Aeroelastic analysis of pre-stressed variable stiffness composite panels

The non-linear stability analysis of composite cylindrical panel subjected to concentrated in-plane mechanical and localized thermal loadings are reported here. The buckling of composite panel subjected to concentrated in-plane mechanical loading/ localized thermal loading is solved in two steps as the prebuckling stress distribution within the panel is not known a priori. In the first step, the semi-analytical expressions for the pre-buckling stresses within the composite cylindrical panel under in-plane mechanical/ thermal loadings are developed by solving in-plane elasticity/thermoelasticity problem. Subsequently, using these in-plane stresses within the cylindrical panel, the governing equations for nonlinear stability of layered composite panel are formulated using variational principle. The cylindrical panel is modeled based on Donnell’s shallow shell theory considering higher order shear deformation theory and incorporating von-Karman geometric nonlinearity. The Galerkin’s method is used to solve the non-linear governing partial differential equations. The influence of different types of mechanical and thermal loadings, initial geometric imperfections, and radius of curvature on the postbuckling equilibrium paths is investigated.

*† ‡ Prediction of the transmission loss of singly curved sandwich composite panels is presented for a special class of symmetric construction. Measurements of the transmission loss for such a panel are presented and compared to the predictions. Additional results for the panel covered with acoustic absorbing foams are presented and compared to predictions. The foam addition increases the panel apparent damping, and results in a larger increase of transmission loss than can be attributable to the added mass. It is concluded that the model accurately predicts the transmission loss and other acoustic properties. It can be employed for the acoustic design of such panels. Sandwich composite panels and cylinders are extensively employed in the aerospace industry. Their applications are commonly found in aircraft, helicopters, launch vehicles, and engine cowlings. Ironically, the light weight advantage of the composite sandwich construction could lead to higher interior noise levels. The prediction of the sound transmission into such structures requires the analysis of acoustic wave propagation in curved composite sandwich panels. Moreover, control of the interior cavity noise almost always requires the introduction of acoustic treatments such as sound absorbing foam or fiberglass. This paper presents an abridged version of a wave approach analytical treatment for predicting the transmission loss of curved composite sandwich panels. Moreover, a test panel was constructed and employed in a transmission loss test for the bare panel and the panel covered with acoustic foam. Description of the test and representative results for the bare and covered panel are given. The transmission loss prediction for orthotropic and multi-layered infinite cylinders was investigated in a series of papers by Blaise et al. 1-3 They first presented a displacement field which neglected the transverse shear and rotary inertia, and followed it by a more general model referred to as the 3-D model. Modal based finite element and boundary element methods were employed for predictions of sound transmission through a curved honeycomb composite panel, and were verified in transmission loss tests.

A novel higher-order coupled finite-boundary element scheme is presented for the computation of the thermoacoustic responses of the layered panel structure under the harmonic excitation. The thermally pre-stressed vibrating composite panel model is derived mathematically using the higher-order shear deformation mid-plane kinematics. The eigen frequencies and the corresponding vibrational mode shapes are computed via the finite element method using Hamilton’s principle. Similarly, the surrounding medium is modeled via Helmholtz wave equations and solved numerically using the boundary element steps for the computation of the acoustic responses. The frequency and sound radiation output are computed numerically by means of an own computer code prepared in MATLAB environment. To avoid excess thermal loading during analysis, the critical buckling temperature of the composite panel structure is obtained and the range of thermal loading is selected accordingly. The model accuracy is demonstrated through the proper comparison studies of different structural responses (critical buckling temperature, natural frequency and radiated sound power level) of the curved composite panel with the available benchmark solutions. The reliability and the usefulness of the proposed novel scheme have been revealed by solving several numerical illustrations for different lamination schemes, panel geometries including the geometrical parameters.

Fast Fourier transform (FFT) has been widely used to analyze distribution patterns of frequency components in dynamic response signals. Given a stationary dynamic response signal, a fixed frequency distribution pattern can be obtained efficiently using FFT. If the system of concern is not stationary, however, the frequency distribution pattern varies with time, and the variation in that pattern cannot be effectively determined via FFT. To overcome this weakness, time-frequency dual-domain signal analysis methods such as wavelet transform and Hilbert-Huang transform (HHT) have been introduced. HHT has been shown to be particularly effective in analysis of non-stationary signals obtained from non-linear as well as linear systems. In the present study, the transient characteristics of a composite panel undergoing high-velocity impact were investigated. The composite panel, along with the colliding bullet, were modeled using the finite element method. To verify the reliability of the analysis model, an impact experiment was carried out, which proved that the model provides reliable, similar-to-experimental results.

Automated Fiber Placement (AFP) machines can manufacture composite panels with curvilinear fibers. In this article, the critical buckling load of grid-stiffened curvilinear fiber composite panels is maximized using a genetic algorithm. The skin is composed of layers in which the fiber orientation varies along one spatial direction. The design variables are the fiber orientation of the panel for each layer and the stiffener layout. Manufacturing constraints in terms of maximum curvature allowable by the AFP machine are imposed for both skin and stiffener fibers. The effect of manufacturing-induced gaps in the laminates is also incorporated. The finite element method is used to perform the buckling analyses. The panels are subjected to in-plane compressive and shear loads under several boundary conditions. Optimization results show that the percentage difference in the buckling load between curvilinear and straight fiber panels depends on the load case and boundary conditions.

Buckling analysis of piezoelectric cylindrical composite panels reinforced with carbon nanotubes

Aims of research. Polymer unidirectional composite laminate panel behavior with interlaminate defects under action of different dynamic loads is consider. Methods. Normal modes and eigenvalues of rectangular composite panels in the presence multiple delamination different sizes ellipsoidal form are calculated. The dependences of the maximum deflections from the frequency of the stationary pressure field action are constructed. Distribution field of panels plies failure index under action of nonstationary pressure field by using different failure criteria for composites is determined. Results. Modeling methodology composite panels behavior in the presence multiple interlaminar defects under action of different dynamic loads is developed. Analysis of failure panel with the use of different failure criteria for composites is carried out.

Vibration and damping characteristics of hybrid carbon fiber composite pyramidal truss sandwich panels with viscoelastic layers

This research aims to design, manufacture, and determine the vibration characteristics of a composite sandwich panel with lattice cores. For this purpose, first, a glass fiber sandwich panel with lattice truss core has been fabricated in the laboratory. In this part, the vacuum-assisted resin transfer molding method has been used to achieve laminates without any porosity. Afterward, the modal tests have been performed to obtain the natural frequencies, shape modes, damping ratio, and frequency responses of the sandwich panel. In addition, a finite element analysis has been developed to calculate the natural frequencies, damping ratio, and mode shapes of the composite sandwich panel. Then the experimental data have been compared to numerical simulation, and good agreement has been found.

Composite cylindrical panels—optimum lay-up for buckling by ranking

Stiffened composite cylindrical panels—Optimum lay-up for buckling by ranking

Based on the refined first-order shear theory (simplified zig-zag model), using quasi-conforming finite element method with path-following and switching approach, the postbuckling behaviors and postbuckling bearing capacity (PBC) of composite sandwich panels (CSPs) axially loaded were studied and discussed in detail. To utilize the carrying potential of CSPs in postbuckling, the effects of the key parameters on postbuckling behaviors of the CSPs were analyzed by finite element method. The numerical results show that the PBC of CSPs increases with the increase of face sheets thickness, core thickness and core shear modulus, but it is insensitive to the change of the side length ratio. The enhancement of core shear strength can increase the PBC of CSPs and change the failure mode, but it is found there is a threshold value, beyond which, the PBC will no longer or slightly increases with the increase of core shear strength. The failure of CSPs is mainly determined by the tensile strength in the direction perpendicular to the fiber. Finally, a parameter selection optimization approach is proposed to effectively improve the PBC of CSPs under axial compression.

Finite element analysis of lightweight composite sandwich panels exposed to fire

Traditionally, modelling panels with curvilinear stiffeners using the Ritz method requires two separate domains: a 2D plate domain for the skin and a 1D beam domain for the stiffeners. These domains are then assembled to determine the overall structural response. In this paper, a novel single-domain Ritz-based approach is proposed for the semi-analytical modelling of curvilinearly grid-stiffened panels. A variable-stiffness domain is constructed to represent a skin concentrically stiffened with an arbitrary number of tow-placed curvilinear stiffeners, which share the same stacking direction as the skin. The proposed approach is implemented for addressing the buckling problem of panels with curvilinear fibres and stiffeners based on the first-order shear deformation theory. Pre-buckling and buckling responses are derived using the principles of stationary complementary energy and total potential energy, respectively. The elements of the resulting matrices are computed through a special integration strategy based on the Romberg integration rule. The quality of the results obtained with the proposed approach is validated by comparison with finite element simulations. The results demonstrate good agreement, highlighting the potential of the developed approach as a valuable tool for modelling curvilinearly grid-stiffened variable-stiffness composite panels.

Thermomechanical postbuckling of multilayered composite panels with cutouts