PSI - Issue 25

174 P.N. Lymperopoulos et al. / Procedia Structural Integrity 25 (2020) 172–179 Panagiotis N. Lymperopoulos, Efstathios E. Theotokoglou, Ioannis A. Antoniadis / Structural Integrity Procedia 00 (2019) 000–000 3 2.1. Materials

In our study three di ff erent materials have been used in order to model metamaterials. The materials that have been considered are listed in the following Table (1).

Table 1. Materials Table Material

Density ( kg

Young Modulus ( GPA )

m 3 )

Steel (Fabbrocino et.al. (2015)) Polymer (Amendola et.al (2017)) Ti-6A1-4V (Amendolad et.al. (2016))

206 1.4 120

8000 1300 4420

3. Computational Analysis

3.1. FEM Model

A typical pentamode structure that that has been modeled in our numerical study is shown in figure (3). Pentamodes have been model using a Finite Element Method software product ANSYS (ANSYS (2019)). The element that was used is the BEAM89 element, which is a typical 2 node linear beam element. In order to better model each rod, 4 finite elements has been used. In our analysis, a constant displacement (15mm) at nodes at the top of the pentamode is considered. The nodes at the bottom of the pentamode are fully constrained.

Fig. 1. Pentamode Structure (Amendolad et.al. (2016))

3.2. FEM Convergence

A meshing sensitivity test, has been performed, in order to justify that the number of elements does not change the result for the displacements. A pentamode with D a = 0 . 174, steel material, is considered. The nodes of the finite element mesh at the bottom are fully constrained, while at the nodes on the top of the structure the vertical displace ment has been restrained. A force 1.5*10 3 N (Fabbrocino et.al. (2015)) has been applied at the nodes on the top of the structure.