Closure mechanisms alone cannot fully explain increasing fatigue thresholds with decreasing test temperature. The implications are that fatigue crack propagation near threshold is a thermally activated process. The effective threshold stress intensity correlates to the thermal component of the flow stress. Fractographic study of the fatigue surface was performed. Water vapor in room air promotes the formation of oxide and intergranular crack growth. At lower temperatures, a brittle-type cyclic cleavage fatigue surface was observed but the ductile process persisted even at 123 K. Arrest marks found on all three modes of fatigue crack growth suggested that fatigue crack growth is controlled by the subcell structure near threshold. The effective fatigue threshold may be related to the square root of (one plus the strain rate sensitivity).
|Original language||English (US)|
|Number of pages||12|
|Journal||Metallurgical transactions. A, Physical metallurgy and materials science|
|State||Published - Jan 1 1984|