Experimental and numerical study on the mechanical behavior of 3D printed re-entrant auxetic structure filled with carbon nanotubes-reinforced polymethylmethacrylate foam

The present study aimed to develop the finite element method to examine the mechanical behavior of 3D printed re-entrant auxetic structure filled with nanoparticle-reinforced foams under in-plane uniaxial quasi-static compressive loading. A multi-scale finite element model of the nanocomposite is created by considering the randomly distributed carbon nanotubes (CNT) in the Polymethylmethacrylate (PMMA) polymer matrix for a specific volume fraction. The interaction between CNT and PMMA foam was simulated using the cohesive zone model (CZM). The effect of the volume fraction of carbon nanotubes and the geometric characteristics of the structure on the performance of these structures is examined. Results from the finite element study are validated by the samples manufactured using 3D printing and experimental testing results. The results show that the addition of carbon nanotubes to the re-entrant auxetic structure avoids the sharp reduction of force after the peak point, while the use of 2 wt% of carbon nanotubes increases the maximum fracture force up to 75%. Results indicate optimal values for carbon nanotube volume fraction and the thickness of the cell walls, for which energy absorption has the highest value. It is concluded that adding 2 wt% carbon nanotubes to the PMMA foam in-creases the energy absorption up to 130%.