Meaning
Advanced constitutive equations for solid-state polymer deformation predict the non-linear stress response of thermoplastics during biaxial drawing. The modified Buckley model is a prominent material model used to describe the viscoplastic behavior of polyethylene terephthalate and other amorphous polymers. It accounts for both the rate-dependent flow and the subsequent strain hardening that occur during high-strain stretching.
Rheological Component
The mathematical formulation separates the material response into two primary contributions. In the modified Buckley model, the first part represents the thermally activated intermolecular resistance to flow. The second part captures the entropic strain hardening caused by the stretching of the polymer network.
This division allows the model to accurately simulate the sharp rise in stress seen at high draw ratios.
Stretch Simulation
Implementing this model in finite element analysis software enables realistic simulation of the blow moulding process. It helps predict where the polymer will undergo rapid stretching and where it will remain thick. This simulation capability reduces the time spent on tooling modifications.
Model Calibration
Determining the material parameters for the model requires extensive experimental data from tension or compression testing. These tests must run at various strain rates and temperatures to capture the temperature-sensitive behavior of the polymer. The calibrated model provides a reliable representation of the polymer behaviour under blow moulding conditions.
