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

A successful cure process must be efficient in time and cost, while satisfying its
minimum requirements. Controlling this process is essentially managing the interactions of
temperature distribution, degree of cure, laminate thickness, and void content by manipulating
only the press temperature and pressure. Design of a cure cycle that consists of temperature
profiles along with adequate pressure over time can ensure an acceptable cure. Models built on
the Loos, Springer (Loos, 1983) thermochemical model foundation are well established in the
literature and are widely used in process development. In attempts to optimize the overall cure
process time, Rai (Rai, 1997) was able to apply numerical physics-based model to seek optimal
cure cycles assuming a standard fixed rate pressure application in an autoclave.
While numerical based optimization approaches are well suited to focus on the
objective function of minimum overall cure time, there are other considerations that knowledge-
based approaches contribute that are important for part quality and uniformity. For example, it is
critical that the laminate be uniform in resin state prior to pressure application so that as uniform
as possible resin flow and fiber volume distributions result before completion of resin cure. The
approach to optimizing the cure cycles for the thick laminate flexbeams in this study combined
the benefits of rule-based methods with numerical optimization.
Fiber waviness (as discussed previously) is a major manufacturing defect issue that
compromises structural strength and part longevity. Some research has investigated the causes
and remedies for this defect, with some experimental results for what process parameters seem
to work vs. not. However, there has been a lack of a explicit or formal description, definition, or
explanation of the underlying mechanisms. An explanation that will be pursued here is this: the
nature of a flexbeam laminate being cured in a closed-cavity mold is that consolidation during
cure reduces the laminate thickness disproportionately with respect to its uncured thickness.
Since the mold is designed to yield the final desired laminate thickness dimensions, there will be
a mismatch of inner mold surface dimensions with the uncured laminate dimensions, creating
areas of noncontact (gaps) towards the middle of the flexbeam length. These gaps will exist
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