Evaluating Parameter Value Identification Methods for Modeling of Nonlinear Stress Relaxation in Polyethylene

Area of Science:

• Polymer Science
• Materials Science
• Rheology

Background:

• Viscous properties are crucial for polymer time-dependent deformation.
• Traditional spring-dashpot models lack unique parameter sets, limiting their use in quantifying viscous properties.
• Polyethylene (PE) and its pipes exhibit complex nonlinear viscous stress responses.

Purpose of the Study:

• To develop a reliable method for determining unique model parameters for spring-dashpot models.
• To quantify the viscous properties of polyethylene (PE) and its pipes.
• To enhance the characterization of PE's mechanical performance, especially for long-term applications.

Main Methods:

• A novel multi-relaxation-recovery test was employed to capture stress response variations.
• A three-branch spring-dashpot model with two Eyring's dashpots was utilized.
• Four analysis methods (mode, peak-point, highest-frequency, best-five-fits) were compared for parameter determination.

Main Results:

• The multi-relaxation-recovery test revealed the complex nonlinear viscous behavior of PE.
• Comparison of analysis methods showed that the best-five-fits method yields the most reliable and unique model parameters.
• The best-five-fits method provides a pathway to quantify PE's viscous properties.

Conclusions:

• The best-five-fits method offers a robust approach for parameter determination in polymer rheology.
• Unique model parameters enable accurate quantification of viscous properties for PE and its pipes.
• This advancement is vital for precise characterization of long-term mechanical performance and load-carrying capacity.