• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.402-407
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• 1995

The effects of room temperature and strain aging treatment are discussed on the critical condition for the onset of growth of non-propagating cracks on 0.15% C low carbon steel, with special emphasis on the length of the critical non-propagating crack and on the crack opening displacement(COD) at the crack tip. It is found from the experimental analysis that room temperature and strain aging of a fatigue pre-cracked specimen introduced the closure of a crack tip of the pre-crack and the reduction of crack opening displacement at the wake of crack, together with an improvement in crack growth resistance of the microstructure. This may cause an increase in the endurance limit of the specimen, through the enhancement of effective stress for the onset of growth of the critical non-propagating crack.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1030-1035
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• 2003

The nanoimprint lithography technology makes higher density of semiconductor device and larger capacity of storage media. In this technology the induced damage while detaching polymer pattern from mold should be minimized. In order to analyze the problem, the basic knowledge of adhesion between the polymer and the mold is required. In this study a contact experiment of polyisobutylene specimen with spherical steel tip and polyisobutylene bead tip was conducted using nano indenter. During the contact experiment with various loading rate under load control the contact behavior of viscoelastic material was measured, i.e., the load and displacement between the tip and the specimen were measured. The data was analyzed by HBK model to obtain the stress intensity factor of contact edge and the contact radius as a function of time. Also the adhesion energies between steel/polyisobutylene and polyisobutylene/polyisobutylene were obtained employing the analysis of the crack of viscoelastic material by Schapery.

• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.3
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• pp.232-238
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• 1982

The behavior of corner crack propagation by unidirectional plane bending fatigue was investigated in the butt welded joints of SS41 and SM50 steel plates including an edge through-thickness notch. The properties of fatigue crack propagation were inspected in the weld metal, heat-affected zone, and base metal of the welded joints. Main results obtained are as follows; (1) When a plate with an edge through-thickness notch is loaded by plane bending fatigue in indirection, the 2 variant corner cracks on the upper and lower edge of the plate are initiated and propagated respectively from the notch. (2) In case of a specimen containing a corner crack, it is more reasonable to estimate the crack propagation rate by area of fracture surface than by crack surface length. (3) The rate of fatigue crack propagation becomes faster in the following order; weld metal, heat-affected zone, and base metal. (4) The specimen including reinforcement shape is rapidly failed throughout bond due to effect of its shape when the repeated load exceeds a certain cycle.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.10a
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• pp.124-125
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• 2016

The various size and shape of cracks in concrete induce deterioration of reinforced concrete structures including nuclear power plants. The wider and deeper the crack is, the concrete structures are more vulnerable to carbonization. Thus, it is essential to develop a reliable measurement technique of cracks inside concrete. In this study, an ultrasonic test method is applied to the crack measurements. The results can be used for evaluation of existing reinforced concrete structures.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.4 no.4
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• pp.42-49
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• 1995

It is not clearly known how defects or inclusions of a low carbon steel affect a fatigue strength. We study this issue using SM15C materials. The investigation is carried out by a quantitative evaluation, and experimental findings are: (1) a fatigue limit of A series smooth specimen is 205MPa, and that of B, C, D series is 245MPa, 304MPa and 245MPa, respectively. (2) the fatigue limit varies with respects to the stress distribution I the vicinity of a defects and crack. (3) the micro hole creates a half-circular shape crack, while the hole depth is not critical to the fatigue strength, (4) considering the fatigue strength, the hole diameter is more significant than the hole depth, and (5) Fatigue limit of artificially defected specimen is lower than that of a flawless one (5-10%), however, there exist allowance size and depth of defect which don't get to influence at fatigue limit.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.3
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• pp.175-183
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• 1994

The effect of batch annealing conditions and austenitizing temperatures on the hardness and microstructural factors were examined by using 420J2 martensitic stainless steel. In spite of the similler hardness after batch annealing, the difference in hardness at the same austenitizing temperature was caused by changes in dissolved carbon during batch annealing. The highest hardness of the specimen was obtained at the batch annealing temperature of $820^{\circ}C$ and austenitizing temperature of $1050^{\circ}C$. The main factor affecting the final hardness of the cold annealed 420J2 specimen was proved to the austenitizing temperature rather than batch annealing temperature.

• Journal of the Korean Society for Heat Treatment
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• v.5 no.1
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• pp.23-31
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• 1992

It is investigated that Fe-C-N compound layer, defusion layer, and induction hardened layer produced by nitrocarburizing blend heat treatment in austenitic temperature with high frequency induction heating of mild steel specimen sprayed sursulf salt-bath. As the temperature of blend-heat treatment got increased, the thickness and hardness of compound layer and diffusion layer were increased. Compound layer(max. $35{\mu}m$), diffusion layer (max. 2.5mm) and induction hardened layer were gained in the shortest time 10 sec and in the case of $1000^{\circ}C$ total hardness depth of those was about 3.5mm. When the blend-heat treated specimen was reheated, maximum hardness of compound layer was dropped more than that of the reheated compound layer after sursulf treated, whereas hardness of diffusion layer was increased.

• Journal of Welding and Joining
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• v.23 no.4
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• pp.48-52
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• 2005

To estimate welding deformation for large steel structures, either experiment result with small specimen or analysis result of FEM with small numerical model is used. Consequently, it is important to decide the welding length of specimen and numerical model not to have an effect on welding deformation for accurate estimation of whole welding deformation. This study experimentally clarifies the effect of welding length on angular distortion due to welding by varying welding length of specimens, but fixing width and thickness of specimens on V-groove butt welding, fillet welding and bead on plate welding. As a resell the critical welding length on fillet welding and on bead on plate welding is over 500mm and on V-groove butt welding is over 1,000mm.

• Journal of Powder Materials
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• v.9 no.4
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• pp.218-226
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• 2002

The purpose of the present study is to investigate the influence of thermal debinding and sintering conditions on the sintering behavior and mechanical properties of PIMed 316L stainless steel. The water atomized powders were mixed with multi-component wax-base binder system, injection molded into flat tensile specimens. Binder was removed by solvent immersion method followed by thermal debinding, which was carried out in air and hydrogen atmospheres. Sintering was done in hydrogen for 1 hour at temperatures ranging from 1000℃ to 1350℃ The weight loss, residual carbon and oxygen contents were monitored at each stage of debinding and sintering processes. Tensile properties of the sintered specimen varied depending on the densification and the characteristics of the grain boundaries, which includes the pore morphology and residual oxides at the boundaries. The sinter density, tensile strength (UTS), and elongation to fracture of the optimized specimen were 95%, 540 MPa, and 53%, respectively.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.05a
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• pp.86-87
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• 2015

An active study on UHPC, which has been recently used in high-rise building and bridges, is in progress. However, research on bonding shear strength of UHPC is required to be studied due to the lack of information. In this study, experimental research progress for bonding shear strength (shear strength of adhesive surface) evaluation of UHPC (Ultra High Performance Concrete) is proceeded. First, specimens that surface treatment methods of concrete bonded section and retardation time of placement are considered are produced. Second, Direct Shear test is applied on concrete bonded section of UHPC. As a result of this study, the highest bonding shear strength specimen in which compared to the non-retardation time specimen is compaction turbulence treatment. From later study, it is judged that strength of UHPC in accordance with direction of steel fiber when steel fiber of UHPC is mixed.