RESEARCH STUDY ON COLD DRAWING PHENOMENA IN HIGH POLYMERS
MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF MECHANICAL ENGINEERING
Pagination or Media Count:
A fundamental study of the phenomenon of cold-drawing plastic yield in polymers has been carried out, through which a better understanding of several of the features of this process has been achieved. The effects of temperature, thermal history, stress-field, chemical structure and pre- orientation on the stress-strain behavior of both glassy and crystalline polymers have been explored. The behavior of several polymers, particularly polystyrene and polymethyl methacrylate, in stress relaxation, relation-recovery cycling and creep, especially with respect to delayed drawing, was investigated in detail. The geometry of neck formation has been quantitatively investigated by photographic techniques, and volume changes during compression have been measured using a mercury dilatometer. Microscopic modes of yielding, particularly the formation of deformation bands, are described. Birefringence changes during deformation of polyacrylonitrile under various conditions and during hot and cold extension of polystyrene and polymethyl methacrylate are presented and related to the molecular processes believed to be occurring. The development of a molecular theory of drawing is attempted through three different paths of approach 1 a defect model analogous to dislocations, 2 a mathematical model of the fiber bundle type, and 3 a description in terms of the breakdown of secondary intermolecular cohesive bonding. General conclusions and recommendations for future studies in these areas are presented.