The role of broken fibres on crack migration into 0° surface plies in adhesively bonded carbon fibre composite joints.

Crack migration into the composite in adhesively bonded joints can cause a major degradation of strength. This usually occurs via cracks in the surface plies, but this paper demonstrates that crack migration can occur in joints even with 0° surface plies. The role of surface treatment is investigated by comparing grit blasted and plasma surface treatment before the secondary bonding process. Unidirectional Double Cantilever Beam specimens and quasi-isotropic Double Lap Joints with surface 0° plies were tested. It was found that with grit blasted specimens, crack migration occurred due to broken fibres present on the composite surface. Plasma treated specimens with no broken fibres on the surface failed in the adhesive with substantial increases in the Mode I fracture toughness and the strength of the double lap joints. [ABSTRACT FROM AUTHOR]