## 3 Results and Discussion
### Analysis of the Blow-Off Impulse  
The elements with temperatures exceeding 3316 \({}^{\circ}\)C are not defined as failures in the electric-thermal coupling module, but selected as the blow-off impulse elements in the blow-off impulse module. Therefore, element failure is not considered in the electric-thermal coupling module. Figure 9 presents the finite element model of blow-off impulse, it can be seen from Figure 9 that there are 38 blow-off impulse elements in the center area of the composite reinforced panel, while the rest areas are non-blow-off impulse elements. These 38 blow-off impulse elements all concentrate on P1 layer and P2 layer of the benchmark skin. Solution time is 2 \(\upmu\)s, the step length factor is set as 0.6, and the output step number is 22. Keyword file is output and submitted to LS-DYNA solver after it is modified in LS-PrePost. Failure elements are defined according to the maximum failure strain. As expressed in Equation (3), yield function can be built through strength parameters and stress tensor  
Figure 7: Temperature change along the thickness direction. of composite materials. Elements will enter the plastic phase when \(f\) is greater than zero. Elements will then deform continuously subject to external load and the stiffness of composite materials will be reduced too. The maximum failure strain is defined in the keyword file of ANSYS/LS-DYNA. If the equivalent strains of elements are greater than the maximum failure strain, the elements are defined as failures and will be deleted. Figure 8: _Cont._  
Figure 8: Temperature distribution of the top 17 layers in the benchmark skin of the composite reinforced panel. (Unit: \({}^{\circ}\)C). Figure 9: Finite element model of the blow-off impulse of the composite reinforced panel. Figure 10 presents the contours of von Mises stress in the top seven layers when the blow-off impulse analysis is completed. It can be seen that the damage caused by blow-off impulse mainly concentrates on the center areas of each layer, and the element deletion phenomenon only appears in the top six layers of the benchmark skin. P1 layer is the most seriously damaged, with 38 elements deleted and size of the failure area is about 50 \(\times\) 21 mm. However, the contours of von Mises stress is not along 45\({}^{\circ}\) in P1 layer but deviates from the fiber direction. In P2 layer and P3 layer, 27 and 40 elements are removed, respectively. The sizes of the failure areas in these two layers are almost the same. There are four elements deleted in P4 layer, P5 layer, and P6 layer, respectively, and no elements deleted after P7 layer. However, there is a large stress concentration phenomenon in the center area of P7 layer. Additionally, the influence on stress distribution between each layer is very significant. For example, stacking sequences of P2 layer and P3 layer are 0\({}^{\circ}\) and \(-\)45\({}^{\circ}\), respectively, but the contours of von Mises stress are not along the fiber direction in each layer. It can be concluded that the damage forms caused by the blow-off impulse effect alter the initial damage distribution caused by the electric-thermal coupling effect, which makes the damage distribution t deviate from the initial fiber direction. Figure 10: Contours of von Mises stress on the top seven layers of the benchmark skin. Figure 11 presents the pressure contours of the composite reinforced panel in several typical moments. It can be seen that the implosion effect starts to appear when time is equal to 0.099 \(\upmu\)s and great pressure is formed immediately. The maximum pressure is 4.443 \(\times\) 10\({}^{8}\) N, but no elements are deleted at this moment. The element deletion phenomenon starts to appear on the top three layers when time is equal to 0.4 \(\upmu\)s. Six layers exhibit element deletion phenomenon when time is equal to 1.5 \(\upmu\)s, and an obvious concave pit is formed around the blow-off impulse area.