411 極低温におけるチタン合金の疲労特性に及ぼす表面粗さの影響

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The high-cycle fatigue properties of Ti-5Al-2.5Sn ELI alloys and the effects of surface roughness and notch on their fatigue properties were investigated at cryogenic temperatures. Surface roughness of specimens was changed by different SiC paper (Grade #600,#100) and notched specimens (Kt=1.5,3) were prepared. The S-N curves shifted to higher stress level or longer life side with a decrease of the test temperature. Regarding the effect of surface roughness, the fatigue strength of the Grade #100-surface-roughness specimens were a little bit lower than those of Grade #600-surface-roughness specimens. Fatigue crack initiation sites of each surface roughness specimen at 4 K were at specimen interior. Using root area analysis, which is the size of the crack propagation plane as a shape parameter, the fatigue strength depends on the √area size. In notched specimens, the fatigue strength of the Kt=3 specimens were lower than those of the Kt=1.5 notched specimens. Although fatigue crack initiation sites of the Kt=3 notched specimens were at the notch root, those of the Kt=1.5 notched specimens were at specimen interior.
2002-09-20