• Composites Research
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• v.33 no.6
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• pp.408-414
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• 2020

The present engineering sector focused on the sandwich composites and almost covered all engineering fields because of decent mechanical properties with a lightweight structure. It mainly consists of high strength fiber skin and porous structure core like corrugated, honeycomb, balsa wood, and foams which is playing a pivotal role in weight reduction. Recently researchers attention grabbed by Natural fiber sandwich composites due to biodegradability, renewable, low-cost, and environmentally friendly. However special focus is highly needed towards the flammability behavior of natural fibers used as reinforcement for composites. Herein, for the first time, the flame retardant natural fiber sandwich composite was fabricated by using flame retardant treated bamboo fabric and vinyl ester via the VARTM process. The impact of flame retardant treated bamboo fabric on mechanical and flame retardant properties were studied. The results concluded that the fabricated bamboo sandwich composites show structurally lightweight with significant mechanical strength and feasibility with respect to the flame.

• Structural Engineering and Mechanics
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• v.88 no.1
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• pp.1-12
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• 2023

In this study, forced vibration behavior of a piezo magneto electric sandwich Timoshenko beam is investigated. It is assumed a sandwich beam with porous core and graphene platelet reinforced composite (GPLRC) in facesheets subjected to magneto-electro-elastic and temperature-dependent material properties. The magneto electro platelets are under linear function along with the thickness that includes a cosine function and magnetic and electric constant potentials. The governing equations of motion are derived using modified strain gradient theory for microstructures. The effects of material length scale parameters, temperature change, different distributions of porous, various patterns of graphene platelets, and the core to face sheets thickness ratio on the natural frequency and excited frequency of a sandwich Timoshenko beam are scrutinized. Various size-dependent methods effects such as MSGT, MCST, and CT on the natural frequency is considered. Moreover, the final results affirm that the increase in porosity coefficient and volume fractions lead to an increase in the amount of natural frequency; while vice versa for the increment in the aspect ratio. From forced vibration analysis, it is understood that by increasing the values of volume fraction and the length thickness of GPL, the maximum deflection of a sandwich beam decreases. Also, it is concluded that increasing the temperature, the thickness of GPL, and the initial force leads to a decrease in the maximum deflection of GPL. It is also shown that resonance phenomenon occurs when the natural and excitation frequencies become equal to each other. Outcomes also reveal that the third natural frequency owns the minimum value of both deflection and frequency ratio and the first natural frequency has the maximum.

• Steel and Composite Structures
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• v.35 no.5
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• pp.659-670
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• 2020

This paper proposes the use of a porous core between layers of laminated composite plates to examine its effect on the natural frequencies of the resulted porous laminated composite sandwich plate (PLCSP) resting on a two-parameter elastic foundation. Moreover, it has been suggested that the dispersion of porosity has two different functionally graded (FG) patterns which are compared with a uniformly dispersed (UD) profile to find their best vibrational efficiency in the proposed PLCSPs. In FG patterns, two types of dispersions, including symmetric (FG-S) and asymmetric (FG-A) patterns have been considered. To derive the governing Eigen value equation of such structures, the first order shear deformation theory (FSDT) of plates has been employed. Accordingly, a finite element method (FEM) is developed to solve the derived Eigen value equation. Using the mentioned theory and method, the effects of porosity parameters, fiber orientation of laminated composite, geometrical dimensions, boundary conditions and elastic foundation on the natural frequencies of the proposed PLCSPs have been studied. It is observed that embedding porosity in core layer leads to a significant improvement in the natural frequencies of PLCSPs. Moreover, the natural frequencies of PLCSPs with FG porous core are higher than those with UD porous core.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.55-58
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• 2005

The present study aims to design electrically and structurally effective antenna structures in order that the structural surface itself could become the antenna. The basic design concept is composite sandwich structure in which microstrip antenna is embedded and this is termed composite smart structure (CSS). The most important outstanding problem is that composite materials of structural function cannot be used without reducing antenna efficiency. Unfortunately, such materials have high electrical loss. This is a significant design problem that needs to be solved in practical applications. Therefore, the effects of composites facesheet on antenna performances are investigated in the first stage and changes in the gain of microstrip antenna due to composites facesheet have been determined. ‘Open condition’ is defined when gain is maximized and is a significant new concept for the design of high-gain antennas considering bandwidth in practical application. The open condition can be made with the outer facesheet by controlling its position. In the design of CSS, glass/epoxy composites and Nomex honeycomb were used with exploiting open condition. Experiments, confirm that the gain is improved and the bandwidth is also as wide as specified in our requirements. With the open condition, wideband antenna can be integrated with mechanical structures without reducing any electrical performances, as confirmed experimentally here.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.2
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• pp.200-209
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• 2011

An analytical solution for rectangular laminated composite plates was obtained via a formal asymptotic method. From threedimensional static equilibrium equations, the microscopic one-dimensional and macroscopic two-dimensional equations were systematically derived by scaling of the thickness coordinate with respect to the characteristic length of the plate. The onedimensional through-the-thickness analysis was performed by applying a standard finite element method. The derived twodimensional plate equations, which take the form of recursive equations, were solved under sinusoidal loading with simplysupported boundary conditions. To demonstrate the validity and accuracy of the present method, various types of composite plates were studied, such as cross-ply, anti-symmetric angle-ply and sandwich plates. The results obtained were compared to those of the classical laminated plate theory, the first-order shear deformation theory and the three-dimensional elasticity. In the present analysis, the characteristic length of each composite was dependent upon the layup configurations, which affected the convergence rate of the method. The results shown herein are promising that it can serve as an efficient tool for the analysis and design of laminated composite plates.

• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.4
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• pp.30-37
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• 2015

iFLASH System is new structural floor system which consists of sandwich panels filled with nano-composite. The nano-composite has low specific gravity and high bonding strength with steel plates. The bonding strength is one of important factors for structural performance of iFLASH System and it can further be improved by surface preparation such as blast metal cleaning. However, using none blast steel plates is recommended since surface preparation generates additional fabrication time and cost. In this study, a bonding strength test and bending experiment were conducted to check feasibility of applying none blast steel plates to iFLASH System. Moreover, stress in bonding plane between steel plates and nano-composite was analytically evaluated by finite element method. Consequently, flexural capacity of the specimen was 11% higher than theoretically calibrated value and its flexural behavior was structurally efficient without defect of bonding.

• Composites Research
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• v.24 no.3
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• pp.25-30
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• 2011

The studies on the non-destructive testing methods of the composite materials are very important for improving their reliability and safety. AE(Acoustic Emission) can evaluate the defects by detecting the emitting strain energy when elastic waves are generated by the generation and growth of a crack, plastic deformation, fiber breakage, matrix cleavage or delamination. In this paper, the AE signals of the filament wound composite cylinder and sandwich cylinder during the pressure test were measured and analyzed. The signal characteristics of PVDF sensors were measured, and an AE signal analyzer which had the band-pass filter and L-C resonance filter were designed and fabricated. Also, the crack detection capability of the fabricated AE signal analyzer wes evaluated during the pressure tests of the filament wound composite cylinder and the sandwich cylinder.

• Structural Engineering and Mechanics
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• v.65 no.6
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• pp.657-678
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• 2018

Sandwich structures are well known for their use in aircraft, naval and automobile industries due to their high strength resistance with light weight and high energy absorption capability. Sandwich beams with soft core are very common and simple structures that are employed in day to day general use appliances. Modeling and analysis of sandwich structures is not straight forward due to the interactions between core and face sheets. In this paper, formulation of Super Convergent finite elements for analysis of the sandwich beams with soft core based on Euler Bernoulli beam theory are presented. Two elements, Eul4d with 4 degrees of freedom assuming rigid core in transverse direction and Eul10d with 10 degrees of freedom assuming the flexible core were developed are presented. The formulation considers the top, bottom face sheets and core as separate entities and are coupled by beam kinematics. The performance of these elements are validated by results available in the published literature. Number of studies are performed using the formulated elements in static, free vibration and wave propagation analysis involving various boundary and loading conditions. The paper highlights the advantages of the elements developed over the traditional elements for modeling of sandwich beams and, in particular wave propagation analysis.

• Steel and Composite Structures
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• v.28 no.5
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• pp.541-557
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• 2018

This paper presents the influence of carbon nanotubes (CNTs) waviness and aspect ratio on the vibrational behavior of functionally graded nanocomposite sandwich annular sector plates resting on two-parameter elastic foundations. The carbon nanotube-reinforced (CNTR) sandwich plate has smooth variation of CNT fraction along the thickness direction. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness and their mechanical properties are estimated by an extended rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. Effects of CNT distribution, volume fraction, aspect ratio and waviness, and also effects of Pasternak's elastic foundation coefficients, sandwich plate thickness, face sheets thickness and plate aspect ratio are investigated on the free vibration of the sandwich plates with wavy CNT-reinforced face sheets. The study is carried out based on three-dimensional theory of elasticity and in contrary to two-dimensional theories, such as classical, the first- and the higher-order shear deformation plate theories, this approach does not neglect transverse normal deformations. The sandwich annular sector plate is assumed to be simply supported in the radial edges while any arbitrary boundary conditions are applied to the other two circular edges including simply supported, clamped and free.

• Structural Engineering and Mechanics
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• v.67 no.6
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• pp.565-578
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• 2018

This research article reported the nonlinear finite solutions of the nonlinear flexural strength and stress behaviour of nano sandwich graded structural shell panel under the combined thermomechanical loading. The nanotube sandwich structural model is derived mathematically using the higher-order displacement polynomial including the full geometrical nonlinear strain-displacement equations via Green-Lagrange relations. The face sheets of the sandwich panel are assumed to be carbon nanotube-reinforced polymer composite with temperature dependent material properties. Additionally, the numerical model included different types of nanotube distribution patterns for the sandwich face sheets for the sake of variable strength. The required equilibrium equation of the graded carbon nanotube sandwich structural panel is derived by minimizing the total potential energy expression. The energy expression is further solved to obtain the deflection values (linear and nonlinear) via the direct iterative method in conjunction with finite element steps. A computer code is prepared (MATLAB environment) based on the current higher-order nonlinear model for the numerical analysis purpose. The stability of the numerical solution and the validity are verified by comparing the published deflection and stress values. Finally, the nonlinear model is utilized to explore the deflection and the stresses of the nanotube-reinforced (volume fraction and distribution patterns of carbon nanotube) sandwich structure (different core to face thickness ratios) for the variable type of structural parameter (thickness ratio, aspect ratio, geometrical configurations, constraints at the edges and curvature ratio) and unlike temperature loading.