Thermal non-destructive testing from in situ measurements of heat flow and surface temperature at the same location on a wall surface

Abstract

Classical thermal non-destructive testing is a technique for obtaining surface temperature profiles on a structure, and subsequently relating this information to some imperfection within the structure. A multilayer wall section exposed to its natural environment is considered; the second layer is assumed to be a defect in the wall. The transient temperature and heat flow responses are analysed assuming a one-dimensional heat flow conduction. The main aim of the authors is to present a technique for obtaining the thermal admittance from recorded heat flow and temperature data and subsequently relating this information to the thickness of the first layer. It is shown how, using in situ measurements, one can determine the time required for a thermal signal to pass through the first layer of a composite wall exposed to its natural random environment. The principle of thermal non-destructive testing of multilayer structures presented is based on the difference between the high-frequency behaviour (with no reflected wave train) and the actual measured 'heat flow-surface temperature' behaviour influenced by the changes in material properties inside the wall.