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3D Printed sandwich structures with nanocomposite flexible metamaterial core (Hierarchical honeycombs)

Mansour Misel-Teontor

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Summary

In the present thesis, the 3D printed nanocomposite materials for composite sandwich constructions are investigated using the developed hierarchical honeycomb structures as cores and outer sheets (skins) reinforced with carbon fibers based on epoxy resin. These complex structures in combination with the use of advanced nanomaterials can be optimized in terms of mechanical and vibration properties through experimental applications and computational simulation.Specifically, the initial section of the dissertation involves the study and determination of the mechanical performance of polymeric matrix composite materials through various experimental applications such as compression, loading-unloading, nanoindentation and scanning electron microscopy (SEM) experiments to characterize the morphology of the examined samples’ surfaces.Futhermore, a general reference is made to the developed model of automatic hierarchization of honeycomb structures with constant relative density, and then is described the printing of hierarchical honeycomb structures using the two optimal materials, based on the previously studied mechanical properties. Also, the compressive behavior of the printed hierarchical honeycomb structures is presented, which was examined experimentally and theoretically through finite element analysis (FEA) and specifically using ANSYS software, in order to extract the stress-strain diagrams of the honeycomb structures and finally a comparison was made between experimental and theoretical results. In addition, the experimental results of the vibration characteristics of the examined hierarchical honeycomb structures are presented.In the last and most important section of the present dissertation, hierarchical sandwich structures were developed and constructed using the three levels of honeycomb structures as their cores. The hierarchical sandwich structures consist of outer sheets of twill fabric carbon fiber based on epoxy resin, which were glued together with a strong epoxy paste and then subjected to static three-point bending tests, in order to evaluate their mechanical behavior and at the same time were examined and assessed through finite element analysis, for the purpose of their theoretical-experimental comparison. The experimental-theoretical evaluation of the mechanical performance of the examined hierarchical sandwich structures showed very good results and for this reason it is considered appropriate to use the examined sandwich structures in applications of optimal materials and composite structures in section beam-based manufacturing components. In this case, applications were performed using I-beam structure. In addition, a simulation is presented in order to investigate their mechanical performance. The conclusions from the simulation results were quite interesting and showed that the section beams consisting of sandwich hierarchies, is a very optimistic future choice for use in constructions of various sectors.

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