Hail impact responses and residual tensile properties of CFRP T-joints

Hail impact is a major challenge encountered by aircraft in flight, and thus is a key concern in the design of damage-tolerant composite T-joints in aviation. The study uses the Z-pinning technique (the pre-hole insertion technology) in combination with fillets of two radiuses to manufacture four types of Carbon Fiber Reinforced Polymers (CFRP) T-joints. The T-joints are then subjected to hail impact tests at two energy levels, as well as post-impact quasi-static tensile tests. The results show that increasing the size of the deltoid and Z-pin-induced reinforcement has a limited influence on the responses of the T-joints to hail impact, but a significant influence on their residual tensile strength after impact. These influences are not only dependent on the structural characteristics of the T-joints, but are also closely related to the degree of discrete damage within the T-joints caused by hail impact. Acoustic Emission (AE) technology is used to monitor the quantitative evolution of damage to the T-joints in a timely manner during the loading process, and helps characterize the characteristics of evolution of various types of damage over different periods. The research here can help design lightweight and damage-tolerant T-joints.