## 3 Results and Discussion  
### Analysis of Electric-Thermal Coupling  
Due to the fact that electric conductivity and thermal conductivity of fiber are much higher than that of the matrix and the anisotropic characteristic of carbon fiber/epoxy composite materials, composite materials present low electric conductivity and thermal conductivity as a whole. When lightning current attaches to the surface of composite materials, it will conduct internally along the attachment points and huge Joule heat will be generated during the conduction process within composite materials. Temperature distribution around the attachment area of the composite reinforced panel is shown in Figure 5 when the calculation is completed. It can be seen from Figure 5 that the temperature profile around the attachment area resembles an ellipse, and the long axis of the ellipse is along fiber direction in P1 layer. The highest temperature is 83937.3 \({}^{\circ}\)C, which is much higher than the ablation and sublimation temperatures of carbon fiber. However, the temperature drops sharply along the thickness direction due to the low electric conductivity and thermal conductivity in the thickness direction. Figure 6 presents the temperature distribution in the cross-section and Figure 7 presents the temperature change in the top 17 layers of the benchmark skin. It can be seen from Figures 6 and 7 that the temperatures around the attachment area mainly focus on the top three layers of benchmark skin, with very a small temperature rise in the P4-P16 layers. Temperatures in P16-P24 layers and the T stripper have almost no change. Therefore, it can be concluded that the Joule heat generated by the lightning current mainly causes significant thermal damage in the top three layers around the attachment area, with very little damage in other areas. Figure 5: Temperature distribution around the attachment area of the composite reinforced panel. (Unit: \({}^{\circ}\)C). Figure 6: Temperature distribution in the cross-section of the composite reinforced panel. (Unit: \({}^{\circ}\)C). Figure 8 presents the temperature distribution in the top 17 layers of benchmark skin. It can be seen that the closer to the top layer, the higher the temperature will be. The temperature profile in the P1 layer is similar to an ellipse shape and the long axis of the ellipse is roughly along the fiber direction (45\({}^{\circ}\)). The influence between each layer is very significant, which can be verified from the temperature contours in P2 layer, P3 layer, P5 layer, P6 layer, and P8 layer. Stacking sequences in these layers are 0\({}^{\circ}\), \(-\)45\({}^{\circ}\), \(-\)45\({}^{\circ}\), 0\({}^{\circ}\), and 0\({}^{\circ}\), respectively, but the temperature distribution is not along the fiber direction in each layer. These serious effects are mainly caused by the low thermal conductivity in the thickness and transverse direction. The Joule heat effect mainly concentrates on the top three layers of benchmark skin, which is due to the fact that the electric conductivity and thermal conductivity in the thickness direction are much lower than that in the fiber direction. Lightning current mainly conducts along fiber direction in P1 layer, P2 layer, and P3 layer, only a small amount of lightning currents conduct along the thickness direction. The high electric resistance blocks the conduction of lightning current along the thickness direction, which can be confirmed through the temperature distribution in the cross-section, as shown in Figure 6. For example, the highest temperatures in P1 layer and P2 layer are 83,937.3 and 42,806.7 \({}^{\circ}\)C, respectively. While the temperature in P3 layer has dropped to 794.83 \({}^{\circ}\)C, indicating that only the top two layers will be ablated around the attachment area under this current waveform. The temperature in P4 layer is just 83.0886 \({}^{\circ}\)C, which is lower than the molten temperature of resin.