Crack tunneling effects on the elastic unloading compliance of C(T), SE(B) and clamped SE(T) specimens and correction methodology

•Crack tunneling affects the elastic unloading compliance mostly reducing it.•Within the allowed ASTM E1820 curvature limits, the compliance errors are mostly negligible. When such limits are violated, the effects on compliance are significant, and results show that a/W estimation employing the elastic unloading compliance is affected. Since fracture mechanics properties are inherently dependent on the instantaneous crack size, these should also be affected to some degree.•Even though the ASTM E1820 is focused on the determination of the nonlinear energy release rate J and resistance curves, this paper is not focused on determining errors directly on the crack driving forces - in this case, J-integral.•A new proposal for measuring the crack front is presented and measuring errors are minimized when those limits are violated.•Additional work is being done to develop a more comprehensive proposal - independent of crack size, thickness and, if possible, specimen type.