| Infrared thermography is a Nondestructive Testing and Evaluating (NDT&E) technique that allows the non-contact inspection and quick monitor large area. In advantages of these that it has been used in aerospace, automobile manufacture, nuclear industry and health monitoring. The analysis is based on the fact that the surface heat wave and the excitation signal have the same frequency. Because of the phase of the wave signal contains more defects information than the amplitude, the analysis of phase has become interesting.The main research is to study the methods of phase analysis and the experimental parameters determine for the active infrared NDT, and provide theoretical basis for the quantitative evaluation of defects in scale and depth and provide a theoretical basis for the excitation parameters determine for the project. The main researches are presented as follows:Based on the principle analysis of active infrared NDT, the analysis of different forms of heat transfer process within the medium is made. According to the modulated periodic signal heat transfer in a multi-media specimen, the relationship between the amplitude and phase of signal and the thermal properties of the sample media is studied. By theoretical research, the relationship between the thermal wave signal phase and the defect properties is gained. Based on the characters of heat conduction of volume element, the three-dimensional heat transfer finite difference model is made and the computer program is developed. The temperature field distribution of the specimen with difference thermal properties of defect under different modulation frequency is simulated by finite difference calculation. It can provide a theoretical basis for the quantitative evaluation of defects in material parameters and defect size information, and through simulated defect tests of specimens to verify its accuracy;Based on the phase method infrared NDT, the domestic production test equipment is established. The system of modulated light resource is developed and the infrared image sequence processing software for infrared NDT is also developed. Through the test of infrared light source spectral distribution and response characteristics, the active infrared light source of experiment is determined. The optical excitation system is developed according to the frequency modulation characteristics. The software system for the phase methods of NDT is developed and multi-algorithms for processing image sequences are achieved;The algorithms for phase extraction are studied to reconstruct the specimen surface thermal wave signal. The surface thermal wave signal pre-processing is made according to the characteristics of heat wave signal contains periodic components and the DC component. The 4-point average algorithm, lock-in algorithm, least squares algorithm, polynomial fitting coefficients algorithm, particle swarm algorithm and principal component analysis method for the amplitude, phase and reconstruction information are developed. By compare these algorithms, the lock-in algorithm can quickly and accurately determine the thermal wave signal phase information with known frequency.The evolutionary neural network algorithm is introduced into the Lock-in NDT to quantitatively determine the defect depth. The temperature-time information and phase information are used as the network input for training, and the defect depth as output. The accuracy of evolutionary neural networks is evaluated by simulated defect testing. In order to determine the optimize test parameters of infrared NDT, the multi-objective evolutionary algorithm is used to optimize the experimental frequency, time and other parameters. The temperature difference between the non-destructive region and the defect region is used as evaluation function, and the optimized experimental parameters are achieved by a multi-objective evolutionary algorithm. The experimental results show that, the method can provide theoretical parameters for engineering inspection.
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