超高サイクル疲労における内部起点型き裂の伝播機構
A Mechanism of Sub-Surface Crack Growth in Very High Cycle Fatigue
著者:
中村 孝 Takashi NAKAMURA 小熊 博幸 Hiroyuki OGUMA
発刊日:
公開日:
High Strength SteelODASub-surface FractureTi-6Al-4VVacuumVery High Cycle Fatigue
概要
This study carried out uniaxial tension fatigue tests of Ti-6Al-4V focusing on sub-surface fractures in very high cycle regime. Crack growth properties in high vacuum were also investigated to simulate sub-surface crack propagation, which is kept away from atmosphere in principle. F racture surfaces were closely compared between the sub-surface crack and the crack propagated in vacuum. As a result, it was clarified that crack growth rate in vacuum was much lower than that in air, which corresponded to longer fatigue lives of sub-surface fractures. Fracture surf aces between the sub-surface crack and the crack propagated in vacuum were quite similar showing a unique granular feature with fine concave convexo pattern. The granular fracture surface was never observed in surface-originating cracks; therefore, it was considered a key process of sub-surface crack growth. The granular features also resembled so-called ODA region of sub-surface fractures in high strength steel. Based on this observation, a common mechanism of sub-surface crack growth regardless of materials was discussed for very high cycle fatigue phenomena.
