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The packing characteristics of fiber/polymer powder in powder bed fusion additive manufacturing exhibit a high correlation with the mechanical behaviours of printed composite parts such as homogeneity and anisotropy. A discrete element model has been developed to investigate the packing characteristics of glass fiber/polyamide 12 (PA12) powder, which include fiber orientations, fiber homogeneity, and packing density. The predicted probability distributions of fiber orientations in the powder bed are comparable with those measured in glass fiber–reinforced PA12 composites printed via multi jet fusion. Three types of fibers with different length distributions are adopted to study the effects of the fiber length distribution on their packing characteristics. The simulation results reveal that a large average fiber length is beneficial to fiber alignment in the powder spreading direction but lowers the fiber homogeneity and packing density of the powder bed. Furthermore, varying the fiber length can provide an effective way to regulate fiber orientations in the powder packing process, which would help achieve satisfactory anisotropic mechanical properties for composite parts.

The segregation and non-uniform distribution of fibers throughout the cement-based materials (CMs) can lead to heterogeneous properties in hardened material with direct impact on mechanical properties. An experimental investigation was undertaken to identify the critical (Fc) and dense (Fd) fiber factor limits to link the packing density, flowability, stability, and fiber homogeneity in the fresh state to material performance in the hardened state of fiberreinforced self-consolidating cement-based material (FRSCCM). The wet packing density approach was employed to determine the optimum suspending fluid thickness (SFT) covering fibers that is required to maintain flow characteristics and secure flow-induced uniform fiber dispersion. To evaluate the effect of fiber rigidity, two fiber types were investigated, including glass (GL) and polypropylene (PP) fibers. The stability of fiber dispersion was quantitatively evaluated along the freshly cast prism of sample. The Fc and Fd fiber factor limits are shown to be affected by the inclusion of solid particles and fiber rigidity. Given higher interlocking, the incorporation of semi-rigid GL fibers results in lower fiber factor limits compared to the flexible PP fibers. The mechanical properties of FRSCCMs were found to be strongly affected by the SFT surrounding the fibers. For FRSCCM made with fiber factors higher than Fd, the thickness of suspending fluid covering fibers is not sufficient, thus leading to higher potential formation of fiber clumping and anisotropy in material performance. The findings in this paper can provide better understanding for mixture design of FRSCCM by adjusting the SFT and fiber factor to enhance the flow-induced fiber dispersion and secure optimal hardened properties. [ABSTRACT FROM AUTHOR]