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复合材料结构在制造和服役过程中易产生不可见损伤,会降低结构强度,影响设备安全性能。基于超声Lamb波的结构健康检测方法可有效地实现对结构损伤的识别。然而,由于受到检测系统复杂的幅值调制作用,接收信号将发生频谱能量分布偏移。在定位检测过程中,群速度的选择以激励信号的中心频率为准,当激励信号的频谱受到较强幅值调制时,此时用于定位的群速度值将不再准确。在幅值调制特性的研究基础上,通过仿真和试验方法,探究了幅值调制对信号频谱能量分布的影响;进而提出了基于频谱偏移的群速度修正方法,并将此方法用于改进的延时叠加算法中以提高损伤定位精度。试验以T300/3231碳纤维复合材料板为对象,对比了群速度修正前后的损伤成像结果。结果显示,经过群速度修正后的定位精度优于未经过修正的结果,验证了群速度修正方法的有效性。
The composite structure is easy to produce invisible damage during manufacture and service, which will reduce the structural strength and affect the safety performance of the equipment. The structure health detection method based on ultrasonic Lamb wave can effectively realize the identification of structural damage. However, due to the complex amplitude modulation of the detection system, the received signal will undergo spectral energy distribution offsets. In the process of positioning detection, the group velocity is selected based on the center frequency of the excitation signal. When the spectrum of the excitation signal is subjected to a stronger amplitude modulation, the group velocity value for positioning at this time will no longer be accurate. Based on the study of the amplitude modulation characteristics, the influence of amplitude modulation on the energy distribution of the signal spectrum is investigated by simulation and experimental methods. Then, the group velocity correction method based on spectral shift is proposed and applied to the improved Delay superimposed algorithm to improve the damage localization accuracy. The T300 / 3231 carbon fiber composite plate is taken as an example to compare the damage imaging results before and after group velocity correction. The results show that the accuracy of group velocity correction is better than that of unmodified results.