SAMPE Journal - July/August 2016 - 9

Feature Article
percentage by weight but potentially a significant
percentage by volume when converted to gaseous
form during a subsequent cure.
With all of the above mentioned factors combining
to determine essentially what the vacuum bag oven
process needs to accomplish, the quality of vacuum
is a key process parameter which impacts the part
quality. A vacuum level as close to absolute as
possible is generally required for success (generally
held to be < 5cm/2" Hg differential). This often
causes confusion as a vacuum gauge gives a reading
relative to the ambient barometric pressure, which
varies with altitude, not relative to absolute vacuum.
Dedicated vacuum pumps are recommended for the
manufacture of VBO parts as shop vacuum systems,
designed to debulk layups prior to an autoclave cure,
rarely deliver an adequate quality of vacuum for a
non-autoclave cure.
Shortened Cure Cycles - "Super-Ambient" Dwells
Recent work has been conducted with CYCOM
5320-1 prepregs to determine whether the 16 hour or
more room temperature dwell cited in the published
literature could be replaced by a shorter dwell at
a mildly elevated temperature while achieving the
same 'drying' effect and removing the small amount
of potentially porosity creating moisture. It has
been found that for this particular prepreg system

a dwell in the 50°C - 60°C range appears to be
highly effective in producing good quality laminates
without the need for the long room temperature
dwell. Introducing a dwell at a temperature of greater
than 60°C was found to be less effective, most likely
because at higher temperatures the resin viscosity
reduces and the dry fiber evacuation channels begin
to collapse and close off prematurely before the
entrapped air and dissolved moisture have been
completely removed. If this theory is correct, it
also implies that the resin viscosity characteristics
will play a major role in determining the optimum
temperature window for such 'super-ambient' dwells
and the optimum range could well be different for
different resin systems. As noted in the discussion
above and3, it is also possible that air and volatile
transport in the through thickness direction for some
reinforcement architectures may become more
efficient at super-ambient temperatures and improve
the ability to evacuate plies which terminate internally
to the laminate. Figure 2 shows a comparison of two
complex CYCOM 5320-1/8HS fabric discriminator
panels built using both a 16 hour room temperature
dwell and a 4 hour super-ambient dwell at 50°C
respectively.
Figure 3 shows the boiling point of water as
a function of vacuum level. At the high levels of
vacuum used for the manufacture of VBO composite

Figure 2. Comparison of discriminator panels built with an accelerated super-ambient dwell cure cycle with one
employing a 16 hour room temperature dwell.
SAMPE Journal, Volume 52, No. 4, July/August 2016

9



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
SAMPE Journal - July/August 2016 - 3
SAMPE Journal - July/August 2016 - 4
SAMPE Journal - July/August 2016 - 5
SAMPE Journal - July/August 2016 - 6
SAMPE Journal - July/August 2016 - 7
SAMPE Journal - July/August 2016 - 8
SAMPE Journal - July/August 2016 - 9
SAMPE Journal - July/August 2016 - 10
SAMPE Journal - July/August 2016 - 11
SAMPE Journal - July/August 2016 - 12
SAMPE Journal - July/August 2016 - 13
SAMPE Journal - July/August 2016 - 14
SAMPE Journal - July/August 2016 - 15
SAMPE Journal - July/August 2016 - 16
SAMPE Journal - July/August 2016 - 17
SAMPE Journal - July/August 2016 - 18
SAMPE Journal - July/August 2016 - 19
SAMPE Journal - July/August 2016 - 20
SAMPE Journal - July/August 2016 - 21
SAMPE Journal - July/August 2016 - 22
SAMPE Journal - July/August 2016 - 23
SAMPE Journal - July/August 2016 - 24
SAMPE Journal - July/August 2016 - 25
SAMPE Journal - July/August 2016 - 26
SAMPE Journal - July/August 2016 - 27
SAMPE Journal - July/August 2016 - 28
SAMPE Journal - July/August 2016 - 29
SAMPE Journal - July/August 2016 - 30
SAMPE Journal - July/August 2016 - 31
SAMPE Journal - July/August 2016 - 32
SAMPE Journal - July/August 2016 - 33
SAMPE Journal - July/August 2016 - 34
SAMPE Journal - July/August 2016 - 35
SAMPE Journal - July/August 2016 - 36
SAMPE Journal - July/August 2016 - 37
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SAMPE Journal - July/August 2016 - 40
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SAMPE Journal - July/August 2016 - Cover3
SAMPE Journal - July/August 2016 - Cover4
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