Several experimental studies revealed that fibers tend to align in printing direction during 3D-concrete-printing, which is a substantial advantage compared to traditionally cast fiber-reinforced concrete components. The utilization of fiber-reinforced concrete as the printing material is one strategy that addresses the lack of reinforcement in printed components. To make 3D-concrete-printing a more reliable and efficient production technology, several challenges, as discussed in the state-of-the-art reports above, must be overcome, among which the incorporation of reinforcement is one of the biggest to be solved. Some state-of-the-art reports about additive manufacturing using fresh concrete are given in. 3D-concrete-printing is characterized by an automated layer-wise deposition of a “stiff” fresh concrete material through an extrusion nozzle to produce structures without formwork. In particular, extrusion-based approaches, like 3D-concrete-printing, are very popular among technologies based on the additive manufacturing using fresh concrete. 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.Īutomated construction techniques, such as additive manufacturing with fresh concrete, have become a rapidly evolving field of research and application in recent years. 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. 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. 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 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. 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 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. So while Van der Waals forces likely exist between nanoparticles of the same type, the mechanism that causes them to agglomerate will be dominated by stronger polar, electrostatic and covalent interactions or surface energy interactions described above.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 of components with desired fiber orientation states. Van der Waals is a very weak interaction so it has a greater influence for smaller molecules at shorter length scales (consider the fact that molecules and atoms are an order of magnitude smaller than the smallest nanoparticles which might be 3-5nm). This type of cohesive interaction unites molecules causing them to form clusters due to their dislike for their surroundings. Van der waals is an intermolecular force that exists between molecules of the same substance. On the other hand, attractive adhesion forces are a completely different mechanism since these attractive forces occur between two substances by sticking together mechanically or by opposing charges. As they agglomerate they become the large particles that you mention. The fact that they have very large surface area to volume ratios enhances this phenomenon. Everything in nature wants to be in the lowest energy state so there is a tendency for nanoparticles to agglomerate to minimize their excess surface energy. Surface energy for solids is defined as the excess energy at the surface of a material compared to the bulk because of the unsatisfied atoms. I apologize, I probably should not confuse surface tension with surface energy.
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