NEW SPECKLE TECHNIQUE FOR NONCONTACT MEASUREMENT OF SMALL CREEP RATES

A highly sensitive method for measuring thermal expansion, mechanical strain, and creep rates has been developed. This technique is based on Yamaguchi's speckle strain gauge concept, but uses a novel data-processing approach that provides estimates of the time rate of in-plane strain. The 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 the technique are compact design, modest resolution requirements, insensitivity to surface microstructure changes (as seen with oxidation), and relative insensitivity to zero-mean noise processes such as turbulence and vibration.