State Key Laboratory of Fluid Power and Mechatronic Systems, China.
Institute of Advanced Digital Technologies and Instrumentation, Zhejiang University, China.
Ultrasonics. 2018 Sep;89:1-12. doi: 10.1016/j.ultras.2018.04.003. Epub 2018 Apr 11.
As essential components of a high-speed railway system, switch rails can be easily damaged by sophisticated operating conditions. Therefore, precise online detection for switch rails is necessary. Methods based on ultrasonic guided waves are ideal candidates for structural integrity of the switch rails, which are natural waveguides with irregular cross-sections. However, energy decentralization in the wave propagation severely restricts detectability. Phased array systems have been developed and implemented to steer and focus acoustic energy in waveguides of ordinary cross-sections such as pipes and plates. This paper proposes a method for ultrasonic guided wave focusing in waveguides with constant irregular cross-sections. We analyzed the characteristics of the guided waves generated by partial loadings based on a semi-analytical finite element method (SAFEM). An algorithm was developed for calculating the amplitude weights and time delays required to modulate excitation signals. Two coefficients were defined to evaluate the wave focusing results, namely the half area coefficient (HAC) and half energy coefficient (HEC). Numerical simulations to verify the proposed method were carried out for a switch rail base with a constant irregular cross-section. The results demonstrate that the guided acoustic beam has been effectively steered to focus at the pre-determined locations with enhanced acoustic wave energy. Furthermore, the influence of various factors on guided wave focusing was studied. Excitation signals of low center frequencies with narrow bandwidths are recommended for ideal focusing results.
作为高速铁路系统的重要组成部分，道岔钢轨很容易受到复杂的运行条件的损坏。因此，需要对道岔钢轨进行精确的在线检测。基于超声波导波的方法是检测道岔钢轨结构完整性的理想选择，因为道岔钢轨具有不规则的横截面，是天然的波导。然而，波传播过程中的能量分散严重限制了检测的灵敏度。相控阵系统已经被开发并应用于普通横截面（如管道和板）的波导中，以控制和聚焦声能。本文提出了一种在具有恒定不规则横截面的波导中实现超声导波聚焦的方法。我们基于半解析有限元法（SAFEM）分析了基于局部载荷产生的导波的特性。开发了一种用于计算调制激励信号所需的幅度权重和时间延迟的算法。定义了两个系数来评估波聚焦的结果，即半面积系数（HAC）和半能量系数（HEC）。为具有恒定不规则横截面的道岔轨基进行了数值模拟以验证所提出的方法。结果表明，导声束已被有效地引导至预定位置，并增强了声波能量。此外，还研究了各种因素对导波聚焦的影响。建议使用中心频率低且带宽窄的激励信号以获得理想的聚焦效果。
