The Use of Extensional Rheometry to Establish Operating Parameters for Stretching Processes

Pearson, G. H.; Connelly, R. W.

doi:10.1007/978-1-4684-3743-0_50

Cited by 10 publications

(6 citation statements)

References 2 publications

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“…However the result is changed by the introduction of chain branching as we shall see in the following section. Moreover, tests have shown that a number of common polymeric materials do indeed show elastic instability at low Hencky strains[17]. It must be remembered that the above result is obtained for the limit of infinite Deborah numbers.…”

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confidence: 66%

“…Coggswell & Moore appear to have been the first to apply the analysis to polymer melts in the rubbery state, apparently as the result of a suggestion by J. R. A. Pearson [16]. Connelly and Pearson [17] subsequently used the analysis together with an integral constitutive equation of the K-BKZ type to quantify the transient extensional stress growth and ultimate strainto-failure of several diverse polymer melt specimens. Their results and other experimental observations are summarized in the review of Malkin & Petrie [5].…”

Section: Introductionmentioning

confidence: 99%

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The Considère condition and rapid stretching of linear and branched polymer melts

McKinley

Hassager

1999

Journal of Rheology

124

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We analyze the onset of 'necking' and subsequent filament failure during the transient uniaxial elongation of viscoelastic fluid samples in extensional rheometers. In the limit of rapid elongation (such that no molecular relaxation occurs) the external work applied is all stored elastically and the Considère criterion originally developed in solid mechanics can be used to quantitatively predict the critical Hencky strain to failure. By comparing the predictions of the Doi-Edwards model for linear homopolymer melts with those of the 'Pom-Pom' model recently proposed by McLeish & Larson (J. Rheol. 42,(1998) p.81-110) for prototypical branched melts we show that the critical strain to failure in rapid elongation of a rubbery material is intimately linked to the molecular topology of the chain, especially the degree of chain branching. The onset of necking instability is monotonically shifted to larger Hencky strains as the number of branches is increased. Numerical computations at finite Deborah numbers also show that there is an optimal range of deformation rates over which homogeneous extensions can be maintained to large strain. We also consider other rapid homogeneous stretching deformations, such as biaxial and planar stretching, and show that the degree of stabilization afforded by inclusion of material with long-chain branching is a sensitive function of the imposed mode of deformation.

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confidence: 66%

Section: Introductionmentioning

confidence: 99%

The Considère condition and rapid stretching of linear and branched polymer melts

McKinley

Hassager

1999

Journal of Rheology

124

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“…However, insufficient measurements are reported in the literature for firm conclusions to be drawn. For instance, tensile tests on some commercial grades of PMMA and polystyrene melts show that the failure strain is independent of strain rate [27]. Fundamental models on the dependence of failure strain upon molecular weight (distribution) in the rubbery state also appear to be lacking [28,29].…”

Section: Failure Strainmentioning

confidence: 99%

Deformation and failure maps for PMMA in uniaxial tension

Loock

Fleck

2018

Polymer

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Uniaxial tensile tests are performed on a polymethyl methacrylate (PMMA) grade over a range of temperatures near the glass transition and over two decades of strain rate.Deformation maps are constructed for Young's modulus, flow strength, and failure strain as a function of temperature for selected strain rates. The glassy, glass transition and rubbery regimes are identified, and constitutive relations are calibrated for the modulus, flow strength and failure strain within each regime.

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“…The FENE network over-predicts the magnitude of the strain-hardening growth in the normal stress difference that occurs just before the sample ruptures, while the modified network model gives more reasonable stress growth functions. The fact that the point of rupture occurs extremely close to the finite extensibility plateau should not be surprising, since the mass rupturing of network junctions dramatically reduces the rate of stress growth in the system and can lead to tearing or necking as implied in the Considère criterion [Considère (1885); Pearson and Connelly (1982); McKinley and Hassager (1999); Ng et al (2006)]. …”

Section: E Comparison With Other Non-linear Deformationsmentioning

confidence: 99%

Large amplitude oscillatory shear flow of gluten dough: A model power-law gel

McKinley

Ewoldt

2011

Journal of Rheology

143

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SYNOPSISIn a previous paper [Ng and McKinley (2008)], we demonstrated that gluten gels can best be understood as a polymeric network with a power-law frequency response that reflects the fractal structure of the gluten network. Large deformation tests in both transient shear and extension show that in the absence of rigid starch fillers these networks are also time-strain factorizable up to very large strain amplitudes ( ). In the present work, we further explore the non-linear rheological behavior of these critical gels by considering the material response obtained in large amplitude oscillatory shear (LAOS) over a wide range of strains and frequencies. We use a Lissajous representation to compare the measured material response with the predictions of a network theory that is consistent with the proposed molecular structure of gluten gels. In the linear viscoelastic regime, the Lissajous figures are elliptical as expected and can be quantitatively described by the same power-law relaxation parameters determined independently 2 from earlier experiments. In the non-linear regime, the Lissajous curves show two prominent additional features. Firstly a gradual softening of the network indicated by the rotation of the major axis. This feature is accounted for in the model by the inclusion of a simple non-linear network destruction term that reflects the reduction in network connectivity as the polymer chains are increasingly stretched. Secondly, a distinct upturn in the viscoelastic stress is discernable at large strains. We show that this phenomenon can be modeled by considering the effects of finitely extensible segments in the elastic network. We apply this model to other large amplitude transient flows such as the start-up of steady shear and extension. In addition to quantitative prediction of the evolution of stress in the gluten gel, we find that the onset of strongly non-linear unsteady phenomena such as edge instability in shear and sample rupture during extension can be understood as consequences of the finite extensibility and increased dissociation of the network filaments. (2008)] have shown that under small amplitude oscillatory conditions, as well as in large deformations in either shear or extension, the gluten gel can best be understood as consisting of flexible/semi-flexible segments that are interconnected to form a gel network. The interstitial spaces are filled with water but have minimal direct effect on the rheology as little or no solvent contribution to the total stress can be detected. For time scales that are greater than the Rouse relaxation time of the polymeric network segments, we also demonstrated that the quasi-linear behavior in an unfilled gluten gel is time-strain separable up to large strains and can be welldescribed by the generalized gel equation: 3 I INTRODUCTIONwhere is the finger strain tensor. The expression can also be rewritten in terms of the finite strain rate tensor in the following way:( 2) where [Bird et al. (1987a)].Our previous studies also showed that in start-up ...

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The Use of Extensional Rheometry to Establish Operating Parameters for Stretching Processes

Cited by 10 publications

References 2 publications

The Considère condition and rapid stretching of linear and branched polymer melts

The Considère condition and rapid stretching of linear and branched polymer melts

Deformation and failure maps for PMMA in uniaxial tension

Large amplitude oscillatory shear flow of gluten dough: A model power-law gel

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