Fishplate Groove Design and Stress Transfer Efficiency of Rail Joints
What are the differences in application scenarios between the symmetrical groove type and asymmetrical groove type of fish plates?
The symmetrical groove type of fish plates has the same upper and lower notch sizes and is symmetrical left and right, which is mainly applicable to ordinary rail joints in straight sections and large-radius curve sections. The rails of such joints are uniformly stressed. The symmetrical groove type can make the fish plate bear uniform force up and down, realize uniform stress transmission, and has simple processing technology and low cost. The asymmetrical groove type of fish plates has different upper and lower notch sizes or is asymmetrical left and right, which is mainly applicable to rail joints in turnout areas, small-radius curve sections and special-shaped rails. The section of the point rail and frog rail in the turnout area is asymmetrical, so a fish plate with an asymmetrical groove type is needed to achieve precise fitting; the rail in the small-radius curve section has lateral force, and the asymmetrical groove type can be designed with a fitting surface biased to the stress side to improve joint stability. The asymmetrical groove type can adapt to special-section rails and ensure smooth stress transmission at the joint.
Why should the transition arc radius of the fish plate groove type not be less than 3mm?
The transition arc radius of the fish plate groove type refers to the arc transition between the notch and the fish plate body. The standard requires the radius to be ≥3mm, and the core purpose is to eliminate stress concentration at the notch. When the fish plate is working, the notch bears the tensile and shear forces transmitted by the rail, which is a high-incidence area of stress concentration. If the arc radius is ＜3mm, a sharp corner will be formed at the notch, and the stress concentration factor will increase significantly. Under train vibration load, fatigue cracks are prone to occur at the sharp corner, which may further lead to fish plate fracture. When the arc radius is ≥3mm, the stress can be evenly dispersed along the arc surface, and the stress concentration factor can be reduced by 40%-50%, effectively avoiding crack generation. In addition, a larger transition arc can facilitate the assembly of the fish plate and the rail, avoiding scratching the rail surface during assembly.
What impact does the fit gap between the fish plate groove width and the rail section have on stress transmission?
The ideal fit gap between the fish plate groove width and the rail section is 0.1-0.3mm. This gap can not only ensure smooth assembly but also ensure efficient stress transmission. If the fit gap is too large, there will be a gap between the fish plate and the rail. When the train passes, the rail will swing slightly in the notch, leading to discontinuous stress transmission at the joint and increased local stress concentration. Excessively large gaps will also make the bolts of the fish plate bear additional shear force, accelerating bolt loosening and fatigue fracture. If the fit gap is too small, the fish plate and the rail are in interference fit, which is easy to damage the rail surface and the fish plate groove type during assembly, and cannot eliminate the manufacturing error of the rail joint. A reasonable fit gap can make the fish plate closely fit with the rail, and the stress is evenly transmitted through the fitting surface, improving the overall strength of the joint.
Why do fish plates for heavy-haul lines adopt a deepened groove structure in their groove design?
Fish plates for heavy-haul lines adopt a deepened groove structure, with the groove depth increased by 2-3mm compared with ordinary fish plates, mainly to increase the contact area between the fish plate and the rail and improve the stress transmission efficiency. Trains on heavy-haul lines have large axle loads, and the tensile and shear forces at the rail joint are much greater than those on ordinary lines. Deepening the groove can increase the contact height between the fish plate and the rail, increase the contact area by 15%-20%, and significantly reduce the stress borne per unit area. The deepened groove type can also enhance the bending stiffness of the fish plate, making the fish plate deform less under load, and avoiding the increase of joint gap caused by fish plate deformation. In addition, the deepened groove type can better wrap the rail end, reduce the stress concentration at the rail end, and prevent rail end damage. Therefore, special fish plates for heavy-haul lines all adopt a deepened groove design to adapt to the large load demand.
What effects does the surface roughness of the fish plate groove type have on the rail joint performance?
The surface roughness of the fish plate groove type requires Ra≤3.2μm, and the surface is smooth and flat, which has an important impact on the performance of the rail joint. A groove type with low surface roughness has better fit with the rail, larger contact area, and more uniform stress transmission, which can reduce stress concentration at the joint. If the surface roughness is high, there are micro-protrusions on the groove surface, which will lead to point contact or line contact between the fish plate and the rail, resulting in a sharp increase in local stress and prone to fatigue damage. A smooth groove surface can also reduce the frictional resistance during assembly, avoid scratching the anti-corrosion coating on the rail surface, and protect the rail from rust. In addition, the surface with low roughness is not easy to accumulate dust and moisture, which can reduce electrochemical corrosion at the groove and extend the service life of the fish plate.