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최병학 ( Byung Hak Choe ),김문규 ( Moon Kyu Kim ),김승언 ( Seong Eun Kim ),심윤임 ( Yoon Im Shim ),이영진 ( Young Jin Lee ),정효태 ( Hyo Tae Jeong ),최원열 ( Won Yeol Choi ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.12
Failure analyses of the screws in spinal fixation devices were carried out. The fractured screws were retrieved from a patient who had spinal surgery in the thoracic vertebrae from number 10 to 15. The failure occurred one month after the removal of the braces. Microstructures and fracture surfaces were examined by optical and scanning electron microscopy. The microstructures of the screws corresponded to annealed Ti-6Al-4V bar. However, in the vicinity of the screw surface, there was an insufficient number of fine precipitates. Fracture surfaces showed typical fatigue failure modes. Regarding the fact that no machining defects were detected, fatigue crack initiation might have been caused by the lack of precipitates near the screw surfaces. Only the fourth of five fixed screws was severely stress-concentrated by the action of the spinal bones, while the stress of the 4th screw was decreased to half of its acceptable level when the screw was supplemented by one more, which might have been fixed in the 6th vertebra under the 5th position by the switching of its position. The stress simulation was conducted by ANSYS with 3D CAD of PRO/E in order to understand the stress concentration behavior and to provide an effective spinal surgery guide.
유사한 전자상태를 가지는 타이타늄 합금의 영률에 베타 안정화 원소 함량이 미치는 영향
유가영 ( Ga Young Yoo ),박찬희 ( Chan Hee Park ),홍재근 ( Jae Keun Hong ),김승언 ( Seong Eun Kim ),강남현 ( Seong Eun Kim ),염종택 ( Jong Taek Yeom ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.4
Previously, Gum Metal (Ti-24(Nb + Ta + V)-(Zr, Hf)-O (at%)) exhibiting an ultralow Young`s modulus, ultrahigh strength and super elasticity was developed by Saito et al., who proposed that three electronic magic numbers, an average electron/atom (e/a) ratio of 4.24, an average bond order (Bo) of about 2.87, and an average “d” electron-orbital energy level (Md) of about 2.45 eV, should be satisfied simultaneously to obtain such “super” properties. The purpose of this study was to find new alloy systems possessing those properties and to examine the effect of beta equivalent content ([Mo]eq) on Young`s moduli of new alloys having the same three electronic numbers mentioned above. It was found that not only three electronic numbers but also [Mo]eq should be considered to obtain a similar Young`s modulus and hardness with respect to the Gum Metal.