Constraint effects within R6 framework: Validation by small and large scale fracture test results for A533B-1 steel

A framework for including constraint effects in the failure assessment diagram approach for fracture assessment was described in the 1994 ASME PVP conference. Constraint effects were treated by modifying the shape of the failure assessment curve. In their simplest form, the modifications involve only two parameters: one quantifying the magnitude of structural constraint which depends on geometry, crack size and loading; and the second quantifying the influence of constraint on fracture toughness. The validity of the framework is investigated in this paper by considering the results and associated analysis of both small and large scale upper shelf fracture toughness tests performed on an A533B-1 steel plate. The specimens had a range of crack-tip constraint conditions. The results demonstrated that: (i) Crack-tip constraint significantly influences the ductile fracture characteristics of this material, (ii) this influence is well quantified by the elastic T-stress or elastic-plastic Q-stress, and (iii) the modified R6 framework provides conservative assessments of fracture initiation.