Superposition of small strains on large deformations as a probe of nonlinear response in polymers

McKenna, Gregory B.; Zapas, L. J.

doi:10.1002/pen.760261103

Cited by 44 publications

(33 citation statements)

References 11 publications

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“…Of course, packing perturbations should be assigned to the above mentioned so called inter molecular fraction of the free volume. This result agrees with conclusions reported in [16][17][18][19]. How ever, unfortunately, it does not bring us closer to the real physical understanding of the observed experi mental picture.…”

Section: α Relaxationsupporting

confidence: 92%

“…The participation of chain motions in the plastic deformation of polymers has been analyzed in a num ber of papers [8,[15][16][17][18], in which chain dynamics during deformation was studied via the method of dynamic mechanical spectroscopy. These investiga tions led to the following results: complex shear mod ulus G*(ω) always declines with an increase in the deformation intensity, and the time spectrum of relax ation motions related to G* becomes narrower and shifts to short times.…”

Section: Introductionmentioning

confidence: 99%

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Effect of plastic deformation on the character of micro-brownian motions in glassy poly(methyl methacrylate)

et al. 2012

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Glassy PMMA samples are plastically deformed at room temperature in the uniaxial compression regime to residual strains of e res = 25%. Dielectric spectra of the initial and deformed samples are recorded via the method of broadband dielectric spectroscopy in the frequency range f = (5 × 10 -4 ) -10 7 Hz. The results are compared with the dynamic mechanical spectra of samples deformed under the same condi tions. Dielectric and mechanical spectra are noticeably distorted by deformation. As a result, dielectric per mittivity ε' increases, shear modulus G' decreases, and the intensity of dielectric β losses slightly increases, while dielectric and mechanical α losses increase appreciably. In addition, the "anomaly" of total dielectric Δε tot and total mechanical ΔG tot dispersions (Δε tot = ε 0 -ε ∞ ≈ Δε α + Δε β and ΔG tot = G 0 -G ∞ ≈ ΔG α + ΔG β ) occurs, that is, the polymer is transformed from the state with Δε α Δε β and ΔG α < ΔG β into the state with Δε α > Δε β and ΔG α > ΔG β . The described phenomenon is related to a strong gain in α dielectric and mechan ical losses in the deformed material. It is found that α losses increase owing to an anelastic deformation com ponent arising during glass loading. This component is responsible for an increase in the internal energy of the glass during its anelastic deformation. Possible causes of the observed effects are discussed.

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Section: α Relaxationsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Effect of plastic deformation on the character of micro-brownian motions in glassy poly(methyl methacrylate)

et al. 2012

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“…Experimentally, the structural relaxation times of deformed polymer glasses have traditionally been studied through rheological measurements, where the segmental dynamics are inferred from the mechanical response [10,[12][13][14][15]. In recent years, experiments and simula- * mya@ctbp.ucsd.edu tions have allowed researchers to directly probe the microscopic segmental dynamics during deformation.…”

Section: Introductionmentioning

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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“…A smaller exponent, with n closer to unity, is consistent with a broader spectrum of relaxation times for real materials, whereas exponents that approach unity as n tends toward zero describe a system that exhibits a much narrower distribution of viscoelastic time constants. McKenna and Zapas 25 impose a large deformation initially and then apply incremental strains at selected time intervals. Askadskii et al 17,26 use a nonlinear integral expansion representation of time-dependent stress to model nonlinear stress relaxation based on the rate of entropy generation.…”

Section: Stress Relaxationmentioning

confidence: 99%

Nonlinear stress relaxation in palladium(II) complexes with triblock copolymers of styrene and butadiene

Das

Belfiore

2004

J of Applied Polymer Sci

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Above 200% strain, the mechanical response of triblock copolymers which contain styrene and butadiene is modified significantly by complexation with dichlorobis(acetonitrile)palladium(II). This pseudosquare-planar transition metal salt forms -complexes with, and catalyzes the dimerization of, alkene groups in the main chain and the side group of Kraton's butadiene midblock. Between 10 and 100% strain, the plastic flow regime is similar for undiluted Kraton™ and its Pd 2ϩ complexes, but the level of engineering stress is approximately twofold larger for the complex that contains 4 mol % palladium(II) [Pd(II)]. Nonlinear stress relaxation measurements in the plastic flow regime (i.e., beyond the yield point but before the large upturn in stress) are analyzed at several different levels of strain. Transient relaxation moduli were modeled by a three-parameter biexponential decay with two viscoelastic time constants. The longer relaxation time for Kraton™ increases at higher strain, and in the presence of 4 mol % palladium chloride. A phenomenological model is proposed to describe the effect of strain on relaxation times. This model is consistent with the fact that greater length scales are required for cooperative segmental reorganization at larger strain. The resistance ⍀ to conformational reorganization during stress relaxation is estimated via integration of the normalized relaxation modulus versus time data. This resistance increases at higher initial jump strain because conformational rearrangements are influenced strongly by knots and entanglements at larger strain. The effect of strain on ⍀ is analyzed in terms of time-strain separability of the relaxation modulus. Linear behavior is observed for ⍀ versus inverse strain (i.e., 1/), and the magnitude of the slope [i.e., Ϫd⍀/d(1/)] is threefold larger in the absence of PdCl 2 (CH 3 CN) 2 .

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Superposition of small strains on large deformations as a probe of nonlinear response in polymers

Cited by 44 publications

References 11 publications

Effect of plastic deformation on the character of micro-brownian motions in glassy poly(methyl methacrylate)

Effect of plastic deformation on the character of micro-brownian motions in glassy poly(methyl methacrylate)

Deformation-induced accelerated dynamics in polymer glasses

Nonlinear stress relaxation in palladium(II) complexes with triblock copolymers of styrene and butadiene

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