Elastic rail stiffness matching technology and fastening adaptation schemes for different rail types
What are the two major influence mechanisms of elastic strip stiffness on rail fastening effect?
The first influence mechanism of elastic strip stiffness on rail fastening effect is the preload retention mechanism. The stiffness of the elastic strip determines the attenuation rate of preload. Under the action of train vibration load, the preload attenuation rate of the elastic strip with moderate stiffness is ≤5%/year, which can maintain stable compression on the rail for a long time; the preload attenuation rate of the elastic strip with insufficient stiffness can reach more than 15%/year, and rail loosening will occur in a short time. The second influence mechanism is the vibration energy absorption mechanism. As an elastic element, the elastic strip needs to absorb part of the wheel-rail vibration energy. The elastic strip with excessive stiffness has poor elastic deformation ability and cannot effectively absorb vibration energy, resulting in direct transmission of vibration load to the sleeper and accelerated sleeper damage; the elastic strip with insufficient stiffness has excessive deformation, which is prone to plastic deformation and loss of fastening function. These two mechanisms are interrelated. Preload retention is the foundation, and vibration energy absorption is the guarantee. Only the elastic strip whose stiffness matches the rail can realize these two functions at the same time. For example, the Type Ⅲ elastic strip adapted to the 60kg/m national standard rail has a stiffness controlled at 60kN/mm, which can not only maintain stable preload, but also effectively absorb vibration energy, with the best fastening effect.
What are the calculation method and key influence parameters of elastic strip stiffness?
The calculation of elastic strip stiffness adopts the beam bending theory of material mechanics. The core calculation formula is k=L33EI, where k is the elastic strip stiffness, E is the material elastic modulus, I is the elastic strip section moment of inertia, and L is the effective cantilever length of the elastic strip. The key influence parameters include three aspects: first, material elastic modulus. The elastic modulus of 60Si2CrVA spring steel commonly used for elastic strips is 206GPa. Replacing it with other materials will directly change the stiffness value; second, section moment of inertia, which is closely related to the section width and thickness of the elastic strip. For every 1mm increase in section thickness, the section moment of inertia increases by about 20%, and the stiffness increases significantly; third, effective cantilever length. For every 5mm reduction in cantilever length, the stiffness increases by about 15%. Adjusting the cantilever length is a convenient way to change the elastic strip stiffness. During calculation, the actual stress state of the elastic strip needs to be considered, and the theoretical calculation value is corrected by finite element simulation software. The deviation between the corrected stiffness value and the measured value must be ≤3%. In addition, the heat treatment process of the elastic strip will also affect the stiffness. The elastic modulus of the elastic strip with insufficient quenching is low, and the stiffness will be about 10% lower than the design value.
What are the stiffness design parameters and optimization points of the elastic strip adapted to the 60kg/m national standard rail?
The Type Ⅲ elastic strip is selected for the 60kg/m national standard rail. The core stiffness design parameters are stiffness value 60±5kN/mm and preload 12-15kN. These parameters can balance the two requirements of preload retention and vibration energy absorption. The first optimization point is section size optimization. The section thickness of the working section of the elastic strip is designed to be 10mm and the width 25mm. The stiffness stability is improved by increasing the section moment of inertia, avoiding the rapid decrease of stiffness with the increase of deformation. The second is material performance optimization. 60Si2CrVA spring steel is adopted, which is treated by "quenching + medium-temperature tempering", with an elastic limit strength ≥1600MPa, ensuring that the elastic strip works within the elastic deformation range without plastic deformation. The last is structural shape optimization. The arc transition radius of the elastic strip is increased from R3mm to R5mm to reduce the stress concentration factor and improve the fatigue resistance of the elastic strip. The optimized elastic strip needs to be verified by bench tests. Under the simulated fastening condition of 60kg/m rail, after 1 million vibration cycles, the preload attenuation rate ≤3% and the stiffness change rate ≤2%, meeting the use requirements.
What are the differentiated stiffness design points of the elastic strip adapted to the UIC60 foreign standard rail?
The differentiated stiffness design points of the elastic strip adapted to the UIC60 foreign standard rail are reflected in three aspects: stiffness value adjustment, structural shape adaptation, and installation interface matching. Stiffness value adjustment is the core. The rail head width and section size of UIC60 rail are different from those of the 60kg/m national standard rail, and the preload required for fastening is higher. Therefore, the elastic strip stiffness needs to be increased to 70±5kN/mm, and the preload is controlled at 15-18kN to ensure effective constraint of rail displacement. In terms of structural shape adaptation, the fastener installation groove size of UIC60 rail is different from that of national standard rail. The cantilever length of the elastic strip needs to be shortened by 3mm, and the end bending angle of the elastic strip is increased at the same time, so that the pressing point of the elastic strip fits accurately with the rail shoulder position of UIC60 rail. In terms of installation interface matching, a positioning protrusion needs to be added at the bottom of the elastic strip to cooperate with the positioning groove of the UIC60 fastener to prevent lateral displacement of the elastic strip during vibration. In addition, UIC60 rails are mostly used in European high-speed railway lines, which have higher requirements for the fatigue performance of elastic strips. Therefore, the elastic strip material needs to use higher-purity 60Si2CrVA steel, with sulfur and phosphorus contents controlled below 0.008% to improve fatigue resistance.
What are the verification methods and judgment standards for the adaptability between elastic strip stiffness and rail type?
The verification methods for the adaptability between elastic strip stiffness and rail type are divided into two categories: laboratory bench verification and field line verification. Laboratory bench verification builds a fastening test platform simulating rail type, installs the elastic strip on the fastener of the corresponding rail type, applies vibration load of train operation with frequency 50Hz and amplitude 1mm, and continues vibration for 1 million times. During the test, the preload attenuation rate, stiffness change rate and fatigue damage of the elastic strip are monitored in real time. Field line verification selects typical line sections, lays rails and elastic strips of corresponding rail types, tracks and monitors for 6 months, and records the lateral displacement of rails and the damage of elastic strips. The judgment standards include three core indicators: first, preload attenuation rate ≤5%/1 million vibrations; second, stiffness change rate ≤3%; third, rail lateral displacement ≤0.5mm. If all three indicators meet the standards, it is judged that the elastic strip is adapted to the rail type; if any indicator fails to meet the standards, the stiffness design parameters of the elastic strip need to be adjusted and verified again. For example, the elastic strip adapted to the 75kg/m heavy-haul rail has a preload attenuation rate of 3%, a stiffness change rate of 2%, and a rail lateral displacement of 0.3mm after verification, which meets the adaptability judgment standard.