TOOLED THICK COMPOSITES by ARVEN H. SAUNDERS III ...

patterns velocity and timing during the process are the major suspects for causing fiber
waviness or marceling. The inclusion of thermal effects of temperature and cure on the viscosity
of the resin via Darcy’s law are known factors affecting velocity. The model was intended to
indicate optimal vs. problematic cure process parameters or scenarios that could create defects.
These scenarios could then be investigated by work on actual laminates.
3.4 Introduction to the Pressure and Consolidation Submodel
A critical portion of the cure process model characterizes the consolidation of the
composite laminate as pressure is being applied during the cure cycle. The application of
pressure to the laminate brings about displacement and volume changes with resin flow out of
the laminate. Laminate volume is occupied by fiber, resin, and to a much lesser degree, by air
that is entrapped during layup, or volatiles as a by-product of curing. The process of
consolidation during the application of heat and pressure of the cure process forces resin flow
out, while reducing the spacing between the fibers, forming a more dense mixture. Void volume
is defined as the relative volume not occupied by fibers or resin; therefore, it is a defect within a
cured laminate. A principal objective of curing is to apply adequate pressure to minimize
porosity. The flow of resin is also an aid in “wicking out ” entrapped air or gases out of the
laminate. For the 2 materials being utilized for this research, IM7/3501-6 and S2/8552, the fiber
volume fraction for a consolidated laminate typically ranges between 50 and 65 percent.
3.5 Darcy’s Law
The laminate being modeled contains both resin and fiber volume and is considered to
have negligible void volume. The focus of the pressure submodel is on the distribution of resin
pressure within the laminate and its resulting resin flow due to pressure application. For a press
cured part, pressure is applied through contact with the tool lid surface as depicted in Figure
3.2. For a simple flat laminate, if pressure is applied uniformly across the top surface, then the
resin pressure within the laminate will increase, causing resin to flow to its outside edges. Here
the resin pressure at the edges of the laminate is assumed to be zero, and pressure is at its
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