Fractography and Fracture Criteria of the Delamination Process

Angle-ply laminates of T300/1034 graphite/epoxy were loaded in tension. Prior to ultimate failure the interlaminar out-of-plane stresses cause edge delamination. The onset of delamination is determined by the strain energy release rate in the interlaminar region. Values of the critical strain energy release rate (Gc) for edge delamination calculated from the strain at delamination onset were fitted to a geometrical fracture criterion. It is seen that Gc increases with the KIII/KI ratio in the interlaminar region. The delamination fracture surfaces exhibit hackle formation, and the tilt of the hackles is characteristic of the interlaminar state of stress.