• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.370-375
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• 2004

Fatigue tests were carried out to find the fatigue characteristics in the super-long life range by using a cantilever type rotational bending fatigue test machine. Three kinds of specimen in bearing steels with the quenched and tempered in air (A and B, B: shot peened after heal treatment) and under vacuum conditions(C:non-shot peened)were tested in this study. S-N curves obtained from fatigue tests of C specimen tend to come dawn again in the super-long life range due to fish-eye type cracking, while most of A and B specimens fractured by surface defects such as scratches and slip lines. This duplex S-N behavior for the high strength steels have to be reviewed by the change of fracture modes.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.385-386
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• 2006

For attaining optimum fatigue resistance of PM steels, high density levels are necessary. In this work, sintered steels Fe-1.5%Mo-0.6%C and Fe-1.5%Cr-0.2%Mo-0.6%C were produced with density levels of 7.1 to $7.6\;g.cm^{-3}$. Ultrasonic fatigue testing with 20 kHz was performed in push-pull mode up to 10E9 cycles. It was shown that the fatigue endurance strength is strongly improved by higher density levels, but also higher sintering temperatures are beneficial. The Cr-Mo steels proved to be superior to the plain Mo alloyed, due to a more favourable as-sintered matrix microstructure.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.136-137
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• 2006

Crack initiation and short crack propagation was studied on the polished notched surfaces of Cr-Mo prealloy sintered steels with 7.35 $g.cm^{-3}$ sintered density. An ultrasonic resonance test system operating in push-pull mode at 20 kHz and R=-1 was used. It showed that crack initiation took place in several places, small cracks growing oriented to the local pore structure rather than to stress orientation. Their growth rate is markedly higher than the corresponding one of long cracks. Finally, several microcracks join to form a dominant crack.

• 대한기계학회논문집A
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• 제36권6호
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• pp.707-712
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• 2012

본 연구에서는 Ti-6Al-4V 합금에 대한 초고주기 피로시험 연구를 통하여 사이클에 따른 파단면 관찰결과 2가지 타입으로 명확히 구분되는 것을 확인할 수 있었다. 첫번째로 106사이클 범위에서 확인할 수 있는 것은 표면부에서 피로크랙 사이트가 시작된 전형적인 피로 파단면이다. 두번째는 107~109사이클에서는 확연히 다른 피로파단 양상으로, 표면으로부터 $500{\mu}m$ 내부에서 피로크랙 사이트가 시작되어 크게 박리되어 나간 형상으로, 크랙 사이트 주변을 관찰한 결과 미세한 마이크로 크랙들이 입계파괴 양상으로 형성되어 있는 것을 확인 할 수 있었다. 이에 내부 크랙 사이트 피로거동에 대한 연구결과와 본 시험에서 사용된 초음파피로시험기술의 이론 및 적용사례를 소개하고 현재 활발히 진행중인 연구동향을 밝히고자 한다.