铝合金板材疲劳损伤的非线性导波检测

Nonlinear guided wave detection of fatigue damage of aluminum alloy plate

针对传统线性超声检测技术无法检测疲劳微损伤的问题,提出了疲劳微裂纹的非线性超声导波检测技术。首先,通过检测信号时频分布与频散曲线的对比分析,确定了铝板中的Lamb波模态,据此优化试验参数,并在板中激发单一模态的兰姆波;其次,通过试验方法判断该模态Lamb波的非线性响应条件,确定该模态在激励微裂纹疲劳损伤上的实用性;第三,提取了非线性超声检测特征参数,分析了各特征参数随疲劳周数的变化关系。结果表明:铝板中的兰姆波频散特性会导致基频幅值波动较大,非线性系数随基波变化无法反映真实的微裂纹非线性响应;二次谐波幅值在疲劳损伤初期随着疲劳周数的增大而增大,可用于评价缺陷的微观损伤。

In view of the problem that the traditional linear ultrasonic detection technology cannot detect fatigue micro cracks,a nonlinear ultrasonic guided wave detection technology for fatigue micro cracks is proposed.Firstly,the Lamb wave mode in the aluminum plate was determined by comparing the detection of signal time-frequency distribution with the calculation of dispersion curve,and then the experimental parameters were optimized and a single mode Lamb wave was excited in the plate.Secondly,the nonlinear response conditions of the mode Lamb wave were determined by the experimental method to determine the practicability of the mode in excitation of microcrack fatigue damage.Thirdly,the characteristic parameters of nonlinear ultrasonic detection were extracted and the relationship between the characteristic parameters and fatigue cycle number was analyzed.The results show that the dispersion characteristic of Lamb wave in aluminum plate leads to a large fluctuation of fundamental frequency amplitude,and the nonlinear coefficient cannot reflect the true nonlinear response of micro cracks.The second harmonic amplitude increases with the increase of fatigue cycle in the early stage of fatigue damage.