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The effect of depth on the quantitative estimation of defect size using pulsed thermography

Although active thermography has traditionally been regarded as a qualitative NDT method, its potential for quantitative measurement of thermophysical properties including wall thickness, defect size and depth, thermal diffusivity has been the subject of numerous investigations. An investigation into the effect of depth on the quantitative estimation of defect size in metalic specimen has been undertaken using pulsed thermography. A 3D model based on finite element method was used to simulate the heat conduction in a flat metal plate containing articial defects. The plate is made of steel with known thermal properties. The defects of different depth are flat bottom holes simulating areas damaged by corrosion. The goal of the1 research was to find if there is a possibility to combine pulsed thermography and numberical modeling to determine the effect of depth on the quantitative estimation of defect size. The temperature distribution on the metal surface can provide proper threshold value to extract edge of defect in thermography. A series of specimen with circular defect of varying diameter and depth were tested. To solve this problem, we analysis the FEM simulation results, investigate the relationship between measured value and true value, and introduce a correction factor related to depth. Using this correction factor, its measured value in the thermography is quite close to the design size of defect in the specimen.