The Large Deformation Mechanics of Annealed and Quenched Isotactic Polypropylene

Professor Ellen M. Arruda
Mechanical Engineering and Macromolecular Science and Engineering
University of Michigan
Ann Arbor, MI  48109
arruda@umich.edu
 
Sponsored by the Dept. of Engineering Mechanics and a grant provided by Professor Emeritus C. Wayne Martin

Date:  Tuesday, May 9, 2000
Time:  3:30 p.m.
Place:  W129 Nebraska Hall


Isotactic polypropylene (iPP) is a semi-crystalline thermoplastic widely used in industrial and commercial applications.  Annealed iPP forms a and b crystalline structures and the role of b crystals in toughening iPP has been the subject of recent investigations.  Large deformation studies of annealed b iPP in compression reveal a continual transformation of b crystals to a crystals with inelastic deformation.  The stress vs. strain responses of a and b iPP at room temperature are nearly identical to true strains in excess of -1.0 despite the different initial morphologies and the b ® a transition.  The morphological evolution, crystal deformation mechanisms and b ® a transition are examined over a range of strain rates and temperatures.

The morphology of quenched iPP includes nanoscale-sized a crystallites in an amorphous matrix.  The deformation mechanics of quenched iPP is of great technological significance because of the widely used processing techniques that produce the quenched morphology.  A viscoelastic-viscoplastic constitutive model for the strain rate dependent response of quenched iPP has been developed.  Theory comparisons with experiments will be discussed.