Research On The Rayleigh Wave Based Plane Stress Measurement Method Using Electromagnetic Ultrasonic

The ultrasonic testing method is commonly utilized to estimate residual stress in critical structure with the advantages of strong penetrating ability,free of radiation,and fast detection.Most of the failure in mechanical structure is caused by surface cracks and surface stress concentration during manufacturing and utilizing processes of structural elements.So,it is very necessary to estimate residual stress quickly,non-destructively and precisely.In current research,LCR wave generated by one-transmitter-one-receiver piezoelectric transducers was used to estimate the plane stress.However,the use of coupling medium limits the application of piezoelectric probe.In contrast,Electromagnetic ultrasonic transducer?EAMT?has a good development prospect because of its advantages of couplant-free and low requirements for material surface.Rayleigh wave generated by Rayleigh EMAT,which propagates along the surface of the workpiece,make it possible to measure plane stress of structural component.However,At present,most of EMAT that generated Rayleigh wave generally only included one transmitter and one receiver and then the probe need to be rotated by manual or using mechanical structure to measure multi-directional ultrasonic velocity,which restrain quick and easy evaluation of plane stress and cause that the results of practical measurement have poor repeatability which leads to a reduction in detection accuracy.Aiming at the issue above,a three-transmitters-three-receivers Rayleigh wave electromagnetic ultrasonic transducer was designed and then the plane stress can be measured when the probe was positioned once.Firstly,model of electromagnetic ultrasonic measurement of plane stress based on three-transmitters-three-receivers was built.The characteristics of surface wave propagation and wave model were introduced at first.Electromagnetic ultrasonic transduction mechanism based on the Lorentz force mechanism and the acoustoelastic theory was introduced.Theoretical deduction and analysis of the generation process of Lorentz force was performed in aluminum plate based on Maxwell equations.And then the configuration of the probe that can excite Rayleigh waves was mainly analyzed.The principle of acoustic elasticity of ultrasonic stress measurement is discussed.The formula for calculating plane stress was modified when the stress field is oriented in an arbitrary direction,which provides theoretical basis for the plane stress measurement.Then,the probe design and parameter optimization based on electromagnetic simulation analysis was performed.The selection and design of the three-transmitters-three-receivers coils and magnets was introduced in details.And then the eddy current field,magnetic field and electromagnetic field in EMAT were simulated and analyzed based on the electromagnetic field module of ANSYS.By comparing the influence of different coil parameters and magnet parameters on the probe transduction efficiency,the simulation and optimization design of the three-transmitters-three-receivers electromagnetic ultrasonic transducer designed above was carried out.The design of the probe structure was optimized and the probe assembly was completed to further improve the probe transduction efficiency.At last,the plane stress measurement experiment was carried out based on electromagnetic ultrasonic Rayleigh wave.An electromagnetic ultrasonic plane stress measurement platform was built,and typical waveforms of three-directional surface waves were collected and analyzed.a calibration test was performed to calibrate the acoustoelastic coefficientsK_{1 1} and K₂₂.A plane stress measurement experiment was performed in 5052aluminum alloy by friction stir welding,And the measurement results were compared with the hole-drilling method.The measurement result of longitudinal residual stress by ultrasound method shown an obvious double-peak characteristic,which meant that there were 2 crests and 1 trough and the shape of curve is similar to"M".In addition,relatively good agreement was found between the measured results,compared to the residual stress from the hole-drilling method,which verified the feasibility of the designed electromagnetic ultrasonic probe.