Mechanics of fused filament fabricated thermoplastics: Modelling the mesostructure

In this thesis, the relation between the manufacturing parameters and the mechanical properties of Fused Filament Fabrication (FFF) materials is analyzed to gain a better understanding of interaction between these two. The existing literature was first analyzed to get an understanding for the process, resulting in a proposed mesostructural and mechanical model of FFF materials. The model was constructed such that only the print settings plus the part weight and dimensions after printing are necessary to calculate the mesostructural dimensions. A sensitivity analysis was performed in order to get a better understanding of the limitations of the model. Subsequently a FEM model was used to verify the above model. This sensitivity analysis was performed using a sweep of different mesostructural parameters was done in order to see the impact on the mechanical properties by means of FEM and analytical-numerical methods. The sweep parameters are the aspect ratio, the infill coefficient and the shrink coefficient. The analytical-numerical methods were added for validation and to get a mathematical feel for the mechanical phenomena. The effect of the shapes and sizes of the filaments were assessed with the three sweeps on the stiffness and stress concentrations. The models did show mostly expected trends, which not all have not been fully described in literature before. In order to verify the mesostructural model, a sintering simulation of the 2D filament crosssections was performed in Comsol. The void shape evolution performed as expected, however the long cusps are found to form upward due to the competition for inflowing of other cusps nearby. This counteracts hypothesis from literature. Additionally, the Comsol simulation did not respond well to the external shrinking variable. The cause behind this is suspected to be in the flow solver having problems in solving around sharp cusps in the fluid mesh.Aerospace EngineeringAerodynamics, Wind Energy, Flight Performance & Propulsion (AWEP)Flight Performance & Propulsio