Detection of internal defect in materials by infrared thermography and its numerical simulation (effect of thermal diffusivity of materials on defect detection)

摘要

A nondestructive testing technique using infrared thermography can remotely detect invisible defects present in materials and structures. However, few investigations have been carried out to detect such defects quantitatively by infrared thermography. In the present study, an irregular temperature distribution due to an invisible artificial defect in a test specimen was observed in thermal images measured by infrared thermography when the specimen was transiently heated by a heater from its back surface. Furthermore, numerical simulation for unsteady-state three-dimensional heat conduction was performed when the specimen with the invisible defect, which had lower thermal diffusivity than that of the parent material, was heated from its back surface. Results of the numerical simulation showed the temperature of the surface above the internal defect to be lower than that of its surrounding surface. These results were in agreement with the experimental results. In a case when specimens are made of different kinds of materials but have the same internal defect, the temperature difference on the specimen's surface due to the defect increases with decreasing thermal diffusivity of the parent material.