Weld Seam Interacts With EMAT Lamb Wave Numerical Simulation And Experimental Research

Electromagnetic Acoustic Transducer(EMAT)detection technology-an emerging non-destructive testing and structural health monitoring method,free from the limitations of conventional detection and low cost,with long-distance detection,no need for coupling agent,harmless to the human body,etc.Remote,large-scale detection has unique advantages.Based on the theory of electromagnetic ultrasonic transducer transducing mechanism and Lamb wave propagation characteristics,combined with the detection requirements of steel plate welds,COMSOL software is used to simulate the propagation of characteristic guided waves in steel plate welds,and the characteristic guided waves in steel plate welds are studied.The propagation characteristics and defect recognition effect,research and design electromagnetic ultrasonic Lamb wave sensor,and build a steel plate butt weld electromagnetic ultrasonic Lamb wave detection test system,the details are as follows.Firstly,the conduction mechanism of electromagnetic ultrasonic transducer is introduced.The propagation characteristics of Lamb wave and the formation of guide wave of weld characteristics are theoretically analyzed.The characteristic frequency equation of Lamb wave is solved by Matlab,and the steel plate with 3mm thickness is finally obtained.Lamb wave dispersion curve.Thus,modal waves corresponding to different frequency-thickness products,as well as group velocity and phase velocity values,can be obtained.Using the COMSOL software,a three-dimensional finite element model of the butt weld of the steel plate was established.The numerical simulation analysis of electromagnetic field,mechanical force field and ultrasonic field under multi-field coupling conditions is carried out.The load is applied at the end of the weld to excite the guided wave of the weld.On this basis,the sound wave propagation process and sound field distribution in the weld and the base metal are simulated,which proves the correctness of the loading method and the guided wave model of the weld.The existence of the state,and simulation analysis of defects and defects in the weld.Furthermore,the interaction between the guided wave and the defect of the weld is simulated.The depth,width and position of the rectangular through-hole defect in the weld,and the influence of the excitation frequency and the lift-off distance of the coil on the identification of the guided wave defect of the weld are studied.It is shown that the weld characteristic guided wave detection can effectively identify the rectangular through hole defect,and when the detection distance is 400 mm,the average positioning error of the defect is less than 2%.Design a welding electromagnetic ultrasonic Lamb wave detection test system,design the excitation and receiving parts,design the FPGA control circuit in the excitation system,and then output the pulse clock signal.After the signal passes through the optocoupler,the driver chip and the full-bridge inverter circuit,The high-frequency high-voltage pulse signal that can excite the EMAT is obtained through the optocoupler and the driving chip and the full-bridge inverter circuit through the output pulse clock signal;the three-stage amplifying circuit and the filtering circuit and the A/D conversion circuit in the receiving system are drawn,and finally Introduce the Labview PC program.The relevant test design was carried out on the completed test platform,and the probes with various excitation frequencies were used for testing,and finally the probe with the excitation frequency of 200 kHz was selected.Firstly,the excitation waveform is identified.Then,the attenuation characteristics of the characteristic guided waves in the steel plate weld are studied.Finally,the artificial rectangular through-hole defects at different distances in the weld are detected by the weld characteristic guide.The test results verify the "trapping effect" of the weld;the characteristic guide wave has a large attenuation within 200 mm of propagation,and the subsequent attenuation is gentle,and the defect echo energy can directly reflect the defect distance.The simulation results are consistent with the experimental results.