Issue 43

N. Montinaro et alii, Frattura ed Integrità Strutturale, 43 (2018) 231-240; DOI: 10.3221/IGF-ESIS.43.18 235 The Finite Element Model The thermal behavior of the sample is simulated by a Finite element model through a transient analysis. To avoid convergence issues, an unconditionally stable implicit integration method was used to solve the heat transfer equations. The used heat transfer finite element model was previously compared with analytical and experimental results in [16]. The model of sample 2 was meshed using 105000 4-node linear tetrahedron elements in order to fit the defect geometry without issues. The continuous wave laser source is simulated by considering a focused laser spot as a circular heat source having diameter of 0.5 mm and power of 1 W, fully absorbed by the sample (black body behavior). The thermal behavior of the hole defects is considered as if they were made of air. The natural heat convection at the sample faces is modelled by adopting a surface film condition with sink temperature of 293 K (~20°C). The FEA provides the distribution of temperature over the whole sample volume for different positions of the heat source, which is supposed to move along a straight line at constant speed. Fig. 4a shows the meshed model of sample 2 while Fig. 4b the lateral view where defects are visible. The element dimensions decrease approaching the zone with the maximum temperature gradient (near the heat source). The heat source is moved at a speed of 5 mm/sec. The thermal properties of the Inconel 600 and of air are: specific heat 444 and 1000 J/kg K and thermal conductivity 14.8 and 0.026 W/m K respectively. Figure 4 : Finite element model of the sample 2: in (a) the meshed sample; in (b) the lateral view of the model with the three defects. NUMERICAL RESULTS ig. 5 shows the temperature map of the modeled sample 2 with the typical trail left by the heat source. In particular maps of the front view (Fig. 5a) and of the transversal x-y section over the heat source deposition (Fig. 5b) are shown. Figure 5 : Temperature map of the sample 2: front view (a) and x-y section view (b) ; temperature scale in Kelvin degree. F (a) (b) (a) (b)