Aplicação de fonte térmica por efeito joule na termografia ativa pulsada para identificação de defeitos em provas de polipropileno

Abstract

The advancement of non-destructive testing techniques is linked to the pursuit of total quality and the improvement of production processes. In this context, thermography has proven to be a valuable tool in various scientific fields. This technique allows for the identification of parameters based on infrared radiation, revealing the thermal behavior of materials and providing insights into their internal structure. The analysis of thermograms enables the detection of internal flaws and the calculation of thermal conductivity for different materials. This study proposes the development of an alternative method of pulsed active thermography for the identification of defects in polypropylene samples, using a resistive thermal source for conduction heating. The source was constructed with an electric resistor, a variac, and a thermal controller. The samples were heated in contact with the source, and the cooling process was subsequently recorded by an infrared camera. Experimental studies were conducted to assess the effectiveness of the method in detecting flaws based on their diameters and depths. The experiments provided a deeper understanding of the application of active thermography, as well as heat transfer, infrared radiation, and digital image processing. The analysis of the collected data enabled the identification of image edges and the evaluation of the thermal cooling of the pixels over time. It was observed that prolonged heating periods can lead to undesirable thermal homogeneity, compromising the analysis of results, as contrast is essential for highlighting relevant information. Notably, the greater the depth of the flaws, the longer the time required for their identification in the thermograms. The relationship between pixel size and the camera distance concerning the recorded area was determined. Finally, the thermal decay model developed by Silva (2020) was applied, allowing for a 98% reduction in data while retaining only essential information. From this approach, images resulting from the summation of variables such as heat flow, time constant, maximum delta T, and thermal contrast were generated.