Study On Elecyromagnetic Lamb Wave Tress Detection Mechanism Based On Acoustoelastuc Effect

Metal materials are widely used in the construction of large-scale equipment and major projects.During the service process of metal thin plate structures,due to the complex and variable actual working conditions,the external load and the internal stress of the metal are superimposed,which will easily cause the structural strength to decline,fatigue,deformation,Microcracks,etc.,eventually evolve into structural fracture and failure.Therefore,studying the metal stress state will provide an important basis for structural service characteristics and life assessment.Carry out research on metal stress in-service characterization methods,and carry out on-line monitoring and effective evaluation of stress conditions of key components of major metal equipment.Because the critical refraction longitudinal wave detection method cannot be applied to the stress measurement of thin plates,the stress detection of metal thin plates based on Lamb waves is gradually becoming the focus of scholars at home and abroad.The electromagnetic ultrasonic Lamb wave(Lamb)detection technology has the advantages of no couplant,simple excitation,etc.,and is widely used in non-destructive testing of metal layered,plate-like,pipe-type components.However,Lamb waves have many problems such as multi-modality,dispersion,and complex wave structure.At present,there are few studies on the application of electromagnetic ultrasonic Lamb waves to stress detection.In this paper,the research of Lamb wave stress detection based on sonoelastic effect is carried out.The main research work is as follows:1)Study the generation mechanism and propagation characteristics of Lamb waves,analyze the wave characteristics(dispersion,multi-mode,complex wave structure)of Lamb waves and their influencing factors,and design a single mode with relatively high suppression State EMAT coil and magnet structure.2)In order to understand the influence of stress loading on the propagation characteristics of Lamb waves in thin metal plates,according to the particle motion equation of Lamb waves in isotropic plates and the theory of sonoelasticity,the dispersion equation of Lamb waves under stress loading is derived and established The corresponding mathematical model lays the foundation for numerical analysis.3)Based on the sonoelastic effect and the derived Lamb wave dispersion equation,and based on the chord intercept method,a numerical analysis model of Lamb wave dispersion characteristics under stress is established,and the dispersion curves of Lamb waves in aluminum plates under different stresses are given.The variation of the propagation characteristics of the basic mode and the first-order mode when the stress is consistent with the Lamb wave propagation direction is analyzed.4)By designing the structure of the electromagnetic ultrasonic transducer and the impedance matching circuit,the energy conversion efficiency of the electromagnetic ultrasonic transducer is improved,an electromagnetic ultrasonic Lamb wave detection platform is established,and the aluminum plate test piece with a thickness of 1 mm is subjected to ultrasonic stress using the Lamb wave The test results are in good agreement with the simulation data.The influence of the obtained stress on the propagation characteristics of ultrasonic Lamb waves provides an important basis for subsequent stress detection of thin metal plates.