Simulations of aging and plastic deformation in polymer glasses

Warren, Mya; Rottler, Jörg

doi:10.1103/physreve.76.031802

Cited by 68 publications

(96 citation statements)

References 36 publications

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“…Other workers later developed a dielectric relaxation method that also indicated enhanced mobility during uniaxial extensionMolecular dynamics computer simulations support the idea that mobility is enhanced during the deformation of polymer glasses. This work has utilized both atomistic models (polyethylene 25 and polystyrene 26 ) and more generic polymer representations [27][28][29] . Both translational displacements and bond vector reorientation occur more rapidly during deformation with enhancements larger than a factor of 100 being reported.…”

Section: Introductionmentioning

confidence: 99%

Measurement of Segmental Mobility during Constant Strain Rate Deformation of a Poly(methyl methacrylate) Glass

et al. 2014

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:We describe an apparatus for performing constant strain rate deformations of polymer glasses while simultaneously measuring the segmental mobility with an optical probe reorientation method. Poly(methyl methacrylate) glasses were deformed at T g -19 K, for local strain rates between 3.7x10 -5 and 1.2x10 -4 s -1 . In these experiments, the mobility initially increases in the pre-yield regime, by a factor of 40 to 160, as compared to the undeformed PMMA glass. The mobility then remains constant after yield, even as the stress is decreasing due to strain softening. This is consistent with the view that the sample is being pulled higher on the potential energy landscape in this regime. Higher strain rates lead to higher mobility in the post-yield regime and, for the range of strain rates investigated, mobility and strain rate are linearly correlated. We observe that thermal history has no influence on mobility after yield and that deformation leads to a narrowing of the distribution of segmental relaxation times. These last three observations are consistent with previously reported constant stress experiments on PMMA glasses. The experimental features reported here are compared to computer simulations and theoretical models.

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Section: Introductionmentioning

confidence: 99%

Measurement of Segmental Mobility during Constant Strain Rate Deformation of a Poly(methyl methacrylate) Glass

et al. 2014

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“…In Figure 3(a), the creep compliance J(t, t w ) = ǫ(t, t w )/σ is plotted as a function of wait time and stress. At small stress, the creep compliance takes the form of a stretched exponential at short times, changing to a logarithmic increase at t ≫ t w due to the effects of aging at long times [10,48]. For increasing wait time, the glass becomes stiffer and the creep compliance curves at short times can be superimposed to form a master curve by rescaling the time variable with a power law in t w ,…”

Section: B Step Stressmentioning

confidence: 99%

Deformation-induced accelerated dynamics in polymer glasses

Warren

Rottler²

2010

The Journal of Chemical Physics

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Molecular dynamics simulations are used to investigate the effects of deformation on the segmental dynamics in an aging polymer glass. Individual particle trajectories are decomposed into a series of discontinuous hops, from which we obtain the full distribution of relaxation times and displacements under three deformation protocols: step stress (creep), step strain, and constant strain rate deformation. As in experiments, the dynamics can be accelerated by several orders of magnitude during deformation, and the history dependence is entirely erased during yield (mechanical rejuvenation). Aging can be explained as a result of the long tails in the relaxation time distribution of the glass, and similarly, mechanical rejuvenation is understood through the observed narrowing of this distribution during yield. Although the relaxation time distributions under deformation are highly protocol specific, in each case they may be described by a universal acceleration factor that depends only on the strain.

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“…As a consequence, the response of glasses to an applied load depends not only on measurement time, but also on the wait time t w that has elapsed since the glass was formed. In general, increasing wait time makes glasses less compliant and increases their resistance to plastic flow [2,3,4,5,6,7,8,9,10,11,12,13,14]. For glasses formed through a rapid quench from the liquid state, the effects of aging take a particularly simple form: response functions such as the creep compliance obey a self similar scaling with the wait time and depend only on the ratio of t/t µ w .…”

Section: Introductionmentioning

confidence: 99%

Mechanical rejuvenation and overaging in the soft glassy rheology model

Warren

Rottler

2008

Phys. Rev. E

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Mechanical rejuvenation and over-aging of glasses is investigated through stochastic simulations of the soft glassy rheology (SGR) model. Strain-and stress-controlled deformation cycles for a wide range of loading conditions are analyzed and compared to molecular dynamics simulations of a model polymer glass. Results indicate that deformation causes predominantly rejuvenation, whereas overaging occurs only at very low temperature, small strains, and for high initial energy states. Although the creep compliance in the SGR model exhibits full aging independent of applied load, large stresses in the nonlinear creep regime cause configurational changes leading to rejuvenation of the relaxation time spectrum probed after a stress cycle. During recovery, however, the rejuvenated state rapidly returns to the original aging trajectory due to collective relaxations of the internal strain.

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Simulations of aging and plastic deformation in polymer glasses

Cited by 68 publications

References 36 publications

Measurement of Segmental Mobility during Constant Strain Rate Deformation of a Poly(methyl methacrylate) Glass

Measurement of Segmental Mobility during Constant Strain Rate Deformation of a Poly(methyl methacrylate) Glass

Deformation-induced accelerated dynamics in polymer glasses

Mechanical rejuvenation and overaging in the soft glassy rheology model

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