• Steel and Composite Structures
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• v.24 no.5
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• pp.603-613
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• 2017

In this research, the free vibration response of laminated composite plates is investigated using a novel and simple higher order shear deformation plate theory. The model considers a non-linear distribution of the transverse shear strains, and verifies the zero traction boundary conditions on the surfaces of the plate without introducing shear correction coefficient. The developed kinematic uses undetermined integral terms with only four unknowns. Equations of motion are obtained from the Hamilton's principle and the Navier method is used to determine the closed-form solutions of antisymmetric cross-ply and angle-ply laminates. Numerical examples studied using the present formulation is compared with three-dimensional elasticity solutions and those calculated using the first-order and the other higher-order theories. It can be concluded that the present model is not only accurate but also efficient and simple in studying the free vibration response of laminated composite plates.

• Journal of Korea Foundry Society
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• v.14 no.5
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• pp.419-428
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• 1994

The microvickers hardness and microstructure of Fe/Al composite fabricated by squeeze casting method were investigated. Pure Al and A356 Alloy were chosen for the matrix composition and Fe preform was fabricated with sintered Fe powder at $1000^{\circ}C$ for 30min. under hydrogen atmosphere. Experimental variables were included preheating temperature, melt temperature and applied pressure. Analysing the experimental result concerning microstructure of fabricated composites, Fe/A356 composite showed improved microstructure at $600^{\circ}C$ melt temperature and $350^{\circ}C$ preform preheating temperature in Fe distribution and Infiltrated distance. The results of EDX and XRD showed that the interfacial zones of Fe/Al composite were composed of non-equilibrium intermetallic layers[$(Al_5Fe_2)_x$, $Al_{13}Fe_4m\;Fe_3Al$, FeAl]. The microvickers hardness of Fe/Al composite showed higher value than Fe/A356 composite in interface.

• Journal of Powder Materials
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• v.2 no.3
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• pp.238-246
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• 1995

The purpose of this study is to establish powder metallurgy (P/M) fabrication processes for high performance 2XXX Al composites reinforced with SiC whiskers. Rapidly solidified 2XXX Al powders produced by commercial atomization technique were mixed with SiC whiskers. The results of mixing processes indicated that fluidized zone mixing technique was considerably effective for the large scale production of the mixture of Al powders and whiskers. In order to consolidate these $Al-SiC_w$ mixtures into $Al-SiC_w$ composite billets, a vacuum hot press was set up, and hot processing variables were investigated. Using the hot pressing temperature of $620^{\circ}C$ under the pressure of 50 MPa, good quality $Al-SiC_w$ composite billets having relatively homogeneous microstructure and sound Al/sic interfacial bonding were obtained. Composite billets were then extruded to bars having relatively homogeneous microstructures at the extrusion temperature of 450~500$^{\circ}C$ under the extrusion pressure of 700~ 1000 MPa. Mechanical properties of the extruded bars were found to be comparable with those of the composite processed by Advanced Composite Materials Corp. To improve mechanical properties of the composites, elimination of coarse intermetallic compounds, uniform distribution of reinforcements, and minimization of whisker breakage are suggested.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.39-45
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• 2002

In this paper, a finite element formulation was introduced for the three-dimensional cure simulation of composite structures. Based on the formulation, a three-dimensional finite element code was developed. Numerical examples found in the literatures were solved for code verification. Results from the present analyses agreed well with the measured cure-induced temperatures. Unlike in one or two dimensional analysis, temperature and degree of cure were able to be calculated at any point within composite structures in the present analysis. The finite element program can be used for the cure simulation of composite structures with arbitrary geometry under non-uniform autoclave temperature distribution.

• Journal of Korea Foundry Society
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• v.28 no.6
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• pp.261-267
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• 2008

In-situ quasicrystalline icosahedral (I) phase reinforced Ti-based bulk metallic glass (BMG) matrix composites have been successfully fabricated by using two distinct thermal histories for BMG forming alloy. The BMG composite containing micron-scale Iphase has been introduced by controlling cooling rate during solidification, whereas nano-scale I-phase reinforced BMG composite has been produced by partial crystallization of BMG. For mechanical properties, micron-scale I-phase distributed BMG composite exhibited lower strength and plasticity compared to the monolithic BMG. On the other hand, nano-scale icosahedral phase embedded BMG composite showed enhanced strength and plasticity. These improved mechanical properties were attributed to the multiplication of shear bands and blocking of the shear band propagation in terms of isolation and homogeneous distribution of nanosize icosahdral phases in the glassy matrix, followed by stabilizing the mechanical and deformation instabilities.

• Composites Research
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• v.28 no.4
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• pp.204-211
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• 2015

This paper presents a theory related to a two-dimensional linear cross-sectional analysis, recovery relationship and a one-dimensional nonlinear beam analysis for composite wing structure with initial twist. Using VABS including a related theory, the design process of the composite rotor blade has been described. Cross-sectional analysis was performed at cutting point including all the details of geometry and material. Stiffness matrix and mass matrix were linked to each section to make 1D beam model. The 3D strain distributions within the structure were recovered based on the global behavior of the 1D beam analysis and visualize numerical results.

• Journal of the Optical Society of Korea
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• v.11 no.2
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• pp.76-81
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• 2007

The compound refractive X-ray lens (CRL) for focusing hard X-rays is investigated to determine the parameters such as the focal length, the focal spot size, and spatial distribution at the focal spot using a simple theoretical calculations and CRLs fabricated by the self-assembly method. The number of individual compound lenses are defined for the given focal length of 1 m. The X-ray energy of 1 to 40 keV is used in the calculations. The CRL for focusing hard X-rays which generated from the X-ray tube is fabricated by nanoparticle-polymer composite in the form of circular concaves. The self-assembly method is applied to form the nanoaluminum-poly (methly meth-acrylate) composite and carbon-polymer composite CRL lenses. Aluminum nanoparticles of 100 nm and carbon microparticles are diffused in the polymer solution then the high gravity up to 6000G is applied in it to form the concave lens shape. X-ray energy at 8 keV is used for characterization of the composite CRLs. The FWHM of intensity for the fabricated nanoaluminium composite CRL system, N=10 is measured as 1.8 mm, which would give about $70{\mu}m$ in FWHM at 1 m of the focal length.

• Steel and Composite Structures
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• v.19 no.2
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• pp.405-416
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• 2015

We proposed the concept of nominal rigidity of a long-span V-shaped rigid frame composite arch bridge, analyzed the effects of structural parameters on nominal rigidity, and derived a theoretical nominal rigidity equation. In addition, we discussed the selection of the arch-to-beam rigidity ratio and its effect on the distribution of internal forces, and analyzed the influence of the ratio on the internal forces. We determined the delimitation value between rigid arch-flexible beam and flexible arch-rigid beam. We summarized the nominal rigidity and arch to beam rigidity ratios of existing bridges. The results show that (1) rigid arch-flexible beam and flexible arch-rigid beam can be defined by the arch-to-beam rigidity ratio; (2) nominal rigidities have no obvious differences among the continuous rigid frame composite arch bridge, V-shaped rigid frame bridge, and arch bridge, which shows that nominal rigidity can reflect the global stiffness of a structure.

• Steel and Composite Structures
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• v.39 no.2
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• pp.149-158
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• 2021

In this research paper, the free vibrational response of laminated composite plates is investigated using a non-polynomial refined shear deformation theory (NP-RSDT). The most interesting feature of this theory is the parabolic distribution of transverse shear deformations while ensuring the conditions of nullity of shear stresses at the free surfaces of the plate without requiring the Shear correction factor "Ks". A fourth-nodded isoparametric element with four degrees of freedom per node is employed for laminated composite plates. The numerical analysis of simply supported square anti-symmetric cross-ply and angle-ply laminated plate is carried out using a special discretization based on four-node finite element method which four degrees of freedom per node. Several numerical results are presented to show the effect of the coupling parameters of the plate such as the modulus ratios, the thickness ratio and the plate layers number on adimensional eigen frequencies. All numerical results presented using the current finite element method (FEM) is presented in 3D curve form.

• International journal of steel structures
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• v.18 no.4
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• pp.1177-1190
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• 2018

This study presents an analytical framework for estimating the thermo-mechanical behavior of a composite beam exposed to fire. The framework involves: a fire simulation from which the evolution of temperature on the structure surface is obtained; data transfer by an interface model, whereby the surface temperature is assigned to the finite element model of the structure for thermo-mechanical analysis; and nonlinear thermo-mechanical analysis for predicting the structural response under high temperatures. We use a plastic-damage model for calculating the response of concrete slabs, and propose a method to determine the stiffness degradation parameter of the plastic-damage model by a nonlinear regression of concrete cylinder test data. To validate simulation results, structural fire experiments have been performed on a real-scale steel-concrete composite beam using the fire load prescribed by ASTM E119 standard fire curve. The calculated evolution of deflection at the center of the beam shows good agreement with experimental results. The local test results as well as the effective plastic strain distribution and section rotation of the composite beam at elevated temperatures are also investigated.