SAMPE Journal - January/February 2016 - 51
PHD STUDENT DIVISION AWARD ARTICLE
Process Map
The purpose of the process map
(Figure 7) is to enable the design
of cure cycles that avoid surface
porosity while minimizing cycle
time, based on quantitative criteria
for volatile release and pressure
drops. First, the baseline cycle A and
the "extended dwell" cure cycles C
though G are shown as dashed black
lines. The times corresponding
to each cycle when α = αcrit are
shown in blue. If cavity pressure
can be maintained until the entire
cure envelope has surpassed αcrit,
minimal surface porosity can be
Figure 7. Process map showing times of critical degree of cure, presexpected. To find the maximum time
sure drop, and gelation, for a range of intermediate dwell temperatures.
that each intermediate temperature
The shaded green area is the process window for intermediate dwells
can be held, the time of pressure
resulting in minimal surface porosity, and the shaded red area shows
drop was measured experimentally
an approximate temperature envelope for Cycle H.
for samples cured under each of the
"extended dwell" cycles (C - G), given
when the cold-side α > αcrit. In addition to using in by the red line on Figure 7.
situ observations, porosity formation can, at least
qualitatively, be identified by the post-drop cavity
pressure behavior. Decreasing pressure corresponds
to increasing cure shrinkage, and jaggedness in the P <
Pcrit regime can be attributed to void growth. Because
the volatile gases are less dense than the resin, their
release counteracts the density increase due to cure
shrinkage. The cavity pressure in Figure 6 shows this
behavior between t = 96 - 99 minutes, followed by a
continued drop in pressure that eventually reaches
negative values, indicating a tensile stress state in the
mold cavity. The pressure jump back up to ~200 kPa
at t = 128 minutes is caused by the laminate ultimately
detaching from the sensor tip.
In contrast to the baseline case, cure cycle B has
been demonstrated5 to result in minimal porosity
(0.12% defective area), by using an intermediate
temperature dwell to slowly progress the cure
reaction and reduce the amount by which the coldside α lags when the pressure drop occurs. Cycle B,
however, requires an additional 3 hours of processing
time. The following section (Process Map) describes
the procedure used to build a process map, which
shows the range of intermediate dwell times and
temperatures that produce behavior similar to
cycle B. The characteristics of a two-stage cycle that
prevent surface porosity formation are described in
more detail in the context of the "optimized" cycle H
in section on Cure Cycle Design.
SAMPE Journal, Volume 52, No. 1, January/February 2016
51
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Table of Contents for the Digital Edition of SAMPE Journal - January/February 2016
Contents
SAMPE Journal - January/February 2016 - Cover1
SAMPE Journal - January/February 2016 - Cover2
SAMPE Journal - January/February 2016 - Contents
SAMPE Journal - January/February 2016 - 2
SAMPE Journal - January/February 2016 - 3
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SAMPE Journal - January/February 2016 - 5
SAMPE Journal - January/February 2016 - 6
SAMPE Journal - January/February 2016 - 7
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