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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 20 (1985), S. 2719-2726 
    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 behaviour and morphological features of PBT films before and after heat treatment are reported. PBT films possess extraordinary mechanical properties comparable to those of the fibres. A non-uniform residual stress distribution is proposed to account for the elastic-plastic behaviour of as-extruded films and the subsequent extensive fibrillization during tensile testing or tension heat treatment. Tension heat treatment results in significant axial modulus and tensile strength increase by improving overall sample orientation and lateral crystallite size with concomitant straightening of buckled regions in the film.
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  • 12
    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 mechanical properties of PRT films feature an interesting temperature and strain-rate dependence. The elastic modulus and yield behaviour have been studied over a wide temperature range from 30 to 650° C. The onset of a structural reorganization is observed at about 300° C. The dependence of yield stress on strain rate at different temperatures was examined in terms of the Eyring theory of an activated rate process. It was found that the stress activation volume varies with temperature. The overall elastic-plastic behaviour as a function of temperature and strain rate was interpreted in terms of a previously suggested model that incorporates residual stresses in a rigid rod-like polymer. Enhancement of modulus was also observed due to deformation of the films under elevated temperatures, where better molecular orientation and lateral ordering are achieved.
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 20 (1985), S. 2727-2734 
    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 Heat-treatment processing of dry-jet wet-spun poly-(p-phenylene benzobisthiazole) fibres was undertaken to enhance fibre tensile mechanical properties. The effects of fibre tension and temperature and time of heat treatment in a nitrogen atmosphere on fibre mechanical properties were systematically investigated. Fibres possessing a tensile modulus as high as 300 GPa along with a tensile strength of 3 GPa have been produced. To attain this level of tensile properties, heat-treatment temperatures of 630 to 680° C for residence times of under one minute were required while applying tensions approaching fibre breaking stress at the elevated temperatures; conditions bordered on fibre degradation. Fibre structural changes associated with heat treatment and enchancement of mechanical properties are discussed in Part 2 of this work.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 24 (1989), S. 3267-3272 
    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 adhesive behaviour of epoxy-glass microballoon composites was studied at 25 and 75° C for plate and tubular lap joints of various combinations. It was found that the adhesive bond for various joints is enhanced through addition of microballoons. High adhesive force is observed at higher temperatures for various joints combinations where the thermal stresses are lowered and the bond is strengthened. The obtained results for various joint combinations demonstrate that high strength can be achieved when significant thermal stresses do not exist. The filler effect on some physical properties such as density, glass transition temperature, thermal expansion and Poisson's ratio of the epoxy composites is also investigated. Simple analysis indicates the differential thermal expansion coefficient between the adhesive and metallic joints and bulk modulus of the adhesive dictates the stress state.
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  • 15
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The mechanism of the solid state oxidation of isotactic polypropylene films and the the mechanism of inhibition by HALS have been investigated by kinetic-ESR and kinetic modelling with derivation of the rate constants for the sensitive steps in the reaction scheme. The results have shown the inadequacy of the Denisov cycle to account for the observed experimental kinetics of the intermediate nitroxyl radicals. The molecular dynamics associated with the oxidation inhibited by HALS in the polypropylene matrix has been investigated by applying the Liouville stochastic method to the analysis of the temperature effects of the ESR spectra of the intermediate nitroxyl radicals used as spin probes. The investigation on the nature and characteristics of the molecular motions available at the oxidation sites has also been carried out with nitroxyl spin labels bound to the PP chains. For this application a novel method of spin labelling was developed based on reactions with some of the oxidation products, namely the terminal and intrachain ketones (keana method), alcohols, peroxides and macroalkyl radicals.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 29 (1984), S. 2529-2535 
    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 phase-separation process in segmented copolymers is treated by first-order kinetics which couples with the Fox equation to derive an expression for describing the change of soft segment Tg with the annealing time. Kinetic data of five commercial polyurethanes have been analyzed. The studies conclude that the phase-segregation mechanisms involve two elementary steps which can be characterized by two discrete relaxation times. It has been shown quantitatively that a polyether-based polyurethane (ET) recovers its original domain structure faster than a polyester soft-segment material. The average activation energy of the demixing process of an ET polyurethane is found to be about 23 kJ.mol-1 and is not influenced by hydrogen bonding.
    Additional Material: 2 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 36 (1988), S. 1113-1120 
    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: A novel method for crosslinking polyetheretherketone via imine formation at carbonyl groups is presented. In polyetheretherketone these Schiff bases form short, stiff crosslink junctions which are stable up to 630°C. Dynamic mechanical and thermal properties of polyetheretherketone and imine crosslinked polyetheretherketone are reviewed. A large reduction in the temperature sensitivity of the material stiffness has been achieved. Increases in the glass transition temperature from 143°C to greater than 280°C have been obtained.
    Additional Material: 8 Ill.
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  • 18
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 35 (1988), S. 1955-1965 
    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 microstructure of composites made from blends of poly(p-phenylene benzobisthiazole) [PBT] and nylon 6,6 has been investigated with wide-angle X-ray diffraction, selected area electron diffraction, and small-angle X-ray scattering techniques. The composite samples investigated were spun in both fiber and film forms dilute solutions of methane sulfonic acid.The structure of the composites was found to be a microfibrillar network of PBT in a matrix of partially crystalline nylon 6,6. The diameters of the PBT microfibrils were in the range of 30 to 70 Å.
    Additional Material: 6 Ill.
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  • 19
    Electronic Resource
    Electronic Resource
    Springer
    Experimental mechanics 34 (1994), S. 306-314 
    ISSN: 1741-2765
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An experimental technique using real-time holographic interferometry combined with digitized image processing has been developed to measure the thermal diffusivity of polymers. This technique uses a cantilever beam or an annular disk with one side subjected to a pulse of radiant energy from a photographic flash. The resulting thermally induced deflection is measured by holographic interferometry. The observed deflection is due to a resultant thermal moment induced by a temperature gradient through the thickness. As time goes on, the heat conducts from the exposed surface through the thickness, resulting in a decrease of the bending moment and transverse deflection. It is shown that the deflection is proportional to the thermal moment, and the thermal diffusivity can be retrieved by moment analysis without deriving the analytical solution to the thermomechanical problem.
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  • 20
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 6 (1970), S. 411-420 
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Résumé On démontre que les observations faites aux niveaux macroscopique et moleculaire au cours de déformations conduisant à rupture peuvent etre expliquées sous la forme d'allongements hétérogènes ou de dilatations a l'échelle microscopique on moleculaire, et de ruptures locales d'éléments de chaine. Dans ce modèle préliminaire, on ne considère que des elements élastiques. On suppose que la dilatation dans une région donnée est distribuée statistiquement au sein de ces éléments. Lorsque se produisent leurs ruptures, il s'effectue une redistribution des contraintes parmi les elements non rompus. On discute les causes qui sent a l'órigine des dilatations hétérogènes, et on propose des moyens pour en determiner la distribution.
    Abstract: Zusammenfassung Der Beweis wird erbracht, daß die auf makroskopischer und molekularer Ebene wdhrend einer zum Bruch führeuden Verformung gemachten Beobachtungen in Form von heterogenen Verldngerungen oder von mikroskopische und molekularen Dehnungen sowie von lokalen Zerstörungen von Kettenelementen erkldrt werden können. In diesem Vormodell werden nur elastische Elemente betrachtet. Es wird unterstellt, daß die Dehnungen in einem bestimmten Bereich statistisch auf these Elemente verteilt ist. Wenn die Elemente zerreissen, vollzieht sich eine Neuverteilung der Spannungen auf die nichtzerstbrten Elemente. Die den heterogenen Dehnungen zu Grunde liegenden Ursachen werden erörtert, und es wird ein Verfahren zur Bestimmung ihrer Verteilung vorgeschlagen.
    Notes: Abstract It is demonstrated that observations during deformation leading to fracture on both the macroscopic and molecular (EPR) levels can be explained in terms of nonhomogeneous elongations or strains on a microscopic or molecular scale and localized failure of elements. In this preliminary model only elastic elements are considered. It is assumed that the strain in a region is statistically distributed among these elements. As the elements rupture, the stresses are redistributed among the remaining unbroken elements. Causes for the strain inhomogeneities and means of determining their distribution are proposed and discussed.
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