A method of evaluation of transverse critical energy release rate (fiber failure mode) in advanced composites

Ultimate failure of composite laminates typically involves fiber failure after a number of spurious cracking modes have developed and grown. The possibility that this failure can be treated as a legitimate fracture process has apparently been neglected due to the difficulty in producing the appropriate failure mode in the laboratory. This issue is addressed in this communication, where we design a specimen in which the 0 degree ply is sandwiched between 90 degree plies which serve as guides to direct the crack propagation across the fibers. The corresponding fracture anisotropy, or the ratio of the transverse and longitudinal critical energy release rates is found to be 1,011 for a graphite-epoxy unidirectional composite, the highest fracture anisotropy measured to date.