Mechanical Characteristics of Thermoplastic Polymers for 3d Printed Hybrid Structures

Abstract

This study focuses on the mechanical properties of different thermoplastic polymers that have been processed by fused filament fabrication, including basic (PLA, PC, PA, ABS, PP, CPE, PET-G), industrial (PEI, PEKK), and with added functionality (thermochromic, electrostatic discharge, electrically conductive). Analysis of the porosity of specimens was performed by X-ray microtomography and optical microscopy of a fractured surface, both giving similar results. During printing, a non-equilibrium polymer macromolecular structure was created. The stiffness and strength of the printed specimens were impacted by the stabilization of the macromolecular structure over time. The maximum values were reached for amorphous materials after 24 hours and for semi-crystalline materials after 160 hours. Tensile properties of “as-received” filaments, extruded mono-fibers, and unidirectional printed specimens were compared. In most cases, the elastic modulus of “as-received” filaments was lower than that of the extruded mono-fibers by 12% on average. Loading rate significantly affects both elastic modulus and strength, confirming the essential contribution of the viscoelastic component to the whole deformability of polymers. The elastic modulus and strength increased by 20 and 80%, respectively. The effects of layer thickness and nozzle diameter on mechanical properties were investigated. The compatibility of different polymer types for hybrid structures was evaluated in the adhesion tests. Tests showed that adhesion at hybrid PLA contact is only slightly affected by the presence of colourant additives in one of the parts. However, approx. 10 times adhesion reduction was observed when one of the parts contained conductive particles.