Browsing by Author "Saunders, D. W."

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    An apparatus for the measurement of tensile creep and contraction ratios in small non-rigid specimens
    (College of Aeronautics, 19) Darlington, M. W.; Saunders, D. W.
    An apparatus is described for precise measurement of creep properties in specimens with gauge lengths down to 1.2 cm. An extensometer has been developed which is supported independently of the specimen and exerts a load on the specimen of less than 5 grams. It can thus be used with small non-rigid specimens. The extensometer will detect strains down to 2 x 10-6. The stability is excellent. An adaptation of the system which allows simultaneous measurement of tensile strain and lateral strain during creep is also described. The apparatus was designed for the measurement of anisotropy of creep properties in oriented thermoplastics and reference to such measurements is given. It is however entirely suitable for general application to small specimens.
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    Creep studies on oriented thermoplastics
    (College of Aeronautics, 1969) Darlington, M. W.; Saunders, D. W.
    The enhancement of many of the mechanical properties of thermoplastics which may be achieved by orienting the molecules has been known for some time. It has been exploited in the production of textile fibres end oriented films. Molecular orientation also occurs during processes such as extrusion, moulding or forming. Here, unless carefully controlled, it may well cause a deterioration in the properties of the finished article. In view of this a systematic study on the anisotropy of the mechanical properties of thermoplastics, resulting from molecular orientation, is being carried out at present in these laboratories … [cont.].
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    The temperature dependence of photo-elastic properties of cross-linked amorphous polyethylenes
    (College of Aeronautics, 1967-08) Saunders, D. W.; Parsons, D. A.; Lightfoot, D. R.
    Cross-linked samples of polyethylene were prepared by electron irradiation of both high and low density polymers in the crystalline state. A further cross-linked sample was obtained by curing a high density polyethylene by reaction with dicumyl peroxide at 180°C. The stress-strain birefringence relations were obtained, on specimens cut from these samples, at temperatures between 130 and 250°C. All samples showed a substantial decrease in stress-optical coefficient with increasing degree of cross-linking and with increasing temperature. The stress-optical properties at each temperature were extrapolated to zero degree of cross-linking to give quantities characteristic of the Guassian network. Comparison of these properties with Gaussian theory of the network leads to a value of ca.1150 cals/mole for the difference in energy between trans and gauche conformations of successive links of the polyethylene chain and also indicates that the optical anisotropy of a - CH2 group in the elastomeric state is more nearly given by Denbigh’s than by Bunn and Daubeny's polaris-abilities.