• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.9
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• pp.663-670
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• 2020

A study on mechanical property characterization and modeling technique was carried out to approximate the behaviour of structures with 2.5D C/SiC material. Several tensile tests were performed to analyze the behaviour characteristics of the 2.5D C/SiC material and elastic property was characterized by applying a mathematical homogenization and a modified rule of mixture. SiC matrix representing the elasto-plastic behavior approximates as a bilinear function. Then the equivalent yield strength and equivalent plastic stiffness were calculated by minimizing errors in experiment and approximation. RVE(Representative Volume Element)was defined from the fiber and matrix configuration of 2.5D C/SiC and a process of calculating the effective stiffness matrix by applying the modified rule of mixture to RVE was implemented in the ABAQUS User-defined subroutine. Finite element analysis was performed by applying the mechanical properties of fiber and matrix calculated based on the proposed process, and the results were in good agreement with the experimental results.

• Journal of Welding and Joining
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• v.26 no.5
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• pp.49-59
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• 2008

Hastelloy C-276, corrosion resistant alloy at high temperature, is used in chemical plant and power generation industry. In this study, process parameter of laser welding for welding property in Hastelloy C-276 using a continuous wave Nd:YAG laser was studied. As the result of experiment, laser welding did not show segregation or crack at heat affected zone compared to conventional GTWA welding. The melting zone showed cell dendritic structure along with welding line. In addition, planer front solidification is occurred from welding structure, and it was progressed to cellular solidification. Optimal process parameter for butt welding was 1.2kW and 2.0 m/min for laser power and welding speed, respectively. While heat input, output density, tensile stress, and longitudinal strain was $441.98{\times}103$ J/cm2, $29.553{\times}103$ W/cm2, 768 MPa, and 0.689, respectively. Lap welding of the same material showed greater discrepancy in tensile property during 1 line and 2 line welding. For 1 line welding, tensile stress was about 320 MPa, and 2 line showed slightly larger tensile stress. However, strain was decreased by 20%. From this result, lap welding of the same material, Hastelloy C-276, with 2 line welding is considered to be more effective process than 1 line welding with consideration of mechanical property.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.154-157
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• 2001

Through this study we investigated the causes of bottom crack. We then redesigned petaloid bottom to prevent bottom crack. We examined the material property variations according to the stretch ratio of PET and analyzed stretches of bottom in blowing processes. We also performed crack test to observe a crack phenomena. The effective stress and maximum principal stress were examined by computer simulation. We concluded that the bottom crack occurs because of not only insufficient strength of material due to the insufficient stretch of PET but also coarse design of petaloid shape. The highest maximum principal stress occurred at valley in petaloid bottom of bottle and this strongly affected the crack in bottom. We redesigned petaloid shape to minimize maximum principal stress, and this result in increasing the crack resistance.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.2
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• pp.96-99
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• 2012

We fabricated fully depleted (FD) SOI-based 1T-DRAM cells with planar channel or recessed channel and the electrical characteristics were investigated. In particular, the dependence of memory operating mode on the channel structure of 1T-DRAM cells was evaluated. As a result, the gate induced drain leakage current (GIDL) mode showed a better memory property for planar type 1T-DRAM. On the other hand, the impact ionization (II) mode is more effective for recessed type.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1991.10a
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• pp.33-36
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• 1991

For its outstanding magnetic property, preparations of MnZn ferrite were studied with various method. In this study, MnZn ferrite powders were prepared from ammonium oxalate and mixed metal sulfate by the controlled coprecipitation process. Considering to low dissolved each metal ion, high production yield and particle size, the established optimum reaction conditon by the statistical analysis of each results are that reaction temperature is $25^{\circ}C$, concentration of metal sulfate is 0.3M, molar ratio of ammonium oxalate/metal sulfate is 1.1:1. The effective experimental factor and characterization of the precipitated powder at optimum condition were studied.

• Computational Structural Engineering
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• v.9 no.1
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• pp.101-113
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• 1996

In this paper, the finite element formulation for the thermal analysis of quasi-static, uncoupled, homogeneous, isotropic and linear viscoelastic problems is presented based on the principle of virtual work. The viscoelastic material is assumed to be thermorheologically simple, which is well known material property in a large class of high polymers. The variational formulation and the finite element equation in matrix from are derived. Effective generation and storage of the hereditary stiffness matrices are given in detail especially for the case of the steady state temperature distribution T=T(x). Some numerical examples are given and compared with published results to show the versatility of the derived finite element formulations.

• Korean Journal of Materials Research
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• v.13 no.10
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• pp.658-662
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• 2003

In this study, we have tried to find the optimized design variables of the matching layer which is important part of thickness mode ultrasonic transducer and finally reach the conclusion that the electrical property of piezo-element must be under consideration when the optimized acoustic impedance is estimated. Proper expression of the effective impedance of front load at free resonant frequency(: $Z_{f}$ $^{(0)}$ /) has been induced by introducing the principle of binomial multilayer transformer and gradient based numerical method is utilized to find the most acceptable value of $Z_{ f}$/$^{(0)}$ . Optimized point of acoustic impedance can be calculated directly from $Z_{f}$ $^{(0)}$ using some simple formula which we propose. We also verify our result by both numerical and experimental method and get a good enhancement especially it concern to the bandwidth of ultrasonic transducer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.588-591
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• 2002

Radiation technology is an effective way for regulating polymeric materials to physicochemical and mechanical properties. The effect of radiation on mechanical and electrochemical properties of new rubber-like polymeric composite materials based on poly(vinyl ether of ethyleneglycol : PVEEG) have been studied for investigating mechanical and electric property of polymer composites applications.

• Journal of the Korea Safety Management & Science
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• v.16 no.4
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• pp.391-396
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• 2014

For the purpose of finding out the acoustical characteristics of exterior materials in bridge, analytical studies are performed with boundary elements method by using the commercial program SYSNOISE. Before analysis, to figure out material property, it was conducted experiments of absorption coefficient for absorptive material. And prediction of pressure were conducted I GIRDER type (before & after installation of absorption panel ) and BOX GIRDER type (before & after installation of absorption panel) The results show that when the absorption panel is installed, environment around bridge can help reduce traffic noise. It was proved to be the effective noise reduction counter-plan for a traffic noise in the bridges.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.11
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• pp.898-903
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• 2001

In this study, we investigated amounts, distributions and sizes of pores of multilayer piezoelectric transformer, and predicted heat emission property and electrical characteristics according to designs of internal electrode. Forming densities of device having MLC, fingered and full filled internal electrode structure were 4.73 g/㎤, 4.80 g/㎤, 4.82 g/㎤ and forming porosities were 17.3737%, 13.1475%, 12.6121%, respectively. And sintered densities of MLC structured, fingered and full filled devices were 7.76 g/㎤, 7.75 g/㎤, 7.84 g/㎤ and sintered porosities were 4.0967%, 2.7132%, 2.5317%, respectively. Therefore, we concluded that fingered and full fi1led internal electrode devices, expecially, fingered internal electrode devices had cost-effective effect and maximum poling effect due to higher sintered density and lower porosity than MLC structured device. Also we can predict that they have an effect on good heat emission and high output properties of multilayer piezoelectric transformer.