This paper presents a finite element formulation for transient dynamic analysis of sandwich beams with embedded viscoelastic material using fractional derivative constitutive equations. The sandwich configuration is composed of a viscoelastic core (based on Timoshenko theory) sandwiched between elastic faces (based on EulerBernoulli assumptions). The viscoelastic model used to describe the behavior of the core is a four-parameter fractional derivative model. Concerning the parameter identification, a strategy to estimate the fractional order of the time derivative and the relaxation time is outlined. Curve-fitting aspects are focused, showing a good agreement with experimental data. In order to implement the viscoelastic model into the finite element formulation, the Grünwald definition of the fractional operator is employed. To solve the equation of motion, a direct time integration method based on the implicit Newmark scheme is used. One of the particularities of the proposed algorithm lies in the storage of displacement history only, reducing considerably the numerical efforts related to the non-locality of fractional operators. After validations, numerical applications are presented in order to analyze truncation effects (fading memory phenomena) and solution convergence aspects. IntroductionMany investigations have demonstrated the potential of viscoelastic materials to improve the dynamics of lightly damped structures. There are numerous techniques to incorporate these materials into structures. The constrained layer passive damping treatment is already largely used to reduce structural vibrations, especially in conjunction with active control [2, 13]. One of the crucial questions is how to quantify such a material damping if the viscoelastic solid has a weak frequency dependence on its dynamic properties over a broad frequency range. Classical linear viscoelastic models, using integer derivative operators, convolution integral or internal variables, become cumbersome due to the high quantity of parameters needed to describe the material behavior. In order to overcome these difficulties, fractional derivative operators acting on both, strain and stress can be employed.Until the beginning of the 80s, the concept of fractional derivatives associated to viscoelasticity was regarded as a sort of curve-fitting method. Later, Bagley and Torvik [1] gave a physical justification of this concept in a thermodynamic framework. Their fractional model has become a reference in literature. Special interest is today dedicated to the implementation of fractional constitutive equations into FE formulations. In this context, the numerical methods in the time domain are generally associated with the Grünwald formalism for the fractional order derivative of the stress-strain relation in conjunction with a time discretization scheme. Padovan [7] derived several implicit, explicit and predictor-corrector type algorithms. Escobedo-Torres and Ricles [6] analyzed a numerical procedure based on the central difference method and its ...

This work presents a finite element formulation for the dynamic transient analysis of a damped adaptive sandwich beam composed of a viscoelastic core and elastic-piezoelectric laminated faces. The latter are modeled using the classical laminate theory, which takes the electromechanical coupling into account by modifying the stiffness of the piezoelectric layers. For the core, a fractional derivative model is used to characterize its viscoelastic behavior. Equations of motion are solved using a direct time integration method based on the Newmark scheme in conjunction with the Grunwald approximation of fractional derivatives. Emphasis is given to the finite element implementation of the fractional derivative model and to the influence of the electromechanical coupling.

The Gear scheme is a three-level step algorithm, backward in time and second-order accurate for the approximation of classical time derivatives. In this contribution, the formal power of this scheme is proposed to approximate fractional derivative operators in the context of finite difference methods. Some numerical examples are presented and analysed in order to show the effectiveness of the present Gear scheme at the power a (G a-scheme) when compared to the classical Gru¨nwald-Letnikov approximation. In particular, for a fractional damped oscillator problem, the combined G a-Newmark scheme is shown to be second-order accurate.

The Gear scheme is a three-level step algorithm, backward in time and second order accurate, for the approximation of classical time derivatives. In this article, the formal power of this scheme is used to approximate fractional derivative operators, in the context of finite difference methods. Numerical examples are presented and analyzed, in order to show the accuracy of the Gear scheme at the power α (Gα-scheme) when compared to the classical Grünwald-Letnikov approximation. In particular, the combined Gα -Newmark scheme is shown to be second-order accurate for a fractional damped oscillator problem.

This work presents a finite element formulation for non-linear transient dynamic analysis of adaptive beams. The main contribution of this work concerns the development of an original co-rotational sandwich beam element, which allows large displacements and rotations, and takes active/passive damping into account. This element is composed of a viscoelastic core and elastic/piezoelectric laminated faces. The latter are modeled using classical laminate theory, where the electromechanical coupling is considered by modifying the stiffness of the piezoelectric layers. For the core, a four-parameter fractional derivative model is used to characterize its viscoelastic dissipative behavior. Equations of motion are solved using an incremental-iterative method based on the Newmark direct time integration scheme in conjunction with the Grü nwald approximation of fractional derivatives, and the Newton-Raphson algorithm.