Thinned array ultrasonic imaging of debonding defects indiscontinuous impedance bonded structures br

Ballastless track is a typical bonding structure with discontinuous impedance. Under the influence of heavyload, deteriorating environment and other situations, the circumstance of debonding occurs frequently andseriously affects the safety of train operation. In this work, a high-precision array ultrasound fast imagingmethod is proposed. Based on the propagation path and time of sound wave in the medium obtained by raytracing method, a theoretical model of sound velocity of discontinuous impedance bonding structure isestablished when the difference in sound velocity among dielectric layers is taken into account. High degree offreedom sparse array based on real number coding as well as synthetic aperture focusing technology (SAFT)imaging method is used to improve detection efficiency. The results of the experiments carried out on ballastless track structure are shown below. The ray tracing method can accurately calculate the propagation path andpropagation time of ultrasonic wave and improve the detection accuracy. The optimized thinned array patternhas narrowed the main lobe width and low side lobe gain, which improves the detection efficiency and soundfield directivity. The efficiency of thinned array SAFT imaging method is improved by 30.9% when the imagingerror of debonding defects is within +/- 5%, which provides a theoretical support fordetecting such debondingdefects.