CoA. Notes: Materials (1963-1969)
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Item Open Access Some microstructural features of fatigue in an aluminium alloy(College of Aeronautics, 1969-01) Hockenhull, B. S.; Panakal, J. D.; Hacking, R. G.The microstructures produced by the heat treatment of a commercial age hardening At-4.4 Cu alloy have been examined by thin foil electron microscopy. Whilst there is similarity of the microstructures in the commercial alloy to those which have been reported for simple binary At-Cu alloys, there is a strong association of dislocation structures and incoherent precipitates with undissolved Mn bearing intermetallic particles. Fatigue tests made on the alloy at both 50 Hz and 20 kHz have shown that there are changes in microstructure during fatigue; more markedly at 20 kHz in which tests the heating effect has some importance. There is some evidence of both accelerated ageing and also the by-passing or resolution of coherent phases during fatigue, particular at 20 kHz.Item Open Access 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.Item Open Access Some further experiments in fatigue testing at 20 kH2(College of Aeronautics, 1968-10) Hockenhull, B. S.Considerations are made of the suitability of acoustic transformers applied to fatigue testing at 20 kH2. A suitable system has been constructed which allows the use of plain cylindrical specimens. The results of fatigue tests on an aluminium alloy are given and discussed in relation to structure and environment.Item Open Access 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.Item Open Access Welding embrittlement of the parent plate outside the visible heat affected zone region(College of Aeronautics, 1968-04) Coward, M. D.Enbrittlement of steels outside the visible heat affected zone region due to plastic straining from the weldment and subsequent ageing has been reported by several authors. The problem is reviewed in this Note and an attempt made to detect this region in a semi-killed mild steel by means of a micro hardness testing survey taken at regular intervals in a direction away from the veld fusion boundary. Recommendations for future work in understanding the magnitude of this Problem particularly in multi stressed welded joints are given.Item Open Access 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.Item Open Access The reaction of perfluoroglutaric acid with methyl magnesium iodide. Part 2(College of Aeronautics, 1968-08) Smith, D. A.Perfluoroglutaric acid when treated with methyl magnesium iodide afforded hexafluoro-2,6-dimethylpyran-2,6-diol in high yield and 2,213,3,4,4-hexafluoro- 5-oxocaproic acid in low yield. The former appeared to exist in a range melting form (61.-79°C) and also in a very labile form melting at 96-98°C. Problems associated with the formation of this latter form were investigated. The hexafluoro-2,6-dimethylpyran-2,6-diol yielded a monosemi-carbazone and also a mono and a di1(2,4-dinitrophenylhydrazone). The mono (2,4-dinitro phenylhydrazone) appeared to be cyclic. Reduction, both with lithium aluminium hydride and sodium borohydride yielded 3,3,4,415,5-hexafluoro-n-heptane-2,6-diol. Reaction with anhydrous calcium sulphate gave 3,3,414,515-hexafluoro-2- methylcyclohex-l-ene-6-one. The acid product of the original reaction of perfluoroglutaric acid and methyl magnesium iodide was characterised as a 2,4-dinitrophenylhydrazone and as an S-benzylthiouronium salt. Infra-red spectroscopic evidence suggests the latter compound exists in a straight chain form.Item Open Access 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.Item Open Access The effect of curing conditions on the extent of cure of Polyester Resin Crystic 189 (Scot-Bader Ltd.)(College of Aeronautics, 1968-06) Smith, D. A.The cross-linking, or cure, of Scot Bader Polyester Resin Crystic 139 (L.V.) was investigated by examining the resin during cure by means of acetone Soxhlet extractions and Barcol hardness tests. The experiments were designed to test Funke’s hypothesis that in the cure of polyester resins the nature of the final network is predetermined by conditions before the gel Point, and that post-gel conditions affect the rate of cure but not the nature of the final network and the final degree of conversion. Funke’s work was based on analysis of the final products of hydrolytic degradation of polyesters, which is quite different from the methods used in this investigation. It was concluded that the evidence did not support Funke’s hypothesis and explanations are afforded for this and suggestions for future work are recorded.Item Open Access The design and construction of a weld heat-affected zone simulator(College of Aeronautics, 1968-02) Clifton, T. E.; George, M. J.Investigation of the structure and properties of the heat-affected zones in welded joints is usually limited by their small size and their complexity. One method of overcoming this problem is to simulate the structure at a particular point in the heat-affected zone in a specimen of larger size by imposing on it the thermal cycle sustained at that point. The equipment described in this note uses a.c. resistance heating and water cooling to impose thermal cycles on 2.5" x O.W' x O.W' specimens, the thermal cycle being chosen by adjustment of a bank of variable resistors to construct a voltage analogue. Control of specimen temperature is achieved using a thyristor and two ignitrons to control the input at 44ov. to a welding transformer. Feedback is applied from a thermocouple welded to the specimen hot-zone. The equipment has been shown to produce the desired thermal cycles in a reproducible manner.Item Open Access 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.].Item Open Access Some aspects of anisotropic plasticity in sheet metals(College of Aeronautics, 1968-03) Pearce, RogerThe prediction of the yielding and flow behaviour of materials under complex stress systems from tensile test or other easily determined data has been the aim of engineers for many years. The yield criteria of Tresca and then Mises for isotropic metals are useful, but the realisation that anisotropy is the rule rather than the exception, especially in sheet metals led to the examination of Hill's anisotropic theory by various workers. In the present paper the stress-strain curves of various sheet metals are determined in uniaxial and balanced biaxial tension. As far as yielding behaviour is concerned it is concluded that the theory is reasonably satisfactory for materials where anisotropy is described with r = 1, with certain anomalies for materials with r< 1. As far as flow behaviour is concerned, the theory only applies for materials for r> 1. Crossing of the uniaxial and biaxial curves is observed for certain metals at low strains and this is not predicted by the theory. More work is necessary on low-r materials to resolve these matters.Item Open Access A study of the thermal degradation of an amine-cured epoxide resin at temperatures below 350 degrees C(College of Aeronautics, 1967-01) Patterson-Jones, C.; Smith, D. A.An epoxy resin made by the reaction of the diglycidyl ether of bis-phenol A and diaminodiphenyl methane was thermally degraded in vacuo at temperatures between 200°C and 350°C. The effect of degradation was examined by means of measurement of changes in the dielectric properties of the material and also by examination of compounds evolved by the cured resin. Definite evidence for the evolution of N-methyl aniline and N:N-dimethylaniline is advanced and added evidence for a dehydration reaction is put forward. Possible degradation mechanisms are discussed.Item Open Access Some aspects of the thermal degradation of epoxide resins. Part 1(College of Aeronautics, 1965-03) Stuart, J. M.; Smith, D. A.This Note contains a review of previous work in the field of pyrolytic degradation of epoxide resins, and a description of the development of an instrument for this purpose, using the principle of gas chromatography. The method depends on the pyrolysis of the material using an electrically heated filament, the difficulties of this method are critically examined, and attempts to overcome them described. The pyrolytic degradation in a nitrogen atmosphere, of unhardened epoxide resin was investigated, likewise the degradation of resin hardened with 1:2 diamino ethane and triethylenetetramine, is described. An attempt has been made to explain, in terms of possible degradation reactions, the actual compounds detected in the pyrolytic break-down.Item Open Access Characteristics of the high temperature mechanisms of creep and recovery in graphite: part 2(College of Aeronautics, 1964-02) College of Aeronautics, (Cranfield),The research reported in this document has been made possible through the support and sponsorship of the U.S. Department of the Army throlleh its European Research Office. This report, not necessarily in final form, is intended only for the internal management use of the Contractor and the U.S. Department of the Army.Item Open Access Characteristics of the high temperature mechanisms of creep and recovery in graphite: part 1(College of Aeronautics, 1963-08) College of Aeronautics, (Cranfield)An apparatus has been developed for determining the high temperature creep and recovery characteristics of graphite by applying torsional stresses to thin-walled tubes. This method has the advantages of a simple stress system, constant stress for constant load, easy rapid removal of load and the independence of the strain measurement from thermal expansion. Torsional, stress-strain curves show a decreasing modulus with increasing temperature from 2000 - 2850°C. The rate of creep in this range is increased by increasing temperature and stress. Recovery rate is not so sensitive to increasing temperature. Using a method developed for metals, where recovery can be subtracted from forward creep, a secondary creep rate is deduced. This rate, when plotted according to the Arrhenius' equation, yields an activation energy for secondary creep of 154 kcals over the temperature range 2100 - 2700°C. These results are critically examined and the future extension of the work discussed.Item Open Access Measurement of thermal cycles in the weld heat affected zone of mild steel(College of Aeronautics, 1967-09) Coward, M. D.; Apps, R. L.The thermal cycles in the mild steel parent plate adjacent to a bead on plate weld have been measured for heat inputs of 108, 54 and 42 kJ/inch, by means of embedded thermocouples connected to high response automatic recorders. The results show that decreasing the heat input increases the cooling rate and decreases the width of the heat affected zone. For thermal cycles in which the peak temperatures reached 900°C or above, two points of inflection have been noted in the temperature ranges 400° - 600°C and 950° - 1200°C. The inflection in the lower temperature range, which has been observed by other workers, has been attributed to latent heat from the exothermic transformation of austenite to ferrite. The higher inflection point, not previously reported, has been tentatively related to the solidification in the weld pool and the release of the latent heat of fusion.Item Open Access 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.Item Open Access The effect of varying strain-ratio on the hydraulic bulging behaviour of aluminium sheet(College of Aeronautics, 1966-11) Bott, Charles H.; Pearce, RogerAnnealed commercial-purity aluminium sheet was cold-rolled up to 32%, and the effect of this treatment on the strain-ratio (r) in various directions in the sheet plane was evaluated. Up to approximately 16% cold reduction ro, r454 and r901 remained approximately constant, while the average strain-ratio, r, showed no change. At cold reductions in excess of 16% ro, and rgo, fall steadily, while the fall in r4s, is less pronounced. Specimens were then 'electromarked' with an array of 0.1 in. dia. circles and bulged, using a pvc 'punch' technique. Plots of natural thickness strain (e) vs. bulge height (h max) show that, for a given height, the strain distribution is more even for an annealed material than for a cold-worked one, due to the effect of work-hardening. The relationship between polar thickness strain and uniaxial uniform elongation (eu) shows a discontinuity at about 10% eu and a further plot of h and r against eu suggests that this is associated with the change in strain-ratio. Thus, bulge height increases linearly with increasing uniform elongation at a constant strain-ratio, but in a more complex fashion with varying strain-ratio. Increased r gives decreased € at the pole, producing a more even strain distribution over the bulge.Item Open Access Rolling recrystallisation textures of commercial grades of low carbon steels(College of Aeronautics, 1966-02) Flavell, T.The work in progress concerning the study of rolling-recrystallisation textures in commercial grades of low-carbon steels is outlined, the influence of aluminium nitride precipitation and recovery phoenomena being the main lines of research. Results to date indicate that the retention of the (100) component of the rolling texture is more favoured during recrystallisation as the prior recovery times and temperatures are increased. Textural variations through the sheet thickness are also being studied, results to date being presented.