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  • 1
    Electronic Resource
    Electronic Resource
    Viscoelastic-plastic behaviour with mean strain changes in polypropylene (1996)
    Springer
    Journal of materials science 31 (1996), S. 4127-4131 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The stress-strain curves and stress-relaxation curves of polypropylene are obtained by using a closed-loop, electrohydraulic, servo-controlled testing machine. Effects of mean strain changes on deformation behaviour are examined in a tension-compression mode under strain control at room temperature (18–23 °C). The hysteresis loops of three mean strains show a steady-state response from the stress-strain curves at a strain rate of 1 × 10−3 s−1 at a strain width of 5%, at a number of cycles of N=50 and at three mean strains (ɛm=0, + 1.0 and + 2.0%). The drop of stress at the mean strain of ɛm= -1.0% is larger in magnitude than that at ɛm=+1.0%; this is caused by the higher stress level at ɛm=- 1.0% as compared with the stress level at ɛm=+1.0%. From the results of stress amplitude and the stress drop behaviour, the magnitude of stress drop is hardly affected by the mean strain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00352678
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  • 2
    Electronic Resource
    Electronic Resource
    Cyclic deformation behaviour and morphology of polypropylene (1993)
    Springer
    Journal of materials science 28 (1993), S. 3845-3850 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The viscoelastic-plastic behaviour and stress relaxation in polypropylene after uniaxial simple tension or cyclic preloading are studied by an electrohydraulic, servo-controlled testing machine. The stress-strain curve data of simple tension at different strain rates show that the magnitude of stress depends strongly on strain rate. The stress relaxation behaviour after simple tension and cyclic preloading indicates complex features and reveals differences in the deformation of molecular chains in polypropylene subjected to different cyclic preloadings. The stress-strain curves and the stress relaxation curves under three mean strains are fairly different from each other. The microstructural changes in samples subjected to different cyclic preloadings were determined by scanning electron microscopy (SEM). The results of the stress-strain curves and the stress relaxation behaviour are discussed in comparison with the observation of SEM fractographs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00353189
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  • 3
    Electronic Resource
    Electronic Resource
    Annealing effects on the viscoelastic anomaly between the β and γ processes for as-polymerized polytetrafluoroethylene (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 39 (1990), S. 1689-1698 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The viscoelastic anomaly found at 208 K for as-polymerized polytetrafluoroethylene (PTFE) is investigated on the basis of thermal treatment dependence of mechanical spectra. The loss intensity and relaxation strength of the anomaly tend to decrease at annealing temperatures much lower than the melting point. The structural region relevant to the anomaly can be rearranged in more ordered states on annealing; accordingly, the loss peak of the crystalline dispersion is intesified, although that of the amorphous γ-relaxation remains nearly unchanged. The anomaly originates from the intermediate or paracrystalline regions, many of which are included in the virgin samples; segmental motions like local mode relaxation are considered.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1990.070390807
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  • 4
    Electronic Resource
    Electronic Resource
    Thermal properties and morphology of hydrostatically extruded polypropylene (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 1101-1107 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The melting point, specific heat, and morphology and hydrostatically extruded polypropylene (PP) were studied to clarify the plastic deformation of three different parts of the extrudates (periphery, intermediate, and core) parallel to the direction of hydrostatic extrusion. Differential scanning calorimeter (DSC) measurements showed that, for all the parts studied, the peak and the end-of-transition, temperatures had a minimum value at a percentage reduction in area, R, of 50% Similar behavior was observed for the specific heat evaluated at several temperatures below the melting point. The morphological structure observed by use of a polarizing microscope indicated that the shape- of spherulites above R = 50% changed from spherulitic to elliptic. It is suggested that the pronounced changes taking place around R = 50% are closely related to the marked bend in the extrusion pressure versus extrusion ratio curve which takes place at the same R value. The molecular chains in the coarse spherulites appear to be deformed below R = 50% in such a way that finer spherulites are formed; but at R values above 50% the presence of elliptic spherulites implies that non-uniform deformation is present under higher hydrostatic pressure of extrusion.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760311505
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of mean strain on the cyclic deformation and stress relaxation in polypropylene (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1455-1460 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The influence of mean strain Changes in the range from 0 to 4% on the cyclic deformation and stress-relaxation properties is investigated using rod specimens of polypropylene. An extensometer measures and controls the axial strain in a closed-loop, electrohydraulic, servocontrolled mechanical testing machine. The hysteresis loop at different numbers of cycles N of N = 35, 45, and 50 are irregular in shape, and the tensile portion decreases in size as the number of cycles was increased. The stress value of the tensile portion for three mean strains of ∊m = 1.0%, 2.0%, and 4.0% remains constant, but the value of the compressive portion decreases as the mean strain was increased. The stress level at a strain width of 3% changes little with mean strain. For the strain widths of 5% and 7%, however, the minimum stress levels at N = 35, 45, and 50 increase with increasing mean strain, in contrast to the behavior of maximum stress level. The stressrelaxation tests show that the drop of stress decreases with an increase in number of cycles. The discrepancy in the results of relaxation tests is due to the effect of the difference in strain rates.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760351805
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  • 6
    Electronic Resource
    Electronic Resource
    Thermal behavior of hydrostatically extruded polycarbonate and high-impact polystyrene (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 1269-1274 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Effects of hydrostatic extrusion on the thermal properties of polycarbonate (PC) and of high-impact polystyrene (HIPS) were studied using differential scanning calorimeter (DSC) measurements. A glass transition temperature (Tg) and a peak temperature were determined from the DSC curves for both PC and HIPS extrudates. The Tg values of the PC extrudates, with a percentage reduction in area, R, from 40 to 50%, change appreciably from the value for the as-received PC. The results of the hydrostatic extrusion of the PC billets suggest that a two stage deformation process of molecular chains may be involved. Shear-banding is observed for HIPS extrudates with R = 30 to 60%; this fact indicates that a sub-glass transition (β-transition) occurs at temperatures below Tg. It is suggested that the molecular chains of the HIPS extrudate with R = 70% are oriented in the direction of hydrostatic extrusion. The deformation mechanism of molecular chains caused by the hydrostatic extrusion is discussed.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760341607
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  • 7
    Electronic Resource
    Electronic Resource
    Extension behavior and morphology in polypropylene extended under hydrostatic pressureOriginally an oral presentation at Macro 90, 33rd IUPAC Symposium on Macromolecules, Montreal, Quebec, Canda, July 8-13, 1990. (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 705-714 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of hydrostatic pressure on molecular deformation of polypropylene extended under hydrostatic pressure is investigated by using internal friction measurements, wide angle X-ray diffraction, and polarizing microscopy. A homogeneously transparent straight part is obtained by extending samples in the pressure range from 78 to 128 MPa. The overall mechanical properties of a sample extended under P = 102 MPa is significantly different from that of a sample extended under P = 128 MPa. The difference is related to the magnitude of hydrostatic pressure, the extension ratio, and the extent of transparency. The observed results on the β relaxation in the extended samples is found to be related to the morphological reorganization from a coarse spherulitic to a fine spherulitic structure. The cold-drawn sample at atmospheric pressure has the γ-peak at around °50°C, while the hydrostatically extruded samples and the extended samples have no γ-peak. Consequently, the hydrostatic pressure suppresses the formation of the molecular structure relevant to the γ relaxation.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760321102
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  • 8
    Electronic Resource
    Electronic Resource
    Cyclic deformation and relaxation characteristics in polypropylene (1993)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 18-25 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Cyclic deformation and stress relaxation after cyclic preloading in polypropylene were investigated by using an electrohydraulic, servocontrolled testing machine. The cyclic deformation tests were performed under various sets of strain rate, number of cycles, and strain amplitude in the as-received sample and a quenched sample. The stress relaxation tests were made after a cyclic preloading in both samples. The distinctive shape of the hysteresis loop, termed a propeller-like shape, is characteristic of the as-received polypropylene with large spherulites, in marked contrast to the behavior of metals. The curves at strain amplitudes from ± 1.5% to ± 5% indicate a propeller-like shape; these loops change into the steady state response as the number of cycles (N) is increased up to N = 30 to 50. The drop of stress in relaxation tests for the quenched samples is smaller than that for the as-received samples at the same strain levels. This stress drop behavior reflects the difference of spherulite structure. The stress relaxation behavior depends on the morphology, the predetermined strain amplitude, and the process of the tests.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760330103
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  • 9
    Electronic Resource
    Electronic Resource
    Viscoelastic-plastic deformation behavior of polypropylene after cyclic preloadings (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 1319-1326 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Stress-relaxation behavior is studied in polypropylene samples subjected to different cyclic preloadings and to simple tension. The relaxation tests are performed under different sets of strain amplitude, number of cycles, and strain rate, using a closed-loop, electrohydraulic, servocontrolled testing machine. The calculated stress-strain curves are determined from a constitutive equation based on an overstress theory in which an equilibrium stress and a viscosity function are treated. The calculated results agree well with the experimental ones. It is concluded that the overstress theory explains the nonlinear viscoelastic-plastic behavior of polypropylene.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760341704
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  • 10
    Electronic Resource
    Electronic Resource
    A constitutive theory for polypropylene in cyclic deformation (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1461-1467 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The shape of the hysteresis loop has been studied for polypropylene subjected to different cyclic loadings. Cyclic tests were performed under different sets of cyclic strain amplitude and number of cycles, using a closed-loop, electrohydraulic, servocontrolled testing machine. A constitutive theory is developed for the interpretation of loop shape behavior in terms of elastic, perfectly plastic materials of different yield strengths. The constitutive equation is based on a simple overlay model of bar elements. The calculated results agree well with experiments, which indicates the distictive shape of the hysteresis loop, termed a propelled-like shape. The truss model reasonably explains the cyclic deformation behavior in polypropylene.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760351806
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