Notched specimens of spheroidal graphite cast iron were fatigued under alternating bending stress. The fatigue fracture surface was observed using a two-stage plastic-carbon replica with Cr shadowing.
The result obtained are as follows:
(1) Ductile-appearing fatigue striations were observed in the ferrite region on the fracture surface of spheroidal cast iron as in the cases of steels, Al alloys, etc.
(3) Roughly speaking, the striation spacing was equivalent to the magnitude of macroscopically measured rate of crack growth. But in the range of lower growth rate, there was a tendency of striation spacing being larger than the macroscopic rate.
(3) The rate of fatigue crack growth (dl/dn) was closely related to the stress intensity factor K and could be expressed by (dl/dn)=c·K2