An Evaluation of Analytical Expressions for the Representation of Plastics Creep Data

Abstract

Various analytical expressions were evaluated for their ability to represent plastics creep data resulting from isothermal, constant stress creep experi ments. The constants for each expression were determined by an iterative least squares analysis performed on published creep data for crystalline, amorphous, crosslinked and multiphased plastics. The expressions were ranked in order of effectivity for the representation of creep data using the sum of the squares of the residuals as the criterion of ranking. It was determined from the analysis that a simple 3 parameter parabolic function was the most accurate, as well as general expression for the analytical representation of the plastics creep data investigated. The best fit constants for the functions investigated were, in general, dependent upon stress. It was found that the extrapolation of 1 day creep data to periods of time as great as 1 year, generally led to large errors.