Evaluation of rotational deformation in compact specimens for CTOD fracture toughness testing

In Crack Tip Opening Displacement (CTOD) fracture toughness tests, the plastic hinge model is used for calculating the plastic component of CTOD, but the accuracy of the plastic hinge model has been a matter of controversy. In this study, 3-D elastic-plastic finite element analysis was conducted by using a stepped notch 1T compact specimen model, in which the ratio of crack length to specimen was set at 0.5. Two steel models, the low yield to tensile ratio, Y/T, of 0.6 and the high Y/T of 0.9, were employed for the analysis. The plastic rotational center was determined by using distributions of the plastic strain increment and the total strain increment in the crack opening direction along the ligament on the mid-thickness plane. The effect of Y/T on the plastic rotational factor was quite small in the C(T) specimen model, and the average of their plastic rotational factors was 0.52 in both Y/T steel models. This plastic rotational factor is consistent with conventional ones, and is reasonably used for CTOD calculation.