Fracture assessment of a cruciform bending specimen using a two-parameter fracture criterion based on crack tip opening displacement

The assessment of the structural integrity of reactor pressure vessels is performed in accordance with regulatory documents based on fracture mechanics criteria. In doing so, it is necessary to account for the effects of shallow cracks, biaxial loading, and crack front length, as these factors alter the in-plane and out-of-plane constraint and influence the fracture toughness. In this study, a series of small-scale cruciform specimens made of 15Kh2NMFAA steel with shallow cracks was used to investigate the influence of biaxial loading on static fracture resistance, to determine the reference temperature T₀ , and to compare it with T₀ ref obtained from standard CT-1 specimens in accordance with the ASTM 1921 standard. Experimental results indicate that biaxial loading of cruciform specimens with shallow cracks reduces the reference temperature T₀ and consequently decreases the conservatism of residual lifetime assessments for nuclear reactor pressure vessels. The influence of biaxial bending on fracture toughness were analyzed based on finite element analyses of stress triaxiality and the constraint parameter derived from crack-tip opening.