Generalized Phase-shifting Method for Measuring Photoelastic Fringe Parameters and its Applications

A generalized phase-shifting method was developed for reducing the influence of noise caused by the variation in light intensity of a light source and so on, and for automatically measuring photoelastic parameters, relative fringe orders and principal-stress directions, in the whole field. The fringe orders obtained using the method were used to measure the stress intensity factor, and the principal-stress directions to extract the zero points. Furthermore the zero points were used to design structural members with holes. The stress intensity factor in a beam with a crack on one side subjected to a three-point bending was accurately obtained from fringe loops multiplied using a technique for drawing a contour map of the fringe order values. The zero points in a T-shaped plate subjected to a compressive load were accurately extracted using a technique for judging the zero points, and were effective to design the plate with holes.