Research On 3D-printed Fiber Reinforced Thermoplastic Honeycombs: Materials Design,Manufacturing And Compressive Behaviors

3D printing has been applied in the development of automotive parts because of the advantages of low cost,high efficiency and environmental protection.However,poor mechanical performance and relatively high price limited the practical application of 3D printed automobile parts.In this paper,two kinds of environmental friendly composites,PLA/KBF and PLA-PCL/KBF are developed for FDM filaments.The mechanical property,viscoelastic and 3D-printability are systematically evaluated.Then circular,hexagonal and re-entrant honeycombs are manufactured by FDM and the in-plane compressive mechanical behaviors are studied,Finally,the effect of celluar geometries of negative Poisson’s ratio honeycombs on compressive behaviors are simulated and predicted.The main contents of this paper are described as follows:(1)Firstly,PLA/KBF composite filament are developed and the effects of fiber distribution,content and average length of KBF on the property of PLA/KBF and the feasibility for 3D printing are investigated.It was found that the mechanical properties of PLA/KBF samples prepared by 3D printing were close to those of casting counterparts,The results suggest that PLA/KBF exhibit comparable tensile properties and superior flexural properties to those of PLA/CF control.With increasing fiber length and weight fraction of KBF,low infill and micro-defects are shown in CT scans.It was found that the mechanical properties of 300μm KBF fibers exhibit superior properties.This chapater proves PLA/KBF as a mechanical-improved and low-cost feedstock for 3D printing applications in complex design and variable sizes.(2)Secondly,PLA-PCL/KBF composite filaments are developed and proposed.The addition of PCL act as a soft elastomer.DSC findings indicate that the crystallinity(Xc)of PLA increases because PCL act as a nucleation agent.DMA and rheological analysis show that the addition of PCL makes PLA-PCL/KBF composite cross-linked structure,which makes the stress transfer between matrix and fiber moreefficient with a viscoelastic behavior.Mechanical tests and SEM show that the introduction of PCL endows the specimens with ductility fracture behavior,which suggest PLA-PCL/KBF composites are promising materials for manufacturing honeycomb strctures.(3)Thirdly,the potential of 3D-printed PLA-PCL/KBF honeycombs structures for inplane compressive properties and energy absorption are explored.It can be seen that the PLA-PCL30/KBF composite filaments show superior energy absorption capacity.Furthermore,the in-plane compression behavior of hexagonal and re-entrant honeycombs are investigated.Results show that and the energy absorption of the honeycomb structure increases with the relative density increases.The re-entrant honeycomb shows a greater advantage in yield stress,modulus and energy absorptionin contrast with hexagonal honeycomb with the same cell wall thickness and the Poisson’s ratio.The finite element model of the re-entrant honeycomb is established,and the experimental results of the in-plane compression test are verified.The FE simulation predicts that the cell angle and cell wall thickness significantly contribute to the energy absorption contribution of the re-entrant honeycombs.The present work demonstrate that the proposed 3D-printing composite materials provide valuable perspective to obtain excellent compressive mechanical performance of honeycomb structures.