Modelling of a LPM filling process with special consideration of viscosity characteristics and its influence on the microstructure of a non-crimp fabric fiber bed

摘要

Recently, in RTM process techniques, in-situ polymerizing thermoplastics are a promising alternative for conventional thermoset matrix systems. The advantages of these systems are given by a low initial injection viscosity in combination with a polymerization process during injection. This means that a fast mold filling is possible even for high fiber volume fractions. Additionally, the process steps of injection and curing are combined to one single step, which leads to a significant reduction in cycle time. From these advantages several problems arise for the simulation of a filling process, which is mainly based on Darcy's Law. The low initial viscosity causes high and inertia affected fluid velocities, violating the Darcy's Law restriction of a sufficient slow flow. With proceeding polymerization the viscosity characteristic is changing from an initial Newtonian to a visco-elastic flow behavior. The shear rate dependency of the fluid is additionally violating the restriction of a constant viscosity. The intention of this paper is to investigate high velocity and therefore inertia affected fluid flow in a non-crimp fabric fiber bed. Several fluids have been characterized by their rehological behavior. Based on these characterizations, flow experiments were executed to investigate the deviations between Darcy flow and fluid flow, which does not fulfill the restrictions. Additionally, the influence of visco-elastic fluid characteristic on the fiber bed microstructure was analyzed.