非金属管道损伤的非线性超声导波延时检测定位方法

由于超声导波难以准确检测非金属管道的早期损伤,本文提出了一种非线性超声导波延时方法对非金属管道结构损伤进行测试和定位。基于非线性超声调制机理分析了非金属管道损伤状态,使用同侧非线性超声的混频信号激励方式并根据超声导波传播速度的差异产生激励信号延时,然后在管道损伤处实现混频信号的非线性调制。采用HHT(Hilbert-HuangTransformation)提取混频延时信号的瞬时特征量,并通过分析非线性分量延时分组进行损伤区域检测,实现了对非金属管道裂纹损伤的定位。PVC(Ployninylchloride)非金属管道实验显示,无损伤状态下延时信号分组的标准化基准值为0.518 8;单裂纹状态下延时信号分组标准值为0.593 7,损伤定位相对误差为3.277%;双裂纹损伤状态下的标准化瞬时平均幅值为0.580 1与0.607 3,损伤定位值绝对误差小于4mm。相对于利用小波包络分解的非线性延时定位检测法,实验得到的单裂纹损伤准确度提高了36.4%。结果表明该方法能够对非金属管道裂纹损伤准确定位,并能够检测早期多裂纹损伤。

Damage detection of nonmetallic pipe by using nonlinear ultrasonic guided wave with signal delay

As the damages on nonmetallic pipes, especially early damages, are difficult to be detected by ultrasonic guided wave, this paper proposes a nonlinear ultrasonic guided wave with signal delay to detect and localize the defects on nonmetallic pipes. Based on the nonlinear ultrasonic wave theory, the damage states of nonmetallic pipes were analyzed and an incentive method with mixed signals from the same end of the signal delay was developed to generate signal delay according to different speeds of the mixing signals and to implement nonlinear modulation. The instantaneous characteristics of delay signal were extracted by HHT(Hilbert-Huang Transformation), and damage location was achieved by analyzing different nonlinear modulation groups with signal delay. PVC(Polyvinyl chloride) pipes were used for experiments. In intact condition, the standardized reference values of signal delay groups is 0.5188. In damage of one crack, standardized value of signal delay groups is 0.5937 and the relative error is 3.277%. Moreover, in damage of two cracks, the standardized value of signal delay groups are 0.5937 and 0.6073, and the absolute error is less than 4mm. Compared to the wavelet envelope location approach, the relative error with one crack rises to 36.4%. These results turn out that the approach proposed in this paper is effective and accurate for the damage detection and location of nonmetallic pipes, and is available for the multi-damaged pipes.