Matching the elastic parameters of the rail pad with the track stiffness
- What are the main elastic parameters of under-rail pads?
The elastic parameters of under-rail pads mainly include static stiffness, dynamic stiffness, elastic modulus and rebound rate. Static stiffness refers to the stiffness of the pad under static load, which affects the static deformation of the track; dynamic stiffness reflects the stiffness characteristics under dynamic load, which is closely related to the vibration response during train operation; elastic modulus is an indicator to measure the elastic deformation capacity of the material; rebound rate indicates the ability of the pad to return to its original state after being loaded, and the higher the rebound rate, the better the elasticity retention.
- What are the requirements for the elastic parameters of under-rail pads for different track types?
High-speed railways require under-rail pads to have low static stiffness (generally 40-60kN/mm) and good dynamic characteristics, and the ratio of dynamic stiffness to static stiffness should be less than 1.3 to reduce train vibration and noise; heavy-haul railways need higher static stiffness (80-120kN/mm) to bear large loads, and the dynamic stiffness should be stable to avoid resonance; ordinary railways have relatively loose requirements for elastic parameters, and the static stiffness can be between 60-100kN/mm to meet basic shock absorption and bearing needs.
- What problems will be caused by mismatched elastic parameters of under-rail pads?
If the pad elasticity is too strong (too small static stiffness), it will cause excessive track subsidence, leading to rail deformation, affecting the running smoothness of the train, and increasing the stress and wear of the ballast; insufficient elasticity (too large static stiffness) cannot effectively absorb vibration, and the train load is directly transmitted to the sleepers and ballast, accelerating the fatigue damage of the track structure, and also increasing the wheel-rail impact force, reducing passenger comfort.
- How to test the elastic parameters of under-rail pads?
When testing static stiffness, a pressure testing machine is used to apply graded static loads to the pad, record the corresponding deformation, and calculate the static stiffness; dynamic stiffness testing uses a dynamic fatigue testing machine to apply alternating loads at a certain frequency (such as 10-20Hz), measure the deformation under different loads, and obtain the dynamic stiffness; elastic modulus can be calculated according to the ratio of stress to strain through material tensile or compression tests; rebound rate testing is to compress the pad to a specified deformation, keep it for a period of time, then unload, measure the deformation after recovery, and calculate the rebound rate.
- How to adjust the elastic parameters of under-rail pads according to track stiffness?
When the track stiffness is large (such as concrete monolithic track bed), pads with better elasticity (smaller static stiffness), such as rubber pads, should be selected to reduce the overall track stiffness and achieve matching; when the track stiffness is small (such as ballast bed), pads with lower elasticity (larger static stiffness), such as polyurethane pads, should be used to avoid excessive track deformation; for track sections with uneven stiffness, local adjustment can be made by replacing pads with different elastic parameters to make the track stiffness tend to be uniform and ensure the smooth operation of the train.