Characterisation of the anisotropic mechanical properties of carbon fibre reinforced thermoplastic composites

Abstract

Fused filament fabrication (FFF) is an additive manufacturing (AM) process of creating solid, three-dimensional objects from a digital file. During this additive process an object is created by laying down successive layers of material (thermoplastic filament) until the entire object is formed. Each of these layers can be seen as a thinly sliced, horizontal cross-section of the final object [1]. A technology called continuous fibre fabrication or composite filament fabrication (CFF) ensures reinforcement of these objects by means of in-layer fibre AM. This CFF technology is prominent at Markforged Inc., where reinforced fibres (carbon, fibreglass or Kevlar) are thoroughly ironed against core materials such as nylon or onyx. From this definition it may appear evident that classical laminate theory (CLT) should be used for the simulation and analysis purposes of these kinds of composites. An investigation was done on the anisotropic effects (specifically carbon fibre with nylon) and was compared with the CLT by means of the Laminated Analysis Program, and the results are thought-provoking. The findings revealed that the CFF technology can be seen as a composite material only for a unidirectional layout combination. For all other combinations a new database was created together with a proposed mathematical model to predict the material properties with different fibre angle combinations. The experimental data in this model revealed an average percentage error of only 9.4 with seven different layout combination categories.