Thin Composite Plates Research Articles

Free and forced vibration of variable stiffness composite annular thin plates with elastically restrained edges

Based on the classical plate theory, free and forced vibration of variable stiffness composite annular thin plates with elastically restrained edges is studied. Material properties are assumed to be varied continuously in the radial direction, and the thickness of the plates also varies linearly. The frequencies and vibration modes of composite annular thin plates with variable stiffness with elastically restrained edges were obtained by the method of weighted residuals. Numerical results demonstrate that the method of weighted residuals has fast convergence and high accuracy. The influence of material parameters, geometrical parameters and the frequency of external forces on the dynamic performance of annular thin plates with variable stiffness is studied. It is found that the transverse mode shapes of the plates with in-plane variable stiffness are different from those with constant stiffness. The results of this paper can provide a reference for the optimization design of annular thin plates with variable stiffness.

Variable kinematic finite element models of multilayered composite plates coupled with acoustic fluid

ABSTRACTThis article presents a novel and advanced finite element formulation of the structural-acoustic problem involving thin and thick multilayered composite plates coupled with a cavity. Exploiting the Carrera's unified formulation, many plate and fluid-structure interface elements based on different kinematic models, including higher-order equivalent single-layer and layerwise theories, are developed within a single mathematical framework. Accordingly, a large number of vibro-acoustic models can be easily obtained and selected according to the accuracy requirements of the application. In particular, it is shown that refined models can be adopted in those cases where models relying on traditional or low-order plate theories fail in providing the correct estimation of the fluid-structure coupling. The proposed formulation is also validated with respect to some reference cases available in the literature.

Semi-analytical solutions to buckling and free vibration analysis of carbon nanotube-reinforced composite thin plates

The multi-term Kantorovich–Galerkin method is proposed to investigate buckling and free vibration behavior of thin carbon nanotube-reinforced composite (CNTRC) plates with the classical plate theory. The properties of CNTRC are determined with the extended rule of mixture. The transverse displacement is expressed in a sum of products of characteristic beam functions in one direction and unknown functions in the other. By applying the Galerkin technique, the governing partial differential equation is reduced to the ordinary differential equations which are then solved through the state-space approach. Non-dimensional buckling loads and frequencies of CNTRC plates with different boundary conditions are obtained, and the effects of number of approximation terms, CNT distribution, CNT volume fraction, aspect ratio, and thickness-to-width ratio are examined. It is shown that the exact solutions can be found using the present method for the CNTRC plates with two opposite sides both simply-supported, as well as the semi-analytical solutions for the ones with two opposite sides both clamped and one clamped the other simply supported.

Nonlinear bending analysis of variable cross-section laminated plates using the dynamic relaxation method

This paper tries to analyze the laminated plates with variable cross section, using the Dynamic relaxation method for solving the governing equations of the thin composite plate, obtained from the CPT theory. Comprehensive comparison and parametric studies prove the accuracy and efficiency of the utilized approach with interesting specifications such as fully vector calculations, independency to the lamina scheme (angle and number of plies) and boundary conditions so that the laminated plates with uniform, variable one direction and variable two direction of cross section could be analyzed. Results show that the behaviour of the composite plates depends on both lamina scheme (the stacking sequences and the number of the plies), and the cross section variation of the laminated plate. In this manner, utilizing the laminated plates with variable two direction of cross section could absorb more potential energy in comparison with uniform and variable one direction of cross section, so that they are useful for using in passive control mechanisms in which the kinetic energy should be removed from the structure by transforming to the potential energy.

Buckling and post buckling characteristics of laminated composite plates with damage under thermo-mechanical loading

The present work addresses the development of a finite element formulation for handling bending, buckling, and post buckling analysis of composite laminated structures with damage. The inverse hyperbolic shear deformation theory (IHSDT) was applied in the finite element formulation. The effect of damage is analyzed for thin composite plates. An anisotropic damage formulation was used to simulate the damage, which is based on the concept of stiffness reduction. Computer programming is developed in the MATLAB environment. The excellent agreement of the results obtained in the present method with those from references shows that the technique is effective and precise. Parametric studies in the buckling behavior of a damaged composite plate are presented. Critical buckling temperatures are computed for a damaged plate using the present model. Thermal post buckling equilibrium paths are traced for various parametric variations for composite plates with mild damage and compared the results with that of undamaged cases. The validation of IHSDT has been demonstrated for buckling analysis in thermal environment for composite plates with an internal flaw. The present work is worthwhile compared with previous works due to the choice of finite element method and inverse hyperbolic shear deformation theory for analyzing the influence of damage on buckling and post buckling behavior of laminated plates.

Polymer-Bonded La(Fe,Mn,Si)13H x Plates for Heat Exchangers

Composite materials containing hydrogenated La(Fe,Mn,Si)13 powder and 5 wt.% of polymer binder have very good magnetocaloric properties and can be machined in a heat exchanger. These heat exchangers have to fulfill certain requirements regarding their mechanical and chemical stability. In this paper, we have investigated the magnetocaloric properties of thin composite plates produced by two different methods: 1) wire saw cutting and 2) cold rolling. The flexural strength of the plates was investigated by three-point bending method. Furthermore, the corrosive behavior of the plates in different heat transfer fluids was investigated. Finally, the adiabatic temperature change and the magnetic entropy change of the plates were observed over a seven-month period in order to evaluate their applicability in a real device.

Nonlinear vibrations of a reinforced composite plate with carbon nanotubes

The nonlinear vibration behaviors of a reinforced composite plate with the carbon nanotubes (CNT) under combined the parametric and forcing excitations are studied in this paper for the first time. Based on the Mori–Tanaka method and the method of calculating the average stress of composite materials, the effective modules for the carbon nanotubes are obtained. The carbon nanotubes are supposed to be long hollow cylindrical structures. The nonlinear partial differential governing equations of motion for the CNT reinforced composite thin plate are derived by using the Reddy’s third-order shear deformation plate theory and the geometric nonlinearity of von Karman. The governing equations are discrete to a set of ordinary differential equations by using the Galerkin method. A perturbation method is then employed to obtained the four-dimensional averaged equations of the CNT reinforced composite thin plate under the cases of 1:1 internal resonances. The nonlinear resonant responses of the CNT reinforced composite rectangular thin plate are analyzed under combined the parametric and forcing excitations. The effects of the forcing excitations on the different kinds of the periodic and chaotic motions of the CNT reinforced composite rectangular thin plate are investigated through a comprehensive parametric study.

Novel FBG rosette for determining impact location in thin plate-like structure

The paper consists of two interdependent parts. The first part presents numerical simulations of output response of single Fibre Bragg Grating (FBG) sensor which is driven by homogeneous deformation along sensor length. The example of such sensor is FBG sensor glued at only two points. The grating length and modulation depth of the refractive index are the critical parameters contributing to performance of the FBG sensors. Numerical analysis allowed to select an appropriate FBG sensors which will be used in the impact detection problem. In the second part of the paper a novel strain rosette with specific sensor array used in impact localisation problem is discussed and presented. The experiment was carried out on thin composite plate with the use of pulse force excitation. The method is based on estimation of principal direction of perturbed travelling wave initiated at impact point and does not use any information about wave propagation velocity.

Exact refined buckling solutions for laminated plates under uniaxial and biaxial loads

This paper presents a unified Lévy-type solution procedure for the buckling analysis of both thin and thick composite plates under biaxial loads. The plates are simply-supported at two opposite edges, while the two remaining sides are subjected to any combination of simply-supported, clamped and free conditions. The problem is formulated in the context of a variable-kinematic approach, offering the advantage of automatically handling theories of various order. Both layerwise and equivalent single layer theories are considered. The governing equilibrium equations are derived analytically from the Principle of Virtual Displacements (PVD), and are solved exactly referring to the Lévy-type procedure. The accuracy of the predictions is demonstrated by comparison with results available in literature, including exact 3D solutions. A comprehensive set of benchmark results is provided for plates subjected to different loading and boundary conditions and characterized by various width-to-thickness ratios.

Analytical study of the propagation of fast longitudinal modes along wz-BN/AlN thin acoustic waveguides.

The propagation of the fundamental symmetric Lamb mode S0 along wz-BN/AlN thin composite plates suitable for telecommunication and sensing applications is studied. The investigation of the acoustic field profile across the plate thickness revealed the presence of modes having longitudinal polarization, the Anisimkin Jr. plate modes (AMs), travelling at a phase velocity close to that of the wz-BN longitudinal bulk acoustic wave propagating in the same direction. The study of the S0 mode phase velocity and coupling coefficient (K2) dispersion curves, for different electrical boundary conditions, has shown that eight different coupling configurations are allowable that exhibit a K2 as high as about 4% and very high phase velocity (up to about 16,700 m/s). The effect of the thickness and material type of the metal floating electrode on the K2 dispersion curves has also been investigated, specifically addressing the design of an enhanced coupling device. The gravimetric sensitivity of the BN/AlN-based acoustic waveguides was then calculated for both the AMs and elliptically polarized S0 modes; the AM-based sensor velocity and attenuation shifts due to the viscosity of a surrounding liquid was theoretically predicted. The performed investigation suggests that wz-BN/AlN is a very promising substrate material suitable for developing GHz band devices with enhanced electroacoustic coupling efficiency and suitable for application in telecommunications and sensing fields.

Enlargement of the locally resonant Lamb wave band gap of the phononic crystal plate at the deep sub-wavelength scale

In this paper, the numerical investigation of Lamb wave propagation in two-dimensional phononic crystals composed by depositing the heavy cylinder stubs squarely onto both sides of a composite thin plate is presented. A significant enlargement of the relative bandwidth by two orders of magnitude compared with two-dimensional binary locally resonant phononic crystal plates and one order of magnitude compared with both the ternary composite plate and the simple plate with stub structures at deep sub-wavelength scale is obtained and discussed. Based on an efficient finite element method, we show that this band gap enlargement is due to the coupling between the plate mode and ‘double mass-spring’ mode, which leads to the enhancement of the locally resonance mechanism. The calculated elastic wave displacement fields illustrate the physics mechanism of opening the low frequency band gap and the existing of the flat bands. We also found that both the band gap and the flat bands depend on the geometry parameters of the heavy stubs and composite plate significantly.

Impact location determination on thin laminated composite plates using an NIR-FBG sensor system

An integration of Structural Health Monitoring (SHM) into composite structures contribute towards the development of smart composites structure. Smart-structure offers an ability have a continuous and real-time information of its circumstances under critical loading applications. One of the main objectives in this research study was the development of the Fiber Bragg grating (FBG) sensor system for SHM of thin composite laminates. Not only that, this work has been utilizing the FBG sensors in the Near Infra-red (NIR) range; ∼830nm, as an alternative to the applications of the conventional 1550nm FBG sensors. The capability of this sensor system was validated with the impact location determination test on a thin composite plate. It showed a very promising result whereby the relative error falls below 10%.

Improved Strength and Toughness of Carbon Woven Fabric Composites with Functionalized MWCNTs.

This investigation examines the role of carboxyl functionalized multi-walled carbon nanotubes (COOH-MWCNTs) in the on- and off-axis flexure and the shear responses of thin carbon woven fabric composite plates. The chemically functionalized COOH-MWCNTs were used to fabricate epoxy nanocomposites and, subsequently, carbon woven fabric plates to be tested on flexure and shear. In addition to the neat epoxy, three loadings of COOH-MWCNTs were examined: 0.5 wt%, 1.0 wt% and 1.5 wt% of epoxy. While no significant statistical difference in the flexure response of the on-axis specimens was observed, significant increases in the flexure strength, modulus and toughness of the off-axis specimens were observed. The average increase in flexure strength and flexure modulus with the addition of 1.5 wt% COOH-MWCNTs improved by 28% and 19%, respectively. Finite element modeling is used to demonstrate fiber domination in on-axis flexure behavior and matrix domination in off-axis flexure behavior. Furthermore, the 1.5 wt% COOH-MWCNTs increased the toughness of carbon woven composites tested on shear by 33%. Microstructural investigation using Fourier Transform Infrared Spectroscopy (FTIR) proves the existence of chemical bonds between the COOH-MWCNTs and the epoxy matrix.

Automatic simultaneous measurement of phase velocity and thickness in composite plates using iterative deconvolution

A new method for the automatic and simultaneous measurement of phase velocity and thickness for thin composite plates was developed based on Ping He׳s method, without any need of a priori knowledge of the material parameters. Two composites were analyzed: a block of clean epoxy and a thin specimen of glass–fiber reinforced plastic produced by resin transfer molding. The proposed method combines cross-correlation functions and iterative deconvolution for accurate measurement of times of flight and gating. The new method has demonstrated to be more accurate than conventional Ping He׳s method, and can be implemented automatically thus saving processing time and increasing accuracy.

Multi-splitting of Lamb waves band gap in one-dimensional quasi-periodic plates of cantor series

We study numerically the propagation of Lamb waves in one-dimensional (1D) quasi-periodic composite thin plates consisting of a row of air holes embedded in the matrix material silicon according to a Cantor sequence; the surfaces of the plate are parallel to the axis of quasi-periodicity. The phenomenon of multi-splitting in the band gap structures is demonstrated. A semi-quantitative explanation is proposed in which the inherent cavity-like structure is proven to play the essential role in the phenomenon of multi-splitting, which gives a reliable way to predict where and how the band gap is splitting in the quasi-periodic systems. Possible applications are discussed.

Modal Properties of Hybrid Carbon/Kevlar Composite Thin Plate and Hollow Wing Model

In any flutter prediction analysis, modal testing is necessary because flutter, a resonant like vibration occurs at a flutter frequency and adopts a mode shape akin to its structural natural modes. Modal testing can be performed computationally with knowledge of the mechanical properties of the structure. In the present work, computational modal analysis is first performed on a cantilevered hybrid composite thin plate and validated experimentally. Then, the computational procedure is demonstrated on a composite hollow wing model of same material. The concept of hollow wing is explored due to the superior mechanical properties of carbon/kevlar composite plate. It is observed that the natural frequencies of the hollow wing model are higher than thin plate due to stiffer configuration. A breathing mode was also observed at mode 4 for the hollow wing.

Identification of Modal Properties of Composite Thin Plate Using OMA in Wind Tunnel Environment

Identification of modal parameters is crucial especially in aerospace applications whereby the interactions of airflow with aircraft structures can result in undesirable structural deformations. This structural deformation can be predicted with knowledge of the modal parameters. This can be achieved through conventional modal testing that requires a known excitation force in order to extract these dynamic properties. This technique can be experimentally complex because of the need for artificial excitation and it also does not represent actual operational condition. The current work presents part of research work that address the practical implementation of operational modal analysis (OMA) applied to a cantilevered hybrid composite plate exposed to low speed airflow in a wind tunnel. A single contactless sensing system via a laser vibrometer is employed to measure the response. OMA technique applied in a wind-on condition succeeded in extracting the modal parameters of the hybrid composite plate which correlate well with modal testing using impact hammer excitation.

Control of geometrically nonlinear vibrations of skew laminated composite plates using skew or rectangular 1–3 piezoelectric patches

This paper deals with the analysis of active constrained layer damping (ACLD) of geometrically nonlinear transient vibrations of skew laminated composite plates using skew or rectangular patches of the ACLD treatment. The constraining layer of the patch of the ACLD treatment is composed of the vertically/obliquely reinforced 1–3 piezoelectric composite material. The Golla–Hughes–McTavish method has been used to model the constrained viscoelastic layer of the ACLD treatment in the time domain. A coupled electromechanical nonlinear three dimensional finite element model of skew laminated thin composite plates integrated with the skew or rectangular patches of ACLD treatment has been derived. The performance of the patches is investigated for different configurations of their placements on the top surface of the skew substrate plates. The analysis reveals that the ACLD treatment significantly improves the active damping characteristics of the skew laminated composite plates over the passive damping for suppressing their geometrically nonlinear transient vibrations. It is found that even though the substrate laminated plates are skew, a rectangular patch of the ACLD treatment located at the centre of the top surface of the substrate should be used for optimum damping of geometrically nonlinear vibrations of skew laminated composite plates irrespective of their skew angles and boundary conditions. The effects of piezoelectric fiber orientation angle and the skew angles of the substrate plates on the control authority of the ACLD patches have been emphatically investigated.

Modal Acoustic Emission Investigation for Progressive Failure Monitoring in Thin Composite Plates under Tensile Test

Acoustic Emission (AE) is one of the popular non-destructive (NDT) techniques and its applications have increased subsequently for Structural Health Monitoring (SHM). During the past few decades, many successful research works have evidently shown remarkable capability of AE for early damage detection of composite materials. This paper investigated the application of single channel acoustic emission (AE) source location detection method, utilizing time-frequency analysis for thin composite plates. Besides, failure characterization using Modal Acoustic Emission (MAE) also presented. Modal analysis of AE signals or MAE can offers a better theoretical background for acoustic emission analysis; which is necessary to get more qualitative and quantitative result and therefore, increase the reliability of early failure characterization for thin composite plates. For this study, tensile tests were conducted on the glass fiber epoxy resin specimen with small notch; and four channels of acoustic emission system were used to acquire AE signals. The results revealed that in practical, single channel AE source location was difficult to be done. Also, the study has successfully showed that matrix cracks and fiber fracture produced AE signals which dominated by symmetric wave mode.

Three-dimensional assessment of low velocity impact damage in particle toughened composite laminates using micro-focus X-ray computed tomography and synchrotron radiation laminography

Results are presented studying the contribution of particle toughening to impact damage resistance in carbon fibre reinforced polymer materials. Micro-focus X-ray computed tomography and synchrotron radiation computed laminography were used to provide a novel, multiscale approach for assessing impact damage. Thin (1mm thick) composite plates containing either untoughened or particle-toughened resin systems were subjected to low velocity impact. Damage was assessed three-dimensionally at voxel resolutions of 0.7μm and 4.3μm using SRCL and μCT respectively; the former being an innovative approach to the laterally extended geometry of CFRP plates. Observations and measurements taken from μCT scans captured the full extent of impact damage on both material systems revealing an interconnected network of intra- and inter-laminar cracks. These lower resolution images reveal that the particle-toughened system suppresses delaminations with little effect on intralaminar damage. The higher resolution images reveal that the particles contribute to toughening by crack deflection and bridging.