Papers by Author: Hyo Jin Kim

Abstract: The spot welded structure operates in diverse climatic situations because of temperature, humidity and precipitation. In addition, factors of environmental pollution such as acid rain, that causes corrosion, have the tendency to increase. But spot welded structure strength is affected by dampness and environment temperature. Therefore, it is important to evaluate the effect of temperature of the spot welded part. In this study, the strength distribution of spot welded plates is evaluated for the environmental temperature of zinc coated steel plates and the test is conducted with the welded part immersed in distilled and synthetic sea water. Specimens are immersed into water for 10, 100, 500 and 1000hours to evaluate the effects of water immersion time on tensile-shear strength under the conditions of -40, 0, 20 and 50°C. Strength is evaluated by using the tensile-shear test. The conditions of spot welding are 240kgf electrode force, 10kA welding current with 0 and 5mm clearance. In this study, spot welded specimens with clearance have lower tensile-shear strength in the distilled water or synthetic sea water compared with spot welded specimens without clearance. And they have lower tensile-shear strength under -40°C and over 50°C.

Abstract: In recent years, the use of natural fibers as reinforcements in polymer composites to replace synthetic fibers like glass is presently receiving increasing attention. Because of their increasing use combined with high demand, the cost of thermosetting resin has increased rapidly over the past decades. However the widely used synthetic fillers such as glass fiber are very expensive compared to natural fibers. Natural fiber-reinforced thermosetting composites are more economized to produce than the original thermosetting. Moreover the use of natural fiber in thermosetting composites is highly beneficial, because the use of natural fibers will be increased. In this study, a bamboo fiber-reinforced thermoplastic composite that made the RTM was evaluated to mechanical properties.

Abstract: Steam generator began having severe problems 20 years ago. The main causes were wastage, wear, loose parts, denting. These problems were solved by changing the water chemistry treatment method. Therefore these damage types were replaced by stress corrosion cracking on the inner surface of the tubes and most recently by intergranular attack and stress corrosion cracking on the external surface of the tube. Steam generator has experienced various forms of damage, most involving some kind of corrosion. Some of these problems have been virtually eliminated, others are successfully managed, but a few have not yet been brought under control. This study is to evaluate the environmental effects on the susceptibility to stress corrosion cracking in Cr-Mo alloy under simulated crevice condition. The test is simulated by producing drop, wet and evaporation process. The XRF measurement is performed to investigate the amount and distribution of chromium carbide of grain boundaries. The tests are performed in the alkalic and acidic solution under various strain rates.