AFM/SEM観察に基づく疲労き裂伝ぱ機構の研究 : (第1報, (110)[001]Fe-3.2%Si単結晶におけるストライエーション形成域での検討)

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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 unloaaing 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.
2000-01-25