Mechanical metamaterials are lattice structures, which are composed of unit cell, which may be extended to all directions [1]. The unit cell is formed by beams, and their arrangement influence significantly the bulk and shear strength and the overall behavior of the structure. The main characteristic of pentamode is the low ratio of shear to bulk modulus [2]. A property that characterizes mechanical metamaterials is the bandgap, where a wave with frequency inside the bandgap can not be propagated through the metamaterials [3,4]. In this study, a numerical investigation of pentamode mechanical metamaterials bangap has taken place. Pentamodes with different beams dimensions are considered. More specifically, the main objective of our contribution is the investigation of different beams dimensions at pentamode bandgap using the Finite Element Method. The proposed process is performed with COMSOL software [4] which utilizes the Floquet-Bloch periodical Boundary Conditions, and the eigenvalue problem. The materials behavior of Clear V4 resin and steel are modeled using nonlinear stress-strain curves. In addition, geometrical nonlinearity is also considered. Dispersion curves of pentamodes structures have been calculated and plotted and the elastic energy of pentamodes have been also calculated. The Von Mises stresses arising for different beams dimensions result in higher stresses near beams connections. In addition, the results for the resin Clear V4 and the steel materials show beams dimensions influence on the bandgap width. REFERENCES [1] F. Fabbrocino, A. Amendola, F. Benzoni and F. Fraternali, Seismic Application of Pentamode Lattices, International Journal of Earthquake Engineering, 62-71, 2015. [2] A. Amendola, G. Carpentieri, L. Feo and F. Fraternali, Bending dominated response of layered mechanical metamaterials alternating pentamode lattices and confinement plates, Composite Structures, 157, 71-77, 2016. [3] Zhaohong Wang, Chengxin Cai, Qingwei Li, Jing Li, Zhuo Xu, Pentamode metamaterials with tunable acoustics band gaps and large figures of merit, Journal of Applied Physics, 2(120), 2026. [4] Lymperopoulos, P.N.; Theotokoglou, E.E. Numerical analyses of pentamodes metamaterials behavior under harmonic loading conditions. Eur. J. Mech. A/Solids, 111, 105536, 2025.