Short fiber composite reinforcements

International audienceThe chapter focuses on fibre 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 fibre addition is to improve the mechanical properties of final parts. However these properties depends on the fibre orientation and therefore the knowledge of link between processing condition and final fiber orientations has a major importance. First the chapter contains results of experimental observations on fibre length distribution, concentration and orientation for complex enough situations in order to describe problems encountered in real industrial processes. It is explained how to get experimental measurements on orientation and interaction tensors from image analysis on polished cross sections or in situ micro-tomography. These information are useful to validate models presented in the next sections. The models describing the evolution of fibre orientation in a flow motion are mainly based on macroscopic tensors and Folgar Tucker's equation. We present also extensions of this equation which takes into account of non-Newtonian behaviour of polymer, confinement effect and interaction between fibers. Finally, a variety of theories predicting the total stress of fiber suspensions in a Newtonian and complex fluid are exposed. In the next section, an industrial software and its inherent numerical methods are described. Examples of numerical computations are presented for typical situations. Then the influence of the coupling between the fiber orientation and rheological behaviour of the suspension are analysed. The comparison with experimental data concerning fibre orientation prediction gives information on the validity and the influence of various parameters associated to these models