Detection of surface defects based on the optimized scanning laser source method

Abstract

In this paper, the interaction between laser-induced surface acoustic wave (SAW) and the surface micro-defect with triangular cross-section is studied. It is found that the reflected wave is greatly affected by the width of the defect, which is mainly suitable for defects whose depth is equal to or larger than the wavelength of SAW. Scanning laser source (SLS) method can detect small defects whose depth is significantly smaller than the wavelength of SAW. It is found that the detection mechanism of SLS method is that the superposition of reflected wave and direct wave increases the peak-to-peak value. The SLS method based on the change of the center peak-to-peak value at the bottom of the defect proposed in this paper is more capable of detecting small damage than the traditional SLS method, and can even find the defect with a depth of only 1/28 of the center wavelength of SAW. The traditional SLS method can only locate defects. This paper proposes a defect width detection method based on SLS method. The detection efficiency of traditional SLS method is low, which limits the application of this method. This paper optimizes the scanning steps of the SLS method by the bisection method, which greatly improves the detection efficiency. Using the optimized SLS method, the position, width and depth of micro artificial defect on the surface of 7075 aluminum alloy is detected quickly and accurately.