Abstract
Behavior of ductile crack initiation from a crack under mixed mode I-II loading has been investigated on a weldable structural steel SM41A. Elastic-plastic fracture toughness tests were carried out on the single-edge-cracked specimens subjected to bending moment and shearing force. The ductile crack initiation from the mixed mode crack occurred in two types -fibrous-type and shear-type- depending on the loading mode. When the mode I component was more predominant, the fibrous-type crack was initiated by the coalescence of microvoids. On the other hand, under the mode II predominant loading, the shear-type crack initiation occurred by large shear deformation. The applicability of J-integral concept to the ductile crack initiation from a mixed mode I-II crack was examined. The condition of ductile crack initiation from a mixed mode crack was shown by contour line on the JI-JII diagram, JI and JII being the mode I and Mode II components of J-integral, respectively. The condition of crack initiation for mode II crack, JiII, was different in value from the condition of crack initiation for mode I crack, JiI.
