Variable Angle Tow reinforcement design for locally reinforcing an open-hole composite plate

The paper proposes the novel Variable Angle Tow (VAT) placement technique to create local reinforcement on fiber reinforced composites with holes which enables to optimize the design for variable stiffness laminates by placing continuous fiber to follow the pre-calculated principle stress trajectories automatically. The potential factors influencing the strengthening effect are investigated, including reinforcement types, lay-up configurations and dimensions. The results from tensile test discusses the failure modes and reveals that with VAT reinforcement, especially the elliptical reinforcement, the ultimate strength of the open-hole specimen can be significantly improved compared with the plain cloth reinforcement. It is also found that the double-sided reinforcement configuration is superior to single-sided or interlayer configurations, and both the circular and elliptical VAT reinforcements possess their optimal dimensions when considering the weight. Subsequent Finite Element Analysis indicates the reinforcing mechanism that the stress concentration in the reinforced region is alleviated by redistributing the stress to the outer unreinforced region.