Mode-I interlaminar fracture behaviour of weft-knitted fabric reinforced composites

An experimental study was undertaken to characterise delamination behaviour of composites reinforced with selected weft-knitted glass fibre preform fabrics, viz. 1×1 rib, full milano and interlock, with respect to the effect of knitted preform structures and fibre volume content. The interlaminar fracture toughness (GIC) was evaluated using mode-I double cantilever beam (DCB) specimens stiffened with aluminum strips, and was compared with that of a uniweave fabric composite. The GIC values for the knitted fabric composites were about 10 or 20 times higher than those for the uniweave composite, and GIC increased with decreasing fibre volume fraction of the knitted composites. Furthermore, GIC was strongly dependent on the tightness factor of the knitted preforms. The variation in GIC is discussed in terms of fracture mechanisms through observation of interlaminar crack growth behaviour and post-fracture surfaces.