Browsing by Author "Hall, M. M."

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    A fracture of rubber in a state of finite torsional shear
    (College of Aeronautics, 1969-01) Hall, M. M.; Sollars, A. R.
    A solid rubber cylinder with metal end plates fractured in the rubber when a torsional deformation was applied 'which corresponded to a shear angle of 56° on the cylinder surface. The height of the cylinder was maintained accurately constant during the deformation. A comparatively smooth fracture surface was created in a direction perpendicular to the principal tensile stress and a rough surface was created perpendicular to the principal compressive stress. The markings on the smooth surface have some feature similar to a cleavage-type failure in a crystalline material.
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    The pressure distribution over the flat end surfaces of compressed solid rubber cynlinders
    (College of Aeronautics, 1968-07) Hall, M. M.
    The shape of the pressure distributions over the flat end surfaces of compressed solid rubber cylinders have been determined. The cylinders were compressed between metal end plates. The pressure distribution for compressive strains of less than 3% is approximately parabolic. It is unaffected by the strains set up in the rubber due to the differential thermal contraction of the rubber and bonded metal end plates. A. method of extending these measurements to large compressive strains, and a possible future programme of work, is outlined.
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    Studies of pure homogeneous deformations in unfilled natural and butyl rubbers
    (1968-04) Hall, M. M.
    Observed deviations from the kinetic theory of rubberlike elasticity have been reviewed, and particular attention focussed upon the Mooney parameter C2. Stress measurements have been made upon thin rubber sheets in a state of pure homogeneous biaxial strain, and the stress relaxation behaviours of a natural rubber and a butyl rubber are reported … [cont.].
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    A study of the stress distributions necessary to maintain rubber in a state of torsion
    (College of Aeronautics, 1968-06) Hall, M. M.
    Quantitative measurements have been made of the time dependent normal stress distributions and torques which are necessary to maintain a state of torsion in: (i) a solid right circular cylinder of rubber, (ii) rubber contained between a cone and touching flat plate. The measurements on the solid rubber cylinder, under quasi-elastic conditions cannot be described by the kinetic theory of elasticity. There are considerable experimental difficulties involved in measurements on the cone and plate system but these results also suggest an inadequacy in the ability of the kinetic theory to describe finite deformations in rubbers.
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    The time-dependent behaviour of anisotropic low density polyethylene
    (1971-03) Clayton, David; Hall, M. M.
    'Low density polyethylene has been oriented into a state of transverse isotropy by cold-drawing an originally isotropic blank in uniaxial tension, and the non-linear creep behaviour of the material has been completely characterised for the first time. The compliance matrix describing the deformation behaviour is characterised by five independent material parameters. Four of the parameters have been determined from uniaxial tensile creep experiments on specimens cut at 0° and 90° to the draw direction, and the fifth from torsional creep studies on a specimen cut parallel to the draw direction. The- development and proof of experimental techniques for use with the respective apparatii have formed an important and necessary part of the work, and the accuracy and internal consistency of the results have been found to be excellent. Measurements of the compliances have been made at ten different: degrees of anisotropy - measured by the draw ratio - over a range of strains from the pseudo-linear to the highly nonlinear region. The anisotropy of the deformation behaviour at a given draw ratio, and the trends of anisotropy with draw ratio, have been interpreted in terns of current structural knowledge. At low draw ratios the deformation is dominated by a c-axis shear mechanism and an inter-lanellar shear mechanism, and a relaxation mechanism has been discovered in specimens cut at 90 to the draw direction. At high draw ratios an inter-fibrillar shear mechanism is dominant in specimens cut: at angles away from the 0° and 90° direction. A simple engineering analysis of the results has examined the applicability- of the formalisms of linear elasticity and viscoelasticity theory to the non-linear, anisotropic visco-elastic state. Also, the assumption of a constant volume deformation, which is commonly used in polymer science for the determination of the Poisson’s ratio terms, has been investigated over the range of strains and compared with directly measured values. The measured values represent the first systematic study of Poisson1s ratio in anisotropic polymers. The constant volume assumption is shown to be in error at all draw ratios.