TRANSFORM METHOD OF PROCESSING FOR SPECKLE STRAIN-RATE MEASUREMENTS

We have developed a highly sensitive method for measuring thermal expa nsion, mechanical strain, and creep rates. We use the well-known techn ique of observing laser speckle with a pair of linear array cameras, b ut we employ a data-processing approach based on a two-dimensional tra nsform of the speckle histories from each camera. This technique can e ffect large gauge sizes, which are important in the assessment of the spatial statistics of creep. Further, the algorithm provides simultane ous global estimates of the strain rates at both small- and large-scal e sizes. This feature may be of value in the investigation of material s with different short- and long-range orders. General advantages of o ur technique are compact design, modest resolution requirements, insen sitivity to slow surface microstructure changes (as seen with oxidatio n), and insensitivity to zero-mean-noise processes such as turbulence and vibration. Herein we detail the theory of our technique and the re sults of a number of experiments. These tests are intended to demonstr ate the performance advantages and limitations of the transform method of processing speckle strain-rate data.