Reversible strain gage

A reversible strain gage was developed for accurately measuring thermal strains, especially for use on large structures where strain gages cannot be welded. These strain gages can be peeled after taking required apparentstrain measurements in a furnace and can be attached reverse-side-up at the points of interest on a test structure. After many trials, a polyimide strain gage was developed that is the same on both the base side and the cover side. The thermal characteristics of the reversible strain gage—repeatability of apparent strain, gage-factor change, creep, drift and the output for a given mechanical strain—were investigated. The repeatability of apparent strains for 100 reversible gages was within 60 microstrain of difference at 250°C. The output of reversible gages for mechanical strain, after 2 to 3 heat cycles which were peeled and cemented in the reverse-side-up position, almost coincided with those of virgin reversible gages.Paper was presented at Fourth SESA International Congress on Experimental Mechanics held in Boston, MA on May 25–30, 1980