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

The authors have explored the use of thermography as a non-destructive test ing technique to detect geometrical defects in both metallic and cementitio us materials which are widely used in the construction industry. The method is based on the characteristics of heat propagation within a conductive me dium of specific geometry, which is intended to model predetermined boundar y conditions. The test specimens have been successfully induced with variou s crack widths under controlled laboratory conditions in order to represent mechanical damage. The finite element (FE) method is applied as an analyti cal tool to predict the heat flow field. The analysis was formulated and pr ocessed as a two-dimensional problem, the thermomechanical properties havin g 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 concre te, based on selected geometric parameters, show a satisfactory agreement w ith the numerical predictions. The results predicted by FE model:ling are also linked through representati ons by simple formulae, to include variables such as crack width and temper ature difference for concrete and metallic materials. So far it has been po ssible to use thermography to estimate the extent of surface cracks in cons truction materials of both a metallic and a cementitious nature.