New through-thickness reinforcement (TTR) method to improve fracture toughness of composite laminates was developed using high speed drilling of sub-millimeter holes with fibrous carbon rods. The proposed technique alleviates certain manufacturing problems encountered when using conventional z-pinning, while showing significant improvements in interlaminar toughness properties.

Failure surface with TTR rods pulled out after delamination propagation

Two to eight times improvement in delamination resistance under mode I conditions using proposed TTR technique depending on the aspect ratio of the rod