Whole field optical methods for structural mechanics: Digital speckle correlation and laser Doppler velocimetry

Optical measurement techniques offer advantages like non contact sensing and limited inertial effects and are hence usable in dynamic and hostile environments. Whole field techniques add the ability to make distributed measurements using a single sensor system. Two new distributed sensing techniques have been developed in this thesis, namely a scanning laser Doppler velocimeter for structural applications and a digital speckle correlation method for measurement of displacement along the line of sight.;In the first technique, an oscillating mirror scanner has been designed and used with a commercial LDV to obtain distributed velocity measurements. Two new data analysis techniques have been developed, the first based on time domain analysis of the scanning LDV output to simulate multiple independent sensors. The second technique is a frequency domain approach to directly obtain Chebyshev series approximations to spatial distributions of time independent and harmonically varying velocity distributions. The viability of the techniques has been established through tests on a rotating disk and a vibrating beam. These tests are the first reported applications of a scanning LDV to structural velocity sensing. The frequency domain technique represents a new approach to scanning LDV data processing. Comparisons to nonscanning LDV measurements and theoretical predictions have been made.;In the second sensing technique, a digital speckle correlation system has been developed for measurement of out of plane deflections of initially flat structures. A new contrast independent correlation scheme has been coupled to a projection speckle set up and used in sample tests to measure displacements and thus validate the measurement technique. The new correlation measure has been compared to the conventional cross correlation and also the recently introduced least squares correlation coefficients. Improvements and limitations have been pointed out, especially with reference to displacement measurement and the capability to handle the low contrast images associated with projection speckle images.