SAMPE Journal - November/December 2016 - 39

Feature Article

Figure 3. Test results. Values are percent
differences between property values
measured at 0 and 6 cures

The above properties were selected for multiple
reasons: a) some properties, such as hardness
and dimensional stability under repeated cycles of
temperature and pressure, are required to characterize
ET materials9; hardness and tensile strength are also
checked by some manufacturers for every batch11;
b) some properties, like hardness and color, could be
measured in manufacturing shops, since they require
short time, basic skills, and inexpensive equipment;
c) other properties, such as tensile and compressive
response, although only measurable with laboratory
equipment in a laboratory, could provide insight in the
material behavior. One key functional requirement of ET
materials is to return to its initial shape and dimension
after use, and experience no residual and permanent
deformation. A way to assess this prerequisite in this
study was the following: used cured carbon-epoxy caul
plates were sandwiched between all the rubber strips
and pre-preg, and oriented at 90 degree to the strip
length. The 621 kPa (90 psi) pressure applied during the
cure cycles pressed the caul plates against the strips
in three locations per strip, possibly leaving mark-off of
measured in depth on the ET. A description of equipment,
test methods, and samples involved is summarized in
Table 3 for each measured property.

Test Results
Overall Results
The test results are summarized in Table 4, and plotted
in Figure 3. The values in Table 4 are expressed as a
percent of the property values measured at 0 cures
being equal to 100.
Shrinkage Results
The shrinkage values were measured on two 1.2 cm
x 5 cm x 120 cm strips, and plotted in Figure 4. Each
point was the average of two readings, one reading on
each strip. In all materials the contraction rate decreased
with the number of thermal cycles, and seemed to level
off. For KE 1310ST this declining trend was consistent
with that another set of data collected on a different lot
of KE 1310ST subjected to the same thermal cycling in
a separate study. Moreover, for KE 1310ST shrinkage
was 1.3% after 6 cures, and this value matched 1.3%
shrinkage detected on KE 1300, precursor of KE 1310ST,
after 24 hr at 180°C.
In some case, dimensional stability is required in
ETD because the part design allows only for limited
excess in the ETD length. Knowing that the shrinkage
rate decreases over repeated heating is beneficial,
because it shows that it is possible to make ETD more
dimensionally stable during service by heating the ETD
prior to their use.

Table 4. Test results.
Values are percent differences between property values at 0 and 6 cures
Comp. = compressive. SSS = stress-strain slope

SAMPE Journal, Volume 52, No. 6, November/December 2016

39



Table of Contents for the Digital Edition of SAMPE Journal - November/December 2016

Contents
SAMPE Journal - November/December 2016 - Cover1
SAMPE Journal - November/December 2016 - Cover2
SAMPE Journal - November/December 2016 - Contents
SAMPE Journal - November/December 2016 - 2
SAMPE Journal - November/December 2016 - 3
SAMPE Journal - November/December 2016 - 4
SAMPE Journal - November/December 2016 - 5
SAMPE Journal - November/December 2016 - 6
SAMPE Journal - November/December 2016 - 7
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