Noninvasive Methods of Active Thermographic Investigation: Short Overview of Theoretical Foundations with an Example of Application

The field of non-destructive testing using thermography (NDT—Non-Destructive Testing and NDE—Non Destructive Evaluation) was established in the 1960s as a competitive and complementary method to ultrasonic or X-ray testing. Non-destructive quality control of objects is essential in modern industry, especially in mass production. It is an integral part of the quality control process. The reason for the introduction of non-destructive testing into diagnostic techniques were disasters and failures of various equipment and structures. Over the years, a division has been drawn between passive and active thermography. The aim of this publication is to present the theoretical basis of non-destructive testing with the use of active infrared thermography methods. It describes selected models of transient heat flow (thermal wave) in objects of various shapes and physical properties. They are the basis for understanding the changes in the surface temperature of the studied objects in time, which are the response to thermal excitation of different nature. An example of their effective application in engineering practice is the author’s software, in which the recorded time response is matched to the analytical solution, and on this basis detected anomalies are parameterized, detected by the fusion of various techniques of thermal image processing and analysis methods.