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

Abstract

ABSTRACT:The strain hardening behavior of model polymer glasses is studied with simulations over a wide range of entanglement densities, temperatures, strain rates, and chain lengths. Entangled polymers deform affinely at scales larger than the entanglement length as assumed in entropic network models of strain hardening. The dependence of strain hardening on strain and entanglement density is also consistent with these models, but the temperature dependence has the opposite trend. The dependence on temperature, rate, and interaction strength can instead be understood as reflecting changes in the flow stress. Microscopic analysis of local rearrangements and the primitive paths between entanglements is used to test models of strain hardening.

Challenges in Multiscale Modeling of Polymer Dynamics

“…The obtained scaling law is found to be consistent with the experimental results on different polymer classes for the entire range, from loosely to tightly entangled polymers [120]. Therefore, including the bending potential into the FENE model is a very common extension [16,[121][122][123]. For example, the FENE model with finite bending stiffness has been applied to study the static structure and dynamics of ring polymers [124][125][126].…”

“…The entropic network models [396,397], based on the rubber elasticity theory, produce good fitting to experimental data. However, the underlying assumptions in these theoretical models are found to be inconsistent with the molecular simulations [121][122][123]. For example, when the segments between entanglements are pulled taut, the corresponding energy contribution to the stress grows rapidly [122].…”

“…Aside from including a bending potential, there have now been a number of studies of the FENE model where the cutoff has been increased to include the attractive well, i.e., r cutoff =1.5∼2.5 σ. With the attractive well, the FENE model has been applied to study the glass transition temperature [127][128][129][130], scission and recombination in worm-like micelles and equilibrium polymers [131][132][133][134], surface tension [135], dielectric relaxation [136], polymer welding [137,138], strain hardening [121,122] and other properties.…”

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

“…Regarding the temperature dependence, it indeed has been found experimentally that the ratio Y / G h is fairly constant over a range of temperatures. 1,59 Simulations have shown 15 that also the dependence on strain rate is about the same for both Y and G h .…”

“…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.…”