Research On Infrared Thermography Detection Method For Inner Holes Defects

Infrared thermography testing is a newly developed non-destructivetesting technology, and obtains the surface temperature field of the object to establishthe relationship with internal defects in order to detect and evaluate internal defects.Infrared thermography nondestructive testing has the advantages of the non-contact,online testing, large detection area, high efficiency and so on compared withtraditional nondestructive testing technology. Although this technology has relativelybroad prospects for application, there are many inadequacies such as theoreticalresearch, detection methods, testing equipments and defect evaluation compared withother countries, and defects quantitative research has been the focus of the study anddifficult at home and abroad.This paper is mainly to study the effects of the depths and sizes of internal holeson the surface temperature field in the heating-cooling process by infraredthermography nondestructive testing technology, and take a combination method ofsimulation of the finite element and experiment to summarize the influence laws indifferent stages. The moment of the maximum center temperature difference valueand the results of image edge detection are used to analyze the depths and sizes ofthe holes defects semi-quantitatively. The main contents of this paper are as follows:Firstly, this paper describes the basic theories of infrared thermographynondestructive testing technology including infrared radiation, infrared temperaturemeasurement and infrared thermography detection, and it analyzes outsideinfluencing factors to infrared thermography technology.Secondly, finite element analysis method is used to analyze and simulateinternal holes defects of the objects by infrared thermography nondestructive testingtechnology. This paper introduces the basic thermal theory of the finite elementanalysis and simulates the surface temperature field by ANSYS finite elementsoftware with temperature field cloud picture, center temperature difference graphand3D temperature field map. It studies the laws on the impact of the sizes and depths to temperature field in different stages of heating-cooling process. Themaximum time of the center temperature difference is used to semi-quantitativelyanalyze the depths of the defects.Thirdly, the experimental method is used to analyze the law of the sizes anddepths to the surface temperature field. An infrared thermography nondestructivetesting experimental system is built to detect internal holes with the infrared thermalexcitation device. The experimental results are compared to the simulation resultsincluding the laws of the change in temperature field and semi-quantitativejudgment.Finally, edges detection algorithms are used to detect the edges of defects ininfrared image to analyze the sizes of the holes. An improved edge detectionalgorithm is proposed to analyze the size of the holes defects by inside edge pixels.The improved edge detection algorithm is proved to be effective contrasted withconventional edge detection algorithms in the aspect of quantitative analysis to thesizes of the defects.