Instead of commonly used SEM, AFM (Atomic Force Microscope) wasused to study the fatigue fracture surfaces and three-dimensionalnano-level information including the height was obtained. Observationwas focused on the fatigue striations obtained at various stressratios in 20l7- T35l aluminum alloy. From their three-dimensional AFMimages, the widths (SWs) and the heights (SHs) were analyzed. Thefollowing results that will be helpful to understand the fatiguecrack growth mechanism were obtained. (l) Coincidence of the da/dNand the SW which is known to hold for da/dN above l0~-4 mm/cycle, isestablished down to smaller da/dN of 6×l0~-5 mm/cycle. (2) Betweenthe SH and the SW a relation of SH=0.0585(SW)~1.2 was obtained. (3)The ratio of the striation height to its width, SH/SW was almostconstant irrespective of the stress intensity factor range AK or thestress ratio R. (4) Not only the SWs but also the SHs were changedlinearly with the crack tip opening displacement (CTOD) when plottedon a log-log scale. From these results, the applicability of the AFMto nano-fractography is discussed.
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