Engineering C-integral estimates for generalised creep behaviour and finite element validation

This paper proposes an engineering method to estimate the creep C-integral for realistic creep laws to assess defective components operating at elevated temperatures. The proposed estimation method is mainly for the steady-state C*-integral, but a suggestion is also given for estimating the transient C(t)-integral. The reference stress approach is the basis of the proposed equation, but an enhancement in terms of accuracy is made through the definition of the reference stress. The proposed estimation equations are compared with extensive elastic-creep FE results employing various creep-deformation constitutive laws for six different geometries, including two-dimensional, axi-symmetric and three-dimensional geometries. Overall good agreement between the proposed method and the FE results provides confidence in the use of the proposed method for defect assessment of components at elevated temperatures. Moreover, it is shown that for surface cracks the proposed method can be used to estimate C* at any location along the crack front