空气耦合斜入射非线性检测方法研究

Research on nonlinear detection method of oblique incidence based on air-coupled

针对金属板结构微观缺陷难以检测的问题,提出一种基于空气耦合超声斜入射非线性微观缺陷的检测方法。首先通过数值分析的方法分别对垂直入射钢板与斜入射钢板时的透射率进行对比,并对3 mm厚钢板进行不同入射角的透射率对比试验。试验证明在斜入射条件下,超声波在钢板中因发生模态转换导致透射率增大。其次,利用空气耦合激励斜入射方法,对3 mm厚的钢板进行空气耦合超声非线性检测试验,其结果表明在入射角为5°时检测信号幅值提高24%,得到最大二阶非线性系数,此时透射率达到最大。因此,空气耦合超声非线性对钢板的检测不仅具备可行性,且在斜入射时可明显提高其检测效果,给检测金属板结构微观缺陷提供一定参考。

Aiming at the problem of microscopic defect in metal plate structure,this article proposed a microscopic defect detection method which is based on air-coupled oblique incidence nonlinear detection.Firstly,the transmittance of the perpendicular incidence steel plate and the oblique incidence steel plate were compared by numerical analysis,and the transmittance comparison test of the 3 mm thick steel plate was carried out at different incident angles.Experiments have proved that under the condition of oblique incidence,the transmittance of ultrasonic in the steel plate increases due to the modal conversion.Secondly,using the aircoupling excitation oblique incidence method,an air-coupling ultrasonic non-linear detection test was carried out on a 3 mm thick steel plate.The results showed that the detection signal amplitude increased by 24%when the incident angle was 5°and the maximum second-order nonlinear coefficient was obtained,at this time,the transmittance reaches the maximum.Therefore,the air-coupled ultrasonic nonlinearity is not only feasible for steel plate detection,but also can significantly improve its detection effect when the incident is oblique,providing the latest method for detecting microscopic defects of metal plate structure.