© Elsevier Sequoia S.A., Lausanne-- Printed in the Netherlands Yield Behavior of Unoriented and Oriented Polycarbonate and Polypropylene as Influenced by Temperature

The yield behaviors of an amorphous polymer (polycarbonate) and a crystalline polymer (polypropylene) were investigated over certain ranges of temperature. Both polymers were used in an unoriented (isotropic) and an oriented (anisotropic) condition. By using proposed yield criteria for the two structural conditions various theoretical yield loci are predicted; these are then compared with experimental findings based on a number of uniaxial and biaxial stress states. With a few exceptions that seem amenable to rational explanation the com-parison between theory and experiment is most promising. The onset of yielding is defined by two methods: using a 0.3 % offset and using the concept of plastic work. Similar findings result. Finally, for the range of parameters used in this study it is possible to compare individual results for a given material condition with a single yield locus, regardless of the temperature at which the tests were conducted. 1