Effect of Delamination on Natural Frequencies of E-glass and S-glass Epoxy Composite Plates

The delamination is one of the major modes of failure occurring in the laminated composite due to insufficient bonding between the layers. In this paper, the natural frequencies of delaminated S-glass and E-glass epoxy cantilever composite plates are presented by employing the finite element method (FEM) approach. The rotary inertia and transverse shear deformation are considered in the present study. The effect of parameters such as the location of delamination along the length, across the thickness, the percentage of delamination, and ply-orientation angle on first three natural frequencies of the cantilever plates are presented for S-glass and E-glass epoxy composites. The standard eigenvalue problem is solved to obtain the natural frequencies and corresponding mode shapes. First three mode shape of S-Glass and E-Glass epoxy laminated composites are portrayed corresponding to different ply angle of lamina.

Critical Frequencies of Composite Cylindrical Shells

The sound radiation characteristics of a structure depend on its critical frequency. The expression for theoretically estimating the critical frequency of a composite cylindrical shell has not yet been reported. Thus, the practice is to use the expression for the composite panel for determining the critical frequency of a composite shell. In this work, critical frequencies of composite shells are investigated. As the critical frequency depends on the speed of the bending wave, an expression for the speed of the bending wave is first derived. It is seen that the curvature causes an increase in the speed of the bending wave and the orthotropic nature of the cylinder reduces the speed. An expression for the critical frequency of a composite cylindrical shell is then derived. The curvature causes a reduction in the critical frequency and the influence is significant in acoustically thick cylinders. Hence, the critical frequencies of such cylinders cannot be determined by using the expression for the panels. Effects of transverse shear deformation on the speed of the bending wave as well as the critical frequency are then investigated. Transverse shear deformation causes both reduction in the speed of the bending wave and an increase in the critical frequency. The orthotropic nature of the cylindrical shell increases the critical frequency further. The critical frequency of a typical composite cylinder is determined through a numerical simulation and the results are in agreement with the results obtained using the expressions derived. The critical frequency of a typical composite cylinder obtained through an experiment is presented. With this work, expressions for theoretically estimating the speeds of the bending waves and critical frequencies are derived for a composite cylindrical shell considering transverse shear deformation.

Modal density and critical frequency of composite panels considering transverse shear deformation and rotary inertia

In this work, expressions for estimating the modal density, speed of the bending wave, critical frequency and coincidence frequency of panels are derived considering orthotropic properties of the face sheets, transverse shear deformation and the rotary inertia. Presence of rotary inertia results in an increase in the modal density and a reduction in the speed of the bending waves. The influence is significant at higher frequencies. The critical and coincidence frequencies increase due to rotary inertia. Results for a typical equipment panel of spacecraft are presented and they show the need for incorporating rotary inertia while determining these parameters.

Exact Solution of the Problem of Elastic Bending of a Multilayer Beam under the Action of a Normal Uniform Load

An exact solution of the theory of elasticity is presented for the problem of a narrow multilayer bar section transverse bending under the action of a normal uniform load on longitudinal faces. The solution is built using the principle of superposition, by imposing common solutions to the problems of bending a multilayer cantilever with uniform loads on the longitudinal faces and an arbitrary load on the free end, and allows to take into account the orthotropy of the materials of the layers, as well as transverse shear deformation and compression. On the basis of a built-in general solution, a number of particular solutions are obtained for multi-layer beams with various ways of the ends fixing.

Aeroelastic Response Analysis of Composite Blades Based on Geometrically Exact Beam Theory

The geometrically exact nonlinear beam theory consisting of the latest version of two-dimensional variational asymptotic beam sectional analysis (VABS) and one-dimensional geometrically exact beam theory (GEBT) has been widely used for the structural analysis of composite beam structures. The theory can be used for establishing the aeroelastic model of composite blades undergoing large deflections to improve computational accuracy and efficiency. In this paper, the theory has been extended from structural analysis to aeroelastic analysis of blade, and an accurate and efficient method for aeroelastic response analysis of composite blades has been presented based on the theory and unsteady aerodynamic model. The geometrically exact nonlinear equations of motion and the latest VABS are used to deal with one-dimensional beam analysis and the structural property of blade cross section, respectively. The Peters–He finite state dynamic wake model and the Peters finite state airloads theory are used to calculate the induced velocity and blade airloads, respectively. The presented method has been used to analyze the aeroelastic responses of composite blades, and its accuracy has been verified by experimental data. The influence of transverse shear deformation on the aeroelastic response of composite blades was also investigated, indicating that the transverse shear deformation has a nonnegligible effect on aeroelastic response analysis of hingeless composite rotors in hover.