SAMPE Journal - July/August 2016 - 53

Feature Article
addition to slow ramp rates VBO requires long PVT
greater than 3 hr, or even 12-36 hr for some cases,
prior to cure. A PVT promotes better consolidation
between plies to help generate a void-free
laminate. Longer dwell times might also be needed,
further extending the total cycle time. Unlike VBO,
autoclave bypasses PVT due to high compaction
pressures utilized, and therefore, no additional time
besides cure time is added to total cycle time. One
way to reduce cycle time further is to introduce
faster ramp rates, which is possible for Quickstep
(QS) only. Yet, one must investigate the effects of
fast ramps on curing.
Figure 2a shows a viscosity profile for the #2511
resin system vs. increased ramp rates up to 10°C/
min through a dynamic temperature sweep. As ramp
rates increased, a much lower minimum viscosity
was observed as compared to the typical rate of
2°C/min. These effects were representative for the

(a)

(b)
Figure 2. Example with #2511 resin system (a)
characteristic of viscosity profile vs. increased ramp rate
up to 10°C/min by rheometer (b) characteristic of heat
flow vs. ramp rate up to 10°C/min by DSC.
SAMPE Journal, Volume 52, No. 4, July/August 2016

prepreg. Further characterization is needed above
10°C/min, but one could anticipate an even lower
viscosity could be achieved but in shorter time.
Based on a high heat transfer process with low
compaction pressure as in QS, a lower minimum
viscosity due to fast ramps would be of most benefit
and should avoid longer PVT. Also noted, increased
ramp rates also promote higher heat generation
and flow of the material as shown in Figure 2b by
DSC temperature sweep. If not controlled, this
could cause an undesired exothermic reaction
and ruin the part, making precise process control
essential to cure the laminate properly. Although
not presented, the #3900-2B resin showed similar
behavior.
Equivalency Study
Non-interlayer toughened prepreg system (P711AG-15)
Based on past VBO studies3 low intermediate dwell
was shown to be effective at accruing complete
consolidation of the prepreg system, and then the
part subsequently able to achieve gelation before
processing at the final curing temperature. In terms
of cure cycle development for the QS process,
the results from VBO studies played an important
role. It was anticipated the QS process would also
require an intermediate dwell within the cure profile
but with shorter time due to the capability of faster
ramp up rates and additional compaction pressure
from the weight of the heating fluid.
To ensure a quality test laminate, the study
involved fabricating c-channel spars using the
same tool as Brosius and Luedtke used5-6 in an
effort to establish optimal processing conditions
and bagging schemes to achieve a void-free part.
A void-free part was verified through a series of
cure experiments as shown in Figure 3 (in which
less than one hour total cycle time was achieved
with precise process control). In addition to bagging
schemes, the following cure profile was established
and utilized to cure all flat laminates on the spar
tool for mechanical testing:
1. PVT held within 30 min prior to start of cure
2. Ramp from room temperature to 100°C, dwell for
25 min, ramp rate up to 30°C/min
3. Ramp to 150°C, dwell for 15 min, cool down to
room temp with similar ramp rate
Total compaction pressure within the mold
achieved was about 0.14 MPa comprising vacuum
pressure and fluid pressure. Both bagging scheme
and debulk schedules remain the same throughout.
Process variable temperature overshoot was kept
53



Table of Contents for the Digital Edition of SAMPE Journal - July/August 2016

Contents
SAMPE Journal - July/August 2016 - Cover1
SAMPE Journal - July/August 2016 - Cover2
SAMPE Journal - July/August 2016 - Contents
SAMPE Journal - July/August 2016 - 2
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SAMPE Journal - July/August 2016 - 5
SAMPE Journal - July/August 2016 - 6
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SAMPE Journal - July/August 2016 - 8
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