Research On Material Crack Detection Technology Based On Optical Low Coherence

As the basis of optical coherence tomography(OCT),optical low-coherence technology has great potential on its application in the field of NDT with its advantages of high resolution,high real time,non-invasion,non-destruction,no radiation and intuitive imaging display.This dissertation conducts a comprehensive survey of material NDT technology,and a nondestructive,noninvasive,high-resolution and high-real-time material crack NDT technology,which is based on optical low coherence,is proposed.In this dissertation,a crack detection system is designed and built based on the principle of swept source optical low coherence and the requirements of material crack detection,and it researches into the crack propagation characteristics of aerospace materials.At first,the dissertation analyzed the causes of short cracks and the characteristics of short crack propagation according to the theory of short cracks,and studied the theory of swept source optical low-coherence detection technology.Based on this,a swept source optical low-coherence crack detection system is designed and built.Subsequently,in order to study the properties of the materials,the tensile properties of the aerospace titanium alloy TC4 and the superalloy GH4169 were tested,and the influence of the microstructure on their properties were studied according to the test results.Finally,the swept source optical low-coherence system is used for dynamic monitoring of crack propagation of titanium alloy TC4 and superalloy GH4169.First,the imaging resolution of the swept low-coherence system is calibrated.The three-dimensional reconstruction of the two-dimensional images of the crack acquired by the system was performed through the volume rendering method.The crack sizes of the materials were calculated from datas obtained by the system,and the short crack propagation characteristics of the materials TC4 and GH4169 were studied in depth.Subsequently,the cross sections of the materials were imaged by the swept source low-coherence system,based on which the crack propagation and fracture characteristics of the materials were analyzed.At last,the relationships between the strength and the fatigue limit of the materials were discussed.After calibration,the detection resolution of this system can reach 16 microns.The research results fully demonstrate the feasibility of optical low-coherence technology for material crack detection and its advantages of high resolution and high real time.