Issue 50

A. Kostina et alii, Frattura ed Integrità Strutturale, 50 (2019) 667-683; DOI: 10.3221/IGF-ESIS.50.57 673 temperature increment. Fig. 7 demonstrates the temperature contrast for two utmost groups of defects located in the first column (defects with the smallest thickness) and the last column (through defects). It is interesting to note that defects with sizes of 10 mm, 8mm and 6 mm have nearly the same curves of temperature contrast evolution. Sensitivity of the temperature contrast to the size of the defect starts with the size equal to 4 mm. As it was expected, the smallest values of C in both columns have defects with the size of 2 mm. The difference in maximum contrast between them is approximately 7%. It should also be noted that there is a discrepancy in the peak contrast time: defects with smaller thickness reach the peak at earlier stages. (a) (b) (c) Figure 6 : Evolution of the temperature increment Δ T = T - T 0 after 2 seconds of cooling for square pulse of various duration: (a) t =1 ms, (b) t =2 ms, (c) t =4 ms. (a) (b) Figure 7 : Evolution of the temperature contrast for defects of two utmost thicknesses obtained for the square pulse of duration of 2 ms: (a) h =0.14 mm, (b) h =3.5 mm. Fig. 8 displays the effect of heating time for the defects located in the first column (defects with the minimal value of the temperature contrast). Qualitative portraits of the obtained results and values of the peak contrast time are similar for all considered heating times. The main difference is the value of C which increases from 0.42 degrees (when heating time is equal to 1 ms) to 0.7 degrees (for the longest heating time of 4 ms) in case of the defect with the minimal size of 2 mm. However, even with the relatively high value of the heating time (4 ms) the temperature contrast is less than 1 degree for the smallest size of the defect. In real experiments, the identification of this defect will be complicated due to the noise which can level off the peak.