Study On Metal Structure Crack Detection By Sonic IR And The Effect Of Excitation Parameters

Once defects of the key structural of mechanical equipment have not been discovered in time, its propagation will lead to the failure of the whole structure which cause the occurrence of safety accidents easily. Nondestructive testing of structural parts is a reliable guarantee for the safe operation of the machine. Sonic infrared thermography nondestructive testing method which combined ultrasonic excitation and infrared thermal imaging technology innovatively have unique advantages. Since the method was put forward, researchers at home and abroad have carried out experimental and theoretical research on this method. For example, the applicability of different materials and different types of defects, the heat generation mechanism and the analysis of infrared thermography sequence and so on. But the effect of ultrasonic excitation parameters on crack defect detection is still not studied so far, and the selection of ultrasonic excitation parameters is still basically rely on the experience of the operator.The effect of excitation parameters in sonic IR was studied in this paper, and sonic excitation parameters included excitation amplitude, excitation frequency and excitation position. The solid heat coupling model and the temperature distribution model of the structure is established by analyzing the process that sonic exciting crack and the heat conduction to the surface with the basic principle of elasticity theory, dynamics theory and the heat and mass transfer theory and so on. The sonic infrared thermography detected metal plate crack simulation model is established by finite element method, and the temperature field distribution of the crack after sonic excitation is solved. The crack detection experiment by sonic IR was carried out, and the result verified the feasibility of the finite element analysis. And the effect of different sonic excitation parameters(excitation amplitude, excitation frequency, excitation position) is researched based on ANSYS.Through the research of the influence of sonic exc itation parameters on the crack heat founded that the heat of crack region with the increases of the sonic excitation amplitude, but in different range of excitation amplitude, the heat rate of crack is not the same. The frequency of sonic excitation in a small range is not linear with the crack heat, and the heat of crack is greatly increased when the excitation frequency is close to the structure’s natural frequency. There is an optimal excitation position where exciting more higher heat than others under the same excitation condition, but exciting in any other position of the structure surface make the crack region heating and the temperature can be detected by infrared thermal image instrument.