铝合金板疲劳微裂纹超声红外成像检测的数值及实验研究

超声红外成像检测技术是一种发展迅速的新型无损检测技术，可用于检测材料表面或近表面的缺陷，由于对缺陷具有选择性加热的特点，近年来备受检测行业的关注。该文在铝合金板中制作疲劳微裂纹，在板中激励声波，裂纹表面因振动摩擦生热，用红外摄像仪记录板表面温度分布。拍摄的红外图像序列经傅里叶变换后得到的幅值和相位图能清晰显示裂纹的特征，测量到的裂纹长度误差达到4.3%。用有限元模拟超声在板中裂纹处的生热过程，研究板中超声在裂纹处的励热机制。超声激励时间、裂纹表面间摩擦系数和裂纹开口宽度直接影响裂纹处的励热效果，最高温度通常位于裂纹尖端附近。模拟和实验结果均表明超声红外成像检测技术能对板中疲劳微裂纹实现快速检测，提供有效、可信的检测结果。

A comprehensive numerical and experimental study on detecting fatigue microcrack in aluminum alloy plate by vibro-thermography

Vibro-thermography (VT) is a new nondestructive testing technique with rapid development that can be used to detect surface and sub-surface defects. Due to its selective heating character to defects, VT has been gaining more attention in Non-destructive testing industry. In this paper, fatigue microcrack was made in aluminum alloy plate and under ultrasonic excitation the heat generated by friction at the crack surfaces. The surface temperature distribution was recorded by an infrared camera. The Fourier transform was implemented to process thermographic sequence, and the characteristics of fatigue crack was clearly revealed from the generated amplitude and phase images. The error of the crack length measured in phase image is about 4.3%. The heat generation process at the crack was also simulated by finite element method, the mechanism on heat generation was studied. The heat generation effect at the crack is directly affected by ultrasonic excitation time, friction coefficient and opening width of crack. The highest temperature is usually near the crack tip. Both the experimental and simulation results demonstrate VT can achieve rapid detection of fatigue microcrack in plate, and provide effective and reliable detection results.