MODELIZATION OF EXTENSIONAL EXPERIMENTS UNDER CONSTANT FORCE USING MEMORY-INTEGRAL CONSTITUTIVE-EQUATIONS AND STREAM-TUBE ANALYSIS

In this paper, we propose a numerical simulation of axisymmetric exten sional experiments on a viscoelastic polydimethylsiloxane (PDMS) mater ial, using a falling-weight extensional rheometer. The polymer behavio ur is represented by a K-BKZ memory-integral constitutive equation, in volving a damping function of the Wagner type. Under the assumption of a homogeneous flow zone in the sample, a numerical model is set up, u sing the stream-tube method and approximating functions. The governing equations of the problem, associated to a limited number of unknowns, are solved by means of the Levenberg-Marquardt optimization algorithm . The numerical results are found to be consistent with the experiment al data and reveal the importance of the non-homogeneous flow zone, in relation to the estimation of the extensional strain rate. The calcul ations involve the sensitivity of the model on the fluid parameters an d those concerning the size of the initial column of fluid. The limite d computing (CPU) time of the code is also to be underlined.