高频纵向导波在钢杆中传播特性的研究

计算了钢杆中纵向轴对称导波模态的衰减频散曲线和群 速度频散曲线. 分析了1~3MHz范围内高频纵向轴对称超声导波在钢杆中的传播特 性. 理论分析表明，各高阶纵向模态都存在一个衰减最小值，在此衰减最小值所对应频率下 的高阶模态能传播较远距离，可用于钢杆导波检测. 建立实验系统，采用轴对称同端激 励接收的方法，根据第1次端面回波做出群速度和端面回波幅值随频率变化曲线，实验结 果与理论分析基本吻合. 表明考虑材料衰减特性的钢杆频散曲线可以作为实验指导依据.

PROPAGATION CHARACTERISTICS OF HIGH FREQUENCY LONGITUDINAL GUIDED WAVES IN STEEL ROD

The attenuation dispersion curve and group velocity dispersion curve of ultrasonic guided waves in steel rod are calculated with consideration of the attenuation. Propagation characteristics of high frequency longitudinal modes between 1 MHz3 MHz in steel rod are studied. In theory, there is one attenuation minimum in every high order longitudinal mode whose attenuation is the smallest in all modes at the special high frequency. The high order mode at this special frequency can propagate a longer distance than other modes at the same frequency. This indicates that high frequency low attenuation longitudinal mode at this special high frequency can be used for the inspection of steel rod. The experiments on steel rod of 22 mm in diameter, 2 m in length are carried out using ultrasonic guided wave. Guided wave signals are excited and received by the same probe at the same end of the rod. The group velocity and amplitude curves of first end reflection against frequency are obtained. The experimental curves are consistent with those dispersion curves of theory. This indicates that the dispersion curve of steel rod with consideration of attenuation characteristics can be a guidance to experiment.