微裂纹扩展的非共线超声混频定位研究

Micro-cracks growth localization by using non-collinear ultrasonic mixing method

金属结构在早期服役过程中易出现微小裂纹,对早期微小裂纹扩展方向的检测与跟踪对避免结构失效而导致的突发性灾难具有重要的现实意义。基于非共线超声混频方法,开展金属材料微裂纹扩展的定位与表征研究。研究中选择两列横波相互作用产生混频纵波的非共线混频模式,通过实验测量验证了其混频效应和信号的传播性。选用铝合金7075-T6中预制的垂直和倾斜微裂纹为研究对象,提取每个测量点的超声混频非线性参数并进行归一化处理绘制成扫查成像图,从而表征微裂纹的长度与扩展方向。最后,将扫查成像图与光学显微镜的金相观察结果进行对比分析。研究表明,超声混频方法能够有效定位和跟踪铝合金材料中不同扩展方向的微裂纹,可为金属结构中微裂纹扩展提供检测方法。

The metallic structure is prone to micro-cracks in the early service process. The detection and tracking of the growth direction of early micro-cracks has important practical significance to avoid sudden disasters caused by structural failure. In this paper, based on the non-collinear ultrasonic mixing method, the research on the localization and characterization of micro-crack expansion in metallic materials is carried out. In the study, a non-collinear mixing mode is selected to produce mixed longitudinal waves by interaction of two series of shear waves, and the mixing effect and signal propagation are verified through experimental measurements. The prefabricated vertical and oblique micro-cracks in aluminum alloy 7075-T6 are selected as the research object, and the ultrasonic mixing nonlinear parameters at each measurement point are extracted and normalized to be drawn into a scanning image to characterize the length and expansion direction of the micro-cracks. Finally, the scanning image and the metallographic observation of optical microscope are compared and analyzed. The research shows that the ultrasonic mixing method can effectively locate and track the micro-cracks in different directions in the aluminum alloy material, which can provide an effective method for monitoring microcrack growth in metallic structure.