鉄系焼結材料の疲労き裂進展挙動

Abstract

The behavior of fatigue crack growth of sintered iron and steel compacts were investigated in comparing with that of the nodular graphite cast irons for various stress ratios and specimen thickness by using 1/2 compact type specimens, prepared by single pressing, sintering and machining.The results obtained were summarized as follows:1) Under the constant stress ratio, the relationship between fatigue crack growth rate(da/dN) and stress intensity factor range(ΔK) of sintered compacts was dependent on the density and the structure. However, the relationship between da/dN and ΔK/E normalized by Young's modulus(E) was linear independently of the density in the sintered iron compacts. Under the same ΔK, da/dN of the sintered compacts was slightly bigger than that of the nodular graphite cast irons.2) As the stress ratio is increased, the fatigue crack growth curves of sintered compacts were shifted to the lower stress intensity factor range. The threshold in stress intensity factor(ΔKth) was decreased with an increase in the stress ratio.3) Effects of specimen thickness on the fatigue crack growth in sintered compacts did not appear in the range of 10.0mm to 12.5mm.