Detection of rail squats based on Hilbert-huang transform by using bogie acceleration measurement

The squat is a type of rolling contact fatigue (RCF) damage, the existence of squats directly impacts the operating condition of urban rail vehicles. The current detection methods of the rail squats damage are mainly based on track inspection car and rail flaw detector. It has some disadvantages, for example, long detection cycle, no real-time detecting and narrow scope, time consuming and etc. In this paper, a new detection method of squats which based on the in-service vehicles is presented. The bogie acceleration signal is used to detect the squats on the track. To validate the possibility of the proposed method. With the help of SIMPACK software, an in-service vehicle-track dynamic model and models of typical squats are built to generate the simulated bogie acceleration signals when the train wheels rolls over the squats. The simulation signals from the normal rail and the rail with squats are studied by HHT, it is found that 0~50Hz and 300Hz are the feature frequency caused by the squats damages. A unique W-shaped natural vibration mode is decomposed from the acceleration signals which is the feature vibration mode of the squat defect. Finally, the above detection method is applied to the field test data of Shanghai metro line 1. The feasibility and reliability of the proposed method are demonstrated. The proposed method provides an alternative for real application.