Researchers at the NASA Lewis Research Center have developed a
unique strain gage and adhesive system for measuring the mechanical
properties of polymers and polymer composites at elevated temperatures.
This system overcomes some of the problems encountered in using
commercial strain gages and adhesives. For example, typical commercial
strain gage adhesives require a postcure at temperatures substantially
higher than the maximum test temperature. The exposure of the
specimen to this temperature may affect subsequent results, and
in some cases may be higher than the glass-transition temperature
of the polymer. In addition, although typical commercial strain
gages can be used for short times at temperatures up to 370 °C,
their long-term use is limited to 230 °C. This precludes
their use for testing some high-temperature polyimides near their
maximum temperature capability.
Lewis' strain gage and adhesive system consists of a nonencapsulated,
unbacked gage grid that is bonded directly to the polymer after
the specimen has been cured but prior to the normal postcure cycle.
The gage is applied with an adhesive specially formulated to cure
under the specimen postcure conditions. Special handling, mounting,
and electrical connection procedures were developed, and a fixture
was designed to calibrate each strain gage after it was applied
to a specimen. A variety of tests was conducted to determine the
performance characteristics of the gages at elevated temperatures
on PMR-15 neat resin and titanium specimens. For these tests,
which included static tension, thermal exposure, and creep tests,
the gage and adhesive system performed within normal strain gage
specifications at 315 °C. An example of the performance characteristics
of the gage can be seen in the figure, which compares the strain
gage measurement on a polyimide specimen at 315 °C with an
extensometer measurement.
Rabzak, C.; Pereira, J.M.; and Roberts, G.D.: Adhesively Bonded Strain Gages for Extended Use at 315 °C on Polymers. ASTM Workshop on Strain Gages in Mechanical Testing, Orlando, FL, 1996.
Rabzak, C.; Pereira, J.M.; and Roberts, G.D.: Adhesively Bonded Strain Gages for Extended Use at 315 °C on Polymers. Submitted for publication in J. Testing Evaluation, 1996.
Previous articleLast updated April 30, 1997
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