Review of deformation and computer simulations in amorphous glassy polymers

As computer simulations become more accurate and faster, and feasible to run on desk-top computers, simulations of polymers and their deformation behaviour offers advantages over standard mechanical testing. This review paper concentrates on the academic aspects of computer simulations of amorphous polymers below the glass transition temperature. The review is preceded by the description of the mechanics of testing and the experimentally measured behaviour of amorphous polymers. The undeformed isotropic polymer can be represented by a dense network of randomly coiled and intertwined polymer chains. A starting point for the description of glassy polymer structure is the concept of densely packed, entangled, random Gaussian coils, derived from studies of polymer melts and solutions. Above the glass transition temperature (T_g), further structural details are provided by the Doi-Edwards theory and experimental measurements. Glassy polymer is formed because the irregular chain architecture prevents crystallisation. The equilibrium end-to-end distance of chains is compressed. The system falls out of equilibrium, becoming trapped in a complex minimum in potential energy phase space (becomes a glass) as its relaxation time rapidly increases beyond the normal experimental measuring time-scale. The image of the glassy structure of polymers has been enhanced by visual displays of unabridged computer simulations of amorphous polymer cells, pioneered by Theodorou and Suter, and now available in several software packages. Computer simulations are approached from the molecular mechanics of molecular dynamics points of view, based on special algorithms, known as Monte Carlo, Metropolis or Newton's equation of motion. Three levels of computer simulations are described: (i) atomistic, (ii) coarse-grain, and (iii) mesoscopic.