Strength-enhanced tapered composite laminate with ply curving termination and its geometry-dependent failure behavior under tensile loading

Ply Curving Termination (PCT) is an effective method to suppress stress concentrations at the composite ply edge by locally curving the reinforcing fibers to reduce the stiffness. Previous studies by the authors revealed that PCT can enhance the tensile strength of unidirectional ply drop-off specimens and that the PCT geometry influences the failure behavior. Following these basic studies, this current study applied PCT to more practically relevant quasi-isotropic tapered laminates and examined the effectiveness of PCT in detail. Tensile tests and X-ray CT observations were performed to evaluate the strength and failure process of the tapered laminates depending on the PCT geometry. PCT with appropriate geometry increased the damage initiation stress and delamination failure stress by more than 50%, and the enhanced strength was close to the strength of the thin section of the tapered laminate. Finite element analysis was then performed to examine the failure mechanism, clarifying that the mechanical interaction between the PCT and the surrounding layers has a significant influence on the damage initiation and delamination propagation. Finally, a design guideline to maximize the PCT effectiveness was discussed based on the PCT-specific failure mechanisms.