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  • Physics  (13)
  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 9 (1971), S. 801-814 
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of temperature and strain rate on the compressive yield behavior of polystyrene is compared with the effect of the same variables on crazing in tension. The results support the conclusion of other, more extensive work, which shows that crazing involves the same types of molecular processes as those which occur during deformation under compression and shear. An improved method of measuring compressive stress-strain curves is then described, and the compressive yield stress is also compared with an extrapolated tensile yield stress. The difference between the two is in line with concepts which assume a dependence of yield stress on the state of hydrostatic tension (or compression). It can be adequately described by the Mohr-Coulomb yield criterion. Application of this criterion also enables a theoretical stress strain curve in tension to be derived from other results in compression. Comparison of the tensile stress-strain curve so obtained with those which can be directly measured with other plastics, supports the hypothesis that crazing is favored by a marked decline in engineering stress during tensile elongation (plastic instability).
    Additional Material: 7 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 7 (1969), S. 219-229 
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The compressibility of polyisobutylene and polystyrene above their glass transition temperature is treated as the sum of two parts; a free-volume compressibility and, as originally suggested by Bridgman, a compressibility of the molecules themselves. Two different models are used to treat the free-volume compressibility, and as a result values for the molecular compressibility are estimated. These are in reasonable agreement with other values in the literature. The magnitude of this “molecular compressibility” is then considered in relation to some existing treatments of intermolecular forces. These suggest that intermolecular contacts are more compressible than covalent bonds, and on this basis the observed levels of molecular compressibility can be explained.
    Additional Material: 6 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 15 (1977), S. 955-967 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: It has been previously shown that when rigid poly(vinyl chloride) is extended by fully necking the test-piece, subsequent fracture takes place by a novel mechanism. Surface crazes grow into “diamond” -shaped cavities which slowly expand while retaining their shape. We have now found that this new mechanism is of general applicability to a wide range of plastics which fracture after yielding. Examples are given from polycarbonate, poly(ether sulfone), and poly(methyl methacrylate) broken at elevated temperatures. The form of the diamond cavity is determined by the continuation of plastic deformation in the whole test-piece while the diamond grows bigger. After fracture a characteristic cavity is left behind on the fracture surface which demarcates the zone of slow growth. At a given point, which is generally easily observable on the fracture surface, the crack speeds up. This change is believed to correspond to a situation where enough elastic energy is available to propagate a crack. It is favored, not only by the increase in size of the diamond in the test-piece but also by an increase in the average energy stored per unit volume of material.
    Additional Material: 9 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 11 (1973), S. 2423-2439 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The extension and fracture under tension of poly(vinyl chloride) strips of different lengths have been studied. It was found that, in spite of decreasing strain rate, long pieces are subject to a type of brittle fracture (necking rupture) occurring immediately after neck formation. This result, which could be expected from previous work, is shown to depend on the elastic energy stored in the longer test pieces. This energy is converted to heat under conditions of neck formation, leading to a temperature rise of 24 ± 4°C, determined by a thermal imaging system. With short test pieces the rise in temperature is much smaller, and a transition to stable neck propagation occurs. Optical and electron micrographs provide additional evidence of heating at the fracture surface. A semiquantitative treatment of the adiabatic process gives upper and lower limits for the predicted temperature change neglecting thermal losses. It is also possible to estimate a minimum length for the initiation of adiabatic deformation. Both calculations give results in reasonable agreement with experiments. Observations with polycarbonate show a similar length effect at low temperatures.
    Additional Material: 9 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 16 (1978), S. 1169-1179 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A craze may fracture either by the breaking of covalent bonds or by a process of “viscous rupture” involving the movement of bulk material in the craze. In the latter case it is necessary that the majority of the chain ends of the polymer molecules passing through the craze-matrix interface terminate within the craze. We have therefore calculated the probability of a polystrene macromolecule spanning a thin craze and shown that for viscous rupture a craze in a normal commercial polystyrene must be something more than 40 nm thick. As the measured craze thicknesses have generally exceeded 100 nm, a viscous fracture process is clearly possible, though, of course, chain rupture is not excluded by the argument. More difficulties arise when fracture occurs within a specified region of the craze and the possibility of a bond fracture under these circumstances is briefly discussed.
    Additional Material: 4 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 16 (1978), S. 1291-1295 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Thermoelastic measurements on a glassy polymer make it possible to measure directly the quantity αV/Cp where α is the coefficient of linear expansion, V the specific volume, and Cp the specific heat at constant pressure. By further measuring the bulk modulus (BT) it is possible to derive a relatively accurate value of the thermodynamic Gruneisen constant (γT) where γT = 3BTαV/Cv. The values obtained decrease only slightly with temperature.
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 16 (1978), S. 1277-1290 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The thermoelastic effect has been measured in compression on four glassy polymers; namely, polystyrene, poly(methyl methacrylate), polycarbonate, and epoxy resin. Quantitative results have been obtained for the first time on three of these polymers. It has been shown that by paying attention to specimen geometry and instrumentation results can be obtained to a high degree of accuracy (better than ±1.5% on a given set of measurements). The polymers are shown to obey the classical Thompson equation for thermoelasticity in solids over the temperature range studied (ca. 220-350°K). By inference such materials can be expected to behave classically in general. The results have been used, as first suggested by Trainor and Haward, to obtain values for the linear thermal expansion coefficient and the values so obtained are shown to be in excellent agreement, in general, with literature values obtained by more conventional methods. Results are given for a range of stress from 5 MN m-2 to between 25 and 50 MN m-2 according to ambient temperature. The method affords a measurement of parameters, in particular, linear thermal expansion coefficient. Values of specific heat for the four plastics have been measured by differential scanning calorimetry and the results compared with published data.
    Additional Material: 9 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 12 (1974), S. 1355-1370 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: p-Divinylbenzene has been polymerized by heating at pressures ranging from atmospheric to 2.5 GN/m2, and the moduli (Young's, shear, and bulk), density, and residual unsaturation of the products have been determined. The results show a marked effect of polymerization pressure upon density and upon the degree of conversion of the second double bond. Linear relations are indicated between modulus and either density or an intermolecular force function based on a 6-12 potential field. These results and others on the densification of polystyrene are discussed and it is concluded that the moduli of the poly-p-divinylbenzene samples prepared under these conditions are still at a level largely determined by intermolecular forces.
    Additional Material: 9 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 12 (1974), S. 1939-1940 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Tab.
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  • 10
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 15 (1977), S. 1077-1088 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ultrahigh molecular weight polyethylene has been crystallized at various pressures (0-330 MN m-2) to material of a wide range of specific gravities (0.928-0.967). Tensile measurements illustrate that the properties of these materials are dependent on specific gravity (sg), in that the yield stress increases linearly with sg. Low sg (0.928-0.944) materials exhibit higher yields stress than low molecular weight materials of the same sg but the opposite is true for higher sg material. Low sg material also extends uniformly after yielding while above a sg of 0.944 necking becomes more marked. Orientation hardening is observed with all these materials above 200% extension and is more marked than with low molecular weight polymers. Differential scanning calorimetry (DSC) analysis of the pressure crystallized materials indicate that in the range 200-400 MN m-2 two phases are present, i.e., chain-folded and chain-extended lamellas. Increasing or decreasing the pressure changes the crystalline component to chain-extended or chain-folded morphologies, respectively. The reorganization of the crystalline components on drawing is discussed.
    Additional Material: 7 Ill.
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