The Correlation Mechanism Between the Preload Attenuation Law of Spring Clips and Temperature Cyclic Loading
How much will the preload of the elastic clip decay when the temperature changes by 30℃, and why does it show periodic changes?
When the temperature changes by 30℃, the preload of the elastic clip will decay by 8%-12%, showing periodic fluctuations with temperature cycles. At high temperatures, the thermal expansion of the elastic clip material increases the elastic deformation, the internal stress decreases, and the preload drops; at low temperatures, the material contracts cold, the elastic deformation decreases, and the internal stress recovers, leading to a rebound in preload. However, slight creep occurs in each cycle, causing stress relaxation, and the preload cannot fully return to the initial value. Under long-term temperature cycles, the preload of the elastic clip will continue to decrease and eventually fall below the design value, causing rail loosening.
Why do lines in high-temperature areas choose 60Si2CrA elastic clips instead of 60Si2MnA elastic clips?
The ambient temperature in high-temperature areas can reach above 50℃. The high-temperature elastic modulus of 60Si2MnA elastic clips decreases rapidly, the creep rate is high, and the preload decay rate reaches 15% per year. 60Si2CrA elastic clips add chromium elements, with better high-temperature stability, a smaller decrease in elastic modulus, a 40% reduction in creep rate, and a preload decay rate of only 6% per year. In addition, the high-temperature tensile strength of 60Si2CrA elastic clips is 120MPa higher than that of 60Si2MnA elastic clips, which can resist plastic deformation at high temperatures. Therefore, high-temperature lines need to choose 60Si2CrA elastic clips with better high-temperature performance.
The relationship between the preload decay of elastic clips and the rate of rail temperature change, why does the faster the rate, the more severe the decay?
The faster the rail temperature change rate, the more lagging the thermal expansion and contraction response of the elastic clip material, and the greater the amplitude of internal stress mutation. During rapid heating, the elastic clip cannot expand in time, generating tensile stress inside and accelerating creep; during rapid cooling, the elastic clip cannot contract in time, generating compressive stress inside and causing elastic fatigue. When the rail temperature change rate exceeds 5℃/h, the preload decay rate of the elastic clip will increase by 30%. The rail temperature change of ordinary-speed lines is gentle, usually ≤3℃/h, and the decay of elastic clips is slow; the frequent braking and acceleration of trains on high-speed lines lead to rapid rail temperature changes, making the decay of elastic clips more significant.
What impact will the decrease in clamping force of elastic clips under low-temperature environment have on the track geometric dimensions?
At low temperatures, the elastic modulus of the elastic clip material increases, and the clamping force decreases, making it impossible to effectively lock the rail. The rail will produce longitudinal displacement due to temperature contraction, leading to the expansion of rail gaps and the increase of gauge deviation. When the gauge deviation exceeds 2mm, the train will generate lateral impact when passing through the curved section, exacerbating wheel-rail wear. At the same time, insufficient clamping force of the elastic clip will cause uneven stress on the under-rail pad, increase local compression deformation, and reduce track smoothness. Under long-term low-temperature environment, the deviation of track geometric dimensions will accumulate continuously, increasing line maintenance costs and even affecting driving safety.
How to control the periodic decay of elastic clip preload through temperature compensation on site?
On site, the temperature compensation method can be used to adjust the installation preload of the elastic clip according to the rail temperature. When the rail temperature is higher than 35℃, increase the preload by 5%-8% to offset the high-temperature decay; when the rail temperature is lower than 0℃, reduce the preload by 3%-5% to avoid low-temperature brittle fracture. At the same time, bimetallic elastic clips can be selected, whose elastic modulus fluctuation range with temperature change is 50% smaller than that of ordinary elastic clips, and the preload decay is more gentle. In addition, regularly detect the preload of elastic clips, and tighten or replace them in time when the decay exceeds 10% to ensure long-term track stability.