Recently, weight lightening is a key issue for various mechanical components to improve the fuel efficiency. For this reason, many researchers have been studying focused on the development of surface hardening treatment and metallic materials with high strength and wear resistance. In this study, we examine the formation of carbide at the surface of the gear machined by SCM420H steel after super-carburizing in order to improve the wear resistance of gear. The experimental results show that super-carburizing heat treatment gives rise to carbide dispersion across wider range of depth and higher carbon concentration than general carburizing heat treatment. Carbide having spheroidal or spherical shape had a size under 2 micro-meter produced in austenite grain boundaries or within austenite grains during super-carburizing. The super-carburized specimen maintained the hardness, HV700 above, at the 0.6mm depth and had a 10.4% lower coefficient of friction which was 0.766. This results from the dispersed carbide which lowered the coefficient of friction and ended up affecting wear resistance. Consequently, we conclude that super-carburizing heat treatment has more influence on the improvement of hardness, wear resistance compared to general carburizing heat treatment.

A method is developed to simulate the fatigue crack growth in a carburized gear tooth considering the effect of residual stress. The calculation of stress intensity factor and the fatigue crack growth rates in the case layer are estimated by the experimental formula obtained in this study. The crack growth of carburized gears is measured by a crack gauge, and the validity of the simulation is confirmed. The critical length of initial crack which corresponds to the fatigue strength is introduced in the method, and a new design procedure of carburized gears is proposed based on the critical length of crack. As an example of the application of the procedure, the size effect is tried to discuss.

In this study, the models before and after improving the support structure of seat motor gear nut are investigated by comparing with vibration analysis. The maximum deformation model 1 becomes higher than model 2. The natural frequency of model 2 becomes higher model 1. The design model to be applied into the safe driving is useful effectively by using the analysis result of the height driving module for automotive power seat.

In order to analysis the tensile properties of the high-tech fibers for fishing gear materials. tensile strength was tested on raw materials, single yarns and netting twines(plied yarns)made of nylon, kevlar 29 and techmilon respectively. The results obtained are as follows: 1. The tensile stress and tenacity of unknotted single yarns in dry and wet conditions were 3 to 3.5 times greater in the high-tech fibers than in nylon. But the elongation of the high-tech fibers was about 15% of that in nylon. 2. The tensile strength of knotted single yarns in dry and wet conditions was arranged in order of as follows : techmilon. kelver 29, and nylon. The ratio of knot strength to tensile strength, knot efficiency, was the highest in nylon. 3. The tensile strength of unknotted netting twines in dry and wet conditions was 2.3 to 2.5 times greater in the high-tech fibers than in nylon. 4. The tensile strength of knotted netting twines in dry and wet conditions was arranged in order of as follows : techmilon, kevlar 29, nylon. The knot efficiency was the highest in nylon.