アルミニウム合金平滑材の超高サイクル疲労強度に及ぼす圧縮平均応力の影響

抄録

Aluminum alloy is used for the compressed hydrogen gas container of the fuel cell electric vehicle. Since aluminum alloys do not have fatigue limit, very high cycle fatigue property is important to obtain by experiment for safe design. Aluminum liners of the container is subjected to compressive mean stress by autofrettage process. The purpose of this study is to evaluate the effect of compressive mean stress on the very high cycle fatigue strength and to clarify the fracture mechanism for the aluminum alloys, 6061 and 6066. The evaluated fatigue strength is independent of the compressive mean stress and alloys of 6061 and 6066.However, the crack initiation and growth behaviors aredifferent. Under fully compressive cyclic loading, many stage I cracks are initiated, but they do not form a main crack. While tensile component in the cyclic loading contributes to the initiation of stage II cracks which grows by opening mode to be a main crack. Detailed observations are performed on the surface and the section of the specimens in order to clarify the mechanisms of crack initiation and growth.