Biaxial loading effects on large -scale cruciform specimens

To address the influence of biaxial stress effects on fracture, experimental work has been reported in theliterature on cruciform specimens containing defects. For example, some large-scale tests were carried outfor the US Nuclear Regulatory Commission at the Oak Ridge National Laboratory in the 1990s,concluding that biaxial loading in the form of an additional out-of-plane stress component has the effectof reducing the fracture toughness. More recently, Hohe et al. (2011) showed that these results could bereproduced using small-scale specimens. Both these studies limited the biaxial stress ratio to between 0.6and 1.This paper focuses on experimental data from tests on large-scale cruciform specimens carried out by theBhabha Atomic Research Centre (BARC) in India, with biaxial stress ratios of 0, 1 and 2. Theexperimental results show that the biaxial loading does have an effect on the failure load. However, suchbiaxial effects can arise from both an influence of stress biaxiality, or constraint, on fracture toughnessand an influence on crack driving force. Both these effects are discussed in this paper. The latter effect isdemonstrated and reflected through an influence on the limit load when the results of the BARC tests arepresented on the R6 Failure Assessment Diagram.