Functional and structural parts, made so far with metals, have been progressively reengineered
by replacing metallic materials by discontinuous fibre reinforced polymers and continuous fibre
reinforced composites. Polymer composites are usually divided into two groups, advanced (or
high performance) composites and engineering composites. They differ principally in the type
and length of the fiber reinforcement and in the characteristics of the polymers used. Polymer
reinforced by low to medium content of discontinuous fibers (LFTs, SMC, BMC…) belongs to
the first one. Polymer reinforced by high content of continuous fiber (CFRP) belongs to the
second one. However there is not sharp division boundary between both groups, one type of
composite changes gradually into the other. Recent studies showed that discontinuous aligned
fibers composites have similar mechanical properties than their continuous counterpart.
An important characteristic of continuous fibers is that they cannot flow with the polymer,
even if the viscosity of the polymer is low. Continuous fiber reinforced polymer (CFRP) always
involves a fluid flow through the fibrous medium, whether to create a semi-product like a
prepreg that will be further processed to make the final part or to directly manufacture a part
from dry fiber reinforcement. However recent works showed that hybrid squeeze-bleeding flow
types may occur in CFRP. In addition, because of the initial low viscosity, some resins can be
combined with medium volume fraction of discontinuous fibres to get a flowable compound.
Increasing the amount of discontinuous fibers to a larger content will lead to a situation where
squeeze-bleeding flow modes can occur during manufacturing of composite parts.
This seminar will illustrate some complex flow mechanisms observed for both continuous and
discontinuous composites. Some models will be presented and discussed.
Keywords : Rheology of composites, flow in fibrous media, microstructure evolution by
processing, numerical modeling, experimental