CoA. Notes: Materials (1963-1969)

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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.
Open Access
An examination of the methods of mixing peroxides into polythene to form polymer networks
(College of Aeronautics, 1963-10) Stuart, J. M.
In the production of peroxide cross-linked polyethylenes it is customary to introduce the organic peroxide by the hot milling process. Inevitably some peroxide is lost by volatilization and the process is, therefore, difficult to standardize. In this paper, the efficiencies of the processes in which the peroxide is introduced by wet and dry powder mixing are compared with the efficiency of the normal method of mill mixing. It is shown that in both the wet and dry processes the loss of peroxide is avoided, but that the dry mixed material shows inhomogeneities in the cross-linked state.
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.
Open Access
Anisotropic creep in a glass-fibre laminate
(College of Aeronautics, 1964-04) Kaye, A.
A glass fibre epoxy resin laminate was prepared from a flexible thermosetting resin and a 'plain weave' glass cloth. Experiments in simple tensile creep were carried out on strips cut with their long dimensions at various angles to the warp threads in the glass cloth. It was found that each of these strips showed, over the limited range of loads and times covered, essentially linear creep behaviour. The creep compliance varied systematically with direction being as much as twenty times smaller in the warp and weft directions as at 45° to these directions. It was found that the shape of the creep compliance versus orientation curves was similar for all times and the behaviour can therefore conveniently be described by two curves, a master curve of reduced creep compliance as a function of direction and a curve of reduction factor versus time. The significance of both these curves is discussed in terms of an extension of linear viscoelasticity theory to the case of antisotropic materials. It is shown that the variation of creep compliance with direction is similar in form to the variation of elastic compliance with direction in orthorhombic anisotropic elastic materials and also that the results are consistent with a similar variation of relaxation time spectrum with direction.
Open Access
Some reactions of perfluoroglutaric acid
(College of Aeronautics, 1964-11) Smith, D. A.
Perfluoroglutaric acid when reacted with methyl magnesium iodide affords 2,6 diol 2,6 dimethyl hexafluoro pyranI in high yield and 4-one, 1,2,3 hexafluoro caproic II acid in low yield. The former material appears to exist in a range-melting form (64-79°C) and a very labile form of melting point 96-98°C. The 2,6 diol 2,6 dimethyl hexafluoro pyranI yields a mono semi carbazoneIII, and also a monoIV and a di 2:4 dinitro phenyl hydrazone. V The mono 2:1l dinitrophenyl hydrazone appears to be cyclic. Reduction both with lithium aluminium hydride and sodium borohydride yields 2,6 diol 3,4,5 hexafluoro n-heptane.VI There is evidence to suggest that reaction with dried calcium sulphate gives 2 ene, 2 methyl 3,4,5 hexafluor 6 one cyclo-hexaneVII Reaction with benzoyl chloride affords 2,6 dibenzoate, 2,6 dimethyl hexafluoro pyran.VIII 4 one 1,2,3, hexafluorocaproic acid was characterised as a 2:4 dinitro phenyl hydrazoneIX and also as an S benzyl thio-uranium salt.X Infra-red spectral evidence suggests the S benzyl thio uranium salt probably exists in the straight chain form. Numbers in the above text refer to the Flow Sheet, Figure 1.
Open Access
The influence of the static and dynamic characteristics of power sources on the behaviour of short circuiting CO2 shielded welding arcs
(College of Aeronautics, 1965-02) Pierozeck, B. S.
The work discussed in this report has examined, oscillographically, the influence of variable slope and variable inductance on the characteristics of short circuiting CO2 shielded metal arcs, and the variables affecting the optimum welding conditions have been determined. It has been established th9.t this optimum is usually below the maximum of the frequency voltage curve. Both the slope of the power source characteristic and the value of the inductance in the circuit have similar qualitative effects on the stability of the short circuiting arc. Nevertheless, control of the dynamic response by varying inductance has been found to be more flexible and effective. For this reason, it is suggested that separate control of the static characteristic and dynamic response is not necessary to obtain optimum conditions. Thus the correctly designed power source for short circuiting CO2 shielded arc welding should have constant slope of the static characteristic and continuous control of the dynamic response.
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.
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.
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, Roger
Annealed 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.
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.
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.
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.
Open Access
The effect of plastic anisotropy on flange wrinkling behaviour during sheet metal forming
(College of Aeronautics, 1967-10) Naziri, H.
During the drawing of sheet metal between a die and a blankholder, compressive hoop-stresses are developed which attempt to thicken or wrinkle the flange. Previous work on this behaviour has ignored any effects due to normal or planar plastic anisotropy. In this paper it is shown that the blankholder pressure necessary to suppress wrinkling increases with decreasing normal anisotropy (r) and increases with increasing planar anisotropy (AO. The approximate plane strain conditions (daz = 0) operating in the flange can be simulated by an edge-notched tensile specimen and this simulation demonstrates the effect of texture hardening and softening upon flange wrinkling behaviour. The results obtained can be interpreted valitatively by the use of anisotropic plasticity theory. The speed of drawing also effects wrinkling, in general, the number of wrinkles decreases with increasing drawing speed.
Open Access
The role of ductility in hot working
(College of Aeronautics, 1967-11) Tegart, W. J. McG.
Strength and ductility are the important characteristics which govern the hot working properties of a material. This paper describes test methods for measuring hot workability and then discusses deformation and fracture mechanisms in hot working. Particular emphasis is laid on the correlation of strength and ductility data in simple materials in terms of dependence on strain rate and temperature. Suitable correlations enable the identification of basic parameters controlling deformation and fracture processes. With complex materials, these correlations cannot be applied due to the occurrence of precipitation reactions and the presence of inclusions and second phases having markedly different strength and ductility characteristics.
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.
Open Access
Some aspects of anisotropic plasticity in sheet metals
(College of Aeronautics, 1968-03) Pearce, Roger
The 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.
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.
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.].
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.
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.