Thermoviscoelastic models for polyethylene thin films
This paper presents a constitutive thermoviscoelastic model for thin films of linear low-density polyethylene subject to strains up to yielding. The model is based on the free volume theory of nonlinear thermoviscoelasticity, extended to orthotropic membranes. An ingredient of the present approach is that the experimentally inaccessible out-of-plane material properties are determined by fitting the model predictions to the measured nonlinear behavior of the film. Creep tests, uniaxial tension tests, and biaxial bubble tests are used to determine the material parameters. The model has been validated experimentally, against data obtained from uniaxial tension tests and biaxial cylindrical tests at a wide range of temperatures and strain rates spanning two orders of magnitude.
KeywordsNonlinear viscoelasticity Free volume model Polymer thin film
We thank Drs. Wolfgang Knauss (California Institute of Technology), James Rand (Winzen Engineering), and David Wakefield (Tensys Limited) for helpful comments and discussions. We thank Dr. He of NASA GSFC for providing DMA test data on StratoFilm, Dr. W.N. Warner of NASA Jet Propulsion Laboratory for assistance in measuring the out-of-plane CTE of StratoFilm, and Dr. L. Young of NASA Wallops for providing test data. This research was supported by the NASA Balloon Program Office. Financial support from the Croucher Foundation (Hong Kong) for Kawai Kwok is also gratefully acknowledged.
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