Modeling of Mechanical Behavior in FFF Lattice Struts: Integrating Porosity and Inter-Filament Bonding

Fused Filament Fabrication (FFF) is an additive manufacturing process that constructs three-dimensional structures through the sequential deposition of thermoplastic filaments. This process inherently produces anisotropic porosity networks, shaped by the filament deposition paths and the formation of bonding regions between adjacent filaments. In thin structural elements such as lattice struts, where dimensions are comparable to filament diameters, these microstructural features have a pronounced effect on the mechanical behavior. In particular, regions of inter-filament bonding, where polymer chain interdiffusion occurs, introduce distinct mechanical characteristics beyond those captured by porosity volume alone. This study develops a numerical model to predict the stiffness of lattice struts produced by FFF, considering the complex interactions among three phases: filaments, pores, and bonding (intersection) regions. The model integrates geometric and morphological aspects of porosity and inter-filament connections within a representative volume framework, enabling the prediction of effective elastic moduli under various deposition configurations. This approach highlights the critical role of filament intersections and bonding morphology in determining the overall mechanical response of FFF lattice structures.