A Basic Study of the Strain Freezing in Photoplastic Experiments : Relationship between Fringe Order and Principal Strain in Biaxial Stress State

Abstract

Recently, to clarify the mechanism for material deformation during plastic working and to outline the guidelines for plastic design, it is necessary to develop the methods of stress-strain analyses in the elastoplastic and plastic states. In the previous paper, the authors attempted to find a possible strain freezing method in photoplastic experiments, and the results showed that a very fine linear relationship is maintained between the isochromatic fringe order N and principal strain difference (ε₁-ε₂) over a very wide range under the uniaxial tensile stress state. In this paper, we discuss the type of relationship between the fringe order and principal strain in the biaxial stress state. The discussions on the results obtained are based on the Moire method and photoplastic method in the use of the strip sheet and cross-type specimens of polycarbonate.