Factors affecting the dynamic stiffness of the rail pad and its test
- What is the difference between the dynamic stiffness and static stiffness of under - rail pads?
Dynamic stiffness is the stiffness of the pad under alternating loads, which is affected by the load frequency. The higher the frequency (such as when the train passes at high speed), the dynamic stiffness is usually 10% - 20% higher than the static stiffness. Static stiffness is the stiffness under static loads, which only reflects the static stress state, while dynamic stiffness can better reflect the shock absorption performance of the pad in actual operation, and they cannot be directly equated.
- What factors will affect the dynamic stiffness of under - rail pads?
The pad material is the core. The dynamic stiffness of rubber pads increases with the increase of hardness. For every 10 degrees increase in Shore A hardness, the dynamic stiffness may increase by 15% - 20%. The load size has an obvious impact. The dynamic stiffness increases with the increase of load. The stiffness under heavy - duty loads (such as 25t axle load) is 20% - 25% higher than that under ordinary loads (16t axle load), with significant nonlinear characteristics.
- How to test the dynamic stiffness of under - rail pads?
Use a dynamic stiffness tester to apply sinusoidal alternating loads (frequency 1 - 50Hz, simulating train vibration frequency), record the pad deformation under different frequencies and loads, and calculate the dynamic stiffness (stiffness = dynamic load/dynamic deformation). During testing, the ambient temperature must be controlled (usually 23℃±2℃), as temperature changes will affect the material performance and lead to deviations in test results, requiring temperature correction.
- What impact does dynamic stiffness have on the comfort of train operation?
Excessively high dynamic stiffness results in poor shock absorption performance of the pad. The proportion of train vibration transmitted to the ballast bed and foundation increases, and the noise and vibration in the carriage increase, reducing passenger comfort. Passengers are prone to fatigue after long - term riding. Too low dynamic stiffness leads to excessive deformation of the pad, making the rail prone to large displacement, affecting the track geometry, and possibly causing unstable train operation, which also affects comfort and safety.
- What are the differences in dynamic stiffness among under - rail pads of different materials?
The dynamic stiffness of natural rubber pads is relatively low (usually 100 - 200MN/m), with good shock absorption performance, suitable for high - speed railways, and can effectively reduce vibration. The dynamic stiffness of chloroprene rubber pads is slightly higher (150 - 250MN/m), with better aging resistance, suitable for ordinary railways. The dynamic stiffness of polyurethane pads is higher (200 - 300MN/m), with strong bearing capacity, suitable for heavy - haul railways.