• 대한기계학회논문집A
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• 제35권8호
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• pp.951-956
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• 2011

원자력 발전설비의 증기발생기용 세관 재료로 인코넬 합금이 사용되고 있다. 인코넬 합금은 고니켈과 크롬의 합금으로 고온에서 내부식성이 뛰어난 특성을 가지고 있다. 본 연구에서는 인코넬 600 과 690 합금에 대해 실제 원전의 운전온도, 즉 $320^{\circ}C$가 프레팅 피로 거동에 미치는 영향에 대해 연구해보았다. 그 결과 $320^{\circ}C$에서의 단순 피로한도와 프레팅 피로한도가 상온에서의 단순 및 프레팅 피로한도에 비해 다소 저하하는 것을 알 수 있었다. 아울러 하중 반복회수와 마찰력의 변화 특성도 얻었다. 또한 파단면을 전자현미경으로 관찰하여 프레팅 피로기구도 검토해 보았다. 이와 같은 결과는 실제 운전온도에서 프레팅을 받는 증기발생기의 구조건전성 평가에 활용 가능할 것으로 생각된다.

• 대한기계학회논문집A
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• 제29권4호
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• pp.584-590
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• 2005

The effect of microstructure on mechanical behavior for Ti-6Al-4V alloy was studied. Two different kinds of specimens are prepared using heat treatments (rolled plate, $1050^{\circ}C)$ in order to Produce different microstructures. Various kinds of mechanical tests such as hardness, tensile, fatigue and fretting fatigue tests are performed for evaluation of mechanical properties with the changes of microstructures. Through these tests, the following conclusions are observed: 1) Microstructures are observed as equiaxed and $widmanst{\ddot{a}}ten$ microstructures respectively. 2) Impact absorbed energy is superior for the equiaxed microstructure, and the hardness and tensile strength are superior for the $widmanst{\ddot{a}}ten$ microstructure. 3) The fatigue endurance of $widmanst{\ddot{a}}ten$ microstritcture shows higher value than that of the equiaxed microstructure. 4) The fatigue endurance in fretting condition was reduced about $50{\%}$ from that of the non-fretting condition.

• 대한기계학회논문집A
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• 제31권2호
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• pp.197-204
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• 2007

Fretting is a contact damage process that occurs between two contact surfaces. Fretting fatigue reduces fatigue strength of the material due to low amplitude oscillatory sliding and changes in the contact surfaces of strongly connected machine and structure such as bolt, key, pin, fixed rivet and connected shaft, which have relative slip of repeatedly extreme low frequency amplitude. In this research, the fretting fatigue behavior of 2024-T3511 and 7050-T7451 aluminum alloys used mainly in aircraft and automobile industry were experimentally estimated. Based on this experimental wort the following results were obtained: (1) A significant decrease of fatigue lift was observed in the fretting fatigue compared to the plain fatigue. The fatigue limit of 2024-T3511 aluminum alloy decreased about 59% while 7050-T7451 aluminum alloy decreased about 75%. (2) In 7050-T7451 specimen using ATSI4030 contact pad, crack was initiated more early stage than using 2024-T3511 contact pad. (3) In all specimens, oblique cracks were initiated at contact edge. (4) Tire tracks and rubbed scars were observed in the oblique crack region of fracture surface.

• 한국정밀공학회지
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• 제27권8호
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• pp.42-47
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• 2010

In this paper, the characteristics of contact surface damage due to fretting in a press-fitted shaft below the fretting fatigue limit are proposed by experimental methods. A series of fatigue tests and interrupted fatigue tests of small scale press-fitted specimen were carried out by using rotating bending fatigue test machine. Macroscopic and microscopic characteristics were examined using scanning electron microscope (SEM), optical microscope or profilometer. It is found that fretting fatigue cracks were initiated even under the fretting fatigue limit on the press-fitted shafts by fretting damage. The fatigue cracks of press-fitted shafts were initiated from the edge of contact surface and propagated inward in a semi-elliptical shape. Furthermore, the fretting wear rates at the contact edge are increased rapidly at the initial stage of total fatigue life. After steep increasing, the increase of wear rate is nearly constant under the load condition below the fretting fatigue limit. It is thus suggested that the fretting wear must be considered on the fatigue life evaluation because the fatigue crack nucleation and propagation process is strongly related to the evolution of surface profile by fretting wear in the press-fitted structures.