A NEW ANALYTICAL REPRESENTATION FOR CREEP CURVES OF PLASTICS

Abstract

In order to have the best prediction of the non-linear viscoelastic behaviour of solid polymers, a new constitutive relationship has been obtained by inserting the stress invariants ( 1 I ) and ( 2 I ) into the formulation of multiple integral representation (MIR). The analytical part for the uniaxial tensile loading, it was found that creep could be separate into three components. First and second components, represent the contributions of the hydrostatic and deviatoric stresses respectively, while the third component represent the contribution of the synergistic effect of the hydrostatic and deviatoric stresses. Also, for the case of pure shear loading it was found that all components of creep are dependent on the deviatoric stress. Thus, new kernels have been obtained which called the hydrostatic, deviatoric and synergistic kernels, in terms of power law. Good agreement has been obtained from the comparison
between the experimental of other studies and theoretical results of MIR under different types of loading for PP, PE and PMMA. This comparison proved that MIR gives the prediction with an average error of 0.05%.