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Temperature Dependence of the Back‐Stress in Shear for Glassy Polycarbonate
Author(s) -
Negahban Mehrdad,
Strabala Kyle,
Delabarre Pierre,
Goel Ashwani,
Feng Ruqiang,
Grene Jean
Publication year - 2007
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.200751216
Subject(s) - polycarbonate , materials science , plasticity , stress (linguistics) , stress relaxation , shear stress , isothermal process , flow stress , composite material , glass transition , shear (geology) , stress–strain curve , mechanics , deformation (meteorology) , strain rate , forensic engineering , polymer , thermodynamics , creep , physics , philosophy , linguistics , engineering
Summary: Back‐stress is the equilibrium stress and represents conditions under which relaxation events in the material stop and the material can carry an applied load indefinitely without a change in strain. In most models for glassy polymers, back‐stress plays a central role since relaxation in materials is closely related to the distance of the current conditions from equilibrium. A number of these models that are commonly used for modeling glassy polymers use a modeling structure similar to large deformation plasticity. The flow rule for the plastic strain in these models are directly connected to the “over‐stress,” a properly invariant difference between the stress and the back‐stress. The importance of correctly evaluating the back‐stress to use in these models is clear. For this class of models, the authors have recently developed a method for directly calculating the back‐stress under shear deformations. This method is based on evaluating the slope of the stress‐strain response under conditions of similar elastic and plastic strain, but different strain rates. Since plastic flow goes to zero at equilibrium, the back‐stress can be found by locating points of zero plastic strain rate. Using the proposed method, the back‐stress in glassy polycarbonate has been evaluated under shear in isothermal tests going from room temperature to 120 °C, just below the glass transition temperature for polycarbonate. The proposed method provided a full map of the back‐stress for polycarbonate over a large range of shear strain and temperature.