Research On Infrared Radar Thermal Wave Imaging And Tomography For Detection Of Defects In CFRP Composite

With the development of aerospace,nuclear industry and medical bioengineering,traditional materials have been unable to meet the requirements of high specific strength,high specific modulus and high heat resistance.In recent years,the rapid development of materials science and technology has resulted in the emergence of composite materials and coating structures.Composite materials and coating structures combine the excellent properties of two or more kinds of materials,such as carbon fiber reinforced polymer(CFRP),functional coating materials,and biomimetic coating structure.CFRP and coating structures can be endowed with excellent performance and function by artificial design,so they are widely used in the modern industrial field.CFRP composite and coating structures are different from the single component material due to strong anisotropy and internal interface effects.In the process of production,processing or use,there are different types of defects and invisible impact damage,such as porosity,bulge,debonding and delamination,which seriously affect the performance of materials or structures.Therefore,for CFRP composite and coating structures,how to effectively and accurately detect and identify internal defects has become a research hotspot and difficulty in this field.Infrared radar thermal wave imaging and tomography detection technology has the advantages of non-contact,large detection area,intuitiveness and high efficiency.It provides new methods and new ideas for non-destructive testing and tomography imaging of CFRP composite and coating structures.Therefore,in this thesis,infrared radar thermal wave imaging and tomography detection technology for CFRP composite and coating structures delamination defects are investigated.Firstly,a one-dimensional thermal wave mathematical model of a finite thickness medium which was stimulated by chirp/chirp-pulsed radar form heat flux was established.The influences of medium depth gradients on the time-domain changes of thermal wave were analyzed to determine the applicability of different forms of heat flux excitation.A three-dimensional finite element heat conduction model of chirp/chirp-pulsed radar heat flux acting on the inner defects of CFRP composite was established,and the temperature field distribution and change process were simulated and analyzed.Fractional Fourier transform(Fr FT)and dual orthogonal demodulation(DOD)algorithm were proposed to extract chirp/chirp-pulsed radar thermal wave characteristics,and were used to analyze the influence and regularity of heat flux modulation parameters and internal defect sizes on radar thermal wave characteristics.Secondly,an infrared radar thermal wave imaging detection system was built,and the software system of infrared radar thermal wave was developed based on Labview.The effective control of hardware platform and the efficient transmission of data were realized.The chirp/chirp-pulsed heat flux excitation experiments were carried out on the CFRP composite and thermal barrier coatings with simulated delamination defects.The effects of modulation parameters and defect size on the thermal wave characteristics of chirp/chirp-pulsed radar were studied to verify the correctness of simulation analysis.Subsequently,based on the contrast enhancement,filtering and segmentation of thermal wave characteristic image,and morphological processing,defect recognition and size quantification were studied.In order to reduce the influence of transverse thermal diffusion effect on defect identification and judgment,an like optical flow method was proposed to suppress transverse thermal diffusion effect,and its applicability was verified by simulation and experiment;The detection ability of infrared radar thermal wave imaging to detect the delamination defects of CFRP composite was studied by Hit/miss statistical method.Finally,the chirp-pulsed radar thermal wave tomography was investigated.The fast Fourier transform and the time delay correlation DOD algorithm were used to extract the frequency-domain and time-domain feature sequences of the chirp-pulsed radar thermal wave signal.Furthermore,a depth-resolved tomography method,which based on the time delay correlation DOD algorithm of radar thermal wave transient characteristic delay characteristics,was proposed to be applied to tomography inspection of composite materials and structures;The defects or cracks of CFRP,glass fiber reinforced polymer(GFRP)and the internal structure of Si C coated C/C composite were detected using infrared radar thermal wave tomography.Ultrasonic C-scan imaging and chirp-pulsed radar thermal wave tomography were used to analyze the delamination defects of CFRP composite.