Research On Metal Defect Detection Technology Based On The Eddy Current Plused Thermography

Based on design requirements,as the powerful,strong sealing performance and ten years or even decades of online running time of some large mechanical equipment and the main components,the maintenance and repair on these devices and main components is particularly important.The purpose of nondestructive testing is not only to detect defect in advance,but also to conduct quantitative analysis on defects,repair the equipment in time,so as to avoid accidents,such as long shutdown maintenance time,associated parts damage,personal casualty and so on.The testing technology of eddy current pulsed thermography is a new nondestructive testing method,as a outcome combining eddy current detection technology and infrared thermal imaging technology,the testing technology can detect defect in conductors through analysis of the surface temperature distribution of components,and compared with the conventional nondestructive testing method,it has many advantages,such as non-contact measurement,high sensitivity,fast response,fast signal processing speed,large detection area,intuition,accuracy and so on.In this paper,COMSOL Multiphysics software is used to simulate the defect detection,and the revelant experimental equipment is selected to build the experimental platform.The main work is as follows:(1)In the simulation,the influence of different materials on the distribution of eddy current density and temperature distribution is analyzed,the results are as follows: Compared with non-ferromagnetic materials,temperature reaction of the ferromagnetic material is sensitive,the relative permeability is very large and the influence of the skin depth can be neglected;Due to the limit of experimental conditions,select the ferromagnetic material as specimen to analyze simulation and experiments.(2)Two models respectively with notch type crack and common crack added in ferromagnetic materials are built in Heat Transfer module of COMSOL Multiphysics software,analyze the heat transfer in specimen surface,the temperature distribution in the crack boundary and specimen surface in the whole heating process;in the case of different depths,the maximum temperature variety and temperature difference in crack are also analyzed,the results show that the defect is always the highest area of the whole specimen temperature;the maximum temperature of the defect increases with the grow of the defect depth;there is a significant temperature difference between the upper boundary temperature and the lower boundary temperature.(3)In the defect detection experiment,the temperature data of specimen surface with ordinary crack is analyzed,the results of data analysis show that the defect is the high temperature region;the highest temperature increases with the grow of defect depth;there is a significant temperature difference between the defect bottom and defect around;the above experimental results are consistent with the simulation analysis.The differential method is used to further process the temperature data,and the results show that the greater the depth of the defect,the larger the temperature difference is;pixels which have the larger temperature difference are selected to judge the approximate position and size.In this experiment,the defect of the ferromagnetic material specimen is tested,and the error of defect width is 0.016 cm,the length error is 0.29 cm,the rationality of the system design is verified.