Optical determination of Poisson's ratio using dynamic photoelasticity
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A new optical method using dynamic photoelasticity to evaluate Poisson's ratio is presented. Theoretically, for the plane stress problem of an impulsively loaded cylindrical cavity embedded in an infinite, homogeneous, isotropic, linear elastic medium, the ratio of the principal stresses associated with the propagating compressional wave is Poisson's ratio. Experimentally, this is simulated by subjecting a thin transparent, birefringent plate to an explosive load acting at some internal point. By drilling a small hole in the plate, away from the explosive, it is possible to make use of the "hole method." The "hole method" allows the calculation of the values and directions of the principal stresses from the dynamic photoelastic response around the small hole. This assumes that the equations by Kirsch for defining the static stress field around a central hole in a biaxially loaded infinite plate, combined with the stressoptic law, apply. The experimentally determined ratio of the principal stresses, as the compressional wave passes, is then calculated. This is expected to be Poisson's ratio. To check the validity of the proposed optical method for Poisson's ratio measurement, another independent measurement is made. It consists of experimentally measuring the dilatational and Rayleigh wave velocities in a semi-infinite plate. The use of the Rayleigh Equation allows the calculation of Poisson's ratio. Reasonable agreement is found between the results of these two experimental measurements.