Experimental investigation into temperature- and frequency-dependent dynamic properties of high-speed rail pads

In order to investigate the temperature- and frequency-dependent dynamic properties of high-speed rail pads excited by rail vehicle's large-amplitude quasi-static loads due to bogie interval and wheelset spacing, the soft pads from WJ-7, WJ-8 and Vossloh 300 fasteners frequently used in China's high-speed railway track systems are taken as test subjects. At first, a series of dynamic tests of the three high-speed rail pads at a specific frequency of 0.3 Hz and under various low temperatures ranging from −60 to 20 °C are carried out. Then, the Time-Temperature Superposition (TTS) and Williams-Landel-Ferry (WLF) formula are used to predict their dynamic performance at frequencies higher than the test frequency, and the Fractional Derivative Kelvin-Voigt (FDKV) model is proposed to represent their frequency-dependent dynamic properties. Finally, the frequency-dependent dynamic performance of the three high-speed rail pads under rail vehicle's small-amplitude dynamic loads due to the surface roughness of rail and wheel is discussed. It is found that the storage stiffness of WJ-7, WJ-8 and Vossloh 300 rail pads is sensitive to low temperatures, as well as much larger than their corresponding loss stiffness. The glass transformation temperatures of WJ-7, WJ-8 and Vossloh 300 rail pads are −40, −45 and −45 °C, respectively. The FDKV model can basically give a satisfactory fitting with the experimental results within 100 Hz, especially at ordinary temperatures. The dynamic properties of rail pads excited by rail vehicle's small-amplitude dynamic loads are time-variable and related to rail vehicle's large-amplitude quasi-static load values on rail pads. Thus, it is very important that the temperature- and frequency-dependent dynamic parameters of the polymer materials in vehicle-track systems must be measured according to the specific operation conditions, since otherwise an accurate prediction of the broadband train-induced vibration and noise at different temperatures is difficult to achieve.