RHEOLOGICAL MODELING OF SHORT-FIBER THERMOPLASTIC COMPOSITES

Quantitative analysis of flows of fiber suspensions in viscoelastic ma trices, which is the general situation for thermoplastic composites, r equires constitutive equations which incorporate specific features of the system and its constituents. Matrix viscoelasticity, fiber orienta tion and fiber/matrix interactions are key parameters to model such sy stems. In this work, the constituents of the system are represented by two second order symmetric tensors: c(r, t) for the viscoelastic matr ix and a(r, t) for the fiber orientation. The time evolution equation for c(r, t) is developed in the generalized Poisson bracket framework with a finitely extensible non-linear elastic (FENE-P) and a Hookean H elmholtz energy functions. Several expressions for the mobility tensor including expressions with fiber matrix interactions are used. The ti me evolution equation for ar(r, t) is based on the classical Jeffery e quation modified to include fiber/fiber interactions in the case of se mi-dilute suspensions. The sensitivity of the model to the choice of t he mobility tensor together with the effect of fiber volume fraction o n the prediction of material Functions in start up and steady shear fl ows are discussed. (C) 1997 Elsevier Science B.V.