STRAIN-ANALYSIS OF NECK FORMATION AND PROPAGATION IN GLASSY-POLYMERS

The mechanism of the phenomenon of initiation and propagation of neck in polycarbonate of Bisphenol A tension specimens, which present a well-defined yield point, is analysed. A detailed analysis of the strain field in the whole specimen at definite loading steps before and during the neck initiation and propagation is undertaken by the mechanical interference (moiré) method. It was found that a strongly non-uniform strain field presenting localized maxima predominates in the neck. The three-dimensional character of this field is revealed and analysed. It was established that, as the neck propagates, the strain distribution in the necked region becomes more and more uniform, while the neck fronts tend to become normal to the boundaries of the specimen. The whole phenomenon of the initiation and evolution of the neck in polycarbonate is compared with the analogous phenomenon in metals and the similarities and differences between them are discussed and analysed. © 1979.