Prony series and spectral function characterization of viscoelastic compliances of a solid polymer
This paper presents two characterization methods that are used to describe viscoelastic behavior. In the Prony series method, a discrete representation of the generalized Kelvin model is used, whereas the spectral method uses a continuous distribution. The Prony series coefficients are determined through the linear least squares technique. The Elastic-Viscoelastic Correspondence Principle and the Laplace transform are used in the spectral function approach, which utilizes a selected distribution function that has the potential to describe a wide range of viscoelastic material behavior. Characterization exercises from both methods used strain histories from short-term unidirectional tensile creep experiments that were obtained at three temperatures below the glass transition temperature of a vinyl ester polymer. Experimental strains in both the longitudinal and transverse directions were measured using the digital image correlation technique and linear viscoelastic material properties were obtained without using Poissonâ€™s ratios. The measured data was subsequently used to determine the tensile creep compliance function for each test configuration. The potential and limitations of each modeling approach are discussed.