A model for the thermoviscoelastic behavior of physically aged polymers

Drozdov, Aleksey D.

doi:10.1002/pen.10245

Cited by 4 publications

(1 citation statement)

References 56 publications

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“…Formula (47) is determined by two adjustable parameters, a and ε: the coefficient a is the rate of sliding of junctions for a developed viscoplastic flow, and the strain ε characterizes transition to the steady flow. Equation (47) was successfully employed in our previous study on the viscoplastic response of iPP at small strains [42]. Similar relation was suggested in [43] to describe the time-dependent response of polyethylene melts.…”

Section: Materials Functionsmentioning

confidence: 68%

The effect of strain rate on the viscoplastic behavior of isotactic polypropylene at finite strains

Drozdov¹,

Christiansen²

2003

Polymer

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Two series of uniaxial tensile tests are performed on isotactic polypropylene with the strain rates ranging from 5 to 200 mm/min. In the first series, injection-molded specimens are used without thermal pre-treatment. In the other series of experiments, the samples are annealed for 51 hour at 160 • C prior to testing.A constitutive model is developed for the viscoplastic behavior of isotactic polypropylene at finite strains. A semicrystalline polymer is treated as an equivalent heterogeneous network of chains bridged by permanent junctions (physical cross-links and entanglements). The network is thought of as an ensemble of meso-regions connected with each other by links (lamellar blocks). In the sub-yield region of deformations, junctions between chains in meso-domains slide with respect to their reference positions (which reflects sliding of nodes in the amorphous phase and fine slip of lamellar blocks). Above the yield point, the sliding process is accompanied by displacements of meso-domains in the ensemble with respect to each other (which reflects coarse slip and fragmentation of lamellar blocks). To account for alignment of disintegrated lamellar blocks along the direction of maximal stresses (which is observed as strain-hardening of specimens in the post-yield region of deformations) elastic moduli are assumed to depend on the principal invariants of the right Cauchy-Green tensor for the viscoplastic flow.Stress-strain relations for a semicrystalline polymer are derived by using the laws of thermodynamics. The constitutive equations are determined by 5 adjustable parameters that are found by matching observations. Fair agreement is demonstrated between the experimental data and the results of numerical simulation. A noticeable difference is revealed between the mechanical responses of non-annealed and annealed specimens: (i) necking of samples not subjected to thermal treatment precedes coarse slip and fragmentation of lamellar blocks, whereas cold-drawing of annealed specimens up to a longitudinal strain of 80% does not induce spatial heterogeneity of their deformation; (ii) the elastic modulus increases with the strain rate for non-annealed specimens and decreases for annealed samples.

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Section: Materials Functionsmentioning

confidence: 68%

The effect of strain rate on the viscoplastic behavior of isotactic polypropylene at finite strains

Drozdov¹,

Christiansen²

2003

Polymer

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Rheological analysis of polyvinyl butyral near the glass transition temperature

Juang

Lee

Koelling

2001

Polymer Engineering & Sci

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In many polymer manufacturing operations, the material is processed near the glass transition temperature (Tg). Examples are thermoforming, blow molding, film blowing, hot embossing, forging, plastic welding, and de-airing in safety glass lamination. In these processes, solid-like behaviors such as strain hardening and yielding play important roles. These material properties cause the material to flow (or deform) in a way that substantially differs from a polymer melt. In order to understand the flow behavior near the Tg, polyvinyl butyral (PVB), a rubbery polymer used in safety glass lamination, was studied in this work. The flow properties of the polymer above the Tg were characterized by using both shear and elongational rheometers, and a tensile tester. The measured flow properties were described by a viscoelastic constitutive model.

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A constitutive model in linear thermoviscoelasticity of polymers based on the concept of cooperative relaxation

Drozdov¹

1999

Continuum Mechanics and Thermodynamics

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A model for the thermoviscoelastic behavior of physically aged polymers

Cited by 4 publications

References 56 publications

The effect of strain rate on the viscoplastic behavior of isotactic polypropylene at finite strains

The effect of strain rate on the viscoplastic behavior of isotactic polypropylene at finite strains

Rheological analysis of polyvinyl butyral near the glass transition temperature

A constitutive model in linear thermoviscoelasticity of polymers based on the concept of cooperative relaxation

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