Prediction of the subyield extension and compression responses of glassy polycarbonate from torsional measurements

Pesce, Jean-Jacques; McKenna, Gregory B.

doi:10.1122/1.550843

Cited by 12 publications

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“…The large values of W 2 ( t ) show up in the observation that both the PMMA and PEMA were found to be non neo-Hookean. As a comparison, this is unlike polycarbonate for which a small value of W 2 ( t ) compared with W 1 ( t ) was reported . The observation of the weak W 2 ( t ) for polycarbonate may be related to its weak and main-chain β relaxation and requires further investigation.…”

Section: Discussionmentioning

confidence: 81%

“…As a comparison, this is unlike polycarbonate for which a small value of W 2 (t) compared with W 1 (t) was reported. 25 The observation of the weak W 2 (t) for polycarbonate may be related to its weak and mainchain β relaxation and requires further investigation.…”

Section: Discussionmentioning

confidence: 99%

“…At the same time the torsional moduli of the samples are approximately the same. 22,25 (The measurements are considered at the same strain magnitudes.) An obvious difference between polycarbonate and PMMA at ambient temperature is the large β-relaxation related to side chain motions observed in PMMA.…”

Section: Introductionmentioning

confidence: 99%

“…In particular, consideration of the limited data available in the literature for the normal force response vs strain for glassy polymers reveals that at ambient temperature the normal force response of poly(methyl methacrylate) (PMMA) can be as much as three times that of polycarbonate. At the same time the torsional moduli of the samples are approximately the same. , (The measurements are considered at the same strain magnitudes.) An obvious difference between polycarbonate and PMMA at ambient temperature is the large β-relaxation related to side chain motions observed in PMMA .…”

Section: Introductionmentioning

confidence: 99%

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Microscopic Origins of the Normal Force Responses of Glassy Polymers in the Subyield Range of Deformation

Flory

McKenna

2005

Macromolecules

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Results from torsional stress relaxation experiments in which we measure the torque and normal force responses of two glassy poly(alkyl methacrylate)s are presented. Tests were performed at temperatures ranging from the dynamic glass transition (α-relaxation) to the first sub-glass transition relaxation (β-relaxation) and in the sub-yield range of deformations (strains ranging from 0.02 to 0.045) and at a fixed aging time of 4980 s. We found a significant difference between the relaxation behavior of the normal force response and the torque response of poly(methyl methacrylate) (PMMA). The results provide evidence that the normal force of PMMA is influenced by the β-relaxation. For specimens having a longer side chain length, i.e., poly(ethyl methacrylate) (PEMA), the difference between the normal force and torque relaxation behaviors is less. This is consistent with the less pronounced β-relaxation mechanism in PEMA. Furthermore, an examination of the effect of temperature on the ratio of the normal force modulus to the shear modulus of PMMA provides strong evidence that the normal force modulus relaxes faster than the shear modulus as the β-relaxation is approached. Also, following the scaling law relations of Penn and Kearsley, the derivatives of the strain energy density function with respect to the first and second invariants of the strain tensor were determined. Finally, the departure of the strain energy density function behavior of PMMA and PEMA from the neo-Hookean material behavior is shown.

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Section: Discussionmentioning

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Microscopic Origins of the Normal Force Responses of Glassy Polymers in the Subyield Range of Deformation

Flory

McKenna

2005

Macromolecules

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“…We propose a unified model for subyield stress−strain behavior in glassy materials at different strain rates and temperatures. For tests at a constant strain rate, the model predictions are compared with experimental data for CALIBRE 200-10 (trademark of The Dow Chemical Company), an amorphous polymer glass bisphenol A polycarbonate with melt flow rate approximately equal to 10 (PC). − The test appears favorable for the model.…”

Section: Glass State Kinetics: a Physical Picturementioning

confidence: 99%

Stress-Biased Rearrangements and Preyield Behavior in Glasses

et al. 2006

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On the basis of a physical picture of a glass as a mosaic of mesoscopic clusters differing in their yield characteristics, we propose a model for the preyield behavior in glassy materials; the model describes the stress-strain relationship at different strain rates in terms of one reduced variable. A test using experimental data for polycarbonate materials at different rates and temperatures appears favorable for the model. The model may be used to interpolate and extrapolate limited experimental data, and also provides a practical means to assess dynamic heterogeneities within polymeric glasses. When applied at different temperatures, the model gives insight into the dependence of the excitation energies on temperature (glassformer fragility) in the glassy state.

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Viscoelasticity

McKenna¹

2002

Encyclopedia of Polymer Science and Technology

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A broad view of polymer viscoelasticity is presented. The article first discusses the basic definitions of stress and strain and the material modulus and compliance properties that relate the two in linear elasticity theory. The time‐dependent analogues in viscoelasticity are presented. The beginnings of polymer viscoelasticity concepts are then presented by building mechanical analogues of springs (elastic) and dashpots (viscous) elements that can capture the general features of polymeric behavior. A brief discussion of the elastic–viscoelastic correspondence principle is also provided. The general viscoelastic response of polymeric materials is presented by emphasizing the amorphous state and how the isochronal modulus changes with temperature. This is analyzed within the context of time–temperature superposition ideas and the Williams, Landel, and Ferry equation. In particular, it is interesting to divide the behavior into that below and far above the glass‐transition temperature. In the former case the local segmental motions of the polymer dominate behavior, while in the latter the long‐chain nature of the polymer dominates behavior. Molecular rheology ideas are briefly presented where the idea of the chain length or molecular weight dependence of the viscosity is introduced. This is extended by considering the scaling of viscosity and plateau modulus due to concentration as well as the introduction of time–concentration superposition principles similar to time–temperature principles. The nonlinear rheological response of polymers far above the glass‐transition temperature is handled within a combined framework of the phenomenological K‐BKZ model and the Doi–Edwards (DE) tube model, which is based on the reptation ideas of de Gennes. The K‐BKZ framework is particularly useful because it looks much like time‐dependent finite elasticity theory that has been widely and successfully applied to rubber network polymers. Extensive discussion is presented of the comparison between theory and experiment of both K‐BKZ and DE models for polymer nonlinear viscoelastic behavior in the melt and solution states. Below the glass‐transition temperature, measurements of the nonlinear viscoelastic response are examined within the framework of the BKZ model, but also considering compressibility. Emphasis is given to torsional experiments in which both the torque and the normal force are measured. This exposition is followed by a description of several other nonlinear viscoelastic models that have been used for describing solid polymers. This article ends with a brief mention of plasticity models for the behavior of polymeric solids.

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Prediction of the subyield extension and compression responses of glassy polycarbonate from torsional measurements

Cited by 12 publications

References 0 publications

Microscopic Origins of the Normal Force Responses of Glassy Polymers in the Subyield Range of Deformation

Microscopic Origins of the Normal Force Responses of Glassy Polymers in the Subyield Range of Deformation

Stress-Biased Rearrangements and Preyield Behavior in Glasses

Viscoelasticity

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