Constrained cracking in glass fibre-reinforced epoxy cross-ply laminates

Specimens of 90° cross-ply glass-reinforced epoxy resins were tested in tension parallel to the direction of reinforcement in the outer plies. The thickness of the inner ply was varied and cracking constraint was observed at small thicknesses. At large inner-ply thicknesses the specimens showed uniform transverse cracking, and at very low inner-ply thicknesses this transverse cracking could be suppressed completely prior to total specimen failure. Fracture toughness values were determined on transverse unidirectional laminates of the same volume fraction. It was found that the cracking constraint observed can be accounted for, using the theory of Aveston and Kelly.