The anisotropy of the elastic constants of transversely isotropic polyethylene terephthalate
TL;DR: In this paper, amorphous polyethylene terephthalate was stretched below the glass transition temperature to various degrees of orientation and the resulting material had transverse symmetry and, according to classical elasticity theory, its elastic behaviour could be described by five independent constants.
Abstract: Amorphous polyethylene terephthalate was stretched below the glass transition temperature to various degrees of orientation. The resulting material had transverse symmetry and, according to classical elasticity theory, its elastic behaviour could be described by five independent constants. Three could be calculated from Young's modulus experiments and the remaining two from torsional measurements. Such experiments were carried out using a 25 second (square) stress cycle. Increasing orientation (birefringence) caused an increase in Young's modulus in the stretch direction to about five times the isotropic value. The transverse modulus and the 45° modulus were little affected by orientation. The shear modulus involved when twisting about the symmetry direction also showed only small variations while the value of the other shear modulus decreased to about half the isotropic modulus. Calculations of the volume and linear compressibilities showed that oriented polyethylene terephthalate behaves under hydrostatic pressure essentially as the isotropic polymer of the same density. This observation implies two further relations between the elastic constants and thus the number of independent constants for the oriented material reduces from five to three.
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01 Jan 1971
TL;DR: A concise, self-contained introduction to solid polymers, the mechanics of their behavior and molecular and structural interpretations can be found in this article, which provides extended coverage of recent developments in rubber elasticity, relaxation transitions, non-linear viscoelastic behavior, anisotropic mechanical behavior, yield behavior of polymers and other fields.
Abstract: A concise, self-contained introduction to solid polymers, the mechanics of their behavior and molecular and structural interpretations. This updated edition provides extended coverage of recent developments in rubber elasticity, relaxation transitions, non-linear viscoelastic behavior, anisotropic mechanical behavior, yield behavior of polymers, breaking phenomena, and other fields.
2,335 citations
TL;DR: Several aspects of the mechanical properties of polymers are discussed in this paper, including linear and non-linear viscoelastic behaviour, anisotropy, rubber-like elasticity, breaking and cold drawing.
Abstract: Several aspects of the mechanical properties of polymers are discussed These include linear and non-linear viscoelastic behaviour, anisotropy, rubber-like elasticity, breaking and cold drawing
134 citations
TL;DR: In this paper, a series of polyethylene terephthalate fibres were made with a range of draw ratios, all from one sample of isotropic fibre, and their mechanical and optical properties were measured.
Abstract: Polyethylene terephthalate fibres in the drawn or extended state show considerable optical and mechanical anisotropy. In the undrawn state the fibres are essentially isotropic and the degree of subsequent anisotropy in the drawn state may be controlled by varying the amount of extension imposed. A series of polyethylene terephthalate fibres were made with a range of draw ratios, all from one sample of isotropic fibre, and their mechanical and optical properties were measured; the mechanical measurements were mainly those of extensional and torsional moduli whereas the optical properties were those of refractive indices and hence birefringence. An attempt to explain the development of both mechanical and optical anisotropy on a theoretical basis in terms of the orientation of the polymer molecules has met with limited success.
63 citations
TL;DR: In this article, the mechanical anisotropy of uniaxially oriented polyethylene terephthalate has been investigated at room temperature, assuming that the polymer is to a good approximation an anisotropic elastic solid.
Abstract: Poly(ethylene terephthalate) and related polymers show two dynamic mechanical transitions in the temperature range −180 to 150°C. There is a low-temperature transition (−40 to −100°C) and the glass transition (110 to 30°C). Nuclear magnetic resonance measurements show that large-scale molecular motions are associated with the glass transition only. The mechanical anisotropy of oriented polyethylene terephthalate) has therefore been studied in detail at room temperature, assuming that the polymer is to a good approximation an anisotropic elastic solid. Compression techniques on fiber monofilaments were developed to complete the determination of the five independent elastic constants for uniaxially oriented polymer. The measured elastic constants of the unoriented polymer lie between bounds obtained from averaging procedures based on the elastic constants of the oriented polymer. This suggests that molecular orientation is the predominant factor in determining the mechanical anisotropy below the gl...
37 citations
TL;DR: In this paper, the authors have made ultrasonic measurements at 10 MHz and between 190 and 270K on extruded samples of polypropylene and polyethylene terephthalate which have a wide range of crystallinity (0-0.6) and extrusion ratio (1-10).
Abstract: The authors have made ultrasonic measurements at 10 MHz and between 190 and 270K on extruded samples of polypropylene and polyethylene terephthalate which have a wide range of crystallinity (0-0.6) and extrusion ratio (1-10) by the use of quartz transducers directly bonded on to sample discs cut parallel, normal and at 45 degrees to the extrusion direction and have thus obtained all five elastic moduli. The results for polypropylene are considered in both the aggregate and the Takayanagi (1966) models. The aggregate model reproduces the development of mechanical anisotropy fairly well. The increase in the ultrasonic Young's modulus along the extrusion direction is much less than that previously observed in low-frequency-modulus data. The Takayanagi model shows that the stiffening effect of intercrystalline bridges is much less important for the ultrasonic moduli than for the room-temperature static moduli because of the much higher amorphous modulus for the glassy state.
32 citations
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TL;DR: The elastic constants of anisotropic materials have been studied in this article, where the elastic constants are defined as the ratio of the elasticity of a given material to its elasticity.
Abstract: (1956). The elastic constants of anisotropic materials—II. Advances in Physics: Vol. 5, No. 19, pp. 323-382.
265 citations
01 Nov 1962
TL;DR: In this article, expressions for the optical birefringence and elastic moduli of an idealized semicrystalline polymer in terms of the molecular orientation were derived for low-extension polyethylene at low extension ratios.
Abstract: Expressions have been derived for the optical birefringence and elastic moduli of an idealized semicrystalline polymer in terms of the molecular orientation. The predicted birefringence and moduli show qualitative agreement with previous experimental data for polyethylene at low extension ratios. A result of particular interest is that this treatment predicts the observed minimum in the Young's modulus with increasing orientation.
239 citations
01 Jun 1962
202 citations
01 May 1961
TL;DR: In this paper, the anisotropy of Young's modulus in samples of polyethylene, drawn by simple tensile loading so as to have transverse isotropy, is studied experimentally at room temperature, 20°C.
Abstract: The macroscopic physical properties of a partially crystalline polymer become anisotropic when the polymer is `drawn', i.e. when the polymer undergoes a large permanent deformation from its isotropic state. The anisotropy of refractive index, X-ray scattering etc. has been investigated by many workers. In this paper the anisotropy of Young's modulus in samples of polyethylene, drawn by simple tensile loading so as to have transverse isotropy, is studied experimentally at room temperature, 20°C. According to classical elasticity theory the Young's modulus of a transversely isotropic material can be defined completely in terms of three independent parameters. These have been chosen to be E0, E45 and E90, the Young's moduli at angles 0°, 45° and 90° to the symmetry axis respectively. It is found that: (a) the polar distribution of Young's modulus in highly drawn polyethylene (draw ratio 4.65) agrees well with the distribution predicted by classical elasticity theory; (b) at draw ratios up to approximately 1.2, E0, E45 and E90 all decrease from the isotropic value and E45 > E90 > E0; (c) at draw ratios greater than 1.2, E0 and E90 both increase with increasing draw ratio but E45 continues to decrease; (d) in the highly drawn material, draw ratio approximately 4.65, E0 similar, equals 1.5E90 similar, equals 12E45 similar, equals 5Eisotropic° These results are discussed in terms of the classical theory of elasticity.
84 citations