Browsing by Author "Murphy, A. J."

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    Materials for astronautic vehicles
    (College of Aeronautics, 1960-11) Murphy, A. J.
    The nature of the environment in outer space and its significance for materials of construction of astronautic vehicles are considered. The most advanced experience with heat-resisting engineering materials has been gained in gas turbine applications. The potential developments towards higher operating temperatures of alloys based on iron, nickel and cobalt are approaching exhaustion. The next stage may use the higher melting point metals, especially molybdenum, columbium and tungsten, non-metallics such as carbon and ceramics, or combinations of metals and ceramics. The s refractory metals are capable of stressed service at 2500[degrees]F. (1370[degrees]C.) and higher, if means of protection against oxidation can be found. On the same condition graphite can be used for much higher temperatures. For the ballistic missile, ablation of surface layers on the nose cone offers the best prospect of successful heat-dissipation. The ablating material may be an organic material, e.g. synthetic resin, or a ceramic compound. For longer spells at high temperatures, as in satellites on re-entry, the alternatives are thermal insulation by nonmetallic surface coatings, and skins of metals having very high melting points. Coatings which provide insulation and protection from oxidation are provided as flame-sprayed ceramic oxides, especially alumina and zirconia, or ceramics reinforced by a refractory metal grid attached to the base metal. The major technical difficulties in applying the refractory metals to service at very high temperatures arise from their reactivity with ambient gases, especially oxygen, and their tendency to brittleness at low and moderate temperatures. Characteristics of materials which acquire special importance in astronautic applications are: thermal conductivity, specific heat, latent heat of fusion and evaporation, coefficient of thermal expansion, reactivity at high temperatures, sensitivity to irradiation, creep strength and resistance to high fatigue stresses at high temperatures and mechanical properties at low temperatures.
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    Research at the College of Aeronautics Cranfield
    (College of Aeronautics, 1960-10) Murphy, A. J.
    The 1,142nd lecture to be given before the Society and the 37th Main lecture to be held at a Branch Centre " Research at the College of Aeronautics " by Professor A. J. Murphy. M.Sc., F.R.Ae.S., F.I.M., Principal, College of Aeronautics, was given under the auspices of the Cambridge Branch on 21st January 1960. Professor W. A. Mair, M.A., F.R.Ae.S., Francis Mond Professor of Aeronautical Engineering, University of Cambridge, and President of the Cambridge Branch, opened the proceedings and then handed over to the President of the Society, Mr. Peter G. Masefield, M.A., F.R.Ae.S., Hon.F.I.A.S., M.Inst.T.
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    Temperature effects on material characteristics
    (College of Aeronautics, 1960-08) Murphy, A. J.; Kennedy, A. J.
    Some of the physical properties of the main elements of interest in high temperature technology are reviewed. Some general trends emerge when these properties are viewed as a function of melting point, but there are a few notable exceptions. Titanium, zirconium, niobium and tantalum all have disappointingly low moduli; chromium is excellent in many ways, but has a limited ductility at lower temperatures; molybdenum oxidises catastrophically above about 700° C, and niobium suffers from severe oxygen embrittlement. Beryllium and carbon (in the graphitic form) both stand out as exceptional materials, both have very low densities, beryllium a very high modulus but an unfortunately low ductility, while graphite has a relatively low strength at the lower temperatures, although at temperatures of 2000° C and above it emerges as a quite exceptional (and probably as the ultimate) high temperature material. Some of the fundamental factors involved in high temperature material development are examined, in the light, particularly, of past progress with the nickel alloys. If a similar progress can be achieved with other base elements then a considerable margin still remains to be exploited. Protection from oxidation at high temperatures is evidently a factor of major concern, not only with metals, but with graphite also. Successful coatings are therefore of high importance and the questions they raise, such as bonding, differential thermal expansion, and so on, represent aspects of an even wider class covered by the term “composite structures". Such structures appear to offer the only serious solution to many high temperature requirements, and their design, construction and utilization has created a whole series of new exercises in materials assessment. Matters have become so complex, that a very radical and fundamental reassessment is required if we are to change, in any very significant way, the wasteful and ad hoc methods which characterise so much of present-day materials engineering.