Short fiber composite reinforcements

Abstract

Abstract The chapter focuses on fiber-reinforced thermoplastics or polymer composites which are mainly produced by injection and compression molding using particles having mostly cylindrical shape (short or long fibers made up of glass, carbon, or flax). The aim of this fiber addition is to improve the mechanical properties of final parts. However, these properties depend on the fiber orientation and therefore the knowledge of link between processing conditions and final fiber orientations has a major importance. First, the chapter contains results of experimental observations on fiber length distribution, concentration, and orientation for complex enough situations in order to describe problems encountered in real industrial processes. We described how to get experimental measurements on orientation and interaction tensors from image analysis on polished cross sections or on in situ microtomography. These data are useful to validate models presented in the next sections. These models describing the evolution of fiber orientation in a flow motion are mainly based on macroscopic tensors and Folgar-Tucker equation. We present also extensions of this equation which take into account the non-Newtonian behavior of polymer, confinement effect, and interaction between fibers. Finally, a variety of theories predicting the total stress of fiber suspensions in Newtonian or complex fluids are exposed. In the last section, industrial software and their inherent numerical methods are described. Examples of numerical computations are presented for typical situations. In particular, the influence of the coupling between the fiber orientation and rheological behavior of the suspension is analyzed. The comparisons with experimental data about fiber orientation prediction give information on the validity and the influence of the various parameters associated to these models. In this way, it is possible to optimize these parameters and get a better modeling.