A theoretical method for determining initiation toughness based on experimental peak load

A theoretical method for determining the initiation toughness was proposed using input conditions of the peak load and the tensile softening curve. In this method, the cohesive stress is considered to calculate the values of critical effective crack length, crack tip opening displacement, and the initiation toughness. The calculated results using the proposed method were compared with those by the double-K method+. The comparison showed that the values obtained by the proposed method were slightly greater than those by the double-K method. Moreover, the calculation results of initiation toughness by the proposed method were verified to be independent of the specimen size and not sensitive to the tensile softening curve.

► A theoretical method for determining the initiation toughness KICini is proposed.
► The KICini obtained by the proposed method were slightly greater than that by the double-K   method.
► The calculated KICini is independent of the specimen size.
► The calculated KICini is not sensitive to the tensile softening curve.