Fibre orientation, rheological behaviour and simulation of the compression moulding process for composite materials

University dissertation from Luleå : Luleå tekniska universitet

Abstract: Compression moulding is a common manufacturing process for composite materials. In order to better predict the processing and performance of components, simulation tools are becoming more important. In this thesis the behaviour of the compression moulding raw material has been studied to provide a platform for better simulations. In Paper I the measurement of the fibre orientation distribution is studied. The necessary sample size is determined by statistical analysis. The full procedure for fibre orientation measurements including sample preparation and image capturing is described. In Paper II non-isotropic rheological properties of GMT are investigated. The reason for this problem is that the fibres are not randomly oriented. The anisotropic behaviour as well as comparisons between different raw materials are shown in the paper. In Paper III, the isothermal rheological properties of GMT are studied on industrial relevant sample sizes and closing velocities in a 310 tonnes press. The experimental data have then been compared to existing models for squeeze flow rheology of GMT. Necessary material coefficients have been derived and the validity of the studied models has been determined. In Paper IV squeeze flow rheology experiments of a generic GMT material have been simulated using a finite volume CFD code. As the material expands (lofts) when the material is heated prior to moulding so that the air content is above 50% compressible effects have been specially studied and modelled using a homogenised model for the density of the two phases system. In the simulations effects corresponding to those observed in experiments that cannot be explained using incompressible theories have been observed. In Paper V the mould filling process of an automotive hood has been simulated using a general purpose CFD (computational fluid dynamics) code. During the mould filling stage, the progress of the flow front and the reorientation of the fibres have been studied especially.

  This dissertation MIGHT be available in PDF-format. Check this page to see if it is available for download.