Research On Early Damage Detection Of Metal Materials Based On Electromagnetic Ultrasound

As a non-contact and non-destructive testing method,electromagnetic ultrasonic testing technology has the characteristics of no couplant required and high temperature resistance,and has broad application prospects in the performance testing of metal objects.Among them,the detection of early plastic deformation and fatigue damage of structural parts is an important issue worth noting in the safe operation and maintenance of equipment.It is difficult to directly detect the early damage of related structural parts.However,it is a feasible solution to collaboratively analyze the early damage of structural parts with the help of specimen thickness changes,internal crystal structure changes or other related characteristics.Firstly,this paper introduces the generation mechanism of electromagnetic ultrasonic wave,analyzes the influence of noise,surface roughness and material properties on the detection results in the process of electromagnetic ultrasonic detection,and verifies the theory by establishing relevant models.In view of the macroscopic plastic deformation detection of metal components,the electromagnetic ultrasonic time difference method and electromagnetic ultrasonic acoustic resonance technology are proposed.The finite element simulation software is used to establish a simulation model,whose theoretical feasibility is verified by analyzing the obtained results;secondly,an electromagnetic ultrasonic testing platform was built to detect the specimens subjected to different axial pressures,and the thickness information of the specimens was extracted through relevant signal processing methods;finally,the stress-strain relationship of the material is obtained by combining the different axial pressures of the specimens with the deformation value.At the same time,aiming at the problem of electromagnetic ultrasonic detection of inhomogeneous plastic deformation,an electromagnetic acoustic resonance rotation scanning detection scheme based on the electromagnetic acoustic resonance theory was proposed.The finite element simulation software was applied to establish the slope model with unequal thickness on both sides,and the simulation results were analyzed to verify the theoretical feasibility of the scheme.Then build an electromagnetic ultrasonic acoustic resonance testing experimental platform to perform fixed "point" rotation scanning detection on the slope specimens to obtain the thickness values of the specimens at different "points".Meanwhile,the probability of detection is introduced to quantitatively analyze the detection success rate of rotating scanning,and the detection capability as well as detection reliability of the proposed ultrasonic detection scheme are evaluated.Finally,aiming at the problem of wheel/rail fatigue damage,this paper elaborates the theoretical basis of nonlinear ultrasound and rolling fatigue wear.A Murnaghan model is established based on the characteristics of the surface wear of the wheel/rail specimens.The nonlinear ultrasonic finite element simulation was used to simulate the friction damage of different degrees through the change of the thickness of plastic deformation layer,and the variation law of the relative nonlinear coefficient was observed.The variation law of the relative nonlinear coefficient in the process of wheel/rail friction damage was discussed by carrying out the experimental study on CL60 and U75 V wheel/rail specimens.