疲劳裂纹的电磁超声混频非线性检测

Nonlinear Detection of Fatigue Cracks by Electromagnetic Ultrasonic Mixing

对金属结构中疲劳裂纹的检测是结构寿命预测和失效分析的关键,线性超声或其他无损检测方法难以有效识别疲劳裂纹。以非线性波动理论为基础,根据电磁超声换能器的激发特点和兰姆波(Lamb波)的波结构特点,设计双线圈Lamb波混频电磁超声换能器,建立混频电磁超声换能器有限元仿真模型,研究混频位置和非线性系数之间的关系,分析了不同裂纹深度对超声调制效应的影响。最后,进行疲劳裂纹的电磁超声混频非线性实验,通过铝板中两个声场是否发生非线性调制来判断铝板是否有疲劳裂纹;根据疲劳裂纹板中不同位置处的非线性系数大小,对疲劳裂纹进行定位;研究非线性系数随不同裂纹长度的变化情况,依据非线性系数的变化可以有效监测裂纹的扩展。研究结果证明了所设计的Lamb波混频电磁超声换能器检测疲劳裂纹的可行性、有效性。

The detection of fatigue cracks in metal structures is the key to structural life prediction and failure analysis.Linear ultrasonic or other nondestructive testing methods are difficult to identify fatigue cracks effectively.Based on the theory of non-linear wave,according to the excitation characteristics of electromagnetic ultrasonic transducer and the wave structure characteristics of Lamb wave,a dual-coil Lamb wave mixing electromagnetic ultrasonic transducer was designed,the finite element simulation model of mixing electromagnetic ultrasonic transducer was established,the relationship between mixing position and non-linear parameters was studied,and the influence of different crack depths on the modulation effect was analyzed.Finally,the electromagnetic ultrasonic mixing experiments were conducted and the fatigue crack of aluminum plate can be judged by the non-linear modulation of two sound fields in the aluminum plate.The fatigue crack can be located according to the size of non-linear parameters at different locations in the plate with fatigue crack.The variation of non-linear parameters with different crack lengths was studied and according to the variation of non-linear parameters,crack propagation can be effectively monitored.The research results show the feasibility and effectiveness of the Lamb wave mixing electromagnetic ultrasonic transducer.