SAMPE Journal - March/April 2016 - 49

Feature Article

Figure 1. Bi-material strip
specimens at different
stages of cure.

promise in measuring OMC laminate displacement
and curvature compared to other techniques such as
LVDTs8. This paper describes a relatively simple and
innovative experimental approach of fabricating a bimaterial strip (BMS), comprised of a cast resin film on
a thin strip of metal, and using two-dimensional digital
image correlation (2D DIC) to capture displacements
with a high degree of sensitivity as the resin undergoes
cure shrinkage and thermal expansion/contraction
when subjected to a specific temperature cycle.

Experimentation
BMS Specimen Fabrication
The BMS specimens were comprised of a cast resin
film on a thin strip of aluminum metal. The resin
used in the fabrication of BMS specimens was Cytec
Engineered Materials (CEM) Cycom® 5320-1 medium
tough epoxy resin. The metal strips were cut from a
0.5 mm-thick sheet of 2024 aluminum. Prior to BMS
fabrication, the aluminum strips were machined
to the dimensions of 127 mm x 17 mm. In addition
to machining, the surface of the aluminum strips
was also prepared for bonding via grit blasting in
the areas where the resin was to be cast. The strips
were blasted with 50µm white aluminum oxide
until a uniform, matte finish was obtained. Grit was
propelled by dry, oil-free nitrogen. Remnant media
was cleaned from the aluminum strips using low-lint
tissues and acetone. Grit blasting with the fine media
was found to be the most effective surface preparation
for the materials in this study. Other methods that
were explored include: no surface preparation, grit
blasting with coarse media and scoring the surface
of the aluminum with several different grits of sand
paper. Final resin film dimensions were 1.95 mm
(thick) x 10 mm (width) x 100 mm (length). Figure 1
depicts the BMS specimen configuration.
The BMS specimens were cured at 90°C for 24
hours in a compression molding procedure at a
maximum pressure of 1 bar. This partially cures the
resin to a degree of cure of 0.51 with a glass transition

SAMPE Journal, Volume 52, No. 2, March/April 2016

temperature (Tg) of 104°C as measured by modulated
differential scanning calorimetry (mDSC). The
partially cured BMS strip shows some curvature as
can be seen in Figure 1 as a result of cure shrinkage
of the resin. Selected specimens were subjected to
specified temperature cycles that fully cured the resin
to a Tg of 236°C. The fully-cured specimens were used
to develop CTE data for the resin versus reduced
temperature. As can also be seen in Figure 1, the fully
cured strip has a larger resultant curvature.

Digital Image Correlation
In this study, the BMS specimens were coated with
an under-layer of white matte aerosol spray paint. A
speckle pattern was achieved on the surface of the
specimen by indirect deposition of black matte paint
splatters from a distance of 12 inches from the nozzle
and at a lateral distance of 6 inches away from the
direct path of the aerosol spray. Displacements in the
collected images were then obtained as the specimen
underwent additional curing during a specified timetemperature cure cycle. Image correlation and the
processing of deflection data was accomplished via
the use of the Correlated Solutions® Vic 2-D 2009
software program.
Images were collected utilizing the Vic 2-D 2009
software program and a 5 Megapixel 2448 x 2048 pixel
Sony ICX 625 CCD camera, fitted with a Nikon AF-S
Micro Nikkor 60 mm f/2.8G ED lens. The Vic 2-D 2009
software also allowed for the simultaneous collection
of time and temperature data using two k-type
thermocouples (one within 10 mm of the sample
and one within 10 mm of the thermocouple in the
oven) and a calibrated MTS® 6-Channel Temperature
Transmitter (which contained Phoenix Contact® MCRT-UI-E temperature measuring transducers). The
temperature transmitter was used to linearize the
collected output voltage of the thermocouples. The
output voltage was later converted to temperature
using the linear equation specified by the temperature
transmitter's calibration.

Table of Contents for the Digital Edition of SAMPE Journal - March/April 2016