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This letter presents an initial version of an optical method for measuring and controlling strain over very short gauge lengths. Reflective indentations which are 200 μm apart are put in a steel microspecimen which is 3 mm long. When illuminated with a laser, interference fringes are produced; their motion is monitored with photomultiplier tubes. A computer system converts fringe motion to strain and controls the test. The specimen preparation and measurement system is described, and the control of peak cyclic strain at 1140 ± 10 μstrain is demonstrated.
Date of Publication: Aug. 2012