Thermographic non-destructive testing damage detection for metals and cementitious materials

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Abstract
The authors have explored the use of thermography as a non-destructive testing technique to detect geometrical defects in both metallic and cementitious materials which are widely used in the construction industry. The method is based on the characteristics of heat propagation within a conductive medium of specific geometry, which is intended to model predetermined boundary conditions. The test specimens have been successfully induced with various crack widths under controlled laboratory conditions in order to represent mechanical damage. The finite element (FE) method is applied as an analytical tool to predict the heat flow field. The analysis was formulated and processed as a two-dimensional problem, the thermomechanical properties having been accurately predetermined. The input preparation requires a number of trial-and-error attempts to generate the appropriate data for FE analysis. Experimental results relating to detection of geometrical faults in concrete, based on selected geometric parameters, show a satisfactory agreement with the numerical predictions. The results predicted by FE modelling are also linked through representations by simple formulae, to include variables such as crack width and temperature difference for concrete and metallic materials. So far it has been possible to use thermography to estimate the extent of surface cracks in construction materials of both a metallic and a cementitious nature.