Viscoelastic Flow

FLOW-3D includes viscoelastic flow models that predict the behavior of material that behave both like liquids and solids, depending on the local strain and strain rate. Viscoelastic materials include polymer solutions, melts, and highly filled suspensions of particles. Elasto-viscoplastic materials exhibit solid-like behavior up to a yield stress limit, beyond which the material exhibits liquid-like behavior.

Viscoelastic models included in FLOW-3D include the Oldroyd-B model, and the Giesekus model. Additional models can be implemented via user customization.

Regardless of the material, the elastic stress is computed incrementally from one time step to the next, allowing simulation of large deformations over long time scales.

Injection molding of a spur gear

One example is that of injection molding of polyethylene melts. The animation above shows the injection molding of a spur gear. The same part is filled by another (fictitious) material with the exact same viscous properties, but no elastic properties. The effect of the elastic stress is clear where the fluid reaches the outer rim of the gear: here the elastic stresses that build up in the spokes alter the flow from a symmetrical “oozing” to a nearly horizontal motion, akin to die swell, seen in extrusion processes of viscoelastic materials.