Novel Methods for Measuring the Mode I and Mixed Modes I/II Interlaminar Fracture Toughnesses of Composite

The present paper devised two novel methods to measure the mode I and mixed modes I/II fracture toughness for composite materials. A double compliance method is proposed for the mode I interlaminar fracture. Only the load and displacement recorded from the test machine are required for the determination of the fracture toughness. It is then used for a DCB test in a cold temperature chamber, where the crack growth length is difficult to get access. Using this method, the finite crack length and fracture toughness can be obtained from the load-displacement relation. In addition, a simple method is proposed to overcome the shortcoming of the current ASTM D6671 by using the mixed modes bending (MMB) specimen. It avoids the measurement of the Young’s moduli from separate tensile tests. The average relative difference between the mixed modes fracture toughness measured from the present method and that from the ASTM D6671 with additional tensile tests to measure the Young’s moduli is within 5%, thus the present paper provides a consistent and simple method for measuring the mixed modes I/II interlaminar fracture toughness. The present methods are simple and accurate, therefore significantly simplifying the procedure for measuring the mixed modes interlaminar fracture toughness.