## 1 Introduction  
Aircraft carbon fiber/epoxy composite materials are insulated and more likely to be damaged by lightning strikes due to their high anisotropic electrical and thermal conductivity. Lightning discharge on composite materials can result in direct physical damage effects such as ablation, erosion, explosion, structural distortion, and strength degradation, influencing aircraft flight safety [1; 2]. Considering the complicated interaction between lightning plasma channels and composite structures, the damage mechanism has been studied through experiment and simulation methods. For example, the lightning damage process of composite laminates has been simulated through the coupled electrical-thermal numerical method [3; 4; 5]. Additionally, coupled thermal-electrical coupled analysis combined with the element deletion technique has also been used to evaluate the lighting ablation damage behavior of composite laminate and its protection structures in our previous study [6; 7]. Although numerical simulation can be used as an auxiliary method, lightning experiment verification and relative damage testing is indispensable for investigating damage behavior of carbon fiber/epoxy composite materials and their protection structures. Lightning experiments are aimed at collecting response information of composite structures exposed to lightning strikes for the development of lightning protection systems. The defect and damage characteristics of composite materials can be evaluated by non-destructive testing methods such as ultrasonic testing, X-ray inspection, optical method, and thermal wave testing [8]. For example, lightning experiments of both pristine composite specimens and specimens with stainless steel fasteners have been carried out by a simulated generator, with which the damage degree and pattern is tested via ultrasonic scanning and optical microscopy [9]. An artificial lightning experiment was also performed to investigate lightning damage behavior of graphite/epoxy composite laminates and concluded that lightning parameters, such as peak current, electrical charge, and action integral of lightning current waveform, greatly influence composite damage, the degree and pattern of which visual inspection, ultrasonic scanning, micro X-ray inspection, and sectional observation is used to test [10]. Available research shows that lightning strikes can induce fiber breakage, matrix cracking, and delamination accompanied with ablation and thermal decomposition under the thermal shock of supersonic plasma. At present, methods of lightning strike protection for aircraft composites include metal mesh or foil bonded with resin, metal or metalized fibers bonded with resin, and polymer-based film or conductive adhesives [11]. Considering the expense, lightning strike protection is generally achieved by covering conductive metals on composite surface such as the sprayed aluminum coating and embedded copper mesh filling. In addition, carbon nanofibers also have excellent electrical conductivity and thermal properties, which have a great potential application in aircraft lightning protection engineering [12]. When carbon nanofiber paper mingled with nickel nanostrands covers the composite surface, research shows that electrical conductivity plays an important role in reducing composite lightning damage [13]. Although these lightning protection strategies are effective, lightning damage to composite specimens is unavoidable. For the damaged carbon fiber/epoxy composite specimens with the embedded copper mesh filling, structural and electrical integrity can be reestablished to some extent by the bonded scarf repair with the embedded copper mesh filling, in which the damage area is overlapped by composite repair to reconnect the path of electrical conductivity [14]. In order to investigate the lightning damage behavior of T700/BA9916 carbon fiber/epoxy composite-reinforced panel and its protection structures, lightning experiments were carried out, and an ideal current waveform was adopted to simulate natural lighting strikes.