Effects of crack front curvature on J–R curve testing using clamped SE(T) specimens of homogeneous materials

• Investigate the impacts of crack front curvature on the compliance, rotation correction factor and J for SE(T) specimens.
• Validate the applicabilities of crack front straightness criteria specified in the seven test standards on SE(T) specimens.
• Recommend new crack front straightness criteria for the SE(T) specimen.

Three-dimensional (3D) finite element analyses (FEA) of clamped single-edge tension (SE(T)) specimens are performed to investigate the impact of the crack front curvature on the elastic compliance, compliance rotation correction factor and average J-integral evaluated over the crack front. Specimens with six average crack lengths (i.e. aave/W = 0.2–0.7) and three thickness-to-width ratios (i.e. B/W = 0.5, 1 and 2) are analyzed. The curved crack front is assumed to be bowed symmetrically and characterized by a power-law expression with a wide range of curvatures. Several crack front straightness requirements for SE(B) and C(T) specimens specified in BS7448, ISO and ASTM E1820 standards are reviewed. Based on results of the numerical investigation, new crack front straightness criteria for the SE(T) specimen are proposed in the context of the nine-point measurement by using as a criterion that the errors in the estimated compliance and average J values should be no more than five percent. The proposed criteria depend on both aave/W and B/W, and are more advantageous than those specified in the BS, ISO and ASTM standards in terms of controlling the differences in J and compliance between the specimens with curved and straight crack fronts.