1974 年 23 巻 244 号 p. 52-57
The transition from flat to shear mode fracture occurs during the crack propagation in polymeric materials under repeated tensile loading. The present study has been made under the condition fulfilling Irwin's criterion for fracture mode transition, to clarify how the transition behavior of an edge-slotted polycarbonate plate is affected by temperature, strain rate and stress amplitude. It has been found that the ratio of the size of plastic zone at the transition point to the plate thickness increases with increasing the temperature or the ratio of stress amplitude to yield stress, but decreases with increasing the strain rate. This size ratio is roughly equal to one half at the static fracture under a given strain rate, but it is less than one half at the fatigue fracture. However, its value calculated with consideration for the local yield stress at the tip of fatigue crack approaches to one half and becomes in good agreement with the ratio of the measured plastic zone size to the plate thickness.