Dresden 2003 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 20: POSTER A
CPP 20.24: Poster
Montag, 24. März 2003, 19:00–21:00, ZEU/250
Finite deformation of glassy polymers: the influence of strain rate on post yield deformation behaviour and its implication into non-linear viscoelastic continuum modeling. — •Michael Wendlandt — ETH Zentrum, CNB E95, Universitätsstrasse 6, CH-8092 Zürich/Schweiz
Recent compression experiments performed with great accuracy on various glassy polymers revealed an interesting feature of post yield glassy deformation: strain rate dependence of the so-called strain-hardening modulus, i.e. the slope of the post yield “true stress - true strain”-curve. Common continuum models treat post yield deformation behaviour as the sum of two processes: a viscoelastic process with stress activated segmental motion, mostly described by an Eyring rate-process, and an additive contribution of the entanglement network represented by rubber-elasticity models. Inherent in this approach is that neither the rubber-elastic network contribution nor the viscoelastic process show post yield strain rate dependence of the strain-hardening modulus in contrast to our experimental findings. This disagreement can be overcome by the implication of a strain dependent “shear activation volume” vshear into common continuum models, where vshear, introduced by the Eyring rate process, represents the change of the stress dependent part of the activation energy for plastic flow with stress, and is commonly treated as a constant parameter intrinsic to the material. This is at least a doubtful assumption, since structural changes of glassy polymers during plastic deformation are present, promoting a non-constant “shear activation volume” as supported by our experiments.