Fishplate Cross-Sectional Design and Rail Joint Stress Balancing Technology
What are the core fitting parts and dimension matching requirements of the special-shaped cross-section design of fish plates?
The core fitting parts of the special-shaped cross-section design of fish plates are divided into three areas: rail head fitting section, rail web clamping section and rail base supporting section. The dimensions of each part must be precisely matched with the corresponding cross-section of the rail to ensure full-section close contact with the rail. The rail head fitting section is the contact area between the fish plate and the rail head, which needs to be designed with a special-shaped curved surface consistent with the arc of the rail head, with a curved surface arc deviation ≤±0.2mm, and the length of the fitting section is not less than 2/3 of the length of the rail head, ensuring the uniform transmission of vertical load and avoiding local stress concentration of the rail head. The rail web clamping section is the core stress area of the fish plate, which needs to be designed with a groove structure adapted to the thickness of the rail web. The groove width is 0.1-0.2mm smaller than the thickness of the rail web, forming elastic clamping after assembly, and the perpendicularity deviation of the clamping section ≤0.1mm/m, ensuring that the lateral clamping force acts on the rail web uniformly. The rail base supporting section is the contact area between the fish plate and the rail base, which needs to be designed with a special-shaped inclined surface consistent with the slope of the rail base, with an inclined surface slope deviation ≤±0.5°, and the contact area of the supporting section is not less than 1/2 of the rail base area, ensuring effective support for the rail base and preventing the rail base from sinking. The dimension matching of the three core parts must follow the cross-section parameters of national standard rails, while international standard fish plates must match the cross-section dimensions of corresponding international standard rails, and the full-section fitting gap is ≤0.1mm to realize seamless fitting between the fish plate and the rail.
How does the length design of fish plates adapt to the joint stress requirements of different rails?
The length design of fish plates is set differently according to rail models, line load types and operation speeds, and the core is to change the stress contact area by adjusting the length to adapt to the stress magnitude and stress distribution requirements of different rail joints. The joint stress of national standard 50kg/m ordinary-speed rails is small, and the adapted fish plate length is designed to be 820mm. This length can ensure a moderate contact area at the joint, which not only meets the basic stress transmission, but also controls material costs, adapting to the medium and low load, low vibration working conditions of ordinary-speed lines. The joints of national standard 60kg/m heavy-haul rails bear large axle weight loads and strong vibrations, so the fish plate length needs to be increased to 1000mm. The extended length can increase the rail contact area, reduce the unit area stress by 20%-25%, effectively disperse the concentrated load caused by heavy haul, and avoid joint stress concentration. High-speed rail (60kg/m ballastless track) joints have extremely high requirements for smoothness, and the fish plate length is designed to be 1250mm. The ultra-long design can make the stress transition at the joint more gentle, eliminate the stress mutation caused by high-speed wheel-rail impact, and ensure the smoothness when the train passes at high speed. The lengths of fish plates for international standard UIC60 and BS113A rails are matched with their rail cross-sections and line working conditions: the fish plate length for UIC60 heavy-haul rails is 1050mm, and that for BS113A ordinary-speed rails is 850mm. In addition, for the special-shaped rail joints in turnout sections, the fish plates need to adopt a customized length design, adjusted to the adapted size according to the stress characteristics of turnout rails, to ensure that the joint stress matches the turnout working conditions.
In what aspects is the thickening and strengthening design of fish plates for heavy-haul lines reflected?
The thickening and strengthening design of fish plates for heavy-haul lines focuses on the core stress parts, mainly reflected in three aspects: thickening of the rail web clamping section, strengthening around bolt holes, and overall material upgrading, which targetedly improve the anti-deformation, anti-fatigue and anti-shear capabilities of fish plates. The rail web clamping section is the core part of the fish plate bearing lateral clamping force and vertical shear force. The thickness of this part is increased from 16mm of ordinary fish plates to 20-22mm. The thickening design can improve the cross-sectional shear strength, increase the shear bearing capacity by more than 30%, effectively resist the large shear force caused by heavy haul, and avoid deformation of the clamping section. The periphery of bolt holes is a key area of stress concentration. When train loads pass through, complex tension-shear stress will be generated around the holes, which is prone to cracks. By increasing the chamfer radius of bolt holes and designing annular reinforcing platforms around the holes on the fish plate, the stress around the holes can be reduced by 25%-30% to eliminate stress concentration. The overall material is upgraded from ordinary Q235 steel to 45# high-quality carbon steel, and some heavy-haul lines even use 42CrMo alloy steel. After material upgrading, the tensile strength of the fish plate is increased from 375MPa to more than 600MPa, the yield strength is significantly improved, which can bear the large load and repeated vibration of heavy-haul lines, and the anti-fatigue life is increased to more than 2×10^7 times. In addition, the rail base supporting section of heavy-haul fish plates is also locally thickened by 2mm to improve the supporting capacity for the rail base, prevent the rail base from sagging and deforming due to large loads, and comprehensively strengthen the bearing performance of fish plates.
Where do the stress concentrations of rail joints mainly occur? How to eliminate them through fish plate optimization?
The stress concentrations of rail joints mainly occur in three parts: around bolt holes, rail head joint gaps, and rail web clamping surfaces. These parts form stress concentrations due to discontinuous load transmission and excessive local stress, which can be targetedly eliminated through the structural optimization of fish plates. The periphery of bolt holes is the most important stress concentration part. When train loads pass through, complex tension-shear stress will be generated around the holes, which is prone to cracks. By increasing the chamfer radius of bolt holes and designing reinforcing platforms around the holes on the fish plate, the stress around the holes can be reduced by 25%-30% to eliminate stress concentration. There is a small gap at the rail head joint due to rail splicing, and impact stress will be generated when wheel-rail loads pass through. By optimizing the curved surface structure of the rail head fitting section of the fish plate to achieve seamless close contact with the rail head, and adding an elastic buffer layer in the fitting section at the same time, the impact energy can be absorbed, and the impact stress at the gap can be reduced by 15%-20%. Local stress concentration will occur on the rail web clamping surface due to uneven fitting. By designing the rail web clamping section of the fish plate as an elastic groove structure to improve the fitting degree with the rail web, and adopting a symmetrical bolt layout to make the clamping force act on the rail web uniformly, the local stress on the clamping surface can be eliminated and the stress can be evenly distributed. In addition, by designing the end of the fish plate as an arc transition instead of the traditional right-angle end, the contact stress concentration between the end of the fish plate and the rail can be eliminated, the stress transition at the joint part can be made more gentle, and the stress concentration problem of the rail joint can be comprehensively eliminated.
How to regulate the bolt pre-tightening force of fish plates and rail joints to achieve stress balance?
The regulation of the bolt pre-tightening force of fish plates and rail joints must be precisely set according to rail models, line working conditions and joint parts, and the core is to realize the reasonable distribution of pre-tightening force through step-by-step pre-tightening, uniform force application and dynamic calibration, so that the stress at the joint part is balanced with the main rail body. First, carry out step-by-step pre-tightening, dividing the bolt pre-tightening force into three levels: initial tightening, re-tightening and final tightening. The initial tightening force of national standard 60kg/m rails is controlled at 80-100N·m, the re-tightening force is increased to 250-300N·m, and the final tightening force is precisely set at 400-450N·m. Step-by-step pre-tightening can avoid deformation of fish plates or rails caused by excessive one-time force application and ensure the stable transmission of pre-tightening force. Second, adopt a symmetrical and uniform force application method, tightening the bolts in the order of diagonal force application, from the middle to both ends, so that the pre-tightening force deviation of each bolt is ≤±5%, ensuring that the clamping force of the fish plate on the rail is uniform and avoiding joint stress eccentric load caused by uneven pre-tightening force. Dynamically adjust the pre-tightening force according to different line working conditions: increase the final tightening force to 500-550N·m for heavy-haul lines to improve the anti-deformation capacity of the joint; control the pre-tightening force at 380-420N·m for high-speed lines, taking into account the smoothness of the joint while ensuring clamping; set the pre-tightening force at 350-400N·m for ordinary-speed lines, adapting to medium and low load working conditions. For special joint parts such as turnouts and curves, the pre-tightening force needs to be increased by 10%-15% on the basis of the basic value to eliminate the additional stress caused by special working conditions. In addition, it is necessary to dynamically calibrate the bolt pre-tightening force regularly: calibrate every 3 months for heavy-haul lines and every 1 month for high-speed lines, and timely supplement the attenuated pre-tightening force to ensure that the joint part maintains a balanced stress state for a long time.