ABSTRACT

Ultrasonic inspection of adhesively bonded Single Lap Joint (SLJ) with composite material as adherend is quite challenging due to very close and overlapping reflections of ultrasonic waves from multiple interfaces across the joint. This study aims to precisely identify gate positions for these reflections in the pulse-echo technique. Further, investigation of surface roughness effects in the bonded region of SLJ is attempted using reflection coefficient R. For a real-valued A-scan signal in ultrasonic pulse-echo mode, a complex-valued analytic signal with amplitude and phase was obtained from the Hilbert transform. A sudden phase change of the analytic signal and a trough in the analytic signal’s envelope was observed at the reflection plane in A-scan. Analysis of spectra of reflected signals shows variation in magnitude at peak frequencies with the surface roughness of adherend. This paper provides a technique for identifying precise gate placement for the reflected signal and R-values evaluation for composite SLJ. For each surface roughness category, reflection coefficient R was experimentally evaluated at the adherend-adhesive interface of SLJ. These R values are correlated with the shear strength of the SLJ obtained from standard destructive tests.

摘要

由于来自多个界面的超声波的非常接近和重叠的反射穿过接头，对以复合材料作为被粘物的粘合单搭接接头 (SLJ) 进行超声波检查是非常具有挑战性的。本研究旨在精确识别脉冲回波技术中这些反射的门位置。此外，尝试使用反射系数 R 研究 SLJ 键合区域的表面粗糙度效应。对于超声脉冲回波模式的实值 A 扫描信号，从希尔伯特变换。在 A 扫描的反射平面上观察到解析信号的突然相位变化和解析信号包络中的波谷。反射信号的光谱分析表明峰值频率处的幅度随被粘物表面粗糙度的变化而变化。本文提供了一种技术，用于确定反射信号的精确栅极位置以及复合 SLJ 的 R 值评估。对于每个表面粗糙度类别，反射系数R在 SLJ 的粘附-粘合剂界面上进行了实验评估。这些R值与从标准破坏性测试中获得的 SLJ 的剪切强度相关。