钢轨中高频超声导波单模态激励技术研究

Research on Excitation of Single-Mode Ultrasonic Guided Wave in High-Frequency Range along Rail

超声导波由于其长程传播和全截面覆盖等特性而在铁路轨道结构安全检测和监测领域中受到密切关注。而由于其频散和多模态特性,现有钢轨超声导波技术研究和应用主要集中于0~90 kHz的相对低频范围,从而导致其对微小缺陷的分辨力不足。对钢轨中的道岔等关键位置的检测,通常不需要长距离监测,对微小缺陷的灵敏度有更高要求。为提高钢轨中超声导波的缺陷检测能力,故提出基于阵列传感技术激励高频范围的单模态超声导波。首先基于半解析有限元法研究钢轨超声导波的传播特性,得到CHN60型钢轨的频散曲线和模态振型。根据模态振型信息选取出对特定位置敏感的导波模态并确定其激励位置。通过三维有限元仿真,对激励传感器的阵元间距、阵列总长、激励周期和窗函数等参数进行学习和优化,实现了轨底100 kHz单模态超声导波的激励。该模态对轨底内部和表面缺陷(小至3 mm)都具有较高灵敏度。试验测试也表明,利用优化的激励条件可以在钢轨中激励出高信噪比的单模态超声导波。本研究所提出的钢轨高频单模态导波技术,可以实现多模态交错复杂高频区(高于100 kHz)模态的选择性激励,将为铁路轨道的关键区域(如道岔)微小缺陷的检测和监测提供理论基础和技术支撑。

Ultrasonic guided waves technology has attracted wide attention in defect detection and health monitoring in railway track because of the advantages of long-range capability and full cross-section coverage. However, due to the natures of dispersion and multiple modes, current researches on ultrasonic guided waves in rail focus on relatively low-frequency below than 90 kHz.Ultrasonics wave with low frequencies is not sensitive enough to small defects. However, the safety-critical region such as the switch rail is very short and its inspection present more request for high sensitivity to small defect. In order to improve the defect detection ability of ultrasonic guided wave in rail, a single mode ultrasonic guided wave excitation in high frequency range based on array sensing technology is proposed. Firstly, semi-analytical finite element method is applied to investigate the characteristics of ultrasonic guided wave propagation in rail. The dispersion curves and modal shape are calculated for CHN60 rail. Then, specific wave mode sensitive to the certain area is carefully chosen are selected based on the dispersion curves and mode shapes. By three-dimension finite element modelling, a single mode at 100 kHz is excited along rail foot, after optimizing the array parameters, including element spacing, excitation length, period number and window function. Also, the interaction between this selected mode and surface and internal defects was investigated. The results show that this single mode is capable to detect the defects as small as 3 mm. Finally,laboratory experiment proved that the single-mode ultrasonic guided wave is excited along rail. This technology to excite single-mode ultrasonic guided wave in high-frequency range along offer a potential technology for defect detection with high sensitivity for the safety-critical region of rail, such as switch rails.