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

(3) Thermal modeling to include heat of resin cure reaction as well as heat from press
tooling/lid, dependent on surface contact.
(4) The capability and flexibility to adapt and expand the model to investigate specific process
scenarios.
3.3 New Model Approach and Assumptions/Groundrules
Certain simplifying assumptions were made while building the model. A flexbeam type
part was chosen because it is relatively simple in geometry, is often cured in a press, and
because of its thickness, can pose significant cure control challenges. Because the geometry of
a flexbeam is planar, that is, it has height that differs over its length but not over its width (or
depth), the 2D model was deemed to be adequate to characterize the part. The predominant
prepreg material fiber orientation used for the flexbeam is along its length (0 degrees) for tensile
strength. The longitudinal permeability that is associated with this orientation is 2 to 3 orders of
magnitude higher than the transverse permeability. Thus, the model was built with the
philosophy that the predominant resin flow for a flexbeam is in the x direction, i.e., along its
length.
The model does not include mass properties of the resin or fiber in the flow and
compaction behaviors. Mass properties are assumed to include momentum, inertia, and time-
dependent effects of resin from viscous flow. The goal of the model is to find, investigate, and
detect worst case conditions in simulated real-time. Mass properties were deemed less critical
to include during the critical part of the cure process when temperature is being applied up to its
final temperature and pressure is being applied up to its final level. During this phase, most
defects occur. The focus of the model was on resin pressure and flow patterns. During this
phase of the cure cycle the applied pressure is generally monotonically increasing. At certain
points, there are applied pressure dwells, during which the resin pressure is expected to bleed
off, and could cause some porosity if not followed soon with resumption of higher applied
pressure. This model was designed to be simple and straightforward but comprehensive in
areas that are suspected to shed the most useful light on suspected areas. The resin flow
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