A concurrent fibre orientation and topology optimisation framework for 3D-printed fibre-reinforced composites

This work proposes a novel framework able to optimise both topology and fibre angle concomitantly to minimise the compliance of a structure. Two different materials are considered, one with isotropic properties (nylon) and another one with orthotropic properties (onyx, which is nylon reinforced with chopped carbon fibres). The framework optimises, in the same particular sub-step, first the topology, and second, the fibre angle at every element throughout the domain. For the isotropic material, only topology optimisation takes place, whereas, for the orthotropic solid, both topology and fibre orientation are considered. The objective function is to minimise compliance, and this is done for three volume fractions of material inside the design domain: 30%, 40%, and 50%. Two classical benchmark cases are considered: 3-point and 4-point bending loading cases. The optimum topologies are further treated and manufactured using the fused filament fabrication (FFF) 3D printing method. Key results reveal that the absolute stiffness, density-normalised and volume-normalised stiffness values within each admissible volume are higher for onyx than for nylon, which proves the efficiency of the proposed concurrent optimisation framework. Moreover, although the objective function was to minimise compliance, it was also effective to improve the strength of all parts. The excellent quality and geometric tolerance of the 3D-printed parts are also worth mentioning.