Interlaminar fracture toughness of hybrid composites based on commingled yarn fabrics

The effect of introducing low-cost thermoplastic fibres to a reinforcing fabric is assessed in terms of the interlaminar toughness values GIc and GIIc of laminates prepared with both polyester and epoxy resins. It is shown that the thermoplastic fibres in general will increase the GIc of the laminates but have little effect on GIIc. This situation, however, changes if the thermoplastic fibres dissolve in the thermosetting resin during the curing cycle. In these cases, the addition of the thermoplastic does not improve the GIc but can substantially increase GIIc. The magnitude of any improvement in GIIc caused by dissolved fibres will depend on the morphology of the matrix in the final composite.