SAMPE Journal - March/April 2016 - 50
Feature Article
Figure 2. Bi-material strip testing apparatus.
BMS specimens were subjected to time-temperature
cure cycles in a convection heated environmental
chamber. BMS specimens were observed during
the cycle through a glass window on the door of the
chamber that was specifically designed for DIC. The
camera was mounted 78 cm (31 in) away from the
specimen on a level optics table that was built onto
the environmental chamber. Figure 2 displays the
manner in which the specimen was mounted to the
testing platform and also shows the location of the
camera that was used for image collection. Images
were collected every 6 seconds for the duration of the
time-temperature cycle.
The sample was mounted in an elevated clamping
fixture to permit a free length of 122 mm for all
specimens. This fixture held the specimen at a height
of 9 mm above the testing platform. Prior testing
indicated this height was necessary to avoid contact
with the platform due to significant relaxation of the
BMS specimens. After the BMS specimen was attached
to the elevated clamping fixture, the entire apparatus
was clamped to the testing platform using a c-clamp.
A black matte background was placed behind the
BMS specimen to reduce vibration caused by the
convection air flow and provide sample color contrast.
It is important to note that the BMS specimens were
not placed under load by any part of the experimental
(a) 38°C, 1/k = 155 mm
50
apparatus. In turn, this means that any deflections in
the BMS specimens were observed as a result of CS
or CTE.
The three images shown in Figure 3 are
representative of the deflections of the strip at different
temperatures during a prescribed temperature cycle.
The DIC software processes the images to provide the
x-y coordinates of 11 points along the length of the
strip (marked by red dots in Figure 3). These points
were fitted by a parabola (green curve in Figure 3)
and the curvature, k, of the strip is obtained by the
second derivative of y with respect to x of the curve.
Results
Data Reduction for Shrinkage-induced Curvature
The data reduction procedure used to date to
obtain cure shrinkage information from the BMS
experiment on partially-cured resin is based on the
assumption that the instantaneous curvature of the
specimen is the sum of an initial curvature, a thermal
expansion-related curvature caused by CTE and
modulus mismatch between the resin and substrate,
and curvature caused by the irreversible resin
shrinkage occurring during crosslinking. Both the
current curvature and its initial value are provided
by the DIC measurements. The thermal expansion
curvature is dominated by one-dimensional behavior
(b) 140°C, 1/k = 222 mm
(c) 219°C, 1/k = 401 mm
Figure 3. DIC images with fitted parabola and calculated curvature.
SAMPE Journal, Volume 52, No. 2, March/April 2016
Table of Contents for the Digital Edition of SAMPE Journal - March/April 2016
Contents
SAMPE Journal - March/April 2016 - Cover1
SAMPE Journal - March/April 2016 - Cover2
SAMPE Journal - March/April 2016 - Contents
SAMPE Journal - March/April 2016 - 2
SAMPE Journal - March/April 2016 - 3
SAMPE Journal - March/April 2016 - 4
SAMPE Journal - March/April 2016 - 5
SAMPE Journal - March/April 2016 - 6
SAMPE Journal - March/April 2016 - 7
SAMPE Journal - March/April 2016 - 8
SAMPE Journal - March/April 2016 - 9
SAMPE Journal - March/April 2016 - 10
SAMPE Journal - March/April 2016 - 11
SAMPE Journal - March/April 2016 - 12
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SAMPE Journal - March/April 2016 - 17
SAMPE Journal - March/April 2016 - 18
SAMPE Journal - March/April 2016 - 19
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SAMPE Journal - March/April 2016 - Cover3
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