Modeling the relaxation of polymer glasses under shear and elongational loads
| Autor: | Robyn L. Moorcroft, Suzanne M. Fielding, Ronald G. Larson, M. E. Cates |
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| Rok vydání: | 2013 |
| Předmět: |
Models
Molecular Materials science Polymers Constitutive equation FOS: Physical sciences General Physics and Astronomy 02 engineering and technology Work hardening Condensed Matter - Soft Condensed Matter 01 natural sciences Rheology 0103 physical sciences Physical and Theoretical Chemistry 010306 general physics Condensed Matter - Materials Science Deformation (mechanics) Relaxation (NMR) Materials Science (cond-mat.mtrl-sci) Disordered Systems and Neural Networks (cond-mat.dis-nn) Mechanics Strain hardening exponent Condensed Matter - Disordered Systems and Neural Networks 021001 nanoscience & nanotechnology Shear (geology) Soft Condensed Matter (cond-mat.soft) Glass 0210 nano-technology Shear flow |
| Zdroj: | Journal of chemical physics, 2013, Vol.138(12), pp.12A504 [Peer Reviewed Journal] The Journal of Chemical Physics |
| ISSN: | 1089-7690 |
| Popis: | Glassy polymers show 'strain hardening': at constant extensional load, their flow first accelerates, then arrests. Recent experiments under such loading have found this to be accompanied by a striking dip in the segmental relaxation time. This can be explained by a minimal nonfactorable model combining flow-induced melting of a glass with the buildup of stress carried by strained polymers. Within this model, liquefaction of segmental motion permits strong flow that creates polymer-borne stress, slowing the deformation enough for the segmental (or solvent) modes then to re-vitrify. Here, we present new results for the corresponding behavior under step-stress shear loading, to which very similar physics applies. To explain the unloading behavior in the extensional case requires introduction of a “crinkle factor” describing a rapid loss of segmental ordering. We discuss in more detail here the physics of this, which we argue involves non-entropic contributions to the polymer stress, and which might lead to some important differences between shear and elongation. We also discuss some fundamental and possibly testable issues concerning the physical meaning of entropic elasticity in vitrified polymers. Finally, we present new results for the startup of steady shear flow, addressing the possible role of transient shear banding. |
| Databáze: | OpenAIRE |
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