Interlaminar bonding performance of 3D printed continuous fibre reinforced thermoplastic composites using fused deposition modelling

Continuous fibre reinforced thermoplastic composites (CFRTPCs) are becoming more significant in industrial applications due to their inherit advantages such as excellent mechanical performance, potential use in lightweight structures and being recyclable. Fused deposition modelling (FDM) is a promising additive manufacturing technology and an alternative to conventional processes for the fabrication of CFRTPCs due to its ability to build functional parts having complex geometries. However, a major concern affecting the efficient use of 3D printed composites is their weak interlaminar bonding performance compared to conventional pre-preg composites. The aim of this study is to evaluate the effect of layer thickness and fibre volume content on the interlaminar bonding performance of 3D printed continuous carbon, glass and Kevlar (R) fibre reinforced nylon composites manufactured by FDM technique. Short beam shear tests were carried out to determine interlaminar shear strength (ILSS). SEM images and cross-sectional micrographs were examined to assess failure mechanics of the different configurations. It was observed that the effect of layer thickness of nylon samples on the interlaminar shear performance was marginally significance. ILSS values decrease as layer thickness increase due to higher porosity. In addition, continuous fibre reinforced samples show higher ILSS values than unreinforced ones but, conversely, the level of increase in ILSS is moderate with continued increase in fibre content, particularly in the case of Kevlar (R) fibre. Carbon fibre reinforced composites exhibit the best interlaminar shear performance with higher stiffness. On the other hand, Kevlar (R) fibre reinforced composites have the lowest interlaminar shear performance due to poor wettability of Kevlar (R) fibre bundles by the nylon, leading to extensive delamination. Finally, the results obtained demonstrate that it is still a challenge to increase shear performance of 3D printed composites with respect to common pre-preg materials. Nevertheless, ILSS values exhibited by 3D printed composites are significantly higher than the usual 3D printed thermoplastics.