Strain Gauges

This semester we decided to attach strain gauges to the large solar oven in order to
characterize the strain of the glass over a range of temperatures. We used strain gauges
from Vishay® Micro-Measurements. We want to characterize the glass, because the users in
Nicaragua have had problems with glass cracking and breaking. The gauges come in pairs,
with each pair measuring strain in perpendicular directions along the surface. We attached
one of these pairs to the top glass outside the oven, one on the bottom glass inside the oven,
and one on a piece of thermally neutral material. The purpose of the thermally neutral
material is to calibrate the strain gauges for the strain of gauge itself due to thermal
expansion. We can subtract the strain reading from the thermally neutral material, from
the readings of the other surfaces to obtain measurements of the actual strain.
After several experiments, we believe the cycling of temperature changes caused the
gauges to become detached from the surfaces. The strain gauges that were in the oven
started producing data, which looked like it was from a strain gauge with a bad connection
after two or three experiments. The strain gauge on the top of the oven continued to give
good data for a few more experiments. This is probably because the temperature range on
the outside glass is less than that of inside the oven. The adhesive we used was M-Bond
600 from Vishay®. We were able to collect some data, but we do not have enough data from
the thermally neutral material to analyze the data from the inside and outside glass.
We have another adhesive we want to use to bond the gauges to the glass: Omega® OB-200.
This adhesive is designed to go through thermal changes, so we think that it will last longer
than the M-Bond 600. Next semester we plan to attach another strain gauge pair to the
thermally neutral material, inside glass and outside glass and collect enough data to figure
out what the strain of the glass is as a function of temperature.