雑音の影響を低減する位相シフト法による主応力方向測定の精度

抄録

An improved phase-shift method called a generalized one is used for automatically measuring the principal-stress directions in the whole field of a model. This method uses light intensity values obtained with the rotation of the polaroids in a dark-field plane polariscope at each point. In order to investigate the accuracy of the measurement, light intensity curves in time series with different noise, ΔI, different numbers of data which constitute the curves, n, and different fringe orders, N, and principal-stress directions, φ, at measured points are used in computer simulation. The magnitude and sign of noise are determined within the range of ±1% to ±20% of the light intensity at a point using random numbers. As a result, the accuracy of the principal-stress directions obtained by the method is not affected very much by noise for the number of data more than 50. The errors, |ΔΦ|, for N=0.1, 0.25 and 0.5 are 0.886, 0.290 and 0.221deg for n=100 and ΔI_max=±15%, respectively. Furthermore, the method is applied to the experimental images obtained from a circular disk subjected to a diametrically compressive load in a dark-field plane polariscope with a white lamp. The result is in good agreement with the theory except for region near the zero-and first-order fringes.