Issue 50

A. Kostina et alii, Frattura ed Integrità Strutturale, 50 (2019) 667-683; DOI: 10.3221/IGF-ESIS.50.57 671 closest to the surface). The peak contrast time for the first row of the subsurface defects is reached at the beginning of the cooling process. A further decrease in the temperature contrast is due to diffusion. The obtained results illustrate that the peak contrast time depends on the depth of the defect that confirms the experimental results [4]. Defects located at depths of 3.36 mm and 3.17 mm from the surface could not been observed at the given time of 2 s. It should be noted that defects with the smallest size (2 mm) are not visible even at the depth of 0.4 mm from the surface. (a) (b) (c) (d) Figure 2 : Evolution of the temperature increment Δ T = T - T 0 : (a) t =0.5 s, (b) t =1 s, (c) t =1.5 s, (d) t =2 s. Fig. 3 shows the temperature contrast in defects of various sizes located at the depth of 1.13 mm obtained as a result of numerical simulation and experimental study conducted in [13]. It can be seen that the results are in a good qualitative and quantitative agreement in all stages of the cooling process. Figure 3 : Temperature contrast for defects of various sizes located at the depth of 1.13 mm from the surface. Experimental results are taken from [13].