Issue 35

S. Glodež et alii, Frattura ed Integrità Strutturale, 35 (2016) 152-160; DOI: 10.3221/IGF-ESIS.35.18 155 transverse model, where it was assumed that the average ratio l / d  15 ( l is the pore length and d is the pore diameter). Because the length of pores is larger as the pore diameter, the plain strain conditions was considered in the case for transversal loading regarding to pore distribution. On the other hand, the plain stress condition was assumed in the case, when loading appears in the longitudinal direction of pores. The boundary conditions are presented as displacement value of 0.01 mm at the top and fixed restraints in the bottom of used computational model (Fig. 3 (a) and (b)). Figure 3 : 2D computational model for pores distribution in transversal (a) and longitudinal (b) direction. In performed computational analyses the lotus-type structure is made of nodular cast iron EN-GJS-400-18-LT as a base material, with monotonic material properties presented in Tab. 1. The true stress-strain behavior of material (Fig. 4), which is needed for determining the crack initiation period N i , is assumed. Yield stress R e [MPa] Ultimate tensile stress R m [MPa] True fracture strain  f [  ] Modulus of elasticity E [MPa] Poisson’s ratio  [  ] 256 417 0.235 1.82  10 5 0.33 Table 1 : Monotonic material properties of nodular cast iron EN-GJS-400-18-LT [20]. Figure 4 : True stress-strain curve of base material [20] True stress-strain  100 200 300 400 500 0 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 Engineering stress-strain  [MPa] a) b) displacement restraints