Photomechanics : a study of inelastic behaviour of polycarbonate of bisphenol A (1970)
AuthorsDanh, Tran-Xuanshow all
The photomechanical relationship of a polymer undergoing finite deformation is examined in light of basic considerations of the relationship between the index tensor and the mechanical tensors: the stress and strain tensor, and from the molecular mechanisms of birefringence and deformation.
For polycarbonate of bisphenol A, it is concluded that, in an isothermal deformation the index tensor can be expressed as a linear function of the strain tensor. For the range of principal strain difference studied (within .15) first order approximation of the linear photomechanical relationship is adequate for polycarbonate of bisphenol A. That is to say that the fringe order per unit optical path is proportional to the difference of the secondary principal strains and that the isoclinics represent the secondary principal strain directions.
Uniaxial tensile tests in the form of creep tests and stress relaxation tests, biaxial plane stress experiments, strain-freezing experiments and experiments involving mechanical non-coincidence are in agreement with the strain-optical law. The strain-fringe coefficient of polycarbonate of bisphenol A decreases with increasing temperature and decreases slightly at large strain in a room temperature deformation. Characterisation tests in uniaxial tension show that the time dependence of inelastic deformation of polycarbonate is non-linear with respect to the stress applied.
The Moire grid analyser method for the analysis of finite strain is presented. The method is well suited for strain measurements in studying inelastic behaviour of polymers.