Eisaku UMEZAKI and Tohru KAWAKAMI

Department of Mechanical Engineering, Nippon Institute of Technology, 4-1, Gakuendai, Miyashiro, Saitama, 345 Japan

(Received August 26, 1996; Accepted December 6, 1996)

A generalized phase-shift method is developed for automatic measurement of principal-stress directions in the whole field of a model from photoelastic experiments. This method uses a set of light intensities obtained from the rotation of polaroids in dark-field plane polariscopes at each point. To investigate the accuracy of the measurement, time-series light intensity curves with different noise and different numbers of data which constitute the curves are used in computer simulation. The error of the measurement of the principal-stress directions obtained by the method is not greatly affected by noise when the number of data exceeds 50. This method is applied to a circular disk subjected to a concentrated load. The principal-stress directions obtained by the method are found to be in good agreement with the theory.

Key words : experimental mechanics, photoelasticity, image processing, phase shift method, principal stress direction

*Presented at 1996 International Workshop on Interferometory (IWI f96), August 27-29, Wako, Saitama, Japan.