Preimpregnated fibers or prepregs are widely used to
produce high quality composite parts. One process in particular, known
as cavity molding, is frequently used to process high quality thick
composite details with exceptionally precise dimensions by using a
platen press to apply heat and pressure to rigid tooling and thereby
entice the prepreg within to cure into the shape of the confines of an
internal cavity. The objective of the research described here is to
develop an mathematical model for glass/epoxy prepreg which simulates
the resin flow, heat transfer, consolidation and curing of cavity-molded
flex beams which varies significantly with location. An enhanced
understanding of the mechanisms involved will help significantly improve
the costeffectivity of molding processes development. The current work
is focused on process modeling of composite flex beams which are
manufactured by cavity molding. The curing kinetics of such parts is
particularly difficult to model because tool/part geometries are
complex. The combined effects of heat transferred by the tool and heat
spontaneously generated by the reacting thermoset during cure results in
significant gradients of resin advancement throughout the part that
range from incomplete polymerization, in the thinnest cross-sections, to
complete cure (and potential embrittlement) at the thickest cross
sections. This causes formidable temperature spikes that result from
internally-generated exothermic heat that cannot be quickly dissipated
because of the low thermal conductivity of composite and tooling.
Various governing equations are presented here that describe the resin
cure kinetics, thermal energy balance and consolidation of this porous
medium. A general-purpose, finite-element package with multiphysics
capabilities is used for simulating the non-isothermal prepreg-press
process, the degrees of cure and temperature field distribution at
different cross-sections are also presented.
http://www.sampe.org/events/Baltimore_2012_Final_Program.pdf