Unreasonable rail section causes bolt hole crack

According to available data, the design of the rail section is flawed, with the rail web being excessively thin, which significantly contributes to the formation of bolt hole cracks. The thickness of the rail web is only 33 mm, a dimension that is insufficient to withstand the repeated stress from wheel-rail contact. This weak structural design makes the rail prone to fatigue damage over time, ultimately leading to the development of cracks around the bolt holes. China's rail joints are typically designed as wedge-shaped connections. This type of joint can induce upward tensile stress on the rails when the bolts are over-tightened. Based on stress analysis of round bolt holes, this configuration increases the likelihood of oblique cracks forming between the holes, particularly in the first bolt hole at the end of the rail. In practical maintenance scenarios, if the joint bolts are not properly maintained or the torque does not meet specifications, the joint's rigidity will be compromised. This results in uneven stress distribution across the rail ends, leading to dynamic irregularities. Over time, these irregularities become permanent, increasing the interaction between the fishplate and the bolt hole, and eventually causing cracks to form. Additionally, if the bolt torque is too low, excessive slippage may occur between the rail and the fishplate as trains pass. This movement can cause the bolts to rub against the edges of the holes, leading to plastic deformation of the hole walls and creating stress concentrations that further promote crack initiation. In northern China, where temperatures are significantly lower, the rails tend to contract, reducing the space between the rail and the fishplate. This increased pressure on the hole walls raises the risk of cracking, especially in areas where stress is already concentrated. If there are existing flaws such as cracks, burrs, or sharp corners in the bolt holes, and these are not properly addressed during replacement, the repeated loading from train traffic can easily trigger further damage. Moreover, rail joints often have other weak points, including low joints, misaligned teeth, blockages on the rail surface, wear, ballast plate knots, and dark pits. These issues can create unevenness on the rail head, which amplifies the dynamic forces between the wheel and rail. As a result, the weak areas—such as the walls of the bolt holes—are subjected to greater stress, accelerating their deterioration and increasing the likelihood of failure.

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