Gravitational intensity influence on the flow behavior of viscoelastic fluids in direct ink writing

Understanding the influence of gravitational intensity on the flow behavior of viscoelastic inks during direct ink writing (DIW) three-dimensional (3D) printing process is crucial for optimizing additive manufacturing processes in space environments. This paper employs three-dimensional direct numerical simulations (DNS) to investigate the impact of gravitational intensity on the flow behavior of viscoelastic fluids during the DIW process. In addition, molecular dynamics (MD) simulations are utilized to elucidate the microscopic mechanism that the effect of gravitational intensity on the dynamics of viscoelastic fluids. DNS results show that gravity significantly influences strand morphology: under normal gravity, hindered vertical momentum transfer leads to flattened strands with top compressive stress, whereas under zero gravity, stress distribution, and momentum transfer within the strand are more uniform, resulting in a rounded shape. The impact of gravity varies with polymer elasticity (Wi), showing greater strand length changes and vertical stress concentration at higher Wi. MD simulations indicate gravity enhances polymer–substrate interactions and horizontal diffusion but inhibits vertical chain relaxation. This work provides theoretical guidance for in situ additive manufacturing technology in space environments.