# Review on Rail Damage Detection Technologies for High-Speed Trains
## 1 Introduction  
With the rapid development of China's railway network, especially the proposal of \"new infrastructure\", the deployment of high-speed maglev trains with a speed of 600 km per hour has put forward higher requirements for the safety of railway tracks. As a new and important means of transportation, railways play an extremely important role. The safety and reliability of railways are receiving increasing attention from relevant research scholars, and the advancement of technology has led to higher requirements for the transportation functions of railways, especially for heavy-duty, high-speed, and other functions. Due to the contact friction between train wheels and rails, during heavy-load and high-speed movements, there is contact sliding friction between the wheels and rails. During the sliding friction process, various types of damage are easily generated on the surface of the rails. As long as there is damage on the surface of the rails, it is inevitable for the wheels to wear out. Some defects in the rails themselves can easily cause train derailment, resulting in unnecessary losses and threatening personal safety. Regarding the detection of rail damage, experts and scholars at home and abroad have conducted in-depth research and proposed some detection methods and theories. However, with the increase in train speed, the requirements for maintenance and operation technology are also increasing. Currently, there are still some shortcomings in the rail damage detection methods, including hardware detection in vehicles and supporting infrastructure. For example, the current manual detection method has disadvantages such as a high false-detection rate, low efficiency, and significant subjective influence. The eddy current testing method has high requirements for its own materials, which must be conductive materials, and has disadvantages such as low detection speed, low efficiency, and susceptibility to magnetic fields. The X-ray detection method has high detection costs, low detection speed, and low efficiency, and radiation has a significant impact on human health. The ultrasonic detection method has low detection accuracy and cannot accurately detect the precise location of rail damage, and the detection speed is easily affected. It has a series of problems and disadvantages such as low detection accuracy for rail structures with complex structures. The detection speed of the leakage magnetic detection method is highly susceptible to the influence of magnetic flux, and there are certain requirements for the lift-off value of the rail surface, which also has a significant impact on the detection speed. Although machine vision inspection can quickly and efficiently detect surface defects on railway tracks in a non-contact manner, there are still certain limitations in detecting internal damage in railway tracks. The comparison of common methods for detecting rail damage is shown in Figure 1. From Figure 1, it can be found that the common drawback of several detection methods is low detection efficiency. To solve the problem of the efficient detection of rail damage, it is necessary to collect and analyze real-time data during the operation of the rail, that is, monitor and provide real-time feedback on the status of the rail during operation, achieving zero delay in operation and maintenance. As shown in Figure 2, the national railway passenger and freight volumes in the past 5 years have been increasing year by year, despite being affected by certain factors. This reflects the increasing importance of railway transportation, as well as the importance of the maintenance and operation of railway transportation. In the face of the current operation and maintenance of high-speed and ultra-high-speed trains, more efficient, intelligent, and digital non-destructive testing technologies and methods are needed to monitor the real-time status of rails and perform intelligent operation and maintenance.