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5 August 2009 Research on CFRP materials nondestructive testing by IR lock-in thermography
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Lock-in thermography which is an active thermography technique for NDT is based on propagation and reflection of thermal waves which are launched from the surface into the inspected component by absorption of modulated radiation. Phase angle images obtained by superposition of the initial thermal wave and its internal reflection display hidden thermal structures down to a certain depth below surface. Defects are found by comparing the observed features with expected features provided by an intact reference sample. This technique has been widely applied to detect the defection of many materials and structure in aerospace and automotive industry. In this study, the law of sine modulated lamp was used for active heat source into the CFRP plate sample. The theory of thermal wave transmission and reflection were studied deeply by finite difference method and thermal-electronic equaling model. The thermal wave image sequences were collected with infrared camera, and the program of IR Lock-in thermography was developed by Visual C++ development platform. So that the phase image was extracted between the reflection thermal wave and reference ones on the surface of sample by means of correlation algorithms or Fourier transform. The experimental results show that the simulation is closed to the experimental ones. The defect character is detected clearly, and the relation between phase and defect depth is obtained by lock-in thermography, this relation can be used to measure the defect depth. Lock-in thermography is an effective tool to detect the Debonding defect of CFRP materials.
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Junyan Liu, Yang Wang, Hui Liu, and Yinhang He "Research on CFRP materials nondestructive testing by IR lock-in thermography", Proc. SPIE 7383, International Symposium on Photoelectronic Detection and Imaging 2009: Advances in Infrared Imaging and Applications, 73833U (5 August 2009);

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