Analysis of characteristic thermal transit times for time-resolved infrared radiometry studies of multilayered coatings

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Abstract
Time-resolved infrared radiometry (TRIR) has been shown to be a valuable thermal characterization technique for the nondestructive evaluation of layered coatings. In this method an external step heating pulse is applied to the coating system and the resulting change in surface temperature is monitored as a function of time. Characteristic times and amplitudes can be ascribed to internal thermal reflections that return heat to the coating surface. A full description of the time dependence of the coating surface temperature can be obtained from these quantities. This paper describes a method for determining these characteristic times and amplitudes and shows their relationship to internal heat-flow patterns. Uses and limitations of the method are discussed, and comparison of the theory with experimental TRIR results is presented.