基于零群速兰姆波的不等厚对接焊缝缺陷检测

Defect Detection of Unequal Thickness Butt Weld Based on Zero-Group-Velocity Lamb Wave

焊接结构由于材料、工艺和环境等差异易出现各种类型缺陷,严重影响结构整体的安全性能。超声检测法是一种有效的缺陷无损检测方法,常规超声缺陷测量技术在处理复杂曲面时会出现模式转换及影响缺陷检测精度的问题,故该文提出了基于零群速兰姆波模态的不等厚对接焊缝缺陷检测仿真研究。首先,基于Bloch-Floquet边界和域约束的有限元特征频率法,研究变厚度薄板中零群速模态频率偏移规律,选取厚度变化敏感的零群速模态并对激励信号进行参数优化。然后,通过建立焊缝仿真模型验证变厚度薄板中零群速模态频率偏移规律,成功重构出焊缝薄板的曲线厚度,误差为±0.05 mm。最后,建立不等厚板焊缝模型进行缺陷检测,成功地重构出焊缝内部的微小缺陷的位置信息(>0.5 mm),厚度方向和水平方向的误差分别为±0.05 mm和±0.02 mm。

Due to the differences in materials,processes and environment,the welded structures are prone to various types of defects,which will seriously affect the overall safety performance of the structure.The ultrasonic method is an effective non-destructive measurement method for defect,but the conventional ultrasonic defect measurement technology has the problem of mode conversion when dealing with the complex curved surfaces,which affects the accuracy of defect detection.Therefore,a simulation study on the unequal thickness butt weld defect detection based on zero-group-velocity Lamb wave mode is carried out in this work.First,based on the finite element characteristic frequency method with Bloch-Floquet boundary and domain constraints,the frequency deviation of the zero-group-velocity mode in a thin plate with variable thickness is studied,and the zero-group-velocity mode sensitive to thickness changes is selected and the parameters of excitation signal are optimized.Then,a welding simulation model is established to verify the frequency deviation law of the zero-group-velocity mode in the thin plate with variable thickness,and the curve thickness of the weld thin plate iss successfully reconstructed with an error of±0.05 mm.Finally,a welding model of the unequal thickness plate is established for defect detection,and the position information(>0.5 mm)of the small defects inside the weld is successfully reconstructed,and the errors of the thickness direction and the horizontal direction are±0.05 mm and±0.02 mm respectively.