Nonlinear creep characteristics of extruded Poly (vinylidene fluoride-co-hexafluoropropylene) with high ß-phase content under extreme conditions: Design, characterization, and modeling

[Display omitted] •Nonlinearities in creep characteristics of extruded Poly (vinylidene fluoride-co-hexafluoropropylene) over wide ranges of stress and temperature.•Design and development of an experimental creep test setup for high tensile stress levels based on load amplification mechanism.•The underlying connection between the crystallinity, polymorphs, storage modulus, loss factor and the nonlinear viscoelastic properties of Poly (vinylidene fluoride-co-hexafluoropropylene)•Development and validation of a temperature- and stress-dependent generalized creep model based on Findley power law.•Generation of time–temperature-compliance mater curves for creep life predictions based on critical creep strain failure criterion. This study is concerned with the nonlinear creep characteristics of extruded Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) dominated by β-phase polymorphs over the temperature range 40 °C − 80 °C and tensile stress levels between 5 MPa and 12.5 MPa. The measured data using the developed experimental setup as well as the dynamic mechanical analyzer invariably suggested a nonlinearity taking place at temperatures near to 60 °C, where αc-relaxation began corresponding to 100 °C above the measured glass transition temperature of PVDF-HFP. The results from accelerated testing conditions indicated the transition to tertiary creep stage at 24% to 28% strain, irrespective of test condition, referred to as critical strain range. Following the identification of Findley power law model constant at different test conditions, a generalized temperature- and stress-dependent model was developed with only 7 constants. The comparisons between the measured and modeled data conveyed the model effectiveness in describing the nonlinear creep characteristics of the polymer over the measured temperature and stress levels. Time-temperature-compliance master curves were consequently constructed using the developed generalized model, which in combination with the critical strain failure criterion, provided the essential design data including the maximum allowable ranges of stress and temperature for achievement of 20 years creep life.