Issue 35

S. Glodež et alii, Frattura ed Integrità Strutturale, 35 (2016) 152-160; DOI: 10.3221/IGF-ESIS.35.18 156 N UMERICAL ANALYSIS ll computational models were discretized with quadratic finite elements with linear interpolation. Previous verification of required finite element size has also been done in respect to the results convergence with relative error 0.05. Fig. 5 shows the FE-mesh for both, transversal (Fig. 5 (a)) and longitudinal (Fig. 5 (b)) pores distribution. Figure 5 : FE-mesh for pores distribution in transversal (a) and longitudinal (b) direction. Crack initiation period for pores distribution in transversal direction When studying the crack initiation period, the stress filed around individual pores and location of the maximum stress concentration should be determined first. The maximum von Mises equivalent stress  M = 350 MPa with the appropriate total strain  = 0.022 are recognized in a cross section No. 1 (Fig. 6 (a)). Considering the pulsating loading (  a =  = 0.011 ) and material properties as presented in Tab. 1, the number of loading cycles N i required for the fatigue crack initiation is then calculated according to Eq. (2). In the next step, the initial crack a i = 0,05 mm is added into the critical cross section No. 1 (Fig. 6 (b)) and the numerical procedure is continued with the crack propagation period. When the fatigue crack reaches the critical length, the complete fracture of cross section No. 1 occurs which mean that two neighboring pores are connected with a seam and the complete procedure is repeated regarding to the other critical cross section. Figure 6 : Schematic procedure of crack initiation period. (a) maximum stress concentration in a cross section No. 1 (b) initial crack in a cross section No. 1. A a) b) No.1 a i =0.05 mm finite elements around crack tip a) b)