• Advances in aircraft and spacecraft science
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• 제3권1호
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• pp.15-28
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• 2016

Although the aircraft industry was the first to use fibre composites, now they are increasingly used in a range of structural applications such as flooring, decking, platforms and roofs. Interlayer delamination is a major failure mode which threatens the reliability of composite structures. Delamination can grow in size under increasing loads with time and hence leads to severe loss of structural integrity and stiffness reduction. Delamination reduces the natural frequency and as a consequence may result in resonance. Hence, the study of the effects of delamination on the free vibration behaviour of multilayer composite structures is imperative. The focus of this paper is to develop a 3D FE model and investigate the free vibration behaviour of fibre composite multilayer sandwich panels with interlayer delaminations. A series of parametric studies are conducted to assess the influence of various parameters of concern, using a commercially available finite element package. Additionally, selected points in the delaminated region are connected appropriately to simulate bolting as a remedial measure to fasten the delamination region in the aim of reducing the effects of delamination. First order shear deformation theory based plate elements have been used to model each sandwich layer. The findings suggest that the delamination size and the end fixity of the plate are the most important factors responsible for stiffness reduction due to delamination damage in composite laminates. It is also revealed that bolting the delaminated region can significantly reduce the natural frequency variation due to delamination thereby improving the dynamic performance.

• 대한조선학회논문집
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• 제33권3호
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• pp.56-65
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• 1996

최근 재료 과학의 발달과 함께 선박의 초고속화를 추구함에 따라 높은 강도와 중량의 경량화를 동시에 만족시킬 수 있는 복합 재료에 대한 요구가 증대되고 있다. 샌드위치 구조 형식은 두껍고 약한 저밀도의 심재와 얇고 강한 고밀도의 면재가 접착된 복합 구조의 한 형태로서 두 개의 면재가 중립 축으로부터 멀리 떨어지게 됨으로써 2차 모멘트가 크게 되어 구조의 강성을 증가시킬 수 있는 가장 효과적인 경량의 구조 형식이다. 본 연구에서는 샌드위치 평판 구조가 분포 하중, 압축 하중, 전단 하중 및 이 들의 복합하중을 받을 때의 응력 및 좌굴 하중을 Rayleigh-Ritz법을 이용하여 정밀 해석하였다. 그리고, 샌드위치 평판에 대한 초기 설계에 응용이 가능하도록 좌굴응력 외에 Wrinkling 응력에 관한 제한조건을 고려하여 샌드위치 평판의 최소 중량 설계를 수행하였다.

• Steel and Composite Structures
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• 제33권6호
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• pp.805-822
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• 2019

In this work, a simple four-variable integral plate theory is employed for examining the thermal buckling properties of functionally graded material (FGM) sandwich plates. The proposed kinematics considers integral terms which include the effect of transverse shear deformations. Material characteristics and thermal expansion coefficient of the ceramic-metal FGM sandwich plate faces are supposed to be graded in the thickness direction according to a "simple power-law" variation in terms of the "volume fractions" of the constituents. The central layer is always homogeneous and consists of an isotropic material. The thermal loads are supposed as uniform, linear, and nonlinear temperature rises within the thickness direction. The influences of geometric ratios, gradient index, loading type, and type sandwich plate on the buckling properties are examined and discussed in detail.

• Steel and Composite Structures
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• 제8권4호
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• pp.281-296
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• 2008

Visco-elastic material and thin metals were adhered to plate structures, forming the composite components that are similar to the sandwich plates, called constrained layered damped (CLD) plates. Constrained layer damping has been utilized for years to reduce vibration, and advances in computation and finite element analysis software have enabled various problems to be solved by computer. However, some problems consume much calculation time. The vibration equation for a constrained layered damped plate with simple supports and an impact force is obtained theoretically herein. Then, the results of the vibration equation are compared with those obtained using the finite element method (FEM) software, ABAQUS, to verify the accuracy of the theory. Finally, the 3M constrained layer damper SJ-2052 was attached to plates to form constrained layered damped plates, and the vibration equation was used to elucidate the damping effects and vibration characteristics.

• Steel and Composite Structures
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• 제41권6호
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• pp.873-886
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• 2021

In this paper, an analytical solution for thermodynamic response of functionally graded (FG) sandwich plates resting on variable elastic foundation is performed by using a quasi 3D shear deformation plate theory. The displacement field used in the present study contains undetermined integral terms and involves only four unknown functions with including stretching effect. The FG sandwich plate is considered to be subject to a time harmonic sinusoidal temperature field across its thickness with any combined boundary conditions. Equations of motion are derived from Hamilton's principle. The numerical results are compared with the existing results of quasi-3D shear deformation theories and an excellent agreement is observed. Several numerical examples for fundamental frequency, deflection, stress and variable elastic foundation parameter's analysis of FG sandwich plates are presented and discussed considering different material gradients, layer thickness ratios, thickness-to-length ratios and boundary conditions. The results of the present study reveal that the nature of the elastic foundation, the boundary conditions and the thermodynamic loading affect the response of the FG plate especially in the case of a thick plate.

• Smart Structures and Systems
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• 제13권1호
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• pp.111-135
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• 2014

Based on the Reissner mixed variational theorem (RMVT), finite rectangular layer methods (FRLMs) are developed for the three-dimensional (3D) linear buckling analysis of simply-supported, fiber-reinforced composite material (FRCM) and functionally graded material (FGM) sandwich plates subjected to bi-axial compressive loads. In this work, the material properties of the FGM layers are assumed to obey the power-law distributions of the volume fractions of the constituents through the thickness, and the plate is divided into a number of finite rectangular layers, in which the trigonometric functions and Lagrange polynomials are used to interpolate the in- and out-of-plane variations of the field variables of each individual layer, respectively, and an h-refinement process is adopted to yield the convergent solutions. The accuracy and convergence of the RMVT-based FRLMs with various orders used for expansions of each field variables through the thickness are assessed by comparing their solutions with the exact 3D and accurate two-dimensional ones available in the literature.

• Advanced Composite Materials
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• 제16권1호
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• pp.63-81
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• 2007

Based on the Kirchhoff hypothesis of normal-remain-normal, the present work analyses piezoelectric laminated plates, wherein poled piezoelectric laminae are transversely isotropic and function as actuators. A quadric electric field is induced inside a piezoelectric lamina under a given applied voltage and mechanical bending. The governing equations for the piezoelectric laminated plate derived from the principle of virtual work in terms of the electric enthalpy have the same forms as those for a conventional composite laminated plate. We use rectangular sandwich plates of Al/PZT/Al and PZT/Al/PZT with four simply supported edges to demonstrate the prediction of the maximum bending stress in the PZT layer. The analytic solutions are verified by three-dimensional finite element analysis.

• Steel and Composite Structures
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• 제47권1호
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• pp.79-90
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• 2023

Nonlinear forced vibration properties of three-layered plates containing graphene platelets (GPL) filled skins and an auxetic core have been inquired within the present paper. Owning reduced weight as well as reduced stiffness, rectangle-shaped auxetic cores have been frequently made from novel techniques such as additive manufacturing. Here, the rectangle shape core is amplified via the graphene-filled layers knowing that the layers possess uniform and linear graphene gradations. The rectangle shape core has the equivalent material specifications pursuant to relative density value. The sandwich plate is formulated pursuant to Kirchhoff plate theory while a numerical trend has been represented to discretize the plate equations. Next, an analytical trend has been performed to establish the deflection-frequency plots. Large deflections, core density and GPL amplification have showed remarkable impacts on dynamic response of three-layered plates.

• Structural Engineering and Mechanics
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• 제43권2호
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• pp.253-271
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• 2012

To analyze the bending and transverse shear effects of laminated composite plates, a thirteen nodes triangular element will be presented. The suggested formulations consider a parabolic variation of the transverse shear strains through the thickness. As a result, there is no need to use shear correction coefficients in computing the shear stresses. The proposed element can model both thin and thick plates without any problems, such as shear locking and spurious modes. Moreover, the effectiveness of $w_{,n}$, as an independent degree of freedom, is concluded by the present study. To perform the accuracy tests, several examples will be solved. Numerical results for the orthotropic materials with different boundary conditions, shapes, number of layers, thickness ratios and fiber orientations will be presented. The suggested element calculates the deflections and stresses more accurate than those available in the literature.

• Computers and Concrete
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• 제32권5호
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• pp.439-454
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• 2023

In this article, the surface stress effects on the buckling analysis of the annular sandwich plate is developed. The proposed plate is composed of two face layers made of carbon nanotubes (CNT) reinforced composite with assuming of fully bonded to functionally graded porous core. The generalized rule of the mixture is employed to predict the mechanical properties of the microcomposite sandwich plate. The derived potentials energy based on higher order shear deformation theory (HSDT) and modified couple stress theory (MCST) is solved by employing the Ritz method. An exact analytical solution is presented to calculate the critical buckling loads of the annular sandwich plate. The predicted results are validated by carrying out the comparison studies for the buckling analysis of annular plates with those obtained by other analytical and finite element methods. The effects of various parameters such as material length scale parameter, core thickness to total thickness ratio (hc/h), surface elastic constants based on surface stress effect, various boundary condition and porosity distributions, size of the internal pores (e0), Skempton coefficient and elastic foundation on the critical buckling load have been studied. The results can be served as benchmark data for future works and also in the design of materials science, injunction high-pressure micropipe connections, nanotechnology, and smart systems.