Viscoelastic Creep Characterization of LDPE Under Multilevel Stress and Temperature Using Time-Temperature Superposition and Constitutive Modeling

Abstract

This study addresses the difficulty of accurately characterizing the long-term viscoelastic creep of low-density polyethylene (LDPE) when sustained stress, temperature, and exposure time vary simultaneously, while conventional short-term testing and single-condition constitutive models provide limited representation of service behavior. The purpose was to quantify multilevel stress-temperature effects on LDPE creep and integrate experimental response, time-temperature superposition (TTS), statistical modeling, and constitutive validation within one framework. A quantitative, cross-sectional, experimental case-based design was adopted using commercial-grade LDPE specimen-condition cases exposed to stresses of 2–10 MPa and temperatures of 25–65°C, with 45°C selected as the TTS reference temperature. Key variables included stress, temperature, creep time, creep strain, creep compliance, creep rate, temperature shift factor, reduced time, and constitutive parameters. Analysis combined descriptive statistics, Pearson correlations, multiple regression, Cronbach’s alpha, TTS master-curve construction, and Burgers-type/generalized viscoelastic model calibration and validation using R², adjusted R², F-statistics, RMSE, and MAE. Findings showed that creep strain increased from 2.84% to 9.67%, creep rate from 0.018% h⁻¹ to 0.071% h⁻¹, and compliance from 0.46 to 1.38 MPa⁻¹. Stress correlated strongly with creep strain (r = 0.76), as did temperature (r = 0.71), both p < 0.001. Regression explained 68.4% of creep-strain variance (adjusted R² = 0.672; F = 58.27, p < 0.001), with stress (β = 0.49) and temperature (β = 0.41) significant. Shift factors ranged from 5.62 to 0.18, extending the creep domain to 0.18–562 h, while constitutive validation achieved R² = 0.94, RMSE = 0.37%, and MAE = 0.29%. Overall scale reliability was high (Cronbach’s alpha = 0.88), supporting consistency of the quantitative assessment across measured analytical constructs. The findings support more reliable long-term LDPE design, material assessment, and engineering prediction under coupled thermomechanical loading.