Research On Metal Surface Defect Detection Based On Laser Thermography

Metallic material has the advantages of high strength,small density,good mechanical properties,good toughness and so on.It has widely used in automobiles,railways,aerospace and other fields.However,the service life of metal materials is limited.Whether it is improper operation during the manufacturing process or metal fatigue during use,it will cause surface damage.In order to ensure the quality of the metal,non-destructive testing of the metal surface becomes particularly important.The laser thermography technology is a fast and effective nondestructive testing technology,and it has a relatively prominent advantage in the testing and characterization of material surface defects.It has gradually become an important means of material defect and damage detection due to its advantages such as non-contact,wide response frequency,and high sensitivity.Aiming at the characterization of metal surface defects,a reflection-based and transmission-based non-destructive testing system was built.Due to the huge potential of laser thermography technology in the field of non-destructive testing,the surface defect detection technology based on laser thermography is studied.The main contents are as follows:(1)The research progress of infrared thermography technology is analyzed,and the research methods of infrared thermography technology and the current research status at home and abroad are introduced.The theoretical mechanism involved in the process of using laser for non-destructive testing is studied.Two sets of infrared thermography non-destructive inspection systems based on reflection and transmission are built,and the composition of the system is introduced.(2)Aiming at the noise problem generated by the imaging system during the experiment,the main components of the infrared image noise are analyzed,and various denoising algorithms are studied.An infrared image noise reduction algorithm based on BM3 D is proposed to process infrared images,which provides support for the subsequent quantitative analysis of defects.(3)Aiming at the depth problem of metal surface defects,the COMSOL software is used to simulate and analyze the transmission-based laser thermography technology.In addition,a transmission-based laser thermography system was built and verified by experiments.In the course of the experiment,aiming at the quantification of defect depth,a temperature field comparison method was proposed to quantitatively analyze the defect depth,and the numerical relationship between defect depth and temperature is optimally fitted.(4)Aiming at the problem that the above system can only deal with the defect depth,a transmission-based laser thermography system was built.Through experiments and data analysis of different depths and different defects in the specimen,the 3D characterization of metal surface defects is realized.This method effectively overcomes the problem of incomplete characterization of defect detail information.