A.L. Araújo

Identification of material properties of composite plate specimens

Abstract An indirect identification technique to predict the mechanical properties of composite plate specimens is presented. This technique makes use of experimental eigenfrequencies, the corresponding numerical eigenvalue evaluation, sensitivity analysis and optimization. The laminate analysis is formulated in terms of non-dimensional material parameters and the discrete model is based on the linear shear deformation theory of Mindlin. The constrained minimization of an error functional expressing the difference between measured higher frequencies of a plate specimen and the corresponding numerical ones is then carried out to find the desired optimum parameters. The required sensitivities with respect to changes in the non-dimensional material parameters have the option of being evaluated analytically, semi-analytically or alternatively by finite difference. Results which show the validation of the sensitivities and the limitations of the model to predict the required quantities and its range of application and accuracy are demonstrated through test cases.

Characterization of material parameters of composite plate specimens using optimization and experimental vibrational data

A numerical/experimental method for identification of material parameters of composite materials is proposed in this paper. This method combines experimental techniques for the determination of vibration eigenfrequencies of plates made of composite materials along with a finite element numerical method for the determination of the corresponding numerical eigenfrequencies. The identification process makes use of optimization techniques, through the minimization of an error measurement that estimates the deviation between numerical and experimental eigenvalues, for a given set of material parameters. The accuracy of the proposed technique is discussed through test cases.

Combined numerical-experimental model for the identification of mechanical properties of laminated structures

Abstract A combined numerical–experimental method for the identification of six elastic material modulus of generally thick composite plates is proposed in this paper. This technique can be used in composite plates made of different materials and with general stacking sequences. It makes use of experimental plate response data, corresponding numerical predictions and optimisation techniques. The plate response is a set of natural frequencies of flexural vibration. The numerical model is based on the finite element method using a higher-order displacement field. The model is applied to the identification of the elastic modulus of the plate specimen through optimisation techniques, using analytical sensitivities. The validity, efficiency and potentiality of the proposed technique is discussed through test cases.

Development of a finite element model for the identification of mechanical and piezoelectric properties through gradient optimisation and experimental vibration data

With the increasing use of surface bonded piezoelectric sensors and actuators in laminated structures, rises the need for knowing accurate values for the resulting properties of these structures. The properties obtained through manufacturer data are in most of the cases not enough to predict the structural behaviour and implement efficient control algorithms for active noise and vibration control. To address this issue we propose a discrete finite element model, associated to gradient optimisation and to an inverse method using experimental vibration data to carry out the identification of electromechanical properties in composite plate specimens with surface bonded piezoelectric patches or layers. The properties to be determined are the elastic and piezoelectric constants of the structures constituent materials. 2002 Elsevier Science Ltd. All rights reserved.

Finite Element Model for Hybrid Active-Passive Damping Analysis of Anisotropic Laminated Sandwich Structures

In this article, we present a new finite element model for the analyzis of active sandwich laminated plates with a viscoelastic core and laminated anisotropic face layers, as well as piezoelectric sensor and actuator layers. The model is formulated using a mixed layerwise approach, by considering a higher order shear deformation theory to represent the displacement field of the viscoelastic core and a first-order shear deformation theory for the displacement field of the adjacent laminated anisotropic face layers and exterior piezoelectric layers. Control laws are implemented and the model is validated using reference solutions from the literature, and a benchmark application is proposed.

Analysis of Active-Passive Plate Structures Using a Simple and Efficient Finite Element Model

In this work a simple and efficient finite element model is developed for vibration analysis of active-passive damped multilayer sandwich plates, with a viscoelastic core sandwiched between elastic layers, including piezoelectric layers. The elastic layers are modeled using the classical plate theory and the core is modeled using Reddy’s third-order shear deformation theory. The finite element is obtained by assembly of N “elements” through the thickness, using specific assumptions on the displacement continuity at the interfaces between layers. To achieve a mechanism for the active control of the structural dynamics response, a feedback control algorithm is used, coupling the sensor and active piezoelectric layers. The dynamic analysis of active-passive damped multilayer sandwich plate structures is conducted in frequency domain to obtain the natural frequencies and respective loss factors, and in time domain for steady state harmonic motion. For both analyses, a finite element code is implemented. The model is applied in the solution of some illustrative examples and the results are presented and discussed.

Damping optimisation of hybrid active-passive sandwich composite structures

Optimisation of active and passive damping is presented in this paper, using a new mixed layerwise finite element model developed for the analysis and optimisation of hybrid active-passive laminated sandwich plates. Optimisation is conducted through maximisation of modal loss factors, using as design variables the viscoelastic core thickness, the constraining elastic layers ply thicknesses and orientation angles, as well as the position of co-located sensor and actuator pairs. Optimal results for passive damping are compared with an alternative optimisation model, based on 3D finite elements included in commercial package ABAQUS. Optimal location for sensor-actuator pairs is also presented and results are discussed.

INTERIOR POINT ALGORITHMS FOR NONLINEAR CONSTRAINED LEAST SQUARES PROBLEMS

We consider Nonlinear Least Squares problems with equality and inequality constraints and propose a numerical technique that integrates methods for unconstrained problems, based on Gauss–Newton algorithm, with FAIPA, the Feasible Arc Interior Point Algorithm for constrained optimization. We also present some numerical results on test problems available in the literature and compare them with the quasi-Newton version of FAIPA. We also describe an application to the identification of mechanical parameters of composite materials. The present algorithms are globally convergent, very robust and efficient.

Natural fibre-reinforced composite parts for automotive applications

In this paper, we conduct a brief revision of the state-of-the-art on vegetable fibre-reinforced composite applications in the automotive industry. We then present some results for the dynamic characterisation of an auto part made of jute fibres and an equivalent one made of traditional glass fibres, where the increase in damping is most evident. An inverse characterisation method based on the free vibration response of composite plate specimens is also applied to estimate damped material parameters in vegetable fibre-reinforced composites. The obtained results are compared with the ones obtained with equivalent specimens made of glass fibre and future application of this technique to the study of environmental parameters on the material properties is proposed.

Parameter estimation in active plate structures using gradient optimisation and neural networks

Two non-destructive methods for elastic and piezoelectric parameter estimation in active plate structures with surface bonded piezoelectric patches are presented. The first of these solves the inverse problem through gradient based optimisation techniques, minimising the difference between experimental and numerical finite element eigenfrequencies for a test plate. Such minimisation is conducted with feasible arc interior point algorithm (FAIPA), a non-linear interior point algorithm. The second method relies on building a metamodel of the inverse problem, using artificial neural networks (ANNs). The training data set is obtained through the same numerical model as in the first approach. The simulation of the network is then used with the experimental eigenfrequency data set in order to produce an estimate for the material parameters. Results from both approaches are compared and discussed through a simulated identification.