Full-field random bending strain measurement of a plate from vibration measurements

Experimental results of a non-contacting, full-field measurement of random bending strain over the surface of a two-dimensional structure are presented. The method is based on a combination of the measurement of random vibration at discrete points on the structure using a scanning laser vibrometer along with an analysis of the measured data using a surface smoothing technique. The power spectral densities of the random bending strains at all points on the structure are estimated by the numerical differentiation of cross-spectral densities of the vibration measured by two transducers, a fixed reference transducer and a roving (or scanning) transducer. The experimental results are compared with those measured directly using strain gages, which shows very good agreement.