Fatigue crack growth tests were carried out on thin plates of a Fe-3.2%Si single crystal with an appropriate orientation for striation formation. To clarify the mechanism of crack growth, behaviors of slips near a crack tip during the loading and unloading parts of a fatigue cycle were observed in-situ with an atomic force microscope and a scanning electron microscope and fracture surfaces were also analyzed. Following results are obtained. (a) Striations on a pair of fracture surfaces reveal peaks to valleys matching other than any kinds of symmetrical matching. (b) Profiles of striations reveal shallow ripples. (c) During loading, a pair of concentrated slips activated alternately at a crack tip lead to crack opening and thus crack advance. (d) During unloading, reverse slips which lead to crack closing are activated in a distributed manner. (e) At much higher growth rate, both opening and closing processes by a number of alternating slips are observed. (f) Vacuum environment facilitates a number of alternating slips: this is one of the causes for observing no distinctive striations on fracture surfaces in vacuum. In result, a fundamental model for fatigue crack growth is proposed on the basis of observations mentioned above.
|Number of pages||8|
|Journal||Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A|
|Publication status||Published - Jan 1 2000|
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Mechanics of Materials
- Mechanical Engineering