球状黒鉛鋳鉄の低サイクル疲労下巨視き裂伝ぱに及ぼす基地組織の影響

抄録

The effect of microstructure on the macroscopic low-cycle-fatigue crack growth rate was examined on ductile cast iron with the same chemical compositions but different microstructures, ie., ferritic (FDI), pearlitic (PDI) and austempered (ADI) structures. The crack growth rate was evaluated by measuring crack closure behavior. FDI showed the fastest crack growth rate, irrespective of the assessing fracture mechanics parameter of δK or δK_eff. The crack opening ratio was constant in PDI and ADI, irrespective of the crack growth stage, while it suddenly increased in FDI when the value of K_max exceeded a certain value. Each material microscopically indicated zigzag-like crack growth caused by the effect of spheroidal graphite. In particular, crack branching, which retarded the crack growth, was often observed in ADI. Each material showed no discernible difference in appearance and roughness of fracture surface at the main stage of crack growth.