## 1 Introduction  
With the rapid development of aircraft industry, carbon fiber/epoxy reinforced composite materials have been widely used in aircraft design in recent decades for its advantages such as lightweight, high specific modulus, high specific strength and designability, etc. However, composite materials have poor electric and thermal conductivity compared with traditional metal materials such as aluminum alloy and titanium alloy, which make aircraft structures more vulnerable to catastrophic damage in a lightning environment because of weak anti-lightning ability. Both military aircraft and civil aircraft will inevitably fly in thunderstorm weather, and probably encounter lightning strike in the process of normal service. Relevant reports show that an aircraft may encounter one lightning strike per 1000-1500 h of flight and this is roughly equivalent to once a year for regular airliner aircraft. Thermal damage induced by lightning strike attributes to ablation, phase-transition, thermal shock, and the blow-off impulse effect, etc. While traditional thermal loading such as fire does not include the dynamical effects of thermal shock and blow-off impulse, etc. When high-energy lightning current attaches to the surface of a composite structure, tremendous Joule heat will be transmitted to the composite structure immediately in the form of conduction and radiation, which will generate great energy deposition and resulting in the temperature to rise rapidly around the attachment area. Furthermore, when the temperature exceeds the critical value of molten, vaporization and decomposition of material, a series of physic-chemical changes will be generated around the attachment area and three-phase transition of solid-liquid-vapor will also be occurred instantly [1]. Temperature is unevenly distributed due to the anisotropic characteristic of composite materials, and then leads to the uneven expansion of materials. Therefore, the gas generated by matrix vaporization is easily surrounded by the non-vaporized matrix and fibers, which will cause a rapid rise in internal pressure. The vapor spatter phenomenon which leads to a thermal explosion will occur when the internal pressure exceeds the constraint strength of surrounding materials, thus resulting in a reverse impact effect on the composite structure. This impact effect can be called the blow-off impulse effect [2]. The huge impact generated by the thermal explosion will cause more serious damage to the composite structure. Therefore, the blow-off impulse effect should be considered when the direct effects of lightning strike are analyzed. At present, many scholars have investigated the thermo-dynamic response of composite materials and there have been abundant achievements on lightning damage of a composite structure. The representative studies on this experiment are as follows: [PERSON] et al. [3] carried out the lightning strike experiment of IM600/133 composite laminates, finding that damage modes of composite materials mainly include fiber fracture, matrix crack, and intra-laminar delamination etc. [PERSON] et al. [4] conducted an experiment to study the electric-thermal behavior of carbon fiber/epoxy composite materials subject to high-lightning current. The results reveal that lightning currents lead to a significant temperature rise around the attachment area, which is a result of the intense Joule heat effect generated in electric conductive fibers. [PERSON], [PERSON], and [PERSON] et al. [5,6]. conducted research on composite specimens using simulated lightning strike, with the fundamental damage responses of specimens studied and the damage mechanism of composite materials subject to three different current peaks compared. [PERSON], [PERSON], and [PERSON] et al. [7, 8, 9, 10] all reported a series of lightning strike experiments, which indicate that electric conductivity exerts a heavier effect on damage degree than thermal conductivity does.