Issue 35

J. Kramberger et alii, Frattura ed Integrità Strutturale, 35 (2016) 142-151; DOI: 10.3221/IGF-ESIS.35.17 146 The following isotropic elastic properties were used to describe the behaviour of base material: Young’s modulus E = 200 GPa, Poisson’s ratio  = 0.33 and linearized stress–plastic strain relationship given in Tab. 1. The linear kinematic hardening model was used to simulate the cyclic behaviour. Stress  [MPa] Plastic deformation  pl [-] 400 0 800 24 Table 1 : Linearized stress-plastic strain behavior of the base material [11, 16]. The mechanical properties considered in the damage analysis were that of a steel, similar as used in the literature [11, 16, 17]. It is noted that the value c 1 and c 3 is dependent on the system of units in which the model is working. 2 2 1 2 c c cycle c N mm        2 c   4 4 3 2 c c mm c cycle N mm          4 c 100 -0.6 2.7e-05 1.27 Table 2 : Parameters used for damage initiation and evolution prediction [11, 16, 17]. Fig. 5 shows the boundary conditions. On the left and bottom edge symmetric boundary conditions were assumed. Figure 5 : Boundary conditions used for finite element analysis of lotus-type porous material. The load was applied to the top edge under displacement rate control. Sinusoidal cyclic displacement loading between 0.01 mm and 0.001 mm (load ratio R=0.1) was applied to the low-cycle fatigue steep with a time period of 0.1 seconds. Displacement load at maximum displacement corresponded to the global deformation  =0.3 %. C OMPUTATIONAL RESULTS AND DISCUSSION tress concentrations in computational models at global deformation of 0.3% (elasto-plastic response) are illustrated with equivalent plastic strain PEEQ contours in Fig. 6. The areas with higher plastic strain values denotes locations where material was started to yield first. A large amount of strain localization takes place in the regions around pores. Fig. 7 shows the evolution of the hysteresis after three loading cycles for global strain range  = 0.27% , for all four models. The macroscopic engineering stress  was determined from the reaction force sum and initial cross-sectional area of the model, while macroscopic engineering strain  was calculated from the applied displacement and initial length of the S y x