# Review on Rail Damage Detection Technologies for High-Speed Trains
## 2 Research Status of Non-Destructive Testing for Rail Damage
[PERSON] proposed a mobile binocular vision measurement model for railway building clearance which calibrates and constructs the spatial relative relationship of various elements in the stereo image through self-checking and multi-sensor system calibration. A building clearance calculation model based on the automatic fitting calculation of the spatial position of the centerline of the line was presented [7]. The traditional eddy current testing method mainly uses periodic pulse current signals as excitation sources to perform post-inspection or the online testing of materials (Figure 5). In 2006, [PERSON] et al. used a time-division multiplexing-based eddy current array testing method to achieve the real-time monitoring of the position of large-area metal curved surface components using a flat flexible eddy current sensor array [8]. In 2017, [PERSON] et al. used an analytical model of a disc eddy current drive based on the equivalent magnetic circuit method [9]. In 2017, [PERSON] studied the problem of using magnetic conductor ring excitation pulse eddy current detection technology to detect circumferential crack defects in small-diameter pipes [10]. The main principle of ultrasonic testing is to use the piezoelectric effect of piezoelectric chips to generate ultrasonic waves for the internal inspection of the specimen. In 2014,  
Figure 4: ACFM Hand Stick Manual Rail Tester. Figure 5: Manual eddy current detector. [PERSON] and [PERSON] conducted qualitative testing on metal fatigue cracks using nonlinear ultrasonic modulation technology [11; 12; 13]. In 2017, [PERSON] used Lamb waves to detect surface microcracks based on the characteristic that the influence of randomly distributed microcracks on the fundamental phase velocity of low-frequency SO can be ignored [14; 15]. In 2017, [PERSON] et al. proposed using multi-sensor ultrasonic pulse echo technology to study the flow characteristics of wind-driven surface water film [16; 17]. In 2017, [PERSON] utilized ultrasound tomography technology to image the interior of materials [18; 19; 20]. The domestically produced GTC-80-II-J rail flaw detection vehicle has outstanding performance, with a maximum operating speed of 120 km per hour and a maximum continuous flaw detection speed of 80 km per hour. The GTC-80-II-J rail inspection car was developed by Baoji CRRC Times Engineering Machinery Co., Ltd., Shaanxi, China and officially put into use in 2023, breaking the technological monopoly of foreign countries in the field of high-end rail inspection equipment. In terms of rail geometric parameters, the domestic standard (TB 10754-2018) [21] requires a gauge deviation of \(\pm\)1 mm, a track direction deviation of 0.3 mm/10 m, and a height deviation of 0.5 mm/10 m, and some indicators are stricter than European standard EN-13848 [22]. The vehicle conducts non-destructive testing by emitting and receiving ultrasonic waves through inspection wheels. A total of 18 probe chips and 26 ultrasonic channels are installed in the six inspection wheels under the vehicle, which can accurately detect steel rails in all directions with a damage detection rate of over 85%. To address the problem of detection deviation caused by rail wear and vehicle \"snake like\" motion, 3D laser track profile measurement technology is adopted, combined with adaptive wear compensation control, to dynamically adjust the position of the probe wheel, and the error can be controlled at the millimeter level. Its detection data support the synchronous storage and playback of A/B display signals, coupled with the automatic analysis of high-definition images of the rail surface, achieving the dual verification of \"waveform+image\" and greatly reducing the risk of missed detections. The diverse service environment of high-speed trains, with large speed fluctuations and unclear shock loads, leads to signals with strong nonlinearity [23; 24; 25]. Domestically, unmanned aerial vehicles equipped with laser radar, AI image recognition, and other technologies are used in track detection.