Evgeny Barkanov

Transient response analysis of structures made from viscoelastic materials

The response of structures made from viscoelastic materials to transient excitations is studied using the finite element method. The viscoelastic material behaviour is represented by the complex modulus model. An efficient method using fast Fourier transform has been developed. This method is based on the trigonometrical representation of the input signals and matrix of the transfer functions. The present implementation gives the possibility to preserve exactly the frequency dependence of the storage and loss moduli of materials. On this reason this time-domain representation is a mathematically correct way to avoid the non-causal effect. Test problems and numerical examples are given to demonstrate the validity and effectiveness of the approach suggested in this paper. Copyright ( 1999 John Wiley & Sons, Ltd.

Active Control of Structures Using Macro-Fiber Composite (MFC)

This paper presents the use of macro-fiber composites (MFC) for vibration reduces of structures. The MFC consist of polyimid films with IDE-electrodes that are glued on the top and the bottom of rectangular piezoceramic fibers. The interdigitated electrodes deliver the electric field required to activate the piezoelectric effect in the fibers and allows to invoke the stronger longitudinal piezoelectric effect along the length of the fibers. When this actuator embedded in a surface or attached to flexible structures, the MFC actuator provides distributed solid-state deflection and vibration control. The major advantages of the piezoelectric fibre composite actuators are their high performance, flexibility, and durability when compared with the traditional piezoceramic (PZT) actuators. In addition, the ability of MFC devices to couple the electrical and mechanical fields is larger than in monolithic PZT. In this study, we showed the experimental results that an MFC could be used as actuator to find modal parameters and reduce vibration for structures such as an aluminium beam and metal music plate. Two MFC actuators were attached to the surfaces of test subjects. First MFC actuator used to supply a signal as exciter of vibration and second MFC show his application for reduction of vibration in the range of resonance frequencies. Experimental results of aluminium beam with MFC actuators compared with finite element model which modelled in ANSYS software. The applied voltage is modelled as a thermal load according to thermal analogy for MFC. The experimental and numerical results presented in this paper confirm the potential of MFC for use in the vibration control of structures.

Transient response analysis of systems with different damping models

A response of systems with different damping models to transient excitations is studied using the finite element method. For this purpose an efficient method using fast Fourier transform has been developed. This method is based on the trigonometrical representation of the input signals and matrix of the transfer functions. As an example, systems with viscous and viscoelastic, structural and external damping are examined. Two forms of viscous damping are available in the present implementation: Raleigh damping and element damping. The viscoelastic material behaviour is represented by the complex modulus model. The present implementation gives the possibility to preserve exactly the frequency dependence of the storage and loss moduli of viscoelastic materials. Logarithmic decrements are determined using the steady-state vibrations of systems to characterize their damping properties. Test problems and numerical examples are given to demonstrate the validity and application of the approach suggested in this paper.

Transient response of sandwich viscoelastic beams, plates, and shells under impulse loading

The transient response of sandwich beams, plates, and shells with viscoelastic layers under impulse loading is studied using the finite element method. The viscoelastic material behavior is represented by a complex modulus model. An efficient method using the fast Fourier transform is proposed. This method is based on the trigonometric representation of the input signals and the matrix of the transfer functions. The present approach makes it possible to preserve exactly the frequency dependence of the storage and loss moduli of viscoelastic materials. The logarithmic decrements are determined using the steady state vibrations of sandwich structures to characterize their damping properties. Test problems and numerical examples are given to demonstrate the validity and application of the approach suggested in this paper.

ACTIVE TWIST OF MODEL ROTOR BLADES WITH D-SPAR DESIGN

Abstract The design methodology based on the planning of experiments and response surface technique has been developed for an optimum placement of Macro Fiber Composite (MFC) actuators in the helicopter rotor blades. The baseline helicopter rotor blade consists of D‐spar made of UD GFRP, skin made of +450/‐450 GFRP, foam core, MFC actuators placement on the skin and balance weight. 3D finite element model of the rotor blade has been built by ANSYS, where the rotor blade skin and spar “moustaches” are modeled by the linear layered structural shell elements SHELL99, and the spar and foam ‐ by 3D 20‐node structural solid elements SOLID 186. The thermal analyses of 3D finite element model have been developed to investigate an active twist of the helicopter rotor blade. Strain analogy between piezoelectric strains and thermally induced strains is used to model piezoelectric effects. The optimisation results have been obtained for design solutions, connected with the application of active materials, and checked...

Optimal Design of the Active Twist for Helicopter Rotor Blades with C-Spar

The active twist control of helicopter rotor blades by an application of macro-fiber composite (MFC) actuators leads to significant vibration and noise reduction without the need for complex mechanisms in the rotating systems. For environmental improvement an optimal design methodology based on planning experiments and response surface technique has been developed for an active twist of helicopter rotor blades consisting of C-spar made of unidirectional GFRP, skin made of +45°/−45° GFRP, foam core, MFC actuators embedded into the skin and balance weight. The structural static analysis with thermal load, static torsion analysis and modal analysis using 3D finite element models has been developed using ANSYS for the optimal design. In this case thermal strain analogy between piezoelectric strains and thermally induced strains is used to model piezoelectric effects. The optimization results have been obtained for four design solutions connected with the application of active materials.

DESIGN OF DYNAMICALLY LOADED FIBER-REINFORCED STRUCTURES WITH ACCOUNT OF THEIR VIBRO-ACOUSTIC BEHAVIOR

Dynamically loaded structures for high-technology applications generally require high material damping combined with low construction weight and adequate stiffness. Advanced lightweight structures will have to meet not only these dynamic demands but also improved acoustic (low noise) standards. High-performance materials like magnesium, aluminum, or titanium, which are mainly used in todays lightweight applications, reach their limits with respect to these dynamic and especially vibro-acoustic requirements. They offer a high specific stiffness and strength, but a relatively low damping, which leads to intense acoustic radiation. Therefore, composites or compound materials with a dynamically and vibro-acoustically optimized property profile are needed. The structural dynamic and vibro-acoustic behavior of these types of lightweight structures cannot be described by the use of classical models. Here, the advanced methods developed at ILK are considered, which take into account the special mechanical properties of the fiber-matrix compound. Also, sophisticated numerical simulation techniques such as the finite and the boundary element method are successfully applied.

Frequency response analysis of laminated composite beams

ConclusionsThe modeling of laminated composite beams has been derived systematically from the three-dimensional elasticity relations. The correctness of the solution found by using the present finite element model is verified by comparison with the results obtained by analytical solutions and other results presented in the literature. Numerical results indicate that the present technique can given accurate results for frequency response analysis for laminated composite beams. Loss factors of structures obtained by the method of complex eigenvalues and the direct frequency response method exhibit very good agreement. Optimum design of a laminated composite beam by the finite element method and the method of experiment planning has been successfully presented.

Effect of Technological Tensioning on the Efficiency of Reinforcement of Pipelines with Composite Bands

A mathematical model for the contact interaction of a cylindrical pipe with a composite band during its repair is constructed. A system of governing equations of the contact problem is formulated by using the Timoshenko theory of shells. An analysis of possible solutions is carried out for various combinations of geometric and elastic properties of shells. The possibility of pretension of a prepreg in order to improve the efficiency of repair is considered. The numerical results obtained allow one to establish the desired level of pretension for various repair situations.

Characterisation of Composite Material Properties by an Inverse Technique

An inverse technique based on vibration tests to characterise isotropic, orthotropic and viscoelastic material properties of advanced composites is developed. An optimisation using the planning of experiments and response surface technique to minimise the error functional is applied to decrease considerably computational expenses. The inverse technique developed is tested on aluminium plates and applied to characterise orthotropic material properties of laminated composites and viscoelastic core material properties of sandwich composites.