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Nonlinearly Viscoelastic Behavior of Polycarbonate. II. The Role of Volumetric Strain

Knauss, W. G. and Zhu, W. (2002) Nonlinearly Viscoelastic Behavior of Polycarbonate. II. The Role of Volumetric Strain. Mechanics of Time-Dependent Materials, 6 (4). pp. 301-322. ISSN 1385-2000. doi:10.1023/a:1021296110580.

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The creep responses of (bisphenol A) polycarbonate at 80°C undercombined two-dimensional shear with superposed tensile and compressivestress states were measured on Arcan specimens in the nonlinearlyviscoelastic regime. Of particular interest is the influence of thedilatational deformation component on the nonlinearly viscoelastic creepbehavior. Because the nonlinear material response determines the stressdistribution under fixed deformation or load, but is not known a priori,a re-estimation of the latter is essential to verify or adjust thestress state(s). This is accomplished by approximating isochronalstress-strain relations derived from shear creep behavior, encompassingthe nonlinear domain, by a classical incremental elasto-plastic materialdescription at appropriate times. To the extent that the two-dimensionalcharacter of the test configuration permits accessing three-dimensionalinformation, a coherent representation of the results is examined interms of maximum shear and/or octahedral representation. It is found that the creep behavior under shear and normal stressor deformation imposition differ significantly: When viewed as aresponse to the imposition of a maximum shear stress, the creepresponses differ depending on whether one or the other dominates. On theother hand, if the response is formulated in terms of an octahedraldescription the representation becomes less sensitive to normal vs.shear behavior. It is clear in either case, however, that normal strainhas a disproportionately large effect on creep response in shear. Withinthe precision underlying the measurements it is found that the shear andnormal strain components accumulate under creep in nearly constantratios. Under this scenario it is demonstrated clearly that theinfluence of negative dilatational stress (or deformation) on pure sheardeformation leads to distinctly lower creep rates. The converse is true,if positive dilatational stresses are added, though not monotonically so.

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Additional Information:© 2002 Kluwer Academic Publishers. Received 18 March 2002. This investigation was sponsored by the National Science Foundation. The authors are also grateful to Drs. V.K. Stokes and D.G. Legrand of General Electric Company: Dr. Stokes provided the test material and Dr. Legrand shared the optimized process for stress-relieving the material.
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Subject Keywords:dilatation-dependent shear creep, glassy polymers, nonlinear creep, nonlinear viscoelasticity, volume, yield-like behavior of polymers
Issue or Number:4
Record Number:CaltechAUTHORS:20200221-155049786
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Official Citation:Knauss, W., Zhu, W. Nonlinearly Viscoelastic Behavior of Polycarbonate. II. The Role of Volumetric Strain. Mechanics of Time-Dependent Materials 6, 301–322 (2002).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101476
Deposited By: Tony Diaz
Deposited On:22 Feb 2020 19:27
Last Modified:16 Nov 2021 18:02

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