• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10a
• /
• pp.739-744
• /
• 2000

Concrete structures generally have cracks, so for the safety and durability of structures, studies to detect cracks using nondestructive tests have been treated in great deal. In order to assure the reliability of concrete structure, microscopic fracture behavior and internal damage progress of concrete under the loading should be fully understood. The purpose of this study predicts location of initial crack and measures direction of crack propagation for on-line monitoring before the crack really grows in structures by using two-dimensional Acoustic Emission(AE) source location based on rectangular method with three-point bending test. This will allow efficient maintenance of concrete structure through monitoring of internal cracking based on AE method.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.14 no.7
• /
• pp.533-538
• /
• 2001

The barrier height is found to increase from 0.25 to 0.690 eV for Schottky contacts on n-InGaAs using deposition of Ag on a substrate cooled to 77K(LT). Surface analysis leads to an interface model for the LT diode in which there are oxide compounds of In:O and As:O between the metal and semiconductor, leading to behavior as a metal-insulator-semiconductor diode. The metal film deposited t LT has a finer and more uniform structure, as revealed by scanning electron microscopy and in situ metal layer resistance measurement. This increased uniformity is an additional reason for the barrier height improvement. In contrast, the diodes formed at room temperature exhibit poorer performance due to an unpassivated surface and non-uniform metal coverage on a microscopic level.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2004.10a
• /
• pp.180-184
• /
• 2004

The tribological behavior of carbon epoxy composites whose surfaces have many small grooves of $100\mu m$ width was experimentally investigated with respect to the sliding direction against groove orientation, surface pressure (P) and velocity (V). The wear mechanism of the composites was observed to calculate the wear volume with respect to the friction coefficient using scanning electron microscopic (SEM). Experimental results show that the abrasive wear is dominant wear mechanism for the grooved composite surface and the friction and wear are greatly reduced when the sliding direction is parallel to the axis of groove because abrasive particles are removed through the grooves effectively.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.25 no.7
• /
• pp.759-766
• /
• 1988

the effect of heat treatment in oxygen ambient on the nucleation and growth of oxidation induced stacking faults(OSF) in n-type(100)silicon wafer has been investigated. The growth of OSF is determind as a function of oxygen concentration in silicon wafer, heat treatment time and temperature, and the activation energy for the growth of OSF can be obtained from the growth kinetics. The activation energies are respectively 2.66 eV for dry oxidation and 2.37 eV for wet oxidation. In this paper, we have also studied the structural feature of OSF with the comparison of optical microscopic morphology and crystalline structure.

• Journal of the Korean Society for Heat Treatment
• /
• v.9 no.2
• /
• pp.91-102
• /
• 1996

Microstructural control to produce multiphase structure has received much attention to improve the high temperature strength as well as low temperature ductility of intermetallics. Transmission electron microscopic investigation has been carried out concerning the effect of Cr-precipitation on the mechanical properties of B2-ordered NiAl containing 4 to 8 mol% of Cr. By aging at temperatures around 973 K after solution annealing, fine spherical precipitates took place homogeneously in the NiAl matrix and the alloys hardened appreciably. Selected area electron diffraction (SAED) patterns have not revealed any additional extra-spots during aging, because the Cr-particles show cube-cube orientation relationship and keep a perfect coherency with the ordered matrix lattice. Dislocations were confirmed to bypass the particles during deformation. Although the dispersion of Cr-particles increased the yield strength of NiAl at intermediate temperature, the strength decreased appreciably at higher temperatures.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
• /
• 2003.09a
• /
• pp.132-135
• /
• 2003

Solution chemistry, sorbate chemistry, and sorbent chemistry were widely investigated to find important factors that affect PAH sorption on mineral surfaces and to elucidate its microscopic mechanism. The solution chemistry, pH and ionic strength caused measurable change of HOC sorption reaction to minerals. The detectable change of Ka occurred at a pH region crossing the PZC (Point of Zero Charge) of each mineral. The PAH hydrophobicity, one of sorbate chemistry, was observed to have a strong correlation with PAM sorption to mineral. Mineral surface area was not found to be a predominant factor controlling PAH sorption. The mineral type might be more likely to play a crucial role in controlling the PAH sorption behavior. The CEC (Cation Exchange Capacity) of mineral, representing surface charge density, has meaningful correlation with regression slope of sorption coefficients (log $K_{d}$) versus aqueous activity coefficients (log Υ$_{w}$).).).

• Journal of Mechanical Science and Technology
• /
• v.18 no.3
• /
• pp.453-459
• /
• 2004

TiNi/ Al6061 shape memory alloy (SMA) composite was fabricated by hot press method to investigate the microstructure and mechanical properties. Interface bonding between TiNi reinforcement and A1 matrix was observed by using SEM and EDS. Pre-strain was imposed to generate compressive residual stress inside composite. A tensile test for specimen, which under-went pre-strain, was performed at high temperature to evaluate the variation of strength and the effect of pre-strain. It was shown that interfacial reactions occurred at the bonding between matrix and fiber, creating two inter-metallic layers. And yield stress increased with the amount of pre-strain. Acoustic Emission technique was also used to nondestructively clarify the microscopic damage behavior at high temperature and the effect of pre-strain of TiNi/ Al6061 SMA composite.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.7 s.178
• /
• pp.1833-1840
• /
• 2000

Commercially pure copper is tested to obtain creep curves at 2500C. Constitutive relations adopting continuum damage mechanics concept is found to be appropriate to model the creep defor mation up to the tertiary stage. Microscopic observation by SEM reveals that creep condition induces cavities and microcracks subsequently. The constitutive equations along with evaluated creep parameters are implemented into finite element analysis code. The analysis reproduces creep curves under step loading as well as constant loading with reasonable accuracy. Distribution and evolution of damage under creep loading are numerically simulated for two different types of notched specimen. Predicted creep life agrees quite well with rupture test results. The influence of mesh size at notch tip on rupture time prediction is studied, and a degree of refinement is suggested for the specific notched specimens.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.04b
• /
• pp.39-44
• /
• 1995

The gas nitro-carburizing treatment with the merits of carburizing and nitriding treatment is recently applied to transmission gears. the shafls of an engine oil pump and steering shafls. For all that, the researches of the gas nitro-carburizing treatment are short of the fatigue behavior and the evaluation of fatigue life. In this paer, it is examined for the effect of inclusions and hole defects with fatigue limit and the evaluation of the fatigue strengthaccording tothe hardness and resifualstress with the specimen of a notro-carburizing treatment.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.14 no.5
• /
• pp.49-54
• /
• 2005

An experimental Investigation was performed to study the characteristics of Electro-Rheological fluid flow in a horizontal rectangular tube with or without D.C electric field control. First, the microscopic behavior of the ER suspension structure between rectangular tube brass electrodes for the stationary ER nut(i and flow of the ER fluid was investigated by flow visualization. The flow of the ER fluid between fluid rectangular tube was solved experimental using the constitutive equation for a Bingham fluid. ER fluid is made silicon oil mixed with $0.2wt\%$ starch having hydrous particles. Velocity distributions of the ER fluids were obtained by particle image velocimetry measuring those of the clusters using an image processing technique.