General

General

Prepared by T. Feest, R.P. Harrison, A.R. Wheatley and M. Mulheron AEROSPACE MATERIALS Aircraft composite materials and structures Dastin, S.J. S A M...

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Prepared by T. Feest, R.P. Harrison, A.R. Wheatley and M. Mulheron

AEROSPACE MATERIALS Aircraft composite materials and structures Dastin, S.J. S A M P E Journal Vol 17 No 6 (November/December 1981) pp 10-15 A review is given of the use of advanced composite materials in the aerospace industry since about 1970. Developments in processing and tooling techniques for composites are discussed together with manufacturing techniques for high volume production which are under current investigation.

CARBON MA TRICES On the oxidation of carbon-carbon composites Rey Boero, J.F. Carbon Vol 19 No 5 (1981) p 401 Two possible sources of error in the measurement of reaction rates in the air oxidation of carbon/carbon composites by thermogravimetric analysis are discussed. Firstly in view of the strongly exothermic nature of the C--O2 reaction, care must be taken to keep the sample temperature constant. Secondly the oxidant gas consumption must be small or the reaction rate will be limited by the 02 input. Previously published results showing anomalously low activation energies are discussed in the light of these two effects.

CEMENT MA TRICES Behaviour of cracked fibre composites under limited cyclic loading Keer, J.G. International Journal o f Cement Composites Vol 3 No 3 (August 1981) pp 179-186 G e n e r a l e q u a t i o n s to d e s c r i b e the load/unload/load behaviour of cracked fibre-reinforced cement, based on the established ACK theory, are presented. The theoretical relationships between the unloading strain and the resulting residual strain at zero load, and subsequent reloading modulus, are examined in some detail. Experiments with continuous fibrillated polypropylene-reinforced cement gave results which were in reasonable agreement with the theoretical predictions. Review paper: Bond in fibre-reinforced cements and concretes Bartos, P. International Journal o f Cement Composites Vol 3 No 3 (August 1981) pp 159-177 The characteristics of different types of bond, and their function in fibre-reinforced cements and concretes, are discussed. In addition, the results of a survey of the methods for testing the bond are presented. A general discussion of information currently available on the bond between cement matrices and different types of fibre is also included. It is concluded that con-

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tinued research on bond phenomena is required; areas for further work are suggested. The dimensional stability of glass fibrereinforced cement Langley, A.A. Magazine o f Concrete Research Vol 33 No 117 (December 1981) pp 221-226 The dimensional changes of glass-fibrereinforced cements 'specimens, containing about 5% by weight of glass fibre in a neat cement paste matrix, have been monitored during controlled cycles of drying and wetting environments. In situ monitoring of large panels of similar material undergoing continuous natural weathring has also been caried out. For specimens stored in moist conditions, initial drying shrinkage increased with storage time and was grea[er than the following storage in dry air. Reversible shrinkage of about 0.35% was observed for material stored in water for two years. Annual variations of around 0.08% were observed in situ during natural weathering of the large panels, together with short-term thermally induced changes. (Author's abstract). Effect of strain-rate on the pull-out behaviour of fibres, in mortar Gokoz, U.N. and Naaman, E. International Journal o f Cement Composites Vol 3 No 3 (August 1981) pp 187-202 Using steel, glass and polypropylene fibrereinforced Portland cement, the pull-out response at various loading velocities was studied. The effects of loading velocity (strain rate) on the load/time response of fibres, their equivalent bond strength and their energy absorption to failure or to complete pull-out are analyzed. Evaluation of polymer concrete using the method of energy dissipated in damage Cook, D.J. and Crookham, G.D. International Journal o f Cement Composites and Lightweight Concrete Vol 3 No 4 (November 1981) pp 247-254 The influence of the addition of polymer to concrete was investigated using a technique which measures the energy dissipated in damage resulting from a cyclic loading sequence. Performance of steel fibre-reinforced concrete in axially loaded short columns Adepegba, D. and Regan, P.E. International Journal o f Cement Composites and Lightweight Concrete Vol 4 No 3 (November 1981) pp 255-259 Compression tests were carried out on columns of concrete with and without steel fibre-reinforcement. Where reinforcement was used up to 2.0% by weight was included. The results indicated that the inclusion of fibres, in the quantities used, did not increase the ultimate loads of the columns.

Polypropylene-reinforced cement composites for surface reinforcement of concrete structures Raithby, K.D., Galloway, J.W. and Williams, R.I.T. International Journal o f Cement Composites and Lightweight Concrete Vol 3 No 4 (November 1981) pp 237246 A review is given of the possible uses of fibre-reinforced cement as local surface reinforcement for concrete structures. Polypropylene-reinforced cement, the principal subject of the investigation, showed considerable promise as an alternative to asbestos and glass-reinforced cement for this particular application. Tensile and flexural tests indicated that the PP/cement composites have the high strain capacity required for controlling crack development; and that the long term effectiveness is likely to be better than that currently available with GRC. Preliminary tests of SFRC under triaxial loading Brandt, A.M., Kasperkievicz, J., Kotsovos, M.D., and Newman, J.B. International Journal o f Cement Composites and Lightweight Concrete Vol 3 No 4 (November 1981) pl~ 261-266 The results from preliminary tests on steel fibre-reinforced concrete, which involved triaxial stress including some tension, are presented. It is shown that the fibre- reinforced concrete is superior to plain concrete, particularly when tensile stresses are involved. Properties of polymer latex-cement steel fibre composites Bentur, A. International Journal o f Cement Composites and Lightweight Concrete Vol 3 No 4 (November 1981) pp 283-289 The load]deflection characteristics, modulus of rupture, and tensile and compressive strength of polymer latex/cement/steel fibre composites were investigated: different types and contents of polymers and defoamers were used. The presence of the polymer latex resulted in an increase in the strength values by a factor of four, compared with the plain cement mortar.

GENERAL Analysis of a bonded joint in a composite tube subjected to torsion Graves, S.R. and Adams, D.F. Journal o f Composite Materials Vol 15 (198l) pp 211-224 An analysis is made of the stress state in bonded joints of laminated composite tubes subjected to torsional and hygrothermal loadings, by means of the finite element technique. The composite is modelled plyby-ply with the adhesive as a separate elastic layer.

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Bounds on the complex permittivity of a two-component composite material Milton, G.W. Journal of Applied Physics Vol 52 No 8 (August 1981) pp 5286-5293 General bounds are "derived of the frequency dependent effective permittivity, Ee, for any two-component composite material. The structure may be anisotropic, isotropic, periodic, or random. Provided that the scale of inhomogeneities in the composite is sufficiently small compared with the applied radiation, the permittivity of the composite is found to be within a simply constructed region of the complex plane. The appropriate region depends on wht is known about the composite material. More restrictive bounds on Ee are derived for fibrereinforced, uniaxial composite materials. Bounds on the transport and optical properties of a two-component composite material Milton, G.W. Journal of Applied Physics Vol 52 No 8 (August 1981) pp 5294-5304 An infinite set of bounds for the effective permittivity Ee of two-component composite materials is derived and expressed in terms of a single function g. Analogous bounds are found to apply to other transport properties such as electrical and thermal conductivity. The analysis also extends to optical properties provided the structure of the composite is small compared to the wavelength. In all cases Ee is confined to a region of the complex plane which becomes progressively smaller as more is known about the composite. Calculation of interJaminar stress concentration in composite l~tminates Bar-Yoseph, P. and Pian, T.H.H. Journal of Composite Materials Vol 15 (1981) pp 225-239 A new method for analyzing the free-edge stress field in composite laminates is developed based on a perturbation and assumed stress approach. Solutions are described for [±0] s , graphite/epoxy laminates, and are compared with solutions obtained by other techniques. Combining rules for predicting the thermoelastic properties of particulate f'dled polymers, polyblends and foams McGee, S. and McCullough, R.L. Polymer Composites Vol 2 No 4 (October 1981) pp 149-161 Following a review of previous models for the prediction of properties of filled systems, from which it is concluded that the predictions both over- and under-estimate observed properties, new theoretical combining rules are presented for predicting various properties in terms of the matrix and filler properties and the filler volume fraction. These new rules give property values in close agreement with experimental data. Crack growth resistance of short fibre composites: 1 - - influence of fibre concentration, specimen thickness and width Agarwal, B.D. and Glare, G.S. Fibre Science and Technology Vol 15 No 4 (December 1981) pp 283-298 Fracture toughness studies were carried out using short glass fibre-reinforced epoxy composites. The results indicated that critical crack growth resistance depends upon the initial crack length and thus cannot be regarded as a material property parameter. Critical crack growth resistance was found

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to be dependent upon fibre volume fraction. The proposed stress intensity factor showed a slight increase with specimen thickness, and a decrease with increased specimen width. Fatigue of composite materials: damage mechanisms and fatigue-life diagrams Talreja, R. Proceedings of the Royal Soceity of London A378 No 1775 (1981) pp 461475 The basic fatigue damage mechanisms in composite laminates are reviewed and a pattern in the fatigue-life diagrams is proposed. A fatigue limit is shown to exist for unidirectional, cross-plied, and angle plied laminates and suggestions for improving the fatigue resistance of composite laminates are made. Fatigue crack propagation of sheet molding compounds in various environments Hoa, S.V., Ngo, A.D. and Sankar, T.S. Polymer Composites Vol 2 No 4 (October 1981) pp 162-166 The effect of the absorption of water and iso-octane on the rate of fatigue crack propagation in two types of SMC was studied. The results show that water absorption decreases the rate initially but then increases in the final cycles; iso-octane absorption decreased the crack propagation rate. Fracture behaviour by two cracks around an elliptic rigid inclusion Viola, E. and Piva, A. Engineering Fracture .Mechanics Vol 15 No 3-4 (1981) pp 303325 The in-plane biaxial loading of partially bonded rigid inclusion in an infinite matrix, where the bond imperfection is two symmetric cracks, has been analyzed. The elastic solution is obtained by assuming incompressibility and plane strain conditions for the matrix. Stress and displacement fields are represented and a stress criterion which takes into account either the crack extension at the interface or its deviation into the matfix is applied to the fracture response of the elastic system. Fracture toughness of short fibre composites in modes II and m Agarwal, B.D. and Giare, G.S. Engineering Fracture Mechanics Vol 15 No 1-2 (1981) pp 219-230 The fracture toughness of short glass-fibre reinforced composites in the shear modes (II and II) has been investigated. The results indicate that the crack growth resistance and critical strain energy release rate are independent of the initial crack length. The critical strain energy release rate in mode II was found to be less than half of that in mode I or mode III indicating that, for fibrous composites, fracture toughness tests in mode II may be more important than tests in modes I or III. How pigments affect reinforced thermoplastics Parikh, S.S. and Wilson, J.R. Materials Engineering Vol 94 No 3 (September 1981) pp 74-79 The affect of organic and inorganic heavymetal pigments on the tensile strength, notched-Izod, and Garner-impact strengths

of three glass fibre-reinforced thermoplastics is reported. The matrix materials used

were polycarbonate, nylon 6/6, and polypropylene. It was found that most pigments reduced the measured mechanical properties of the composites except for the tensile strength of the glass-reinforced polypropylene which was unaffected. Isochromatic patterns in a plate with a rigid fibre inclusion Gdoutos, E.E. Fibre Science and Technology Vol 15 No 4 (December 1981) pp 299311 An analysis of the isochromatic fringe patterns developed in the vicinity of the end point of a rigid fibre embedded in an elastic plate was carried out. The general characteristic properties of the patterns and their dependence on the Poissonic ratio of the plate were analyzed for the case of an infinite plate subjected to a uniaxial uniform stress at infinity. The stress field distribution in the local neighbourhood of the fibre end was used for the determination of stress intensity factors Kl and K2 for any form of geometry and loading of the plate. (From author's abstract) Liquid absorption of a sheet molding compound Hoa, S.V. and Ouellette, P. Polymer Com-

posites Vol 2 No 4 (October 1981) pp 167170 The absorption of water, iso-octane, methanol and ethanol into a proprietary SMC at room temperature was studied. The results show that for all four liquids the absorption behaviour was Fickian, with constant diffusion coefficients. Desorption of methanol and ethanol soaked specimens caused extensive surface cracking. Materials that control noise Wehrenberg, R.H..Materials Engineering Vol 94 No 4 (October 1981) pp 50-60 The principal acoustic characteristics of sound-absorbing materials are discussed along with the various merits of materials such as foams, glass fibres, filled rubbers and metal sheet. The use of foam/glassfibre/metal composites to produce a noisecontrol material whose properties can be tailored to the requirements is the outlined and illustrated with examples. A new impact modified and heat resistant phenolic

Bertolucci, M.D. S A M P E Quarterly Vol 13 No I (October 1981) pp 14-16 The properties of a glass fibre and mineralfilled phenolic resin, to which a thermoplastic elastomer has been added, are presented. The addition of this reactive thermoplastic' elastomer improves the Izod impact strength and heat resistance of the reinforced phenolic: the stiffness and flexural strength remain unchanged. Nonlinear adhesive behaviour effects in cracked metal-to-composite bonded structures Kan, H.P. and Ratwani, M.M. Engineering Fracture Mechanics Vol 15 No 1-2 (1981) pp 123-130 A technique to analyze metal-to-composite bonded structures based on non-linear adhesive behaviour is presented. Planestress loading is considered, and the adhesive is treated as a non-linear shear spring. The problem is reduced to a set of integral equations which are solved numerically so

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that the stress intensity factor ahead of the crack tip in the cracked metal layer can be computed. Notched strength of sheet molding compounds Hoa, S.V. Polymer Composites Vol 2 No 4 (October 1981) pp 145-148 The tensile strength of a proprietary SMC, containing 30% glass fibre, was studied using test pieces containing circular holes of various sizes. The reults showed that SMC materials contain inherent voids which dominate the effect of notches smaller than a particular size. Novel improved PMR polyimides Pater, R.H. SAMPE Journal Vol 17 No 6 (November~December 1981) pp 17-25 N-phenylamide modified PMR resins, and composites made with the resin and graphite fibres, were investigated. The principal objective was that of improving overall flow characteristics of PMR-15 type resins without compromising composite properties. It was shown that the addition of N-phenylamide to PMR-15 achieved this; and that concentrations of 4 and 9 mole percent PN appear to improve the thermo-oxidative stability of P M R composites. On elastodynamic fracture mechanics analysis of bi-material structures using finite element method Wen-Hwa, C. and Chei-Wei, W. Engineering Fracture Mechanics Vol 15 No 1-2 (1981) pp 155-168 An elastodynamic hybrid-displacement finite element model is developed to deal with problems involving bi-material cracked structures subjected to dynamic loadings The impact effects of two crack surfaces are considered and modelled with a rigorous finite element procedure. Several typical bi-material crack problems subjected to dynamic loading are discussed and results presented for various crack geometries. On stiffness and strength of an aligned short-fibre reinforced composite containing penny-shaped cracks in the matrix Minoru, T. Journal of Composite Materials Vol 15 (1981) pp 198-210 A study was conducted on the prediction of the stiffness and fracture toughness of an unidirectional short-fibre reinforced composite containing numerous matrix cracks. It was assumed that the fibres were aligned in the uniaxial loading direction and the cracks, perpendicular to the loading axis. The interaction between fibres and between fibres and cracks were accounted for by Mori-Tanaka's back stress analysis. The results are thus valid for large volume fractions of fibres or cracks. Plane strain interracial fracture analysis of a bi-material incompressible body Viola, E. and Piva, A. Engineering Fracture Mechanics Vol 15 No 1-2 (1981) pp 131142 The biaxial loading of two dissimilar media with a crack along the common interface has been analyzed assuming plane strain conditions, incompressible media, and biaxial, and shear loading at infinity. The influence of the load parallel to the crack direction and that of the shear stress on the critical tensile stress to cause brittle failure are discussed. Some results illustrating the crite-

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rion formulated are presented graphically. Production and properties of fibres spun from nylon 6/lithinm chloride mixtures Richardson, A. and Ward, I.M. Journal of Polymer Science: Polymer Physics Edition Vol 19 No 10 (1981) pp 1549-1565 The possibility of producing high-modulus nylon 6 fibres by incorporating lithium chloride in the polymer prior to spinning and drawing has been studied. Drawn fibe moduli in the range 8-9 GPa were obtained, compared with 5-6 GPa for unsalted material. The salt is readily removed by washing in boiling water but this results in a significant reduction in moduli which militates against commercial application of the salted fibre. Reliability calculations for strength of a fibrous composite under multiaxial loading Wetherhold, R.C. Journal of Composite Materials Vol 15 (1981) pp 240-248 A closed form expansion method is introduced which offers a systematic way of calculating statistical information for a function of several strength variables, when applied to strength predictions for multiaxially loaded composites. The developed expansion method is applied to the maximum distortional energy criterion using an orthotropic composite. The results are equivalent to those obtained with a simulation method, but are attained with far less computation. The rheology and mold flow of polyester sheet molding compound Lee, L.J. Marker, L.F. and Griffith, R.M. Polymer Composites Vol 2 No 4 (October 1981) pp 209-218 The flow properties of SMC materials were measured using different test procedures. It was found that the deformation under shear forces was substantially different from that under tensile loading; and that extensional viscosity was much higher than the shear viscosity. The flow of SMC material during, moulding showed that the surface layers flowed further than the inner layers when the mould surfaces were hot, causing inner plies to show through at the surface, resulting in some wavy glass orientation. Simultaneous determination of shear and Young's moduH in composites Fischer, S., Roman, I., Harel, H., Marom, G. and Wagner, H.D. Journal of Testing and Evaluation Vol 9 No 5 (September 1981)pp 303-307 A method is described to calculate both the shear (G) and Young's modulus (E) of a composite material by three-point bending. The importance of the two ratios, E/G, which ~s a measure of the degree of anisotropy of the material, and L/d, the span-todepth ratio, is underlined. Experimental results for a glass fibre-reinforced epoxy composite are compared with values calculated from theory and are found to be in good agreement. Stiffness and strength of short fibre composites as affected by cracks and plasticity Fukuda, H. and Chou, T-W. Fibre Science and Technology Vol 15 No 4 (December 1981) pp 243-256 An analysis for predicting the stress/strain relationship and the strength of unidirectional short fibre-reinforced composites is presented. Classical shear-lag analysis is

modified to take into account the effects of load transfer at the fibre ends in addition to the plasticity of the matrix. Stress intensity factor measurements in composite laminates with various notch configurations Roman, I., Havel, H. and Marom, G. Polymer Composites Vol 2 No 4 (October 1981) pp 199-203 K-calibration procedures were applied to determine different K-calibration functions for various notch tip locations within a glass fibre/epoxy angle-ply plate. On the basis of the functions being anisotropic it is concluded that the selection of an appropriate K-calibration function depends on both the reinforcement geometry and the notch tip location. Studies on polymer impregnated composites A m i n a b h a v i , T.M., Patel, R.C. and Birachar, N.S. Polymer Composites Vol 2 No 4 (October 1981) pp 171-178 The properties of eleven composite materials made with waste products were investigated. After impregnation with a polymer these waste materials (such as rice husk, jute, groundnut shell) were found to have better physico-mechanical properties than ordinary cement concrete. Such impregnation, combined with fine sand and epoxy hardener, takes advantage of the optimum properties of the composites. It is suggested that these polymerized composites could be used in building construction, with resultant economies in the use of Portland cement. Sudden stretching of a four-layered composite plate Sih, G.C. and Chen, E.P. Engineering Fracture Mechanics Vol 15 No 1-2 (1981) pp 243-252 An approximate theory of laminated composite plates with cracks subjected to timedependent extensional loads is developed by assuming that the extensional and thickness mode of vibration are coupled. Dynamic stress intensity factors for a crack subjected to a suddenly applied stress vary as a function of time and depend on the laminate construction. Stress intensification at the crack front is reduced when the shear modulus of the inner layers is larger than that of the outer layers. Syntactic foam extrusion Kwok, F.T. and Woodhams, R.T. Polymer Composites Vol 2 No 4 (October 1981) pp 185-191 The mechanical properties of syntactic foams, reinforced with four types of commercially available glass microspheres, were determined. Test pieces were made by pultruding the composites into circular crosssection rods. Although incorporating microspheres decreases strength and modulus, these losses were compensated for by a corresponding decrese in density such that a 50% material cost saving was possible without significant loss of flexural or torsional properties.

METAL/VIA TRICES Development of wear resistant aluminiumaluminium oxide powder composites Grosch, J. and Brockmann, G.J. Powder Metallurgy International Vol 13 No 3 (1981)

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