THE LOW-TEMPERATURE BRITTLE-FRACTURE BEHAVIOR OF STEEL IN MIXED-MODES I AND II

Cleavage fracture in four grades of steel subjected to mixed mode I/II loading has been investigated using edge-cracked bend bar specimens loaded in anti-symmetric and symmetric four-point bend configurations. All four grades (En3B mild steel, 1Cr-1Mo-0.3V, HY130, and a C-Mn weld) were tested at -196-degrees-C. These results, and the results of previous studies on similar steels, were found to agree with predictions made according to a maximum tangential tensile stress (sigma-theta-theta) criterion based on the HRR elastic-plastic stress field. This finding is consistent with the present understanding of the fracture micro-mechanisms of these steels. In some cases it was also found that a brittle to ductile transition could be exhibited in going from mode I to mode II loading, and this is explained using a near crack tip analysis that incorporates crack tip blunting.