Mechanical Performance of Long-fibre Reinforced Polymer Composites by 3D Printing

Abstract

Additive Manufacturing (AM), also known as 3D Printing, has been around for more than 2 decades and has recently gained importance for use in direct manufacturing. The quantified physical properties of materials are required by design engineers to inform and validate their designs, and this is no less true for AM that it is for traditional manufacturing methods. Recent innovation in AM has seen the emergence of long-fibre composite AM technologies, such as the Mark Two (Markforged Inc, USA) system, enabling the manufacture of thermoplastic polymer composites with long-fibre reinforcement. To date though, the mechanical response of the materials with respect to build parameter variation is little understood. In this project, selected mechanical properties (ultimate tensile strength – UTS and flexural modulus) of samples processed using the Mark Two printer were studied. The effect of the reinforcement type (Carbon, Kevlar®, and HSHT glass), amount of reinforcement, reinforcement lay-up orientation, and the base matrix material (Onyx and polyamide) on these properties were assessed using accepted standard test methods. For Onyx, the UTS and Flexural Modulus was improved by a maximum of 244 ± 10 MPa (1228 ± 19%) and 14.2 ± 0.3 GPa (1114 ± 6%) (Carbon), by 143 ± 1 MPa (721 ± 18%) and 7.1 ± 0.3 GPa (560 ± 6%) (Kevlar®) and 209 ± 4 MPa (1049 ± 19%) and 6.0 ± 0.1 GPa (469 ± 6%) (HSHT glass). For Nylon the UTS and Flexural Modulus was improved by 235 ± 4 MPa (1431 ± 56%) and 14.1 ± 0.2 GPa (1924 ± 5%) (Carbon), 143 ± 3 MPa (867 ± 56%) and 6.79 ± 0.08 GPa (927 ± 5%) (Kevlar®) and 204 ± 2 MPa (1250 ± 55%) and 5.73 ± 0.09 GPa (782 ± 5%) (HSHT glass). A regression and ANOVA analysis for UTS indicated that the number of layers of reinforcement had the largest impact on UTS (F = 11,483 P < 0.005), with the second most important parameter being the type of reinforcement (F = 855 P < 0.005). The parameter effects for all four parameters were significant (P ≤ 0.05). For the Flexural Modulus, the number of layers of reinforcement was again the most significant parameter (F = 2733 P < 0.005), with the second most important parameter again being the type of reinforcement (F = 1339 P < 0.005). Again, the parameter effects for all four parameters were significant (P ≤ 0.05), although the influence of base material had much less significant effect on determining the Flexural Modulus than it did in controlling UTS.