## 4 Results and Discussion
### Comparative Analysis of Composite Sleeper Track under Different Temperatures  
The DMA test shows that the mechanical parameters of the composite sleeper are sensitive to temperature. Its modulus is larger at low temperatures and smaller at high temperatures. Therefore, it is necessary to analyze the vibration characteristics of composite sleeper-ballasted track at different temperatures. In this section, the mechanical parameters of tested and characterized composite sleepers at 5, 15, and 25 \({}^{\circ}\)C are selected and calculated based on the above model to obtain the power flow of the track structure at different temperatures.  
Figure 12 shows the rail power flow at different temperatures. It can be seen from the figure that the change of the composite sleeper's mechanical parameters caused by the temperature has a small effect on the rail power flow and only produces a small amount in individual frequency ranges. For example, at the center frequency of 40 Hz, the rail power flow values at 5 and 15 \({}^{\circ}\)C are reduced by 0.67 and 0.40 dB, respectively, compared with that at 25 \({}^{\circ}\)C.  
From Figure 13, the composite sleeper power flow values at different temperatures show that as the temperature increases, the input and output power flow of the sleeper hardly change in the frequency range below 31.5 Hz, while in the frequency range above 31.5 Hz, the power flow changes slightly. As the temperature increases, the sleeper input power flow shows an increasing trend; however, the sleeper output power flow shows a decreasing trend. At the center frequency of 80 Hz, the sleeper input power flow values at 5 and 15 \({}^{\circ}\)C are reduced by 3.2 dB and 2.8 dB, respectively, compared with that at 25 \({}^{\circ}\)C. At a center frequency of 125 Hz, the sleeper output power flow values at 5 and 15 \({}^{\circ}\)C are increased by 3.5 dB and 1.5 dB, respectively, compared with that at 25 \({}^{\circ}\)C. It can be seen from Figure 13b that as the temperature increases, the power flow of the sleeper transmission loss shows an increasing trend. This also shows that the smaller the modulus of the composite sleeper, the larger the internal power flow consumption. At the center frequency of 31.5 Hz, the loss power flow values of sleepers at 5 and 15 \({}^{\circ}\)C decrease by 5.8 dB and 3.0 dB, respectively, compared with at 25 \({}^{\circ}\)C.  
Figure 14 shows the ballast bed power flow. It can be seen that in most frequency ranges, temperature changes have little effect on the ballast bed power flow. In some frequency ranges, as the temperature increases, the ballast bed power flow decreases. At a center frequency of 125 Hz, the ballast bed power flow values at 5 and 15 \({}^{\circ}\)C are increased by 3.5 dB and 1.4 dB, respectively, compared with 25 \({}^{\circ}\)C. On the whole, the higher the temperature, the better the vibration reduction effect of the ballast bed.  
Figure 12: Rail power flow.  
Figure 14: Ballast bed power flow.  
Figure 13: Sleeper power flow: (**a**) Sleeper input and output power flow; (**b**) Sleeper consumption power flow.  
In summary, the temperature change mainly affects the power flow of the composite sleeper track structure in the frequency range above 50 Hz. The temperature change has little effect on the rail or ballast bed. However, the impact on the sleeper power flow is slightly greater. The higher the temperature, the smaller the modulus of the sleeper and the better the vibration reduction effect of the track bed.