Papers by Author: Tae Gyu Kim

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Authors: Tae Gyu Kim, Hyun Soo Kim, In Duck Park, Hye Sung Kim
Abstract: In this study, we investigated the fatigue characteristics of SMA40 materials as a potential application in connecting rod material for an automobile. Average fatigue life of 168,700 cycles and fatigue limit of 437 MPa was determined from SMA40 specimens. However, when tested under fretting condition, decrease in fatigue lifetime was 20% and fatigue limit was reduced to 350 MPa.
Authors: Jeong Wan Kim, Yeong Min Park, Dae Wook Kim, Kelimu Tulugan, Tae Gyu Kim
Abstract: Color glasses are fabricated with Titanium target by RF magnetron sputtering. The physical properties of the Ti thin films are investigated according to preparation conditions, such as argon and oxygen gas flow ratio, RF power and Working pressure. The results indicate that it is possible to deposits various Ti thin film’s of different colors on glass substrate, such as yellow, orange, brown, purple. The thickness according to the color was analyzed using Veeco's Stylus profiler (model: dektak 6M).
Authors: Jeong Seok Oh, Jun Komotori, Jung Il Song, Tae Gyu Kim
Abstract: Rotational bending fatigue tests were carried out on a medium carbon steel with a thermally sprayed Co-based alloy coating. The effect of two different fusing treatments on the fatigue strength of fused specimens was investigated. Fusing treatment was performed using a vacuum furnace, and an induction heating system. When the specimens were treated in vacuum furnace at 1373 K for 4 h, the diffusion layer providing a strong adhesive force were formed at the interface between the coating and substrate. As a result, fatigue strength remarkably increased in comparison with the uncoated specimens. On the contrary, for the treated specimens with an induction heating system at 1373 K for 120 s, since these specimens had a lower adhesive force due to no formation of diffusion layer, leading to delamination of the entire coating.
Authors: Jong Cheon Park, Ok Geun Jeong, Sang Youn Kim, Tae Gyu Kim, Jin Kon Kim, Hyun Cho
Abstract: SF6/O2 plasma surface texturing was employed to pretreat Si substrate for achieving enhanced diamond nucleation density. Surface roughness of the textured Si was found to be strongly dependent on the process pressure and normalized roughness values in the range of 2-16 were obtained. Remarkably enhanced nucleation densities of ~1010 cm-2 compared to conventional mechanical abrasion were obtained after seeding for the surface textured Si substrates. Raman spectroscopy revealed that ultrananocrystalline diamond films with grain size below 10 nm were grown on the surface textured Si.
Authors: Jeong Seok Oh, W.K. Ju, Yi Qi Wang, Tae Gyu Kim, Jung Il Song
Abstract: The static and dynamic properties on the hoist hook of a vessel are necessary since they are affected by the damages of a static and dynamic load. Al-Si-Mg casting alloy (AC4C-T6) is widely used due to its good mechanical properties as well as the light weight and good casting with complex geometries. This study accomplished a static tension test and an impact test. Based on the test results and fracture surface analysis, we found that there are great differences between the fracture strain and yield stress in the different extracted regions of specimen. In tensile test, yield stress were 205 MPa at a low strain rate of 5 mm/min and 220 MPa at a high strain rate of 25mm/min. In Charpy impact test, impact properties of AC4C aluminum alloy were analyzed by impacting loading versus displacement and impacting energy versus displacement. Compared the fracture strains in different strain rates, maximum fracture strain of low strain rate was mainly 10 % higher than that of high strain rate. There were more than 20 % differences in the strain rate. The ductile and brittle behaviors were showed in low strain rate and high strain rate in static tensile test, respectively. The impact energy reached high when they were extracted from a plane region in the mold. But impact energy reached low when they were extracted from a curved and edge region. It is demonstrated that mechanical properties and impact energy of the samples where were extracted from a curved and edge region was lower than that of the samples where were extracted from a plane region.
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