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수소 첨가 열처리에 따른 Ti-6Al-4V 합금 분말의 격자 변형 및 내산화성 향상
조계훈,오정민,임재원,Cho, Gye-Hoon,Oh, Jung-Min,Lim, Jae-Won 한국분말야금학회 2019 한국분말재료학회지 (KPMI) Vol.26 No.2
In the present work, a new hydrogen added argon heat treatment process that prevents the formation of hydrides and eliminates the dehydrogenation step, is developed. Dissolved hydrogen has a good effect on sintering properties such as oxidation resistance and density of greens. This process can also reduce costs and processing time. In the experiment, commercially available Ti-6Al-4V powders are used. The powders are annealed using tube furnace in an argon atmosphere at $700^{\circ}C$ and $900^{\circ}C$ for 120 min. Hydrogen was injected temporarily during argon annealing to dissolve hydrogen, and a dehydrogenation process was performed simultaneously under an argon-only atmosphere. Without hydride formation, hydrogen was dissolved in the Ti-6Al-4V powder by X-ray diffraction and gas analysis. Hydrogen is first solubilized on the beta phase and expanded the beta phases' cell volume. TGA analysis was carried out to evaluate the oxidation resistance, and it is confirmed that hydrogen-dissolved Ti-6Al-4V powders improves oxidation resistance more than raw materials.
태권도 선수와 일반인의 등척성 무릎신전 토크-각도 관계 특성 비교 분석
조계훈 ( Gye Hun Jo ),오정훈 ( Jeong Hoon Oh ),이해동 ( Hae Dong Lee ) 한국운동역학회 2015 한국운동역학회지 Vol.25 No.3
Objective : In order for Taekwondo athletes to perform destructive kicking performance, they are expected to have Taekwondo-specific muscle properties such as high muscle strength and power. The purpose of this study was to investigate the joint angle-dependent force-producing property of Taekwondo athletes’ knee extensor muscles, which is one of the primary muscle groups involved in kicking performance. Method : Ten Taekwondo male athletes (age: 19.9±0.7 yrs, height: 180.6±6.2 cm, body mass: 75.9±8.9 kg, career: 9.2±2.9 yrs.) and 10 healthy male non-athletes (age: 26.3±2.6 yrs, height: 174.2±4.8 cm, body mass: 72.8±7.7 kg) participated in this study. Subjects performed maximum isometric knee extension at knee joint angles of 40°, 60°, 80°, and 100° (the full knee extension was set to 0°) with the hip joint angles of 0° and 80° (the full extension was set to 0°). During the contractions, knee extension torque using an isokinetic dynamometer simultaneously with muscle activities of the rectus femoris (RF), and the vastus lateralis (VL) and vastus medialis (VM) using surface electromyography were recorded. Based on the torque values at systematically different knee-hip joint angles, the joint torque-angle relationships were established and then the optimal joint angle for the knee extensor was estimated. Results : The results of this study showed that the isometric knee extension torque values were greater for the Taekwondo athletes compared with the non-athlete group at all hip-knee joint angle combinations (p<.05). When the hip joint was set at 80°, the peak isometric torque was greater for the Taekwondo athletes compared with the non-athlete group (313.61±36.79 Nm and 221.43±35.92 Nm, respectively; p <.05) but the estimated optimum knee joint angles were similar (62.33±5.71° and 62.30±4.67° for the Taekwondo athletes and non-athlete group, respectively). When the hip joint was set at 0°, the peak isometric torque was greater for the Taekwondo athletes compared with the non-athlete group (296.29±45.13 Nm and 199.58±25.23 Nm, respectively; p<.05) and the estimated optimum knee joint angle was larger for the Taekwondo athletes compared with the non-athlete group (78.47±5.14° and 67.54±5.77°, respectively; p<.05). Conclusion : The results of this study suggests that, compared with non-athletes, Taekwondo athletes have stronger knee extensor strength at all hip-knee joint angle combinations as well as longer optimum muscle length, which might be optimized for the event-specific required performance through prolonged training period.