Browsing by Author "Dootson, M."

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    The creep behaviour of fibre reinforced plastics
    (College of Aeronautics, 1969) Dootson, M.
    Synopsis: This paper describes the tensile creep behaviour of fibre reinforced plastics under a uniaxial stress system. In particular, unidirectionally and bidirectionally reinforced plastics are considered for the relative ease with which samples of them can be manufactured. A composite model that has previously been described 1, 2 is used as the basis of theoretical predictions of the variation of the creep compliance with certain material parameters. The parameters whose effects are examined are the volume fraction of the fibres, the distribution of fibre orientations, and the angle between a specified direction and the direction of application of a uniaxial stress system. Specimen experimental results are included to show the accuracy of these predictions and any shortcomings of the theoretical model are examined in the light of this comparison.
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    The time-dependent mechanical properties of fibre reinforced polymers
    (College of Aeronautics, 1969-03) Dootson, M.
    1. General Progress In the six months from October, 1968 to March, 1969 the work has been divided into two main sections. The first of these has been the collection of tensile creep data both for the unreinforced resin and for the uni- and bi-directionally reinforced composites. The second section has been the continued quest for a successful lateral extensometer. In Progress Report No. 2 it was reported that five creep machines were in production. These have now been installed and are all functioning satisfactorily. Longitudinal extensometers of the type described in Progress Report No. 2 have been manufactured for use on these rigs. Comparisons have been made2between the experimental creep results of the composites described in this report and theoretical predictions based on the Elemental model.3'4 Good agreement was shown to exist between the experiment and theory.
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    The time-dependent mechanical properties of fibre reinforced polymers
    (College of Aeronautics, 1968-03) Dootson, M.
    Progress Report No. 1: A report of work carried out during the period lst October, 1967 to 31st March, 1968
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    The time-dependent mechanical properties of fibre reinforced polymers
    (College of Aeronautics, 1969-09) Dootson, M.
    1. General Progress The six months from April to September 1969 have been spent mainly in consolidating the work of the previous eighteen months. Firstly, due to major servicing problems, it became necessary to redesign the resin impregnating head of the filament winding machine. By the removal of all moving parts from the vicinity. of the resin, these servicing problems have been completely overcome. Using the redesigned machine many sheets of high quality glass reinforced epoxy resin have been produced. A sophisticated version of the spring mounted lateral extensometer described in Progress Report No. 3 has been designed and tested. Six of these have now been produced and are now in service yielding satisfactory results. The majority of the period has been spent in setting up the tensile creep testing machines. This has been necessitated by the discovery that errors of up to 10% in creep compliance have been obtained through misalignments of the loading linkages of the order of .01 inch. All the apparatus is now functioning correctly and more creep results for uni- and bi-directionally reinforced specimens are being obtained. Included in these current creep results are not only values for creep compliances but also for the creep contraction of these specimens.
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    The time-dependent mechanical properties of fibre reinforced polymers
    (College of Aeronautics, 1968-09) Dootson, M.
    1. General Progress In the six months from April to September 1968 the task of primary importance has been to design lateral extensometers and to improve the longitudinal extensometer and consequently enable reproducable measurements of the deformations undergone by creep specimens to be made … [cont.].
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    The use of a simple composite element to describe the creep properties of fibre reinforced composites
    (College of Aeronautics, 1968-08) Dootson, M.
    The stress-strain relationship for a composite material is dependent on both the geometry and the stress-strain relationships of the component phases. This note describes a technique by which the stress-strain relationship can be calculated for any fibre reinforced composite where the matrix has linear viscoelastic properties and the fibres are linearly elastic. The distribution of fibres within the composite is assumed to be macroscopically homogeneous but the distribution of fibre orientation can take any configurations. The problem is solved initially for the case where both phases are linearly elastic. A simple composite element from which a composite can be built up is defined and the stress-strain relationship for this element is calculated using variational methods. By summing these elements assuming either uniform stress or uniform strain throughout the composite, upper and lower bounds to the stiffness matrix of the composite are obtained. Using the correspondence principle these bounds for the purely elastic case are transformed to give the bounds for the viscoelastic case. The theoretical answers obtained using this method are compared with those obtained using a more simple model for the mode of combination of the two phases.