SAMPE Journal - July/August 2016 - 11

Feature Article

Figure 4. CYCOM 5320-1 93°C initial cure
and freestanding postcure to 177°C.

Figure 5. CYCOM 5320-1 121°C initial cure and
freestanding postcure to 177°C.

It can be seen that the material effectively gels
during the 177°C dwell and the Tg lags behind the
cure temperature until the 177°C dwell is started.
Such a cure cycle is therefore used when the entire
cure takes place with the part supported in a tool
and the tool in question needs to operate at 177°C.
The cure duration is however considerably shorter
than that of the prototype part cure cycles shown in
Figures 4 and 5 and permits a production efficiency
comparable to that of autoclave cured parts.
As noted in the previous discussion above, efficient
air and volatile extraction prior to the commencement
of any cure cycle is highly desirable and may be
achieved by the addition of a super-ambient dwell
at 50°C - 60°C to each of the cure cycles shown in
Figures 4, 5 and 6.
It should be noted that for all of the scenarios
considered in this discussion and the variables
identified in several previous coverages on these
topics, the characteristics of the prepreg and in
particular viscosity, will change as the material
SAMPE Journal, Volume 52, No. 4, July/August 2016

accumulates out time during layup. There is therefore
an out time limitation in a given case which may be
part construction specific and not purely a material
characteristic. A discussion of this and related issues
may be found in Reference4.
There are also certain circumstances where
something other than a 'standard' cure cycle may be
needed. The use of ultra-high modulus fibers such
as Hexcel® HM63 or Toray® M46J in unidirectional
tapes produce a different pattern of residual stresses
compared with that arising from the use of standard
or intermediate modulus carbon fiber. These
materials can exhibit microcracking after cure or
subsequent thermal cycling if a standard cure cycle
such as one of those shown in Figures 4, 5 or 6 is
used, particularly in applications involving cryogenic
service temperatures. Figure 7 shows an example
of microcracking in a discriminator panel built from
MTM45-1/HM63 unidirectional tape after a standard
cure/postcure and thermal cycling.
11



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
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