## 4 Numerical Simulation of Interface Damage of Ballastless Track under Temperature Load
### Interface Damage Analysis under Uniform Temperature Load
When \(\Delta t\)\(=\) 5.9 \({}^{\circ}\)C, QUADSCRT at the expansion joint increased to 1, suggesting that the interface microcracks started to generate. When \(\Delta t\) was 19.2 \({}^{\circ}\)C, interface macroracks initiated and propagated. From the initiation of interface microcracks to the initial debonding of the adjacent layers, the temperature increase was about 13.3 \({}^{\circ}\)C. The temperature rising range was 45.8 \({}^{\circ}\)C for the macroracks to expand completely and the whole interface to delaminate. Then, the interface under the expansion joint of the base plate was selected as the research object--the effect of interface parameters and temperature loads on the interface cracking performance was analyzed. The interface parameters included interfacial shear strength, interfacial shear stiffness, and critical fracture energy, and their values are listed in Table 5. When analyzing the impact of one parameter, the other parameters, in the middle column of Table 5, are the corresponding values. Figure 7: Interface damage evolution process under uniform temperature load. The variation curve of the QUADSCRT index at the adjacent joint under different working conditions with the temperature rising range is plotted in Figure 9. As shown in Figure 9a, \(\Delta t\) needed for the initiation of interface damage (microcracks) increased with the increase in interfacial shear strength, but \(\Delta t\) needed for the initiation of macrocracks was not impacted by the interfacial shear strength. Also, the slopes of the QUADSCRT temperature rising range curves in Figure 9a indicate that the larger the interfacial shear strength, the faster the interfacial damage propagation rate. Increasing the interfacial shear strength is conducive to the stability of the whole structure. \(\Delta t\) needed for the initiation of microcracks decreased as the interfacial shear stiffness increased, while \(\Delta t\) needed for macrocrack initiation remained unchanged (Figure 9b). These results indicate that an increase in interfacial shear strength makes the interfacial damage (microcrack) more sensitive to the temperature changes, but has a little influence on the initiation behavior of interfacial macrocracks. As shown in Figure 9c, with an increase in the critical fracture energy, \(\Delta t\) needed for initiation of the interface damage remained unchanged, while \(\Delta t\) needed for the macrocracks' initiation increased. One effective way to reduce the sensitivity of the interfacial macrocracks to temperature changes is to increase the interfacial critical fracture energy. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Temperature** & **Rising Range (\({}^{\circ}\)C)** & **Interfacial Damage Area Ratio** & **Interfacial Detached Area Ratio** \\ \hline
5 & 0 & 0 \\
10 & 20 & 0 \\
15 & 40 & 0 \\
20 & 70 & 12 \\
30 & 90 & 43 \\
40 & 95 & 55 \\
50 & 98 & 80 \\
60 & 99 & 92 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Interfacial damage and detachment area ratio. Figure 8: QUADSCRT and SDEG varying with \(\Delta t\). As per the above analysis, the interface with larger interfacial strength and toughness has a smaller damage area. The greater the interfacial stiffness, the stronger the interaction between adjacent layers and the easier the generation of interface damage. Therefore, appropriate material and necessary measures (such as toughening by brushing) should be adopted in the construction of the interface. Figure 9: QUADSCRT-\(\Delta t\) curves of different interface parameters: (**a**) Impact of interfacial shear strength; (**b**) Impact of interfacial shear stiffness; and (**c**) Impact of critical fracture energy. of asphalt concrete layer to guarantee excellent strength and toughness at the interface, in order to enhance the deformation coordination ability between CCBP and ACWL, especially in the shear direction. During the maintenance stage, patching material with high strength, high toughness, and lower stiffness should be selected. Meanwhile, measures (such as laying geotextiles, etc.)