We have developed a highly sensitive method for measuring thermal expansion, mechanical strain, and creep rates. We use the well known technique of observing laser speckle with a pair of linear array cameras, but employ a novel data processing approach that provides estimates of the time rate of in-plane strain. Our approach is appropriate for assessing very small strain rates in hostile environments. It provides simultaneous global estimates of the strain at both small and large gauge sizes. This may be of importance in studying materials with different short- and long-range orders. General advantages of our technique are compact design, modest resolution requirements, insensitivity to surface microstructure changes (as seen with oxidation), and insensitivity to zero mean noise processes such as turbulence and vibration. We detail the results of a number of experiments and of a simulation of vibration. These tests are intended to demonstrate the performance advantages of the transform method of processing speckle strain gauge data.
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