Molecular Dynamics Simulation of Uniaxial Deformation of Glassy Amorphous Atactic Polystyrene

Abstract

Molecular dynamics computer simulations have been carried out of a chemically realistic many-chain nonentangled model of glassy atactic polystyrene under the influence of uniaxial mechanical deformation. Both the initial elastic and the postyield (up to 100% of the deformation) behavior have been simulated. The Poisson ratio, the Young modulus, and the temperature dependence of the yield peak are well reproduced. The simulated strain-hardening modulus is in quantitative agreement with existing experiments. The deformationally induced anisotropy in the global and local segmental orientation is accompanied by an anisotropy of the local translational mobility: the mean-square translational displacement of the individual segments in the direction of the deformation is drastically increased just beyond the yield point as compared to the isotropic sample. The mechanical deformation of a quenched sample leads to an almost complete erasure of the aging history.

Deforming glassy polystyrene: Influence of pressure, thermal history, and deformation mode on yielding and hardening

“…As can be seen in Table I our present and previous 25 simulation results are in accordance with experimental values for PS. Another way of interpreting the fast initial density decrease is that the Young modulus E is not negligible with respect to the bulk modulus K, as = ͑3K − E͒ / 6K.…”

“…For some mechanical properties such as the Young modulus, the yield peak, and the strain-hardening modulus this has been successful, as being illustrated by numerous studies on various polymer models, such as on bead-spring models [6][7][8][9][10][11][12][13] and on bead spring with bond-angle-potential models. [14][15][16][17] More chemically realistic MD simulations of polymers have been carried out on amorphous polyethylene ͑PE͒, [18][19][20][21][22][23] PS, [24][25][26][27] and PC. 24,[26][27][28] Also other simulation techniques are applied to study the deformation of polymers, such as Monte Carlo algorithms or variants of energyminimization methods for PE-alike, 29 polypropylene, 30,31 poly͑oxypropylene͒, 32 PC, [33][34][35] and PE.…”

“…The importance of mechanical history is recently observed. 27 Simulations on chemically detailed [25][26][27] and model polymers 16,17 showed that strain hardening can even occur for chains below the entanglement length contributing once more to the need for a view different from the rubber-elasticity theory of the physical mechanism behind strain hardening.…”

Strain hardening of polymer glasses: Effect of entanglement density, temperature, and rate

“…[9][10][11][12] For fundamental studies of strain hardening, compressive rather than tensile deformation is preferred because it suppresses strain localization. This allows the stress to be measured in uniformly strained systems.…”

“…4 In this paper we examine the effect of entanglement density, temperature, chain length, and strain rate on the strain hardening behavior of model polymer glasses. Several previous simulation studies have considered strain hardening, [9][10][11][12][13][14] but none have examined the factors controlling G R over a wide parameter space. This is desirable to understand the results of van Melick et al and other recent experiments.…”