Research On Ultrasonic Lamb Wave Detection Of Q235 Steel Plate Corrosion Defects

Compared with conventional NDT methods, ultrasonic Lamb wave detection technology has great advantages in large area of sheet metal structure of quickly and efficiently detect, so ultrasonic Lamb wave has broad prospects in the detection of sheet metal corrosion defects. However, due to the ultrasonic Lamb wave has a complex dispersion, multi-modal and attenuation characteristics, so it there are still many problems to be solved in practical engineering test applications, such as the select and identify of mode and the defects qualitative and quantitative evaluation.Firstly, this paper made a introduction about the theory of ultrasonic guided wave testing, including the phase velocity and the group velocity of the guided waves, the propagation characteristics, the motivation and receive and the modal identification of Lamb waves; Secondly, set up a platform of ultrasonic Lamb wave detection, which uses the wedge transducer and multi-channel ultrasonic transceiver equipment is simulated in standard reference plate for defect detection experiments; Finally, the relevant factors were explored including the incidence angle impact testing, the relationship between the probing distance and the echo signal amplitude, as well as the relationship between the size of the defect and the echo signal amplitude. Studies show that: For thickness of 6.8mm Q235 steel the optimum angle of incidence for the corrosion defect detection is 50.8°and the incentive is a mixed mode Lamb wave contains A0 and S0 under the conditions of surface without liquid load and testing frequency is 1MHz, when the Lamb wave is inspired by using the wedge transducer. Furthermore, the attenuation of each mode is different with the change of detection distance, but the overall trend of plate end echo signal amplitude is increasing with detection distance decreases. For some modes, its acoustic signal is not proportional relationship between the attenuation and the detection distance. In addition, the echo signal amplitude of A0 and S0 mode are increases with defect depth and cross-sectional area of defects increasing for the same type of defect. the defect that the corrosion depth of corrosion defects can be predicted according to curve of the defect echo signal amplitude changes with cross-sectional area and depth.The research on this subject will promote the Lamb wave ultrasonic corrosion defects in Q235 steel structure detection applications, and provide a theoretical basis for the qualitative and quantitative sheet metal structure corrosion defects.