第2段階疲労き裂進展における球状黒鉛鋳鉄と高張力鋼の相違

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Fatigue crack propagation characteristics at the stage 2 of spheroidal graphite cast iron and high strength steel with equivalent tensile strength and yield stress have been studied and compared by means of fracture mechanics and fractography. In the high ΔK region, the stage 2c cracks consisting of cleavage fractures were found only in the spheroidal graphite cast iron. Thus, its fatigue propagation rate was faster than that of high strength steel without the stage 2c cracks. In the medium ΔK region, on the other hand, both materials showed the fatigue crack propagation at the stage 2b, although the propagation rate of the spheroidal graphite cast iron was faster than that of the high strength steel due to the smaller Young's modulus of the former. Nevertheless, the propagation rates of both materials were the same, when their Young's moduli and crack closures were taken into consideration. In the low ΔK region, both materials showed the fatigue crack propagation at Stage 2a, although the propagation rate of the spheroidal graphite cast iron was slower than that of high strength steel, different from the high and medium ΔK regions. This is due to a more significant crack closure caused by the roughness of fracture surface and the formation of oxide in the cast iron than the steel. Moreover, the crack branching phenomenon was found in the cast iron where K_<max>=16 to 33Mpa√<m>. In the case that this branching phenomenon occurred in the low ΔK region, the propagation resistance of fatigue cracks became higher.
社団法人日本材料学会の論文
1988-07-15

第2段階疲労き裂進展における球状黒鉛鋳鉄と高張力鋼の相違

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