多层介质复合结构中超声波激励与传播特征的研究

Research on Excitation and Propagation of Ultrasonicon the Interface of Multilayer Structure

在多层复合结构的无损检测中,覆盖层以下贴近异质材料结合界面的垂直方向裂纹往往难以被检测到,而此类缺陷对多层结构的力学性能影响较大,需要可靠的无损检测手段对其进行检测。在铜钢复合层结构背景下,通过理论分析的方法求解两者界面上的Stoneley特征方程,得到理论上该界面上的衰减界面波波速。通过对超声波在多层复合结构中倾斜入射的传播特性进行分析,得到理论上激发铜钢界面上界面波的方法。在仿真试验中,使用倾斜入射方法并选取合适的角度,使超声波依次通过铜、钢两层介质并在其界面上激发出界面波,试验测得该界面波传播速度与理论值吻合良好。利用其对铜钢堆焊结构界面下的人工模拟裂纹进行检测,结果表明该方法能有效地检测出此类裂纹,灵敏度较高。

In compound multilayer structures,a subsurface crack whose orientation is vertical to layers is hard to detect.Unfortunately,the mechanical properties of a multilayer structure are significantly influenced by this very kind of flaws,which raise the need of a reliable NDT method for them.For copper-steel layered structures,the Stoneley＇s secular equation of the interface is solved by means of theoretical analysis,and the theoretical velocity of the attenuated interface wave is acquired.Efforts are also made in analyzing the propagating characteristics of oblique incident ultrasounds to multilayer structures,and a theoretical method of exciting interface waves on copper-steel interface is proposed.In simulating experiments,a interface wave is obtained by making the ultrasound propagate obliquely onto the medium of copper-steel structure with selected angle.The experimentally measured velocity of the interface wave accords well to the calculated one.Furthermore,the mentioned interface wave is applied to the examination of artificial cracks in copper-steel bead welded structures,and it is shown that this method is capable of detecting this kind of cracks with relatively high sensitivity.