DEFORMATION MECHANISMS AND YIELD STRENGTH IN AMORPHOUS POLYMERS

The paper starts with essentials of continuum mechanics, including sol utions for tension, compression, simple shear, pure shear, Poisson's r atio, ideal elasto-plastic body and the definition of yield strength. The phenomenology of yield is considered in terms of: state of stress and dependence on hydrostatic component; temperature effects and limit s; thermo-mechanical history effect; change of intrinsic properties (v olume, heat capacity and molecular conformations). Molecular theories of yield are reviewed, including state transition and conformational c hange theories (Eyring, Robertson, and others), free volume theories ( Rush and Beck), dislocation/disclinations theories (Bowden and Raha, a nd Argon) and segmental motion theories (Yannas and Stachurski). The m ost recent computer modelling results (Suter, Theodorou, Argon, Roe) a re described and discussed in terms of the microstructure of the amorp hous polymers and in relation to the previously proposed theories. (C) 1997 Elsevier Science Ltd.