球状黒鉛鋳鉄の強度評価に関する基礎的研究 : 第3報, 鋳肌面を有する薄肉材の低サイクル疲労

抄録

Push-pull low-cycle fatigue tests were conducted on ferrite-base spheroidal graphite cast iron using thin plate specimens with as-cast surface. Both stress-controlled and strain-controlled fatigue testing conditions were employed. The fatigue crack initiation and propagation processes were observed microsopically as well as macroscopically. The material tested showed intensified cyclic hardening behaviour at an early stage of the fatigue life. The fatigue lives under both testing conditions indicated no noticeable difference and satisfied the Manson-Coffin type of relationship. The microcrack initiation originated at the surface defect, a cluster of inclusions or spheroidal graphite. Macroscopic crack initiation sites examined through fractographic observation were also different according to the specimen and were classified into four patterns. The microcrack propagation law satisfied a linear type of relation, (dl/dN)/Δε_p^α=Cl. The microcrack propagation rate was also characterized in terms of a cyclic J integral, ΔJ Finally, the effect of amount of silicon content on fatigue life and its scatter was discussed.