Experimental Study On Ultrasonic Modulation Of Closed Crack Based On Electromagnetic Loading

Aluminum sheet is widely used in various mechanical equipment due to its good metal properties.When the equipment is in service,it often bears the influence of various loads,so it is inevitable to produce minor defects,such as closed cracks.Because of the strong transmissivity of ultrasonic wave at the closed crack,the reflection and scattering waves are very weak,so that the reliability of conventional linear ultrasonic detection is greatly reduced.In order to achieve effective detection of closed cracks,in this paper,nonlinear ultrasonic nondestructive testing technology is used to detect the closed crack.Electromagnetic loading at the closed crack makes the nonlinear response more obvious and improves the detection rate of closed crack to some extent.The research mainly includes the following aspects:1)The electromagnetic ultrasonic simulation model was established based on the Lamb wave energy exchange mechanism of electromagnetic ultrasound.The propagation characteristics of Lamb wave in aluminum plate were studied and analyzed.On this basis,the electromagnetic ultrasonic simulation model with closed cracks was established to study the influence of ultrasonic excitation parameters,closed crack length and depth on ultrasonic nonlinearity.2)The experimental platform for electromagnetic ultrasonic testing was set up to study the nonlinear effect of closed cracks,and the effects of ultrasonic excitation period,voltage,boundary support and experimental system on ultrasonic nonlinearity were analyzed.3)The closed crack ultrasonic nonlinear modulation phenomenon under electromagnetic loading was studied through simulation and experiment,and the influence of electromagnetic loading parameters on ultrasonic propagation characteristics was analyzed.The structure of the electromagnetic loading device was designed through the experiment,and the ultrasonic non-linear test was carried out on aluminum plates with different thickness under electromagnetic loading.4)When the closed crack is squeezed by external force,the electromagnetic ultrasonic experiment and the ultrasonic modulation experiment under electromagnetic loading are respectively performed,to study the influence of external pressure on the ultrasonic high harmonic and modulation frequency.Further study analyzed the relationship between closed cracks of different lengths and ultrasonic nonlinear coefficient and ultrasonic nonlinear modulation coefficient.