SiC微粒子ペースト浸透による疲労き裂の遅延効果と変動応力条件の影響

抄録

Fatigue crack retardation with the infiltrated SiC paste into a crack is examined in low carbon structural steel. Two different sizes of SiC powders, whose average diameters are 15μm and 53μm, are used. The SiC powder mixed with oil is infiltrated into a through thickness fatigue crack from the crack mouth. Fatigue crack growth retardation is examined by the ΔK increasing test of R=0.1, comparing with the base plate property, where ΔK is stress intensity factor range and R is stress ratio. Crack growth is retarded just after infiltrating SiC paste into the crack mouth, and the deceleration of crack growth rate to 1/50 of the base plate appears in the maximum. It is revealed that this crack retardation behavior results from the crack closure induced by the wedge effect of SiC particle into a crack. The crack retardation effect is investigated with several combinations of the SiC particle size and the cyclic stress conditions. The crack growth rate, da/dN and the stress intensity factor, K_cl for the crack closure depend on both of the maximum stress intensity factor, K_max and the stress ratio, R. While the better retardation effect can appear in the higher K_max and the higher R ratio, it disappears in the R ratio over 0.7. The SiC paste with 15μm powder stably brings the crack retardation effect in the wider cyclic stress condition than the SiC paste with 53μm powder.