A simple method for determining the mode I interlaminar fracture toughness of composite without measuring the growing crack length

The modified beam theory (MBT), compliance calibration method (CC) and modified compliance calibration method (MCC) were recommended by the ASTM standard D5528 to determine the interlaminar fracture toughness of composite materials. Their shortcomings are the requirement of measuring the growing crack length, which is tedious and the source of uncertainty. By using the solution from two dimensional elasticity analysis of orthotropic double cantilever beam, a double compliances method is proposed to determine the fracture toughness. The procedure of the present method is nearly the same as that recommended by the ASTM standard, except avoiding measuring the growing crack length. The fracture toughness determined from the present method is consistent with the results obtained by using the ASTM standard methods. However, the present method is easier to conduct and has wider applications, compared with the ASTM standard methods.