Application of Laser Speckle Interferometry to Measure Strain at ElevatedTemperatures and Various Loading Rates

摘要

This report investigates the application of speckle interferometry for themeasurement of strain when a material is subjected to various loading rates and elevated temperature conditions. The Medium Strain Rate Facility at the U.S. Army Materials Technology Laboratory was used to conduct uniaxial tension tests at strain rates of .00001/sec to .1/sec, temperatures up to 250 deg F and heating rates of 250 deg F/sec. Strain was measured by laser speckle interferometry technique and strain gages, the results of both methods were compared. Laser speckle interferometry was also used for the measurement of strain at large deformation, i.e., necking region of tensile specimens. The laser speckle interferometry results are in agreement with strain gage results at strain rates up to .1/sec for temperatures up to 250 deg F. This investigation also indicated laser speckle interferometry would be an excellent noncontact localized strain measuring device for adverse conditions if the following drawbacks were overcome. When using the ruby laser system, only one stress-strain data point can be obtained, the present system is not suited for strain rates over .1/sec and no results can be obtained if the specimen is heated to a point that it begins to emit intense red light. The shortcomings of laser speckle interferometry could be overcome by using another laser and data acquisition system. Keywords: Interferometry, Strain rate, Deformation temperature, Tension, Stress/strain relations, Speckle lasers. (cp)