Numerical Simulation And Experimental Research On The Detection Of Weld Crack Based On Electromagnetically Stimulated Infrared Thermography

Metal weld crack has been one of the most dangerous large mechanical equipment defects, using nondestructive testing method to detect defects is the key to ensure the safe operation of the equipment, electromagnetic excitation infrared thermal image technique is a new nondestructive testing technology, has advantages of non-contact, portability and high efficiency. This article focuses on the weld surface crack defects, with electromagnetic excitation infrared thermography technique for testing, including theory, simulation, test and crack identification algorithms research, the abnormal temperature distribution of infrared thermal image was analyzed, to judge the existence of crack, it has an important value of weld crack detection.The main contributions are:1)First of all, this paper introduce the basic theory of electromagnetic excitation infrared thermography testing on weld crack. Base on the theory of electromagnetic induction and the eddy current effect, established the vortex flow field, temperature field mathematical model of weld crack,and the vortex flow field, temperature field distribution of crack area. It has also made a theoretical analysis and guidance on the stimulated parameters that influence efficiency of induction heating.2) Secondly, through the finite element analysis software, simulate the electromagnetic excitation induction heating and testing process on weld crack. Electromagnetically stimulated infrared thermography testing of weld crack model was established by COMSOL, simulates 3 kinds heat transfer process, which are the steel weld surface crack, near surface crack and no crack. Research the electromagnetic excitation method in terms of crack size and shape detection rule by various crack lengths, widths, heights and directions. Analysis the influence of excitation parameters on the surface temperature distribution, by changing the excitation coil lift-off height, excitation frequency. By simulating different welding structures, explains the application scope of electromagnetic excitation thermal method.3) Finally, design the test system of electromagnetic excitation infrared thermography aimed at weld crack, and has set up the test platform, including control the excitation power supply, design different shape and turns of the drive coil, process different welding structure with various crack size and directions. Through recording the specimen surface temperature in the test process by infrared thermal imager, to obtain the test results.4)According to the specimen surface temperature distribution characteristics on the thermal image, this paper proposes a crack geometry characteristics identification algorithm based on the morphology, by calculating the length-width ratio of connect area on image, keep the largest length-width ratio which is the crack area, in order to extract the crack. And design the software interface to extract crack with the MATLAB software, the crack shape and position can be automatically extracted, make the crack identification more forthright, reduces the labor intensity of operators, improve the detection efficiency.Through the above research, the electromagnetically stimulated infrared thermography is comprehensive verified in the metal structure of weld crack recognition, the research on electromagnetic excitation method laid a solid foundation in the field of weld crack detection.