Digital photoelasticity

Photoelasticity is an experimental technique for stress and strain analysis . The method is based upon an optical property called double refraction, or birefringence, of some transparent materials. The birefringence in a stres sed photoelastic model is controlled by the state of stress at each point i n the model. It is very useful for problems in which stress or strain infor mation is required for extended regions of the structure or member, and par ticularly for those having complicated geometry, complicated loading condit ions, or both. While the traditional areas of application have largely been taken over by numerical techniques, advances in computer technology and di gital image processing techniques have made photoelastic analysis more effi cient and reliable for solving engineering problems. The main aim of this r eview is to provide the reader with a brief background of the computer-base d digital image processing approaches for evaluation of photoelastic fringe patterns, and for the determination of isochromatic fringe orders and prin cipal stress directions from photoelastic images.