Formulation of non-linear viscoelastic-viscoplastic constitutive equation for polyamide 6 resin

Jun Koyanagi; Kodai Hasegawa; Akio Ohtani; Takenobu Sakai; Kenichi Sakaue

doi:10.1016/j.heliyon.2021.e06335

Formulation of non-linear viscoelastic-viscoplastic constitutive equation for polyamide 6 resin

Heliyon. 2021 Feb 26;7(2):e06335. doi: 10.1016/j.heliyon.2021.e06335. eCollection 2021 Feb.

Authors

Jun Koyanagi¹, Kodai Hasegawa², Akio Ohtani³, Takenobu Sakai⁴, Kenichi Sakaue⁵

Affiliations

¹ Department of Materials Science and Technology, Tokyo University of Science, Japan.
² Department of Materials Science and Technology, Graduate School of Tokyo University of Science, Japan.
³ Department of Mechanical Engineering, Kyoto Institute of Technology, Japan.
⁴ Department of Mechanical Engineering, Saitama University, Japan.
⁵ Department of Mechanical Engineering, Shibaura Institute of Technology, Japan.

Abstract

In this study, a non-linear viscoelastic-viscoplastic constitutive equation for polyamide 6 (PA6) is formulated and a new model is suggested for the viscoplastic part of the equation. The suggested model is empirical but can accurately predict the viscoplastic strain. In this study, creep and recovery tests are conducted to evaluate the viscoplastic strain. Using a non-linear dashpot, a viscoplastic strain is formulated and its parameters are identified for PA6. In addition, a stress relaxation test is conducted, and the relationship between the viscoelastic strain and stress is identified when considering the viscoplastic strain. In this study, the time-temperature superposition principle is thoroughly applied to include the effect of elevated temperature on the viscoelastic-viscoplastic behavior. All material constants in the non-linear viscoelastic-viscoplastic constitutive equation including the time-temperature superposition principle for PA6 are presented in this study.

Keywords: Constitutive equation; Polymer; Time-temperature superposition principle; Viscoelastic; Viscoplastic.