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

Area of Science:

• Materials Science
• Fluid Dynamics
• Additive Manufacturing

Background:

• Material extrusion additive manufacturing (AM) requires understanding complex fluid rheology during extrusion.
• Thixotropic elastoviscoplastic (TEVP) fluids present unique challenges due to their time-dependent behavior.

Purpose of the Study:

• To investigate the impact of physical parameters on material rheology during extrusion in AM.
• To analyze the influence of nozzle structure and fluid properties on the extrusion stability of TEVP fluids.

Main Methods:

• Utilized the multi-lambda isotropic kinematic hardening (ML-IKH) model to predict TEVP fluid rheology.
• Compared four rheological models to differentiate thixotropic behavior.
• Performed numerical simulations analyzing pressure, height changes, and vortex formation.

Main Results:

• TEVP fluid extrusion exhibits oscillations due to breakdown and buildup state interactions.
• Pressure and height change rates correlate linearly with elasticity and vary with yield stress.
• Increased elasticity leads to a twofold increase in maximum vortex area compared to the minimum.

Conclusions:

• Flow stability of thixotropic fluids is highly dependent on structural parameters.
• Optimizing nozzle design and printing parameters can suppress instabilities and vortex formation.
• Provides insights for enhancing extrusion stability in additive manufacturing processes.