Micromechanics study of short carbon fiber-reinforced thermoplastics fabricated via 3D printing using design of experiments

Abstract

In this study, short carbon fiber-reinforced thermoplastic (sCFRTP) was 3D-printed under different printing parameters, and the influence of the combination of printing parameters on the tensile properties and internal structure (void volume fraction, fiber orientation, and fiber length) of the 3D-printed sCFRTP was investigated through tensile testing, X-ray computed tomography, microscopic observations and theoretical analysis based on a micromechanics model (MM). A total of ten printings and characterizations were performed via the design of experiments, and the outcomes displayed specimens that were fabricated under optimal printing parameters (specimen DoE) exhibited a Young's modulus of 5.1 ± 0.3 GPa and a tensile strength of 73.3 ± 0.9 MPa, resulting in the highest Young's modulus and tensile strength. The MM analysis successfully reproduced the experimental stress-strain response as well as the equivalent stiffness of the sCFRTPs with a much shorter time than finite element analysis by inputting the measured fiber length, void volume fraction, and fiber orientation distribution into the in-house MM code. From this MM analysis, it was suggested the higher Young's modulus and tensile strength observed in the specimen DoE is due to more of the relatively long fibers are oriented in the print direction with fewer voids. Furthermore, the influence of internal structure parameters on the mechanical properties of the 3D-printed sCFRTPs was analyzed, revealing that fiber length has a greater impact on the mechanical properties than void volume fraction and fiber orientation distribution.