MEASUREMENT OF STRAIN RATES IN REINFORCEMENT FIBERS

We have developed a highly sensitive method for measuring thermal expa nsion, mechanical strain and creep rates. We use the well-known techni que of observing later speckle with a linear array detector, but emplo y a novel data processing approach based on a two-dimensional spectral transform of the speckle history as recorded by the detector. This te chnique can effect large gauge sizes, which are important in the asses sment of the spatial statistics of creep. Furthermore, although the me asurement approach uses objective (non-imaged) speckle, the algorithm provides simultaneous global estimates of the strain rates at both sma ll- and large-scale sizes. Such estimates may be of value in investiga ting materials with different short- and long-range orders. General ad vantages of our technique are compact design, modest resolution requir ements, insensitivity to slow surface microstructure changes (as seen with oxidation) and insensitivity to zero-mean-noise processes such as turbulence and vibration. Herein we describe the theory of our proces sing algorithm, present results of measurements of strain in titanium wires and discuss the resolution limits of the measurement technique a nd subsequent data processing.