Heating characteristics of metal plate crack in sonic IR imaging

Sonic infrared imaging is a new kind of hybrid nondestructive testing method. Research on heating characteristics of defect region is propitious to the optimization of testing scheme. Experimental results show that temperature rising of crack region measured at the excitation side is higher than that at the excitation opposite side; however, the heating rate of crack contact surface is stable in the mass. Based on the phenomenon of crack heating under intensive ultrasonic pulse, a finite element model of experimental setup was established and a thermal-stress analysis was performed by an explicit finite element method. In the finite element model, a piezoelectric-force analogy method was employed to simulate inverse piezoelectric effect in the ultrasonic excitation system, and dynamic relaxation was introduced into the simulation in order to cover the effect of engagement force on the initial state of specimen. During the FEM simulation, the crack frictional heating excited by ultrasonic pulse was calculated, and temperature distribution in space and time domain was described. The relationship between friction heating, friction force and relative velocity at contact surface was revealed. Simulated results reveal the engagement force between horn and testing plate makes the heating position in crack surface shift to the excitation side.