Stiffness Matching and Vibration Reduction Effect of Rail Pads
What are the clear requirements for the stiffness indicators of under-rail pads for high-speed railways?
The static stiffness of the under-rail pads matched with the high-speed railway elastic strip Ⅳ/V type fasteners should be controlled at 60±10kN/mm to ensure the buffering effect on wheel-rail vibration. Its dynamic-static stiffness ratio must be ≤2.0 to avoid sudden stiffness changes under dynamic loads that cause track diseases. The tensile strength of the pad should be ≥14MPa before aging to ensure structural integrity during long-term service. The working resistance of the pad should be ≥1×10^9Ω to meet the insulation requirements of electrified lines. In addition, the pad must pass 3 million fatigue tests to ensure that it does not fail under high-frequency vibration.
What is the basis for selecting the stiffness of under-rail pads for mixed passenger and freight railways?
The static stiffness range of under-rail pads for mixed passenger and freight railways is 55-120kN/mm, which needs to be adjusted according to the axle load and train density of the line. For heavy-haul sections with an axle load of 25t, high-stiffness pads of 80-120kN/mm should be selected to ensure bearing capacity. Passenger-dominated sections can choose low-stiffness pads of 55-80kN/mm to improve vibration reduction effect. The dynamic-static stiffness ratio of the pad also needs to be ≤2.0 to maintain stability under dynamic loads. At the same time, the pad must be compatible with the fastener type of the line to ensure the coordination of the overall system.
How does the material of under-rail pads affect stiffness stability?
Pads made of natural rubber have good stiffness stability, with small stiffness fluctuations in the temperature range of -40℃ to 60℃, suitable for alpine and high-temperature areas. Composite pads are formed by vulcanizing stainless steel and rubber, and their stiffness is less affected by temperature with higher peel strength. Pads made of reclaimed rubber are prone to stiffness attenuation over time and are not suitable for mainline railways in long-term service. Rubber pads added with reinforcing agents such as carbon black can improve the uniformity of stiffness and reduce batch differences. In addition, polyurethane pads have high stiffness and are suitable for the special needs of heavy-haul lines.
Why can't the dynamic-static stiffness ratio of the pad exceed 2.0?
If the dynamic-static stiffness ratio is greater than 2.0, the pad will experience a sharp increase in stiffness under dynamic loads, which cannot effectively buffer wheel-rail vibration. An excessively high dynamic-static stiffness ratio will intensify the dynamic response of the track and increase the risk of fatigue damage to rails and fasteners. Exceeding this ratio will reduce the ride smoothness of the train and affect passengers' riding experience. An excessive dynamic-static stiffness ratio will also transmit track vibration to the track bed, accelerating the deterioration of the track bed structure. At the same time, exceeding this indicator will reduce the service life of the pad and increase the frequency and cost of later maintenance.
How to detect whether the stiffness performance of under-rail pads meets the standard?
To test the static stiffness of the pad, the test method in Appendix A of TB/T 3395.1 should be adopted, and graded loads should be applied through special equipment to record the deformation. The dynamic-static stiffness combined test can obtain the dynamic and static stiffness values synchronously to calculate the dynamic-static stiffness ratio. Tensile strength testing should be carried out in accordance with GB/T 528 standard, and samples should be taken for testing before and after aging to compare performance changes. Insulation performance testing should be performed in accordance with Appendix B of TB/T 2626 to ensure that the working resistance meets the requirements. For fatigue performance, 3 million cycles of load tests are required to observe whether the pad has cracks or sudden stiffness changes.