• Structural Engineering and Mechanics
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• v.16 no.5
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• pp.519-531
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• 2003

Piezoelectric actuators have long been recognised for use in aerospace structures for control of structural shape. This paper looks at active control of the swept shock wave/turbulent boundary layer interaction using smart flap actuators. The actuators are manufactured by bonding piezoelectric material to an inert substrate to control the bleed/suction rate through a plenum chamber. The cavity provides communication of signals across the shock, allowing rapid thickening of the boundary layer approaching the shock, which splits into a series of weaker shocks forming a lambda shock foot, reducing wave drag. Active control allows optimum control of the interaction, as it would be capable of positioning the control region around the original shock position and unimorph tip deflection, hence mass transfer rates. The actuators are modelled using classical composite material mechanics theory, as well as a finite element-modelling program (ANSYS 5.7).

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.3 s.73
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• pp.247-258
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• 2006

For the perforated cylindrical shell submerged in fluid, it is almost impossible to develop a finite element model due to the necessity of the fine meshing of the shell and the fluid at the same time. This necessitates the use of solid shell with equivalent material properties. Unfortunately the effective elastic constants are not found in any references even though the ASME code is suggesting those for perforated plate. Therefore in this study the equivalent material properties of perforated shell are suggested by performing several finite element analyses with respect to the ligament efficiencies.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.309-309
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• 2009

In-Ga-Zn-O (IGZO) has drawn much attention as a compatible material for transparent thin film transistors (TTFT) channel layer due to its high mobility and optical transparency at low processing temperatures. In this work, we investigated the effect of oxygen ambient on structural, electrical and optical properties of amorphous In-Ga-Zn-O (IGZO) thin films by using pulsed laser deposition (PLD). The films were deposited at various oxygen pressures and the structural, electrical and optical properties were investigated. X-ray diffraction (XRD) analysis showed that amorphous IGZO films were grown at all oxygen pressures. The surface morphology and optical properties with various oxygen pressures were studied by field emission scanning electron microscopy (FE-SEM) and UV-VIS spectroscopy, respectively. The grain boundary was observed more apparently and the calculated optical band gap became larger as oxygen pressure increased. To examine the electrical properties, Hall-effect measurements were carried out. The films showed high mobility.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.343-351
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• 1998

This paper was investigated degradation of the fracture toughness caused by sensitizing heat-treatment of the cryogenic structural material JN1 base metal using unloading compliance method reported as useful a method in evaluating the elastic-plastic fracture toughness at cryogenic temperature. The specimens used in this paper were 20% side-grooved 0.5T-CT specimens which were machined in the JN1 base metal. Also, to investigate cryogenic fracture toughness of the fusion line region in the JN1 GTA weldments, it was also used 20% side-grooved 0.5T-CT specimens that was machined fusion line to located in the middle of the specimen. The cryogenic fracture toughness values of the JN1 base metal were significantly decreased with increasing the time and temperature of the heat treatment. The fracture toughness value obtained from the fusion line specimen was invalid, but it was lower value than that of the JN1 base metal. Especially, this value was approximately equal with that obtained from the JN1 650.deg. C-5h heat-treated material.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.2_2
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• pp.289-299
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• 2020

The composition of convergence cross-section of the material is a technique that provides reasonable design and construction of structures. It is frequently used in medium-sized bridges and architectural structures. However, the structural behavioral spare capacity enhancement of the structure by the application of the convergence cross-section is still limited by the expandability due to the limiting state of each material. In order to overcome these limitations, this study reasonably analyzed the construction stages before and after the convergence cross-section constructed and developed a technique for forming multi-point boundary conditions using struts, which are compression members. Based on the existing cases, a reasonable construction step for forming the material composite section of the entire structural system of the structure was derived, and a numerical analysis model for a specific part was constructed to analyze the behavior of the strut application. As a result of this study, the effect of reducing the sectional force of 7.40% in beam-column joint and 6.31% in the center of girder was derived, and the deflection, which is a measure of the serviceability of the structure, improved by 54.41% from the installation and dismantling of strut members at each construction stage.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.4
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• pp.52-59
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• 2012

The subframe has been generally manufactured by using stamped steel material. Recently, automotive designers are considering aluminum as lightweight material. This paper describes the development process of an aluminum subframe which is made by high level vacuum die casting process, which is beneficial for minimizing gas contents and material properties. The weight of manufactured subframe is reduced by 4kg with the comparison of steel subframe. The aluminum subframe is packaged for the current vehicle layout and the imposed requirement is to attain a better structural performance that is evaluated in terms of mounting stiffness, noise and vibration, and endurance performance. The NVH evaluation results show that sound level is decreased by 8dB with the help of high roll-rod mounting stiffness as well as high structural modes.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.4
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• pp.33-38
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• 2012

Sandwich composite panel with high strength steel face can reduce the weight of the automotive structural parts. Unlike the parts in aerospace application, the automotive parts are made by the forming process for mass production. The CAE simulation can predict the failures caused by forces and deformation during the forming process. Since the material properties are very important factor for the simulation, we performed the tensile test to get the material properties. The inspections by the optical microscope at each strain level show the states of the polymer resin. The material properties measured by the tensile tests are used for the input data of simulation. The simulation predicts the forming process of the bumper back beam very exactly compared with the try out results.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.4
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• pp.118-125
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• 2009

Bumper is designed to protect the automotive frame without damage at low velocity. Expanded polypropylene (EPP) foam is used in the bumper as an energy absorbing material. In order to exactly predict the energy absorbing performance of the foam material under impact loading condition, it is important to use high strain rate material properties. In this study, a new apparatus for dynamic compression tests was developed to investigate the high strain rate behavior of EPP foams. Three kinds of EPP foams which have different expansion ratios were tested to investigate the quasi-static and dynamic compression behavior. Quasi-static compressions were performed at low strain rates of 0.001/s, 0.1/s and 1/s. The dynamic compressions were carried out at high strain rates of 50/s and 100/s with the developed apparatus. It was observed that the EPP foam has significant strain rate effect as compared to quasi-static behavior.

• Structural Engineering and Mechanics
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• v.6 no.6
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• pp.659-671
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• 1998

Exercise of complete control on all aspects of any manufacturing / fabrication process is very difficult, leading to uncertainties in the material properties and geometric dimensions of structural components. This is especially true for laminated composites because of the large number of parameters associated with its fabrication. When the basic parameters like elastic modulus, density and Poisson's ratio are random, the derived response characteristics such as deflections, natural frequencies, buckling loads, stresses and strains are also random, being functions of the basic random system parameters. In this study the basic elastic properties of a composite lamina are assumed to be independent random variables. Perturbation formulation is used to model the random parameters assuming the dispersions small compared to the mean values. The system equations are analyzed to obtain the mean and the variance of the plate natural frequencies. Several application problems of free vibration analysis of composite plates, employing the proposed method are discussed. The analysis indicates that, at times it may be important to include the effect of randomness in material properties of composite laminates.

• Computational Structural Engineering
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• v.8 no.2
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• pp.115-121
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• 1995

The object of this study is to propose a rational method of resistance strength and flexural deformation for structures using high strength concrete(400-700kgf/cm/sup 2/). The material property(stress-strain relationship) is to be modelize using regression analysis of experimental result. And the applicability of trapezoidal stress model is to be verified. An analytical method is used by the moment-curvature relationship which is based on stress-strain relationships of material for discreted element of section. The evaluation method of moment-curvature of high strength concrete structures is also proposed by using the Monte Carlo Simulation based on a probabilistic concept that could minimize an error due to iterated calculations and random variable of material properties.