To address the influence of biaxial stress effects on fracture, experimental work has been reported in the literature on cruciform specimens containing defects. For example, some large-scale tests were carried out for 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 effect of reducing the fracture toughness. More recently, Hohe et al. (2011) showed that these results could be reproduced using small-scale specimens. Both these studies limited the biaxial stress ratio to between 0.6 and 1. This paper focuses on experimental data from tests on large-scale cruciform specimens carried out by the Bhabha Atomic Research Centre (BARC) in India, with biaxial stress ratios of 0, 1 and 2. The experimental results show that the biaxial loading does have an effect on the failure load. However, such biaxial effects can arise from both an influence of stress biaxiality, or constraint, on fracture toughness and an influence on crack driving force. Both these effects are discussed in this paper. The latter effect is demonstrated and reflected through an influence on the limit load when the results of the BARC tests are presented on the R6 Failure Assessment Diagram.
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