金属材料微裂纹取向与超声波和频非线性效应

针对非线性超声无损检测金属材料微裂纹取向角度的问题，开展了微裂纹取向与超声波的和频非线性效应研究，建立了超声和频非线性特征系数与微裂纹取向角度的关系模型。理论和有限元仿真实验结果表明，随着微裂纹取向角度的逐渐增大，超声和频非线性特征系数与微裂纹取向角度之间呈现明显的正相关趋势，而且相比二次非线性特征系数，和频非线性特征系数对微裂纹取向检测更为敏感。同时，从超声波平均能流密度（即声强）的角度出发，计算可知和频分量声强会随着微裂纹取向角度的增大而增大，而二次谐波声强基本不会发生变化，同时和频分量声强占比相比于二次谐波声强占比也得到了明显提高。超声波声强计算结果与仿真计算结果趋势基本一致，证明了理论模型的正确性。通过实验验证了模型的有效性，为金属材料微裂纹取向的检测提供了一种有效的手段。 

Sum frequency nonlinear effects of micro-crack orientation and ultrasound in metallic materials

In order to study the non-destructive testing of micro-crack orientation angle of metal materials, the research of the ultrasonic sum frequency nonlinear effect about the micro-crack orientation of metallic materials is carried out. In theory, the relationship between the ultrasonic nonlinear frequency characteristic coefficient and the orientation angle of micro-crack is established. Then, the results of finite element simulation and calculation show that with the gradual increase of the orientation angle of the micro-cracks, there is a clear positive correlation trend between the ultrasonic nonlinear frequency characteristic coefficient and the micro-crack orientation angle, and compared to the secondary nonlinear coefficient, the sum frequency nonlinear coefficient is more sensitive to micro-crack orientation detection. At the same time, from the perspective of the average ultrasonic wave energy density, for example, the sound intensity, the sound intensity of the sum frequency component will increase with the increase of the orientation angle of the micro-crack, and the sound intensity of the second harmonic component will not change substantially. The ratio of the sound intensity of the sum frequency component is also significantly higher than that of the second harmonic component. The calculation results of the ultrasonic intensity are basically consistent with the simulation results, which proves the correctness of the theoretical model. Finally, through the design experiments, the use of simulated cracks to verify the validity of the model provides an effective means for the detection of micro-crack orientation of metallic materials.