Novel method for detection of void defects under track slabs using air-coupled ultrasonic sensors

Void defects under track slabs are the main danger affecting the safe operation of high-speed railways. In the short high-speed railway maintenance periods, China’s high-speed railway line maintenance operations must quickly and dynamically determine void defects under track slabs that are in service without contact. However, the detection of void defects under track slabs still mainly relies on the manual inspection and flaw detection by railway workers during the railway maintenance period. If the defects are not quickly identified, the consequences could be disastrous. This article presents a new method for the non-contact dynamic detection of void defects under track slabs. The method involves the use of air-coupled ultrasonic sensors to generate and receive ultrasonic guided waves in the track slab to quantitatively represent the size of the void defect according to the principle of energy leakage of guided waves in the propagation process. The characteristics of the position-amplitude curve, taking the position of the beam axis as the abscissa and the amplitude of the time domain signal as the ordinate, were numerically calculated and analyzed. The quantitative relationship between the convex interval of the position-amplitude curve and the size of the void defect was obtained, and an imaging method of the void defects based on x, y two-dimensional line scanning data fusion is proposed. The excitation and reception methods of air-coupled ultrasonic guided waves were studied, and a 1:1 model of the track structure was built in the laboratory to verify the method and detect the void defect under the track slab. The experimental results show that ultrasonic guided waves can be excited and received in the track slab by air-coupled ultrasonic sensors. Based on the guided wave energy leakage principle, the quantitative characterization and imaging of the void defect under track slabs can be realized.