By using dynamic stress rheometer-DSR-200

linear viscolelasticity of four polyethylene melts has been characterized by small amplitude oscillatory shear test. From data of storage moduli G′(w) and loss moduli G″(w)

discrete relaxation spectra have been obtained for four polyethylene melts by means of linear regression method

regularization method and nonlinear regression method

respectively. Effects of the calculation methods

computing parameters

temperatures and materials on the spectrum have been discused. It was found that computing parameters-relaxation time numbers and relaxation time rangehave a strong effect on linear regression and regularization method

but less influence on nonlinear regression method. Three calculation methods can obtain nearly the same relaxation spectrum when choosing fewer relaxation time numbers

but quite different results when chossing more relaxation time numbers. Both temperature and materials have strong effects on discrete relaxation spectrum due to the structural charcteristic of polymers. It is concluded that nonlinear regression method seems to be the best method for the calculation of the discrete relaxation spectrum.