On-line Measurement Of Acoustoelastic Coefficient Of Metal Plate Based On Electromagnetic Loading

Structural health monitoring of metal components is indispensable in engineering practice,and stress detection of components is a very important part.Based on the principle of ultrasonic acoustic elasticity,the critical refraction longitudinal waves(L_CR waves)can be used for non-destructive testing of residual stresses inside metal components.However,the structural state and working environment of metal materials have a large impact on the acoustic-elastic response characteristics of L_CR waves,resulting in a lower accuracy of in-service detection of metal residual stress in engineering practice.Therefore,realizing in-service calibration of acoustoelastic coefficient will be a key step to improve the accuracy of stress detection.In view of the above problems,by performing in-service electromagnetic loading on metal plates and measuring the L_CR waves velocity in the metal plates under electromagnetic loading,the online measurement of the acoustoelastic coefficient of metal plates is carried out as follows:1)Research on on-line measurement of acoustoelastic coefficient in metal plates.Using L_CR waves to detect residual stress in metal materials is based on the theory of acoustic elasticity.However,it is found that the existing calibration methods for acoustoelastic coefficient in in-service metal plates generally use approximate substitute materials as experimental samples,and do not fully consider the influence of material working environment and internal residual stress on the acoustoelastic coefficient of metal plates.In view of the above considerations,this paper uses electromagnetic loading method instead of mechanical loading method to characterize the propagation characteristics of L_CR waves,and thus obtains the theory of on-line measurement of acoustoelastic coefficient.2)Design of electromagnetic loading device.According to the mechanism of Lorenz force,this paper designs an electromagnetic loading device which can be used to calibrate the acoustoelastic coefficient of non-ferromagnetic metal plate.The device consists of a static magnetic field and an exciting coil,which is provided with an exciting current by a pulse power supply.The two-dimensional simulation model of the electromagnetic loading device is established,and the influence of the size parameters in each part of the electromagnetic loading device on the electromagnetic loading force is simulated and analyzed to select the size parameters of the device.The three-dimensional simulation model of electromagnetic loading device is established to simulate the electromagnetic loading force on the metal plate.The experimental platform of electromagnetic loading device is built to measure the average stress of aluminum plate under electromagnetic loading.The experimental results are basically consistent with the simulation results,which verifies the feasibility of electromagnetic loading device.3)Extract the arrival time of ultrasound.The calculation accuracy of on-line measure-ment of acoustoelastic coefficient proposed in this paper depends largely on the accurate measurement of the arrival time of L_CR waves.After comparing and analyzing the existing ultrasonic arrival time calculation methods,this paper uses the method of synchronous com-pression transformation to decompose and reconstruct the L_CR waves,and accurately extract the arrival time of L_CR waves from the reconstructed signal waveform.In this paper,a two-dimensional simulation model of L_CR waves is established to analyze the propagation char-acteristics and waveform signal characteristics of L_CR waves.The propagation time of L_CRwaves in 1060 Aluminum plate was measured accurately and the velocity of L_CR waves in aluminum plate was calculated.