1977 年 26 巻 280 号 p. 74-79
In order to grasp the concept of crack propagation in surface hardened materials, the observation of crack propagation and the measurements of the residual stress and the plastic zone size ahead of the crack tip were performed on a tufftrided steel. The specimens used were made of 0.12% carbon steel, machined to the shape of single notched plate type and tufftrided after annealing.
The results obtained are summarized as follows:
(1) The relation between the crack propagation rate and the stress intensity factor could not be represented by a simple power law.
(2) The compressive residual stress was observed in the vicinity of the notch root before the fatigue test. When the pulsating bending stresses were applied to such a specimen, the decrease of residual stress was observed at the crack tip while the crack length was short.
(3) The size of the plastic zone ahead of the crack tip was in proportion to the 4th power of stress intensity factor. However, if the effective stress intensity factor was corrected based on the residual stress, this relation was in agreement with the theoretical relation, the square of stress intensity factor being proportional to the plastic zone size.