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In this research, high-order shape functions commonly used in different finite element implementations are investigated with a special focus on their applicability in the semi-analytical finite element (SAFE) method being applied to wave propagation problems. Hierarchical shape functions (p-version of the finite element method), Lagrange polynomials defined over non-equidistant nodes (spectral element method), and non-uniform rational B-splines (isogeometric analysis) are implemented in an in-house SAFE code, along with different refinement strategies such as h-, p-, and k-refinement. Since the numerical analysis of wave propagation is computationally quite challenging, high-order shape functions and local mesh refinement techniques are required to increase the accuracy of the solution, while at the same time decreasing the computational costs. The obtained results reveal that employing a suitable high-order basis in combination with one of the mentioned mesh refinement techniques has a notable effect on the performance of the SAFE method. This point becomes especially beneficial when dealing with applications in the areas of structural health monitoring or material property identification, where a model problem has to be solved repeatedly. [ABSTRACT FROM AUTHOR]

This study deals with free vibration analysis of integrated and non-integrated corrugated core sandwich panels with rectangular core together with free vibration analysis of integrated corrugated core sandwich panels with hat-type and triangle core. Bonding of the core to skin in non-integrated sandwich panels was achieved by resin, while in the integrated sandwich panels that were reinforced with 3-D weft-knitted fabric bonding was achieved using yarns and resin. Results revealed that the integrated structures have higher natural frequency than the non-integrated structures. It was also found that the natural frequency of the triangular-core sandwich panels and the rectangular-core sandwich panels was the highest and the lowest, respectively. It was established that weft-knitting fabric technology is suitable for the production of both integrated and non-integrated corrugated core sandwich panels with a high degree of similarities in terms of geometry, weight, and characteristics. [ABSTRACT FROM AUTHOR]

Abstract In this paper the isogeometric method is used to present a shear refined composite beam model through the concept of dimensional reduction method. A one-dimensional (1D) beam model is extracted from three-dimensional (3D) elasticity problem. The 1D beam model is developed using cross-sectional properties from two-dimensional (2D) beam sectional analysis. The 2D analysis of the cross-section is presented by implementing the transverse shear effects in isogeometric analysis. In beam cross-sectional problem, the influence of linear parameterization is investigated for isogeometric modeling of beam cross-section. Moreover, the effect of delamination on cross-sectional stiffness constants is discussed. Using isogeometric analysis (IGA), less degrees of freedom is needed in contrast to classical finite element method and automatic mesh refinement capability is attained. The present composite beam model eliminates the expensive use of 3D finite element analysis with its high precision and fidelity to 3D problem. [ABSTRACT FROM AUTHOR]

A novel isogeometric-based cross-sectional analysis of composite beams with arbitrary cross-section geometry and a one-dimensional composite beam model is presented via the concept of dimensional reduction method. In dimensional reduction method, three-dimensional beam problem is decomposed into a two-dimensional beam cross-sectional analysis and a one-dimensional beam problem. To achieve this goal, warping displacements should be computed by solving a cross-sectional eigenvalue problem. The cross-sectional analysis is accomplished by spline basis functions to describe unknown warping fields as well as beam cross-section geometry in an isogeometric framework. The present method benefits from the exact geometric definition of beam cross-section, greatly simplifying mesh refinement and better convergence in contrast to classical finite element method. The proposed beam cross-sectional analysis is applied to a variety of beam cross-section configurations with isotropic and anisotropic materials, which show good correlation with the available results in the literature. [ABSTRACT FROM AUTHOR]

This paper, presents the static analysis of composite beams with transverse shear effects using polynomial based dimensional reduction method. In dimensional reduction method, a three dimensional elasticity problem is split into a two dimensional cross section analysis and a one dimensional beam analysis. FEM is commonly used to analyze beam cross section in the literature. In this study, polynomial functions and Rayleigh-Ritz method are used to present an analytical procedure for two dimensional cross section analysis. Variational Asymptotic Method (VAM) is employed considering shear stiffnesses of composite beam cross section. VAM, asymptotically generates fully coupled cross section stiffness matrix. VAM benefits small parameters, related to characteristic length of cross section, to find stationary values of beam energy functional. By minimizing the energy functional with respect to warping, in and out of plane warping functions are acquired. In this article, isotropic beams with different cross section geometries and symmetric as well as anti-symmetric composite box beams are investigated. Presented results show appropriate correlation of the present study with theoretical and experimental results, as well as 3D Finite Element analysis. Using dimensional reduction method reduces the computing time and empowers researchers to design and optimize composite beam-like structures. [ABSTRACT FROM AUTHOR]

This paper presents prediction of static behavior of composite beams with arbitrary anisotropic materials. The procedure is based on decomposing a 3-D nonlinear elasticity problem into a 2-D analysis of cross section and a 1-D analysis across the beam length. This is accomplished by assuming that magnitude of strain is small compared to unity and cross section size is small relative to wavelength of deformation, inherent to beam-like structures. In 2-D cross sectional analysis warping functions are calculated in terms of 1-D strain parameters and finally, fully coupled classical stiffness constants are derived which include extension, torsion and bending in two directions. 1-D analysis is modeled by Finite Element Method through calculating beam strain energy. In this article warpings are derived using Rayleigh-Ritz method. The great advantage of using Rayleigh-Ritz is simplifying cross sectional analysis in contrast with the mesh generation in FEM of similar procedures. Different cross section stiffnesses are investigated for ply orientation angle. Calculated results for symmetric and anti-symmetric composite box beams correlate well with 3-D FEM using Abaqus software as well as the experimental results. The present solution has more accurate results for anti-symmetric composite box beam. According to costly use of 3-D FEM analysis, the present procedure with high speed and acceptable accuracy is sufficient for preliminary and optimization problems. [ABSTRACT FROM AUTHOR]

In the present study, the frequency analysis of a smart sandwich plate is investigated using the finite element method. The sandwich plate is consisted of a magnetorheological elastomer (MRE) layer between two cross ply composite elastic faces. MRE is a smart material with controllable properties and a short time response when subjected to a magnetic field. This property can be used for improvement of the dynamic behavior of the structure. To model the sandwich plate with MRE layer, a complex shear modules is used to show the pre-yield behavior of MRE layer. In this study, effect of imperative parameters are discussed. In the present paper, the effect of different parameters such as applied magnetic field, the stacking sequences of the cross ply laminated faces in the sandwich plate and applying different boundary conditions on the natural frequencies and modal loss factors of the smart sandwich plate with MRE is investigated. The results show that considering special value for magnetic field, the stacking sequences of the composite layers of the sandwich plate and the boundary condition of the sandwich structure can lead to the satisfactory design of the sandwich plate. [ABSTRACT FROM AUTHOR]

Abstract: The objective of the present study is to enlighten the influence of external electrorheological (ER) dampers on the dynamic behavior of composite laminated plates. Short time response along with electric field depended rheological behavior of ER fluids make these materials attractive for active vibration control of structures. To demonstrate the effect of ER damper on dynamic response of the composite plate, the finite element formulation based on the first order shear deformation theory (FSDT) is obtained for laminated plates. Moreover, the Bingham plastic model, which presents the post-yield behavior of the ER material, is used to model the ER fluid. Several numerical results are presented and effects of imperative parameters are discussed. It is shown that parameters such as applied voltage, controlled electric field, radius and initial gap of the electrodes, position of the ER damper and the stacking sequences of the composite plate have considerable effect on the vibration suppression time of the plate. [Copyright &y& Elsevier]

The flutter of orthotropic sandwich plates with an electrorheological fluid layer subjected to supersonic airflow is discussed in this article. The sandwich plate consists of an electrorheological fluid layer, a base and a constraining orthotropic layer. The first piston theory is used to model the aerodynamic forces. Hamilton’s principle is employed to derive the finite element equations of motion. Taking the aerodynamic damping into account, an iterative complex eigenvalue solution is conducted to determine the flutter boundaries. The effects of electric field strength, electrorheological layer thickness, electrorheological fluid type, constraining layer thickness, and fiber angle of orthotropic faces on the critical aerodynamic pressure are investigated. Both simply supported and clamped boundary conditions are considered. The results show that the electrorheological core layer is capable of shifting the flutter instability of the system. It is also found that the electrorheological fluid type and the thickness ratios have significant effects on the flutter bounds. [ABSTRACT FROM AUTHOR]

This article focuses on dynamic stability of smart sandwich beams resting on Winkler elastic foundation subjected to harmonic axial loads. To increase the dynamic buckling load and the stability region of the beam, an electro-rheological layer is adhered as a core. The finite element method is employed to derive a three layer smart sandwich beam element. By inspecting dynamic response of the beam in different load amplitudes, critical dynamic loads are calculated. Parametric study is done to investigate effects of various parameters such as beam geometry, foundation stiffness, static load, applied voltage and properties of core layer on critical dynamic loads and stability regions of the beam. This study indicates that by applying electric field to the electro-rheological core, dynamic critical load and consequently, dynamic stability of the beam increase efficiently. Furthermore, the elastic foundation reduces the unstable region and increases the critical dynamic load of the smart beam. Proper use of these parameters makes the beam less sensitive to axial harmonic loading by relocating the instability region. [ABSTRACT FROM AUTHOR]

In this article, an effort has been made to deal with stability analysis of a smart sandwich beam with cross-ply faces and ER core. An ER layer is adhered to the laminated composite beam to increase dynamic stability of the beam. Bingham’s model is applied to model dynamic behavior of ER layer. A smart beam element is derived for the sandwich beam and finite element modeling is carried out. Transient response of the beam to an initial excitation is calculated using direct integration method. By analyzing the dynamic responses of the beam in different load amplitudes, critical loads and stability regions are obtained. Parametric study has been done and effects of various parameters such as the electric field, stacking sequence of the layers, and thickness ratio of elastic faces on static and dynamic stability of the beam are investigated. Obtained results show that stacking sequence and thickness ratio of elastic faces affects both static and dynamic stability of the beam. On the other hand, ER layer affects damping properties of structures as a result of which only dynamic stability of the beam is improved. [ABSTRACT FROM PUBLISHER]

The dynamic buckling of the patched perforated cylindrical panels, subjected to axial impact load, is investigated. Effects of various parameters such as load time duration, sector angle, cutout size, and thickness of the cylindrical panel are investigated. Furthermore, the effectiveness of the application of single or double-sided composite patches in enhancement of dynamic load carrying capacity of the perforated panels is presented. Due to complexity, material anisotropy, and discontinuity in geometry involved in the dynamic analysis of perforated/repaired panels, closed-form solutions are practically unobtainable. Numerical studies using commercial finite element code is used for the analyses. The results presented herein indicate that patches with a different number of plies and stacking sequences can be found, which improve the dynamic buckling load of the perforated panels. [ABSTRACT FROM PUBLISHER]

The performance of damaged metallic plates reinforced with fiber-reinforced polymer composite materials (composite patches) are presented in this study. A square aluminum plate with a central circular cutout is considered as a damaged structural element. Numerical studies using commercial finite element code were conducted to investigate the effects of variation in patch geometries and lamination parameters on buckling responses of repaired plates. The varying laminate parameters, such as fiber angles and stacking sequences, are considered in this study. A quantitative measure for the effectiveness of the composite patches is taken to be the relative change in buckling loads of the reinforced plates compared to that of the unreinforced one. The results presented herein indicated that, for buckling response of a repaired metallic plate with central cutout, a set of laminated composite patches with different number of plies and stacking sequences can be found which improve the load-carrying capacity of damaged plates. [ABSTRACT FROM AUTHOR]

This paper is intended to investigate the static behavior of pre-twisted composite beams using an isogeometric-based cross-sectional analysis. The three-dimensional pre-twisted beam problem is decomposed into a two-dimensional cross-sectional analysis and a one-dimensional beam model. The cross-sectional analysis obtains stiffness constants by considering three-dimensional warping deformation effects. The influence of pre-twist ratio is investigated on the stiffness constants and one-dimensional deformations of isotropic beams, composite strips and box-beams. Inconsistencies in results of pre-twisted composite beam theories in the literature are addressed and discussed. The present method eliminates the costly use of three-dimensional finite element analysis in the initial design steps. • An IGA-based cross-sectional analysis of pre-twisted composite beams is presented. • The effect of pre-twist is investigated on stiffness constants and 1D deformations. • Using IGA, automatic mesh refinement and good convergence behavior are attained. • Inconsistencies in results of pre-twisted beam theories in literature are discussed. [ABSTRACT FROM AUTHOR]