Two-parameter (J-Q) fracture characterization of ductile tearing

CTOD tests have been carried out for compact tension specimens with a/W=0.6, double-edge notched tension specimens with a/W=0.9 and 0.5, single-edge notched tension specimens with a/W=0.5, three-point bend specimens with a/W=0.5 and 0.1 and center-cracked tension specimens with a/W=0.5. The results of the CTOD tests show that the crack initiation toughness of the material increases as the in-plane plastic constraint of the specimens decreases. The recently proposed two-parameter (J-Q) fracture characterisation technique has shown that the near-tip fields under very general conditions of loading in finite bodies can be described by two parameters, J and Q. A theoretical model of void nucleation and growth in the J-Q fields ahead of the crack tip is given in this paper. This model predicts the relationship between the crack initiation toughness (J _i or δ _i) and the constraint parameter Q. Comparison of experimental results of CTOD tests gives good agreement with theory.