Elastic Modulus, Temperature Coefficient, and High-Temperature Service Performance of Elastic Clips
The temperature coefficient of the elastic modulus of the elastic clip is -0.02%/℃, how will it specifically cause the clamping force to change?
For every 10℃ increase in temperature, the elastic modulus of the elastic clip decreases by 0.2%, and the clamping force decreases synchronously by 0.2%. For example, when the normal temperature is 25℃, the clamping force of the elastic clip is 10kN, and at 55℃ high temperature, the clamping force drops to 9.7kN, a 3% decrease. If the temperature continues to rise to 70℃, the clamping force decay can reach 9%, which cannot effectively lock the rail. This is because the increase in temperature will aggravate the molecular chain movement of the elastic clip material, enhance the elastic deformation ability, leading to a decrease in preload. The high temperature in ordinary-speed lines lasts for a short time, and the decay is acceptable. However, high-speed and heavy-haul lines need to reduce the temperature coefficient through material optimization.
Why are 60Si2CrA elastic clips selected for high-temperature areas instead of 60Si2MnA elastic clips?
The temperature coefficient of 60Si2MnA elastic clips is -0.025%/℃, and the elastic modulus drops faster under high temperature, with a clamping force decay rate of 0.25%/℃. 60Si2CrA elastic clips add chromium elements, reducing the temperature coefficient to -0.015%/℃, a 40% reduction in the elastic modulus drop rate. At 50℃ high temperature, the clamping force decay of 60Si2CrA elastic clips is only 3%, while that of 60Si2MnA elastic clips reaches 5%. In addition, the high-temperature strength retention rate of 60Si2CrA elastic clips is ≥85%, much higher than 70% of 60Si2MnA, which can resist plastic deformation under high temperature. It is the preferred elastic clip for high-temperature areas.
What impact will too low elastic modulus of the elastic clip have on track smoothness?
Too low elastic modulus of the elastic clip will cause excessive deformation under the same load, the rail settlement exceeds the design value, and the track smoothness decreases. For example, when the elastic modulus drops from 200GPa to 160GPa, the rail settlement increases by 20%, and the rail surface becomes uneven. When the train passes, it will generate additional impact, exacerbating wheel-rail wear, and at the same time, the under-rail pad is subjected to uneven stress, increasing local compression deformation. Long-term too low elastic modulus will lead to cumulative deviation of track geometric dimensions, increasing line maintenance frequency and affecting driving safety. Therefore, the elastic modulus of the elastic clip must be controlled within the range of 190-210GPa to ensure track smoothness.
How to detect the elastic modulus and temperature coefficient of the elastic clip on site to judge the high-temperature adaptability?
On site, a high-temperature elastic modulus tester can be used to detect the elastic modulus of the elastic clip at three temperatures: 25℃, 50℃, and 70℃, and calculate the temperature coefficient. Elastic clips with a temperature coefficient ≤-0.015%/℃ are suitable for high-temperature areas, while those with a temperature coefficient >-0.02%/℃ are not. At the same time, a high-temperature clamping force test can be carried out. Place the elastic clip in a 50℃ environment and detect the clamping force decay rate; a decay ≤5% is qualified. In addition, observe the deformation of the elastic clip under high temperature; no plastic deformation is qualified, and deformation indicates insufficient elastic modulus, requiring replacement.
What impact does the fluctuation range of the elastic modulus of the elastic clip have on the overall stiffness of the fastening system?
A ±10GPa fluctuation in the elastic modulus of the elastic clip will cause a 15%-20% fluctuation in the overall stiffness of the fastening system. Too high elastic modulus will cause small deformation of the elastic clip and excessive clamping force, increasing the sleeper compressive stress and accelerating sleeper damage; too low elastic modulus will cause large deformation of the elastic clip and insufficient clamping force, leading to rail displacement and decreased track stiffness. The overall stiffness of the fastening system must match the line load. The fluctuation of the elastic modulus of the elastic clip must be controlled within ±5GPa to ensure the stability of the system stiffness, avoid sudden stiffness change of the track, and affect the running smoothness of the train.