Abstract
The through-the-thickness and in-plane strain behaviours at the crack tip for HT80 and SM41 steels were observed continuously on various specimen geometries, using optical interference method. The relationship between the elastic-plastic strain distribution, or the elastic to plastic zone size ratio and specimen geometry was investigated. In addition, the characteristics of the transition behaviours from plane strain to plane stress condition were clarified on two steels.
Main results obtained are as follows.
(1) Under the same loading condition, the larger the specimen thickness is, the larger the elastic zone size on specimen surface and the elastic to plastic zone size ratio become.
(2) Under the same loading condition, the plastic zone size in plane of SM41 steel of which the transition boundary of elastic-plastic deformation is clear, is larger than that of HT80 steel, while the throughthe-thickness strain is the about same on two steels.
(3) The transition from plane strain to plane stress condition in SM41 steel, takes place after the hinge type plastic flow achieved the general yield. However, the transition of that in HT80 steel takes place when the plastic zone size is about a quarter of specimen thickness.
