Ultrasonic Detection Method Of Steel Plate Defects Based On Lamb Wave Time-frequency Diagram

Metal sheet is widely used in aerospace,automobile,shipbuilding and other manufacturing fields.However,the steel plate will inevitably produce defects during the processing and forming process,or in the later product use.The defects of the steel plate will cause hidden dangers to accidents in aircrafts,automobiles,and ships,especially in the cutting-edge research fields of aerospace and warships.Such hidden dangers must not be allowed.Therefore,the detection of steel plate defects and the development of its technology have far-reaching significance.Ultrasonic non-destructive testing technology is widely used in steel plate defect detection because of its advantages of low equipment cost and high detection accuracy.At present,in the detection of steel plate defects,the most widely used technology is ultrasonic Lamb wave detection technology.Due to the multi-mode and dispersion characteristics of Lamb waves,different modes are often mixed together and randomly change,which results in signal complexity and difficulties in defect detection.And because the current ultrasonic Lamb wave detection technology is mostly based on the time domain waveform,or based on the power spectrum,it cannot solve the problems caused by the Lamb wave mode aliasing and random changes,so the recognition rate is low.In view of the current problems,this paper studies a method of ultrasonic detection of steel plate defects based on Lamb wave time-frequency map,and builds a corresponding virtual instrument detection experimental system.In this paper,a wideband rectangular pulse excitation signal is selected,and a straight probe is used to excite the ultrasonic Lamb wave.Through time-frequency analysis of the echo signal collected by the system,a parameter based on the energy predominance of the gray histogram and the shape parameter of the boundary direction histogram The defect type detection method;proposed a method to identify the size of the defect using the volume parameter of the energy-dominated area.Experiments have proved that the feature extraction method proposed in this paper can effectively identify the defect type and defect size,which provides a research basis for the development of steel plate defect detection technology.The main research contents of this article include:(1)Conducted a literature survey,through a review of the literature,found the current problems in the detection of steel plate defects,and used this problem as the main scientific and technical problem to be solved in this article.(2)The propagation characteristics and detection principle of ultrasonic Lamb wave are discussed,the Lamb wave wave equation is solved,the influence of excitation frequency and steel plate thickness on the propagation mode is clarified,and the theoretical basis is laid for the subsequent research.(3)Constructed the ultrasonic testing experiment system in this paper.By selecting appropriate excitation and receiving methods,probes and excitation signals,through the construction of external devices and Lab VIEW software,the acquisition,analysis and processing of echo signals are realized,which provides an experimental platform for the research of this paper.(4)The time-frequency analysis of the Lamb wave mode propagating in the steel plate.Through the comparative analysis of the presence and absence of defects,the size of the defects and the Lamb wave modes of different defects,and the comparative analysis of the time domain,frequency domain and time frequency,it highlights the superiority of the time-frequency map to identify defects Defect feature extraction of steel plates provides a basis.(5)The feature extraction method of defect type and defect size is studied.Through the experiment,the gray histogram energy feature parameter and the boundary direction histogram shape feature parameter are used as the feature vector for defect type identification;Characteristic Parameters.(6)The effectiveness of the feature extraction method was experimentally verified.The experimental results proved the effectiveness and feasibility of the defect type feature extraction method and defect size feature extraction method proposed in this paper.