Tensile stress overshoot in uniaxial extension of a LDPE melt

Wagner, Manfred H.; Raible, T.; Meissner, J.

doi:10.1007/bf01515835

Cited by 87 publications

(35 citation statements)

References 10 publications

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“…Steady stress following the stress overshoot was reported firstly by Rasmussen et al [11] and has been experimentally confirmed by comparing the measurements from the filament stretching rheometer and the cross-slot extensional rheometer [12], as well as by comparing the constant stretch rate and constant stress (creep) experiments [13]. Several models have been developed [12,14,15] for the attempt to understand the physics behind the stress overshoot. However, none of the models can be practically used for predicting the rheological behavior of LDPEs in industry, since the models contain numerous fitting parameters which are not directly related to molecular structures.…”

Section: Introductionmentioning

confidence: 70%

A new look at extensional rheology of low-density polyethylene

et al. 2016

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The nonlinear rheology of three selected commercial low-density polyethylenes (LDPE) is measured in uniaxial extensional flow. The measurements are performed using three different devices including an extensional viscosity fixture (EVF), a home made filament stretching rheometer (DTU-FSR) and a commercial filament stretching rheometer (VADER-1000). We show that the measurements from the EVF are limited by a maximum Hencky strain of 4, while the two filament stretching rheometers are able to probe the nonlinear behavior at larger Hencky strain values where the steady state is reached. With the capability of the filament stretching rheometers, we show that LDPEs with quite different linear viscoelastic properties can have very similar steady extensional viscosity. This points to the potential for independently controlling shear and extensional rheology in certain rate ranges.

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Section: Introductionmentioning

confidence: 70%

A new look at extensional rheology of low-density polyethylene

et al. 2016

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“…If we neglect the second term in brackets, i.e. the potential function have no dependence on the second invariant I 2 , (Wagner, Raible, and Meissner (1979)), then for the specific kinematics of a shear deformation, the expression for the shear stress can be written as (Larson (1988))…”

Section: B Nonlinear Viscoelasticity and The K-bkz Modelmentioning

confidence: 99%

A fractional K-BKZ constitutive formulation for describing the nonlinear rheology of multiscale complex fluids

Jaishankar

McKinley

2014

Journal of Rheology

134

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The relaxation processes of a wide variety of soft materials frequently contain one or more broad regions of power-law-like or stretched exponential relaxation in time and frequency. Fractional constitutive equations have been shown to be excellent models for capturing the linear viscoelastic behavior of such materials, and their relaxation modulus can be quantitatively described very generally in terms of a Mittag-Leffler function. However, these fractional constitutive models cannot describe the nonlinear behavior of such power-law materials. We use the example of Xanthan gum to show how predictions of non-linear viscometric properties such as shear-thinning in the viscosity and in the first normal stress coefficient can be quantitatively described in terms a nonlinear fractional constitutive model. We adopt an integral K-BKZ framework and suitably modify it for power-law materials exhibiting MittagLeffler type relaxation dynamics at small strains. Only one additional parameter is needed to predict nonlinear rheology, which is introduced through an experimentally measured damping function. Empirical rules such as the Cox-Merz rule and Gleissle mirror relations are frequently used to estimate the nonlinear response of complex fluids from linear rheological data. We use the fractional model framework to assess the performance of such heuristic rules and quantify the systematic offsets, or shift factors, that can be observed between experimental data and the predicted nonlinear response. We also demonstrate how an appropriate choice of fractional constitutive model and damping function results in a nonlinear viscoelastic constitutive model that predicts a flow curve identical to the elastic Herschel-Bulkley model. This new constitutive equation satisfies the Rutgers-Delaware rule. that is appropriate for yielding materials. This K-BKZ framework can be used to generate canonical three-element mechanical models that provide nonlinear viscoelastic generalizations of other empirical inelastic models such as the Cross model. In addition to describing nonlinear viscometric responses, we are also able to provide accurate expressions for the linear viscoelastic behavior of complex materials that exhibit strongly shearthinning Cross-type or Carreau-type flow curve. The findings in this work provide a coherent and quantitative way of translating between the linear and nonlinear rheology of multiscale materials, using a constitutive modeling approach that involves only a few material parameters.

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“…just close to the highest extensions of the experiments in the two figures above for the same elongational rates of e 0 = 0.1 s -1 and e 0 = 0.03 s -1 . Although the measured data accounted for a maximum, only, an overshoot was described theoretically by adapting the data to the MFS theory [23].…”

Section: Stressing Experimentsmentioning

confidence: 99%

Elongational experiments on polymer melts and their assessment

Münstedt¹

2013

AIP Conference Proceedings

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Abstract. Regarding the literature, steady-state values of the elongational viscosity are not widely documented and it is still an open question, whether the time-dependent elongational viscosity of strain-hardening polymeric materials runs through a maximum as a function of time before it reaches its steady state. For the assessment of molecular theories reliable experimental data are essential, however. From a survey of extensional experiments at constant elongational rates it becomes very probable that an extended stationary state of elongational exists and that maxima of the tensile stresses or even overshoot phenomena are due to non-uniform deformations of the samples. This conclusion is supported by creep experiments for which a steady state is reached at comparatively smaller total elongations corresponding to a better uniformity.

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Tensile stress overshoot in uniaxial extension of a LDPE melt

Cited by 87 publications

References 10 publications

A new look at extensional rheology of low-density polyethylene

A new look at extensional rheology of low-density polyethylene

A fractional K-BKZ constitutive formulation for describing the nonlinear rheology of multiscale complex fluids

Elongational experiments on polymer melts and their assessment

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