A mechanics based study of crack closure measurement techniques under constant amplitude loading

► The CR and ACR methods are equivalent near the crack tip. ► The ACR method provides significant higher values for the crack closure ratio U than ASTM (2% offset) and Elber's method. ► The ACR method shows a small sensitivity to the measurement location behind the crack tip on the crack surface. ► A higher sensitivity to the location is demonstrated by the ASTM (2% offset) standard method when compared with the ACR method. ► The ASTM (2% offset) method is very sensitive to the measurement location. ► Elber's method (0% Offset) provided constant values of U for the complete range of locations evaluated. Elber's method (0% offset) is independent of measurement location and agreed fairly well with FE solution.