Detection of Layered Defects of Stainless Steel Plate by Total Focusing Algorithm of Lamb Wave in Phased Array

Due to the pores generated by the inclusion of aerospace metal plate, a kind of closed delamination defect is gradually formed with the stretching and extrusion during processing. Aiming at the detection of such defects, this paper presents a detection method that combines phased array total focusing method imaging algorithm with Lamb wave detection. Firstly, the mode, frequency and wedge angle of the excitation Lamb wave were analyzed and determined in principle. Secondly, the layered defects of different specifications and shapes in the 3 mm thick stainless steel plate were tested and studied experimentally. Experimental results show that the method proposed in this work can image the contour of layered defects. Lamb waves are susceptible to the reflection of the upper surface of the defect, resulting in a tailing image of its lower end, and the positioning accuracy of the upper end of the defect is higher than that of the lower end. The positioning errors of the upper end surface defects are all within 4%.