Impact damage characterization of carbon fibre/epoxy composites with multi-layer reinforcement

Low-velocity impact tests were performed to investigate the impact behaviour of carbon fibre/epoxy composite laminates reinforced by short fibres and other interleaving materials. Characterization techniques, such as cross-sectional fractography and scanning acoustic microscopy, were employed quantitatively to assess the internal damage of some composite laminates at the sub-surface under impact. Scanning electron microscopy was used to observe impact fractures and damage modes at the fracture surfaces of the laminate specimens. The results show that composite laminates experience various types of fracture; delamination, intra-ply cracking, matrix cracking, fibre breakage and damage depending on the interlayer materials. The trade-off between impact resistance and residual strength is minimized for composites reinforced by Zylon fibres, while that for composites interleaved by poly(ethylene-co-acrylic acid) (PEEA) film is substantial because of deteriorating residual strength, even though the damaged area is significantly reduced. Damages produced on the front and back surfaces of impact were also observed and compared for some laminates.