Model analysis of thixotropic polymer flow in extrusion-based additive manufacturing

Material extrusion additive manufacturing (AM), which is utilized across a wide range of industries, necessitates the study of the extrusion and swelling of materials with complex rheological properties in the nozzle. This work aims to investigate the effects of physical parameters on the rheological properties of materials during extrusion. The rheology of thixotropic elastoviscoplastic (TEVP) fluids is predicted using the multi-lambda isotropic kinematic hardening (ML-IKH) model. Four different rheological models are initially examined to explore the distinctions between thixotropic behavior and other non-time-dependent rheological models. Results demonstrate that the interactions between the breakdown state and buildup state lead to stronger oscillations during the time evolution of the strands. Furthermore, the physical properties of the ink and structure of the nozzle are investigated to determine the rheology of the thixotropic fluid. Numerical results indicate that the rates of pressure and height change vary linearly with slopes of 49.3 and -12.8, respectively, for different elasticities and exhibit different patterns at varying yield stresses. Vortex analysis reveals that the maximum vortex area increases twice the minimum vortex area with increased elasticity. These findings demonstrate that the flow stability of thixotropic fluids is critically governed by structural parameters, with optimized configurations significantly suppressing flow instabilities and vortex formation. This research provides both qualitative and quantitative assessments of how structural and physical parameters influence the extrusion stability of thixotropic fluids. These findings offer crucial insights for optimizing nozzle design and printing parameters.