LOSS OF CRACK-TIP CONSTRAINTS FOR SHALLOW CRACKS IN BENDING

Single-edge notched bars (SENB) in bending with a/W ratios ranging fro m 0.05 to 0.5 are examined for fracture toughness in terms of the J-in tegral approach. The corresponding results indicated that, for a a/W r atios less than 0.3, there is a significant loss of J-dominance, which is attributed to the impact of plastic deformation on the cracked fac e. For larger a/W ratios, J-dominance is maintained into a large-scale yielding regime. According to the recently developed two-parameter cr iterion (J,Q), compressive Q-stress was interpreted as an indication o f low crack-tip stress triaxiality for shallow cracks, whereas positiv e e-stress was associated with high crack-tip stress triaxiality for d eep cracks. For the material properties and specimen geometries consid ered herein, a fracture toughness locus is constructed in terms of the (J-Q) parameters for each of the a/W ratios. The overall fracture dat a, which are in agreement with those predicted by other approaches, ap pear to provide a rigorous framework for interpreting the effect of lo ss of crack-tip constraint in elastic-plastic fracture analysis.