Photo-elasto-metric strain measurement - involves determination of magnitude and direction of principal strains at any point of two-dimensional specimen

摘要

The method uses two light-beams of different wave lengths, both processed simultaneously and in similar manner. Quarter-wave strips are rotated to detect the principal directions at a set point of the model. The rotation is made until the two signals corresponding the beams modulated by the rotating analyser are in-phase or out-of-phase, or until the alternating component of one of the signals has minimal amplitude. This gives a first position for the quarter-wave strip. The strip can be rotated by 45 deg. to give a second position. The phase difference between the two light beams at the second position gives a measure of the difference between principal strains.