弯折小径管中槽型缺陷的L(0,1)模态导波检测

L(0,1) mode guided wave detection for notch defects in small-diameter and bending tubes

利用L(0,1)模态超声导波对直径为10 mm,壁厚为2 mm的不锈钢小径弯折管中的槽型缺陷进行检测。首先,建立有限元仿真模型,分析L(0,1)模态在具有不同弯折角度弯头处的模态转换和反射特性,观察到不同模态的反射回波信号能量与弯折角度间存在非单调关系;其次,利用磁致伸缩传感器在小径管中激励中心频率为90 kHz的L(0,1)模态的超声导波,对槽型缺陷进行检测,分析了弯折角度对导波缺陷检测能力的影响。结果表明:弯头处导波模态转换成F(1,1)模态后会影响导波对弯头后端槽型缺陷的检出能力,将提出的特征波形能量比值β作为表征参数,可以实现缺陷的检出,弯折角度为90°时检测效果最佳。

The L(0,1) mode guided waves were investigated for detecting notch defects in small diameter and bending tubes of stainless steel. The tested tube has a diameter of 10 mm and a wall thickness of 2 mm. Firstly, finite element simulation models were established to analyze the mode conversion and reflection characteristics of L(0,1) mode at the elbow with different bending angles. It is observed that there is a non-monotonic relationship between the energy of reflected waves of different modes and the bending angles. Secondly, a magnetostrictive sensor is used to excite L(0, 1) mode with a central frequency of 90 kHz for detecting notch defects in the tested small diameter tubes under test. The effect of bending angle on the defect detection ability of guided wave is analyzed. The results show that the F(1, 1) mode generated at the elbow appears to disturb the performance of guided wave in detecting the defect behind the elbow. Using the proposed energy ratio β of featured wave packets as the characterization parameter, the guided wave can effectively detect the notch defects behind the elbow. Among the tested cases, the detection ability is the best when the bending angle is 90°.