Carbon-Fiber- and Nanodiamond-Reinforced PLA Hierarchical 3D-Printed Core Sandwich Structures

The aim of the present paper is to investigate the mechanical behavior of FFF 3D-printed specimens of polylactic acid (PLA), PLA reinforced with nanodiamonds (PLA/uDiamond) and PLA reinforced with carbon fibers (PLA/CF) under various experimental tests such as compressive and cyclic compressive tests, nanoindentation tests, as well as scanning electron microscopy tests (SEM). Furthermore, the current work aims to design and fabricate hierarchical honeycombs of the zeroth, first and second order using materials under investigation, and perform examination tests of their dynamic behavior. The mechanical behavior of hierarchical sandwich structures was determined by conducting experimental bending tests along with finite element analysis (FEA) simulations. The results reveal that the incorporation of nanodiamonds into the PLA matrix enhanced the elastic modulus, strength and hardness of the 3D-printed specimens. In addition, the second order of the PLA/uD hierarchical sandwich structure presented increased strength, elastic and flexural modulus in comparison with the zeroth and first hierarchies. Regarding the dynamic behavior, the second order of the PLA/uD honeycomb structure revealed the biggest increase in stiffness as compared to PLA nanocomposite filaments.