraft. The research method is based on the use of a mass model that includes a mass due to systems hardware and a mass due to the system energy usage. An Airbus A320 aircraft wing is used as a case-study application. The mass model parameters are based on first-principle physical analysis of electric and pneumatic power systems combined with empirical data on system hardware from existing equipment suppliers. Flow control methods include direct fluidic, electromechanical-fluidic, and electrofluidic actuator technologies. The mass cost of electrical power distribution is shown to be considerably less than that for pneumatic systems; however, this advantage is reduced by the requirement for relatively heavy electrical power management and conversion systems. A tradeoff exists between system power efficiency and the system hardware mass required to achieve this efficiency. For short-duration operation the flow control solution is driven toward lighter but less power-efficient systems, whereas for long-duration operation there is benefit in considering heavier but more efficient systems. It is estimated that a practical electromechanical-fluidic system for flow separation control may have a mass up to 40% of the slat mass for a leading-edge application and 5% of flap mass for a trailing-edge application.This work is funded by the Sixth European Union Framework Programme as part of the AVERT project (Contract No. AST5-CT-2006-030914

Numerical modeling of a MEMS actuator considering several magnetic force calculation methods

Purpose: The purpose of this paper is to investigate the accuracy of different force calculation methods and their impact on mechanical deformations. For this purpose, a micrometer scaled actuator is considered, which consists of a micro-coil and of a permanent magnet (PM) embedded in a deformable elastomeric layer. Design/methodology/approach: For the magnetic field evaluation a hybrid numerical approach (finite element method/boundary element method (FEM/BEM) coupling and a FEM/BEM/Biot-Savart approach) is used, whereas FEM is implemented for the mechanical deformation analysis. Furthermore, for the magneto-mechanical coupling several force calculation methods, namely the Maxwell stress tensor, the virtual work approach and the equivalent magnetic sources methods, are considered and compared to each other and to laboratory measurements. Findings: The numerically evaluated magnetic forces and the measured ones are in good accordance with each other with respect to the normal force acting on the PM. Nevertheless, depending on the used method the tangential force components differ from each other, which leads to slightly different mechanical deformations. Research limitations/implications: Since the force calculations are compared to measurement data, it is possible to give a suggestion about their applicability. The mechanical behavior of the actuator due to the acting forces is solely calculated and therefore only an assumption concerning the deformation can be given. Originality/value: A new kind of micrometer scaled actuator is numerically investigated by using two different hybrid approaches for the magnetic field evaluation. Based on those, the results of several force calculation methods are compared to measurement data. Furthermore, a subsequent structural analysis is performed, which shows slightly different mechanical deformations depending on the used force calculation method. © Emerald Group Publishing Limited

Magnetic circuit design for miniaturized magnetic shape memory alloy actuators

Conference of Conference Smart Sensors, Actuators, and MEMS VI ; Conference Date: 24 April 2013 Through 26 April 2013; Conference Code:98305International audienceMagnetic shape memory alloy (MSMA) is a relatively new kind of smart material. Upon application of a large magnetic field, it exhibits actuation strains up to 10% similar to thermal shape memory alloy (SMA) but shows significantly reduced response time in the millisecond range. Currently, application is restricted by the brittleness of the single crystal material, its nonlinear behaviour and the difficulty to generate and apply a magnetic field around 0.6T in order to exploit the full actuation potential. The focus of this work is on the design of miniaturized magnetic circuits for bulk MSMAs. Various circuit designs are compared such as toroidal and series-parallel shapes. Equivalent circuit as well as finite element simulation is used to increase the magnetic field in a characteristic air gap where the smart material is placed. A symmetrical toroid coil layout with the MSMA element at the center that allows easy integration of the actuator in various applications is described. Static characterization results of this actuator are provided. Using the described magnetic circuit and 5M - MSMA rods with dimensions of 20x2.5x1mm3 , a peak displacement of 0.8mm and a blocked force of 4.5N was obtained. Further design guidelines for such miniaturized actuators are given

Actionneurs piézoélectriques miniaturisés pour le contrôle d'écoulement à haut vitesse.

This work describes the development of miniaturized piezoelectric actuators for high-speed flow control on airfoils. The goal is to delay the laminar-turbulent transition by active wave cancellation of so-called Tollmien-Schlichting waves introducing appropriate counterwaves. The first design concept is based on a mechanically amplified actuator where an external elas-tic lever-type amplification unit is located above a piezoelectric disc. This actuator provides direct control ability, a linear transfer function, and fast response time facilitating its integra-tion in controller systems. The second design concept is based on a tapered membrane driven in one of its axisymmetric eigenmodes, excited by a piezoelectric ring placed at the outer edge. The tapered membrane focuses the induced waves to the centre, where maximum amplitudes can be observed. Ampli-tude modulation allows the actuator to attain a wide frequency range as required for active cancellation of Tollmien-Schlichting waves, where the carrier frequency is provided by the eigenfrequencies. Its robustness, simple fabrication, and closed surface qualify this actuator for aircraft implementation. The effect of both actuators on the airflow around a wing profile at open-loop control has been measured with hot-film anemometers during a wind tunnel experiment. For device di-mensions adapted to the flow conditions both actuators exhibit the desired effect on the air-flow required for active transition control. It has been shown that amplitude modulation is an option for this type of flow control if the carrier frequency is selected adequately (>40 kHz) in order to not disturb the airflow.Cette thèse décrit le développement d'actionneurs piézoélectriques miniaturisés pour le contrôle actif d'écoulement à haute vitesse. L'objectif est de retarder la transition laminaire turbulente par le contrôle actif des ondes de Tollmien-Schlichting par introduction d'ondes artificielles à phase inversée. Le premier concept étudié dans cette thèse est un actionneur amplifié mécaniquement avec une structure de type levier élastique situé au-dessus d'une céramique piézoélectrique. Les avantages de cet actionneur sont le contrôle direct, la fonction de transfert linéaire, et le temps de réponse très rapide, ce qui facilite l'intégration dans un système asservi. Le deuxième concept est basé sur l'utilisation d'une membrane conique actionnée par un anneau piézoélectrique dans un mode propre axisymétrique. La géométrie conique focalise les ondes générées par l'anneau piézoélectrique vers le centre ou les amplitudes sont le plus importantes. Pour le control des ondes de Tollmien-Schlichting, la modulation d'amplitude est appliquée pour atteindre une gamme de fréquence large ou la fréquence porteuse est délivrée par les modes propres. Cet actionneur à l'avantage d'utiliser une membrane robuste fermée et une intégration simple. L'effet des actionneurs sur l'écoulement a été mesuré avec des capteurs film chaud dans une soufflerie en boucle ouverte. Pour les dimensions des actionneurs adaptés sur l'écoulement, l'effet désiré pour le contrôle actif de la transition a été observé. Enfin, il a été démontré que la modulation d'amplitude est une alternative intéressante si la fréquence porteuse est sélectionnée de manière optimale pour qu'elle n'agisse pas sur l'écoulement (> 40kHz)