Mechanical properties of model polyethylenes: tensile elastic modulus and yield stress

Crist, Buckley; Fisher, Christopher J.; Howard, Paul R.

doi:10.1021/ma00194a035

Cited by 247 publications

(206 citation statements)

References 9 publications

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“…This is an alternative presentation of the above observation that the strain rate dependence of e y decreased with increasing temperature under the same strain rate dependence of y . Other y =e y variation results follow the general, reported results on the Young's modulus, 13 e.g., y =e y was lower at higher temperature but higher for more developed structure. A slightly negative strain rate dependence observed for 20 C, which is unusual, originates from the secant modulus calculation at the load maximum but not from the intrinsic material properties.…”

Section: Resultssupporting

confidence: 76%

Yield Strain Behavior of Poly(ethylene terephthalate): Correlation with Yield Stress Behavior in Strain Rate, Temperature, and Structure Dependence

Lim

Kim

2004

Polym J

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Studies on the mechanical properties of polymers such as yield behavior have been the keys to successful use of polymers in various mechanically functional purposes. The yield behavior of polymers has been investigated by using polymers with varying structure (copolymer structure and composition, 1,2 amorphous or crystalline, 3,4 differential orientation and crystallinity, 5,6 presence of functional linkage, 7 etc.). Strain rate and temperature have been the experimental parameters in those studies, as polymeric molecules display temperature and rate dependent phenomena. On the nature of the yield behavior of polymers, there have been reported a variety of phenomenological descriptions and molecular interpretations. One is to correlate the yield behavior with secondary mechanical relaxation behavior. 2,[6][7][8] It is based on the general understanding that such relaxations mediate macroscopic mechanical properties. We previously observed for oriented, semicrystalline poly(ethylene terephthalate) (PET) that tan maxima of both primary and secondary relaxations are linear increasing functions of the activation volume calculated by the Eyring's yield model. 6 All the above researches have focused mainly on the yield stress with no particular interest on the yield strain. In practical cases in mechanical applications, however, an elongational limit before the onset of a plastic deformation is also critical. To our knowledge, only one article can be found in the literature focusing on the yield strain, 9 in which it was reported that there is a transition in the yield strain for polyethylene at a temperature where a change in deformation mode occurs from elastic-plastic to viscoelastic manner. In this study, we report the yield strain variation in PET as a function of stain rate, temperature, and PET structure to reveal the similarity and difference with the yield stress behavior. In addition, a novel dimensional analysis correlating the yield strain with the activation volume of the yield was proposed. EXPERIMENTALPET samples with varying orientation and crystallinity were produced by the high speed melt spinning of high molecular weight PET (intrinsic viscosity of 0.98 dL/g). PET was extruded at a constant mass flow rate and spun at a take-up velocity range of 2.5-5.5 km/min to have different degree of melt draw ratio. Details of the melt spinning process and characterization methods are reported elsewhere, 10 and the properties of PET samples are listed in Table I. Tensile tests were performed using an Instron 4303 equipped with a temperature-controlling chamber. Measurements were done at various temperatures, e.g., 20, 50, and 75 C. Filament sample was clamped under a pretension of 0.01 g/den and placed inside the chamber preset to a desired temperature. The tensile test started after the thermal force generated in the sample became equilibrium (after 300 s).11 To impose strain rate variation, the crosshead speed varied at 0.3-300 mm/min at a constant gauge length of 50 mm corresponding to seven nominal strain ra...

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Section: Resultssupporting

confidence: 76%

Yield Strain Behavior of Poly(ethylene terephthalate): Correlation with Yield Stress Behavior in Strain Rate, Temperature, and Structure Dependence

Lim

Kim

2004

Polym J

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“…1a). Figure 2 illustrates changes in density ρ of the com puter sample during its cooling from 250 to 50 K. At 50 K, ρ = 0.996 g/cm 3 , a value that agrees with the experimental data [44][45][46][47][48]. Volume thermal expan sion coefficient β v shows a jump at ≈165 K; in this POLYMER SCIENCE Series A Vol.…”

Section: Structure Of the Initial Computer Glasssupporting

confidence: 74%

Plastic deformation of glassy polymethylene: Computer-aided molecular-dynamic simulation

et al. 2010

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“…As both the (log) modulus and the yield stress were directly related to the crystallinity, the yield stress-(log) modulus relationship should be simple [6,18,[33][34][35][36]. The yield stress-(log) modulus relationship is often studied on polyethylene [33][34][35], however in these studies the PE crystallite thickness is frequently changed at the same time as the PE crystallinity and probably also the aspect ratio of the crystallites. Since the T6A6T segments of the studied segmented block copolymers were mono-disperse in length, the crystallite thickness in these copolymers was expected to be constant and also the crystallinity of the T6A6T segments was constant.…”

Section: Dmtamentioning

confidence: 99%

Tensile properties of segmented block copolymers with monodisperse hard segments

2008

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The tensile properties of segmented block copolymers with mono-disperse hard segments were studied with respect to the hard segment content (16-44 wt.%) and the temperature (20-110°C). The copolymers were comprised of poly(tetramethylene oxide) segments with the molecular weights of 650-2,900 Da and of mono-disperse bisester-tetra-amide segments (T6A6T) based on adipic acid (A), terephthalic acid (T) and hexamethylene diamine (6). An increasing content of T6A6T gave rise to an increased modulus, yield stress and fracture stress. The modulus could be modeled by a composite model. Moreover, a strain-softening was observed well below the yield stress, due to the shearing of the T6A6T crystallites. At strains [200%, a strain-hardening of the PTMO segments took place and this even for PTMO segments that were amorphous in the isotropic state. The strain hardening increased the tensile properties. An increase in temperature had little effect on the modulus of the copolymers, but was found to lower the yield and fracture stresses. At temperatures above the melting temperature of the oriented PTMO, no strain-hardening took place. The yield stress as a function of temperature could be described by the Eyring relationship, but a modulus-yield stress relationship could not be established.

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Mechanical properties of model polyethylenes: tensile elastic modulus and yield stress

Cited by 247 publications

References 9 publications

Yield Strain Behavior of Poly(ethylene terephthalate): Correlation with Yield Stress Behavior in Strain Rate, Temperature, and Structure Dependence

Yield Strain Behavior of Poly(ethylene terephthalate): Correlation with Yield Stress Behavior in Strain Rate, Temperature, and Structure Dependence

Plastic deformation of glassy polymethylene: Computer-aided molecular-dynamic simulation

Tensile properties of segmented block copolymers with monodisperse hard segments

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