Computational Modeling of Fiber Orientation During 3D Concrete Printing (2023-03)¶

During 3D-printing of fiber-reinforced concrete, fibers tend to align with the printing direction due to strong shearing deformation of the material, allowing for the controlled production ofcomponents with desired fiber orientation states. The accurate prediction of the fiber orientation state in printed components poses a major challenge due to the large number of processing and material parameters involved and due to the complex mechanisms of flow and fiber reorientation during printing. This contribution presents a novel incorporation of the Folgar–Tucker fiber orientation model within a fluid dynamics framework based on the Particle Finite Element Method for simulations of the fiber orientation evolution during 3D-concrete-printing. The fiber orientation state is represented using a second-order orientation tensor, which is coupled with a new anisotropic Bingham constitutive model used for the viscous fiber-concrete mixture to account for the effect of fiber orientation on the velocity field. Further, the orientation distribution function is reconstructed from the second-order orientation tensor, following the maximum entropy method for a more convenient interpretation of the results. The model is validated by comparing the simulated orientation numbers of a 3D-printed concrete layer for different extrusion nozzle diameters with experimental values from the literature. Several parametric studies are performed to examine the flow and fiber reorientation mechanisms and the influence of process parameters on the fiber orientation state in printed components. Stronger fiber alignment in the printing direction is obtained for higher printing speeds or smaller extrusion nozzles, associated with higher shear stresses developing in the extrusion nozzle.