Constraint Assessment for Specimens Tested Under Uniaxial and Biaxial Loading Conditions

In the integrity analysis of a reactor pressure vessel (RPV), a postulated shallow crack is subjected to biaxial far-field stresses. However, the fracture toughness K_c or J_c, which is an important material property for the integrity assessment of a RPV, are usually tested with deeply-cracked compact tension [C(T)] or single-edged bending [SE(B)] specimens under uniaxial loading. Thus, the fracture toughness data do not reflect the biaxial loading state that the cracks in a RPV are subjected to. Cruciform bending specimen is therefore developed to simulate the biaxial stress state. In this paper, a series of finite element (FE) simulations of the cruciform specimens containing different crack geometries and of different material properties are conducted. The crack tip constraint is investigated using the J-A₂ theory and the stress field near the crack tips is analyzed. The results show that the biaxial effect is material property dependent. This can contribute to the lifetime prediction of a RPV as well as better design of cruciform specimens.