Department of Mechanical Engineering, University of South Carolina, 300 Main Street, Columbia, SC 29208, USA.
Sensors (Basel). 2020 May 27;20(11):3035. doi: 10.3390/s20113035.
Piezoelectric transducers are convenient enablers for generating and receiving Lamb waves for damage detection. Fatigue cracks are one of the most common causes for the failure of metallic structures. Increasing emphasis on the integrity of critical structures creates an urgent need to monitor structures and to detect cracks at an early stage to prevent catastrophic failures. This paper presents a two-dimensional (2D) cross-correlation imaging technique that can not only detect a fatigue crack but can also precisely image the fatigue cracks in metallic structures. The imaging method was based on the cross-correlation algorithm that uses incident waves and the crack-scattered waves of all directions to generate the crack image. Fatigue testing for crack generation was then conducted in both an aluminum plate and a stainless-steel plate. Piezoelectric wafer transducer was used to actuate the interrogating Lamb wave. To obtain the scattered waves as well as the incident waves, a scanning laser Doppler vibrometer was adopted for acquiring time-space multidimensional wavefield, followed with frequency-wavenumber processing. The proof-of-concept study was conducted in an aluminum plate with a hairline fatigue crack. A frequency-wavenumber filtering method was used to obtain the incident wave and the scattered wave wavefields for the cross-correlation imaging. After this, the imaging method was applied to evaluate cracks on a stainless-steel plate generated during fatigue loading tests. The presented imaging method showed successful inspection and quantification results of the crack and its growth.
压电换能器是产生和接收兰姆波用于损伤检测的便捷工具。疲劳裂纹是金属结构失效的最常见原因之一。对关键结构完整性的日益重视，迫切需要对结构进行监测，并在早期发现裂纹，以防止灾难性故障。本文提出了一种二维（2D）互相关成象技术，不仅可以检测疲劳裂纹，还可以精确地对金属结构中的疲劳裂纹进行成像。该成像方法基于互相关算法，利用入射波和各个方向的裂纹散射波生成裂纹图像。然后在铝板和不锈钢板中进行了用于产生裂纹的疲劳测试。压电晶片换能器用于激励询问兰姆波。为了获得散射波和入射波，采用扫描激光多普勒测振仪获取时-空域多维波场，并进行频-波数处理。在带有微裂纹的铝板上进行了概念验证研究。采用频-波数滤波方法获得互相关成象的入射波和散射波波场。之后，将该成像方法应用于评估疲劳加载试验中不锈钢板上产生的裂纹。所提出的成像方法成功地对裂纹及其扩展进行了检测和定量评估。
