BEST FIT FOR DIFFERENTIAL CONSTITUTIVE MODEL PARAMETERS TO NONLINEAR OSCILLATION DATA

Non-linear, transient model parameters of non-linear constitutive equa tions can be fitted objectively with large amplitude oscillatory shear flow by minimizing the function GAMMA = SIGMA(j odd) 1/j. (Sigma(j)m- sigma(j)p/sigma(j)m)2, where sigma(j)m is the stress amplitude of the jth harmonic of the experimentally measured shear stress response and sigma(j)P is the stress amplitude of the jth harmonic of the predicted shear stress. Minimizing this function gives unique, best fits for no n-linear differential constitutive theories to the measured shear stre ss response of a low density polyethylene melt in large amplitude osci llatory shear.