抄録
The behavior of fatigue cracks in plain specimens of eutectoid steel subjected to macroscopic tensile and shear stresses was examined by cyclic torsion tests at -60°C. The results obtained were compared with those at room temperature. The critical propagating stress of the fatigue crack was higher at -60°C than at room temperature for the same crack length. At the critical propagating stress, however, the size of slipped region at the crack tip and micro-Vickers hardness measured at room temperature in this region were little affected by both the crack length and the difference in fatigue test temperature. The hardness value in this region was smaller in the specimen subjected to tensile stress than to shear stress. The fatigue process from slip initiation to crack propagation at a crack tip was affected by the test temperature, the stress mode generated at the tip and the existence of the hardened layer at the tip.
