Pichet PINIT and Eisaku UMEZAKI

Department of Mechanical Engineering, Nippon Institute of Technology, 4-1 Gakuendai, Miyashiro, Saitama 345-8501, Japan

(Received September 16, 2004; Accepted April 7, 2005)

In this paper, we propose a new three-wavelength method for automatic measurement of principal-stress directions over an entire model on the basis of four-step phase shift method. This method uses four fringe patterns captured by a color charge-coupled devices (CCD) camera corresponding to four angular position arrangements of polaroids in a dark-field plane polariscope. The principal-stress directions can be determined by a single calculation. The method is applied to a circular disc under compression. The principal-stress direction distributions obtained from the proposed method are compared with those obtained from a conventional method and theory. It can be obviously seen that the proposed method accurately yields the principal-stress directions compared with the conventional method.

Key words: photoelastic experiment, plane polariscope, phase-shift method, principal-stress directions, isoclinic angles, image processing