层状无砟轨道结构脱层缺陷超声成像

无砟轨道是典型的层状混凝土结构，脱层缺陷是其最常见的损伤形式，影响着高速列车的安全运行。传统的合成孔径聚焦成像方法是基于恒定声速的超声检测方法，忽略层间的声阻抗差异以及声波在层间界面处的折射，导致声束难以在缺陷处聚焦，声波在层状结构中传播的时间误差较大。鉴于此，提出了一种多层结构合成孔径聚焦成像方法，充分考虑多层结构中的层间声速差异，采用射线追踪方法准确获取声波在多层结构中的传播时间。在此基础上，分析了不同入射波模式以及不同激发频率对多层结构合成孔径聚焦成像结果的影响。结果表明：采用多层结构合成孔径聚焦成像方法，使用频率为50 kHz的横波入射成像分辨率更高，对无砟轨道脱层缺陷检测效果更好。该研究为该类缺陷检测提供了理论支撑。

Ultrasonic imaging of delamination defects in layered ballastless track structure

Ballastless track is a typical layered concrete structure, and the delamination defect is its most common form of damage, which affects the safe operation of high-speed trains. The traditional synthetic aperture focusing imaging (SAFT) method is an ultrasonic testing method based on constant sound velocity. Ignoring the differences between the interlayer acoustic impedance and the refraction of the acoustic wave at the interlayer interface makes it difficult for the acoustic beam to focus at the defect, and the temporal error of the acoustic wave propagation in the layered structure is large. Therefore, a synthetic aperture focusing imaging method for multilayer structures is proposed in this paper, which fully considers the difference of sound velocity between layers in multilayer structures and uses ray tracing method to accurately obtain the propagation times of sound waves in multilayer structures. On this basis, the effects of different incident wave patterns and different excitation frequencies on the results of synthetic aperture focusing imaging of multilayer structures are analyzed. The research results show that with the multi-layer structure synthetic aperture focusing imaging method, the imaging resolution of shear wave incidence at 50 kHz is higher, and the detection effect of the delamination defects of ballastless track is better, which provides a theoretical support for the detection of such defects.