自立ナノ薄膜の疲労き裂進展試験法の開発 [in Japanese] Development of Fatigue Crack Propagation Technique for Freestanding Nano-Films [in Japanese]
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We developed an experimental technique for evaluating fatigue crack propagation properties of freestanding nano-films and conducted tensile and fatigue crack propagation experiments for about 500-nm-thick freestanding copper (Cu) films. We employed a sacrificial etching method for fabricating freestanding metallic nano-film specimens. A piezoelectric-actuator with long stroke and a load cell for small load were used for applying cyclic loading to nano-films. We developed original jigs for handling and aligning the nano-film specimens. Focused ion beam (FIB) was employed to introduce a single side-edge-notch in the nano-film specimens for fatigue crack propagation experiments. The results of tensile experiments revealed that the nano-films have resistance to plastic deformation comparable to cold-rolled Cu bulk, but have lower ductility. The results of fatigue crack propagation experiments revealed that a fatigue crack stably propagates in the nano-film by a uniaxial cyclic loading with constant maximum stress before unstable fracture. The fatigue crack propagation rate d<i>a</i>/d<i>N</i> of the Cu nano-films is higher than that of Cu bulk counterpart in higher stress intensity factor range, Δ<i>K</i>. Fatigue crack started to propagate from the notch tip below the threshold value of Cu bulk with coarse grains, and the Cu nano-films show similar fatigue crack propagation properties to Cu bulk with ultrafine grains in lower Δ<i>K</i>. Morphology of the fracture surface transited from microstructure-sensitive rough surface to microstructure-insensitive ductile surface or chisel point fracture as fatigue crack propagated. This suggests that the dominant fracture mechanism changes from the accumulation of cyclic deformation to the monotonic tensile-dominant fracture.
- TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series A
TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series A 78(790), 808-816, 2012
The Japan Society of Mechanical Engineers