Modified hybrid closure approximation for prediction of flow-induced fiberorientation

Distribution of fiber orientation in flow molding processes with short-fibe r reinforcements is of great importance because it affects the mechanical p roperties of molded parts. Due to trade-off between the computational effic iency and accuracy, a second-order orientation tensor has been widely used to describe the fiber orientation distribution. For calculation of this fib er orientation tensor, a closure approximation has been introduced to reduc e a higher fourth-order orientation tensor to a lower second order. Ln the present investigation, a hybrid closure approximation has been modified. Tw o parametric forms of the distribution function, which accurately describe the random-in-space, random-in-plane, and uniaxial distributions of the fib er orientation were linearly interpolated. The interpolating factor was obt ained as a function of the fiber interaction coefficient by fitting the dis tribution function calculations. Test simulation in homogeneous flow and no nhomogeneous flow fields, respectively, showed that the proposed closure ap proximation gives good performance for a wide range of C-I values without s howing nonphysical behavior. (C) 1999 The Society of Rheology. [S0148-6055( 99)01603-X].