Comparative study of composite scarf and strap joints for equivalent repair signature under uniaxial tension

Scarf joints are preferred in aerospace composite repairs that offer better strength, flushed surface and nearly uniform shear and peel stress distribution along the bond length. However, a shallow scarf angle repair of 2 to 3 as practiced requires significant parent material removal thus increasing the repair signature and cost. Scarfing the single side accessible, multi-layered composite structures is difficult. Herein, different repair designs based on 8.6 scarf, thin CFRP strap (0.5 mm and 1.1 mm), 0.5 mm thin Ti-6Al-4V straps (with and without pins) are used in bonding CFRP composites, their repair strength is measured through tensile testing. Results show that the failure load of the scarf and Ti-6Al-4V strap joints are similar implicating that the higher scarf angle designs can be replaced with Ti-6Al-4V straps for better repair efficacy. Failure analysis depicts that delamination due to the inner edge peel stresses is a critical failure mode of the strap repaired joints.

Automated summary

Scarf joints are commonly used in aerospace composite repairs due to their improved strength, surface quality, and distribution of shear and peel stress. However, shallow scarf angle repairs require removing a significant amount of parent material, increasing cost and complexity. This study compared different repair designs and found that higher scarf angles can be replaced with Ti-6Al-4V straps for better repair efficacy.