Вестник МГТУ. 2019, Т. 22, № 4.

Thermal Image Analysis The profile plot of the test specimen, as shown in Fig. 5, indicates an irregular distribution with substantial temperature drops. This uneven distribution is caused by cracking in the coating on the test specimen, which clearly display the difference in radiation emitted from the white paint and unpolished steel. An estimated temperature distribution was created by only using the peak-values in the profile plot. Fig. 6 shows the coated test specimen before and after fracture. The emissivity of the paint was calibrated and found to be 0.95. Fig. 5. Irregular distribution thermal distribution Рис. 5. Неравномерное распределение температуры a - before fracture b - after fracture Fig. 6. DIN 50125 standard steel sample before and after fracture Рис. 6. Стандартный стальной образец DIN 50125: a - до разрушения; b - после разрушения Results and Discussion The heat generation exhibited in the steel specimens in Fig. 7 was not thermally isolated therefore there were thermal loses due to conduction and convection. Nonetheless the thermal images obtained via infrared thermography reflect qualitative visualization of the development of stresses as shown in Fig. 8. This shows the mechanical energy entering the test specimen in form of applied stresses is converted into heat due to internal friction. The steel specimen exhibited the same temperature change throughout the specimen in the initial phase, as the applied stresses were homogeneous. Following, a temperature gradient developed in the specimen, as a result of the non-homogeneous stress due to the plasticity. The first frame illustrates the steel specimen in the start of the tensile test, right before the stress was applied, indicating an approximately equal temperature as its surroundings. The increase in temperature is noticeable for each frame recorded, with the development of a temperature gradient, until the fracture of the specimen. I a - start b - end (45s) Fig. 7. Infrared thermography of DIN 50125 standard steel sample Рис. 7. ИК-термография стандартного образца стали DIN 50125