Issue 29

A. Infuso et alii, Frattura ed Integrità Strutturale, 29 (2014) 302-312; DOI: 10.3221/IGF-ESIS.29.26 310 As far as the numerical simulations are concerned, the increase of NLI leads to a transition from a sparse connectivity matrix to a very dense one, see Fig. 12 where systems with NLI=1, 2 and 3 are compared. Flaw-tolerance In this section, the behaviour of the bi-dimensional system subjected to uniaxial tension in the vertical direction is investigated. We compare the case where all the links are present with other three cases presenting defects: (1) removal of a single node in the centre of the specimen; (2) removal of 2 not adjacent nodes; (3) removal of 2 adjacent nodes. Three different values of NLI are considered for each system: NLI=1 (local system), NLI=2, NLI=3. A sketch of the three configurations with defects are shown in Fig. 13 for the case with NLI=1. (a.1) NLI=1 (a.2) NLI=2 (a.3) NLI=3 (b.1) NLI=1 (b.2) NLI=2 (b.3) NLI=3 Figure 12 : (a) Representation of the bidimensional hexagonal geometric network by varying NLI. (b) Connectivity matrices for the same NLI. (a) Case 1 (b) Case 2 (c) Case 3 Figure 13 : Representation of the bidimensional hexagonal network with different types of flaws (NLI=1). The global force vs. displacement curves for all the examined configurations are shown in Fig. 14. For a given value of NLI, we note that Case 3 leads to the higher load and stiffness reduction. Case 1 is the less critical one, whereas Case 2