| The purpose of this investigation was to characterize fracture under combined mode I-mode III loading conditions. To characterize mixed mode fracture under linear elastic conditions, a 1.25% C steel in bainitic condition was chosen. Suitably defined resolved critical stress intensity factors, denoted K;In the bainitic 1.25% C steel, as the mode III component in the system was increased, the critical mode I stress intensity factor was relatively unaffected while the critical mode III stress intensity factor increased. Thus the fracture is controlled predominantly by mode I deformation fields. The total energy expended in fracture increases as increasing mode III components are added to the system.;In the 1090 steel, as the mode III component in the system is increased, the resolved mode I J initiation decreases, while its mode III counterpart increases and the total J value remains nearly a constant. The slopes of the mode I and total J resistance curves and the mode I and total J exclusion values after 1.5 mm of crack growth behave differently from the initiation values. They increase from their pure mode I values until a maximum in these values is reached and they fall off rapidly for larger mode III components. This drop is accompanied by the breakup of the crack front into mode I and mode III steps, an energetically more favorable process.;Linear elastic and elastic-plastic materials respond in fundamentally different ways to mixed mode loading conditions. In linear elastic materials, the normalized mode I J values are relatively insensitive to additions of mode III load components. In elastic plastic materials, this value drops off rapidly as mode III components are added. |
