Fracture Mechanics Approaches to Transverse Ply Cracking in Composite Laminates

The growth of transverse ply cracks in composite laminates has been investigated both theoretically and experimentally. Some of the closed-form strain energy release rate based analyses of this problem in the literature have been compared and extensions to these approaches are presented. These models have been shown to be consistent with an alternative approach based on an approximate expression for the stress intensity factor at the tip of a growing transverse ply crack. An experimental study of transverse ply crack growth has been carried out using a simple model array of transverse ply cracks in a glass/epoxy laminate. By making the transverse ply sufficiently thick, the specimen compliance was found to change measurably as individual cracks grow. Hence, the strain energy release rate could be determined experimentally (via the compliance relationship) and compared with analytical predictions. Agreement was found to be satisfactory.