Literature survey Carbon fibres

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'atum

Prepared by M. E. Adams and 7-. Nensi

CARBON FIBRES Evaluation of single-fibre strength distribution from fibre bundle strength Phani, K. K. Journal o f Materials Science Vol

23 No 3 (1988) pp 941-945 A modified Weibull distribution, characterised by two share and location parameters is presented for analysing the strength of fibres used in advanced composites and provides an upper and lower limit to strength. A m e t h o d for determining the parameters of this distribution from results of tensile tests on fibre bundles is outlined. Application of the m e t h o d to results for Thornell-300 carbon fibres shows that the share parameters b e c o m e modified in the case of bundles. Strain dependencies of the first- and secondorder Raman spectra of carbon fibres Galiotis, C and Batchelder, D. N. Journal of

Materials Science Letters Vol 7 No 5 (1988) pp 545-547 In this work the strain dependencies of the first- and second- order R a m a n spectra of high m o d u l u s carbon fibres are reported. It is concluded that the very high value for the strain d e p e n d e n c e of the second-order Ram a n band, a - 2 4 c m ~ shift for 1% strain, m e a n s that this could be used to evaluate strain distributions in carbon fibres composites.

CEMENT MA TRICES Bending of thin flexible fibre reinforced sheets Bar-Shlomo, S. International Journal o f

Cement Composites and Lightweight Concrete Vol 9 No 4 (November 1987) pp 243-247 A simple dimensionless correction factor is derived which m a y be used with bending formulae normally employed to calculate the bending m o m e n t of thin fibre-reinforced c e m e n t slab (based on the assumption that small deflexions are obtained) when deflexions, just before failure, are large. Equations for the calculation of the slope at the e n d of a simply-supported beam loaded at mid-span and of the secant of the m o d u l u s of elasticity of such b e a m s are also presented. Cement reinforced with steel wool B e n t u r , A and Cree, R International Journal

o f Cement Composites and Lightweight Concrete Vol 9 No 4 (November 1987) pp 217-223 T h e results of a preliminary investigation to determine the feasibility of producing steel fibre-reinforced c e m e n t for thin sheet application by slurry infiltration of commercially available steel wools are reported. It is s h o w n that with fibre contents of < 2 volume % it was possible to prepare composites with

COMPOSITES. NOVEMBER 1988

m o d u l u s of rupture of 1 7 - 2 0 M P a and a t o u g h n e s s seven times greater than that of the unreinforced matrix. T h e composites were also found to be insensitive to orientation effects. Further investigation of the m e t h o d of preparation would be required to prepare composites with higher steel wool contents. Design of ferrocement under combined bending and axial loads M a n s u r , M. A. International Journal of

Cement Composites and Lightweight Concrete Vol 9 No 4 (November 1987) pp 229-233 T h e 'rigid-plastic' concept is shown to be satisfactory for predicting the strength of f e r r o c e m e n t (mortar reinforced with uniformly distributed wire mesh) under combined bending and axial loads. It is also s h o w n to be suitable for the development of non-dimensional design charts. Direct incorporation of silica fume into glass fibre strands as a means for developing G F R C composites of improved durability Bentur, A. and D i a m o n d , S. International

Journal o f Cement Composites and Lightweight Concrete Vol 9 No 3 (August 1987) pp 127-135 Accelerated ageing tests indicate that by i m m e r s i n g glass fibre strands in a microsilica slurry, to incorporate the silica fume in the strands, prior to their insertion in a Portland c e m e n t matrix the durability of the G R C composite was greatly improved. The modulus of rupture of the composite was m a i n t a i n e d at its initial value and, after a loss of m e a s u r e d toughness over the first two m o n t h s , no further loss was observed. Fracture characteristics of sisal fibre reinforced concrete Baluch, H . , Ziraba, Y. N. and Azad, A. K.

International Journal o f Cement Composites and Lightweight Concrete Vol 9 No 3 (August 1987) pp 157-168 A theorectical fracture model equation (requiring input data obtained from tests on notched tensile specimens) to predict the crack resistance curve for sisal fibrereinforced concrete has been developed. Experimental data for computation of fracture energy was obtained from fracture tests using double cantilever b e a m specimens and it is shown that the fracture energy curve so obtained is in close a g r e e m e n t with the theoretical model. It is also shown that the concept of critical crack opening angle as a fracture criterion is applicable to sisal fibrereinforced concrete. Strain rate effects on steel fibre concrete in uniaxial tension K6rmerling, H. A. and Reinhardt, H. W.

International Journal o f Cement Composites and Lightweight Concrete Vol 9 No 4 (November 1987) pp 197-204 Results of an extensive research p r o g r a m m e on the influence of strain rate and low

t e m p e r a t u r e on the mechanical properties of steel fibre-reinforced concrete are reported. T h e straight steel fibres of 0.4 m m diameter were used at 1.5 and 3.0 volume %. The results are compared with those for the unreinforced concrete. It is shown that there was a significant increase of tensile strength of all materials tested due to high strain rates. The fracture energy and strain at m a x i m u m stress also increased. However, the increase in the fracture energy of the fibre-reinforced concrete was considerably higher than that of the plain concrete. In general, the low temperature ( - 1 7 0 ° C ) led to higher strength and fracture energy but, at high strain rates, the fracture energy of the F R C was not increased. It is concluded that the F R C appears to be an efficient material for structures which m a y be exposed to low t e m p e r a t u r e s ( L N G storage) and/or loadings of very short duration (impact, explosion).

CERAMIC FIBRES A comparison of the uniaxial tensile and pure bending strength of SiC filaments Siemers, P. A . , Mehan, R. L. and Moran,

H. Journal o f Materials Science Vo123 (1988) pp 1329-1333 T h e uniaxial and bend strengths of A V C O SCS-6 SiC filaments are reported to be 3 2 5 0 M P a and 4320MPa, respectively, at room temperature. A relationship between the uniaxial and the bend strength was derived using Weibull statistics and compared favourably with experimental data. T h e elastic modulus of the filements has been determined using a gauge length extrapolation technique. Mechanical properties and structure of a new commercial SiC-type fibre {Tyranno) Fischback, D. B., Lemoire, P. M. and Yen,

G. V. Journal o f Materials Science Vo123 No 3 (1988) In this paper the properties of a new titanium-doped polymer-pyrolysis SiC fibre (Tyranno) are compared with those of Nikalon SiC fibre. The results show a narrow distribution of fibre diameters (mean = 8.5 ~tm); an average tensile strength/> 3 G P a which is nearly independent of gauge length in the range 1 - 4 c m ; Weibull p a r a m e t e r m = 7 . 3 and a m e a n Y o u n g ' s modulus of 170GPa. Heat treatment at 1300°C in N 2 appreciably reduced the physical and mechanical properties which were associated with significant crysallite growth and the formation of some Si3N~. Strength distribution and gauge length extrapolation in glass fibres Phani, K. K. Journal o f Materials Science Vol

23 No 4 (1988) pp 1189-1194 A modification of the Weibull distribution is suggested for analysing fibre strength data. T h e applicability of the suggested function

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has been evaluated in terms of experimental tensile strength data reported by previous workers on E-glass and S-994 glass fibres. The function provides upper and lower limits of strength and is characterized by two shape parameters. Based on the strength data at two gauge lengths, predictions of the strengths at other gauge lengths are made and are in good agreement with experimental data.

CERAMIC MA TRICES Effect of particulate additions in the contact damage resistance of hot dashed pressed Si3N4 Page, R. A., Blanchard-Ardid, C. R. and Wei, W. Journal o f Materials Science Vo123 No 3 (1988) pp 946-957 Silicon nitride composites containing particles of SiC, TiC, and BN were tested for contact damage resistance at 900°C in an oxidizing atmosphere. Damage was characterised with profilometry, scanning electron microscopy, bend tests and measurements of coefficient of friction. The addition of TiC was found to dramatically improve the friction and wear charateristics compared to the original silicon nitride due to the formation of a lubricating oxide containing both Ti and Si. ESCA study of amorphus CVD Si3S4 -BN composites Goto, T. and Hirai, T. Journal o f Materials Science Letters Vol 7 No 5 (1988) pp 548-549 The microstructure of three types of amorphous Si3N4 -BN composites, having different boron contents, prepared by chemical vapour deposition, have been investigated using electron spectroscopy for chemical analysis (ESCA). The results indicated that the amorphous CVD (Si-N-B) composites consist of a mixture of amorphous Si3N4 and BN. Glass matrix composites for higher use temperature applications Allaire, R. A., Janas, V. F., Stuchly, S. and Taylor, M. P. S A M P E Quarterly Vol l9 No 1 (October 1987) pp 25-30 The fabrication and properties of several glass and glass-ceramic matrix composites are discussed. Matrices of alkali borosilicate, alkaline-earth aluminosilicate, or calcium aluminosilicate types reinforced with graphite or Nicalon (SIC) fibres were considered. It is shown that the properties of the composites were greatly influenced by the properties of the fibres (i.e. high modulus fibres yielded composites with high moduli). The properties of the graphite/glass composites were maintained at temperatures up to 500°C, while those of the Nicalon/glass and Nicalon/glass-ceramic were maintained up to 700°C and 1250°C respectively. Oxidation resistance of carbon-ceramics composite materials sintered from ground powder mixes of raw coke and ceramics Ogawa, I., Kobayashi, K. and Nishikawa, S. Journal o f Materials Science Vo123 (1988) pp 1363-1367 The preparation of carbon-SiC-B4C composite materials by powder sintering without the use of a binder or hot pressing process is reported. The oxidation resistance of the

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composites was found to depend on the SiC/(SiC + B4C) ratio and the total contents of SiC and B4C in the composites. At optimum ratios (63-87%) the composites showed an oxidation resistance comparable to SiaN4 at 1200°C. Statistical fibre failure and single crack behaviour in uniaxially reinforced ceramic composites Suteu, M. Journal o f Materials Science Vol 23 No 3 (1988) pp 928-933 A lower bound to the work of pull-out is estimated for a ceramic composite under uniaxial loading. The analysis assumes that matrix crumbling does not occur and that fibre strength follows a Weibull distribution. A lower bound for the energy dissipation is computed by assuming that failure occurs by a single matrix crack and that the fibre/ matrix interface is constrained only by friction.

GENERAL An adhesive interleaf to reduce stress concentrations between plys of structural composites Krieger, Jr, R. B. S A M P E Journal Vol 23 No 4 (July/August 1987) pp 30-32 It is shown that by interposing a film of a high-strain low-flow adhesive between strategic layers of a composite laminate, the shear stress concentrations of the structure may be considerably reduced. The film should be thicker than the matrix plies and the adhesive so formulated that it does not mix with the matrix resin. On the applicability of JRo integral for perpendicular interface crack Wen-Hwa Chen, Kuen-Tsann Chen and Chun-Ron Chiang Engineering Fracture Mechanics Vol 30 No 1 (1988) pp 13-19 The applicability of the JRO integral for a perpendicular interface crack is investigated by detailed numerical experiments. Based on an established hybrid displacement finite element model for bimaterial fracture problems, the values of JRO integral are accurately computed. The stress intensity factors for a bimaterial composite, calculated from JRO were found to be in excellent agreement with the solutions available in the literature and those obtained by the direct method. Automated composites cure control implementation - A cure modeling approach to automation Roberts, R. W. S A M P E Journal Vo123 No 5 (September/October 1987) pp 28-33 Further refinements in an automated process for curing composites, which take into account the chemical requirements of the resin, are discussed. A 'cure modelling environment' which utilizes the capabilities of a computer to trace and monitor the component materials from the raw state through to complete cure is presented. It is indicated that the method shows promise, requiring refinement to details. Autoweave - a unique automated 3D weaving technology Rolincik Jr, P. G. S A M P E Journal Vol 23 No 5 (September/October 1987) pp 40-47 The autoweave technology which was pioneered in France and then transferred to

the USA is described and discussed. The method uses foam mandrels into which radial rods are implanted and a yarn, either dry or prepreg, is weave/wound in an axial/ circumferential direction in the corridors formed by the radial rods to fabricate a 3D preform. Various types of contoured near net-shaped carbon fibre preforms, suitable for rocket motors and exit cones, have been produced and reproduced by this automated process. Hybrid cylinders using carbon, quartz, Kevlar, Nextel (alumina borosilicate), Nicalon (silicon carbide) and glass have also been fabricated. Computer controlled resin impregnation for fibre composite braiding Kruesi, A. H. and Hasko, G. H. S A M P E Journal Vol 23 No 5 (September/October 1987) pp 12-15 A resin applicator ring system which has been developed for the adequate wetting of fibres to allow the adaption of braiding for automated production of advanced composites is described. The system has been found suitable for glass, Kevlar, and carbon fibres. The process may be used for the production of structural components such as space station tubes, rocket motor cases, rotor blades and stiffeners. Convergence of strain energy release rate components for edge delaminated composite laminates Rayn, I. S., Crews, Jr, J. H. and Aminpour, M. A. Engineering Fracture Mechanics Vol 23 No 3 (1988) pp 383-396 The near field stress distribution for cracks between dissimilar isotropic or orthotropic materials under plane stress or strain are examined. The delamination between the two different isotropic materials was studied using the Q3D finite element analysis. The strain energy release rates for a [0/+35/90]s laminate with a resin interface are presented for various size delamination tip elements. The results are compared with those obtained for the bare interface (ie one without a resin layer). Crack-arrest study in Mode II delamination in composites Vu-Khanh, T. Polymer Composites Vol 8 No 5 (October 1987) pp 331-341 The methodology used to measure the crack-arrest toughness in Mode II interlaminar fracture in two glass fibre-reinforced epoxy laminates is described and discussed. Strain energy available for the crack propagation was calculated by simple beam theory and found to be in good agreement with experimental measurements and finite element analysis. The results of this study indicate that the fracture energy of the material in shear Mode II delamination is not time-dependent. (Paper presented at 'Composites 86', Canada) The current-carrying capacity of twisted multi-filamentary superconducting composites Mints, R. G. and Rakhmanov, A. L. Journal o f Physics D: Applied Physics Vol 21 No 5 (1988) pp 826-830 The superconducting state stability in twisted multi-filamentary wire is investigated. It is shown that the current-carrying capacity, Ira, of such composites increases with decreasing twist pitch, L, and attains a maximum value when L is less than some critical value.

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The determination of the normal interaction term in the Tsai-Wu tensor polynomial strength criterion Evans, K. E. and Zhang, W. C. Composites

Science and Technology Vol 30 No 4 (1987) pp 251-262 A method, using a single uniaxial strain test, for the determination of the normal interaction term, F12, in the Tsai-Wu polynomial strength criterion is proposed. The appropriate formulae are derived and numerical estimates from existing experimental data for two graphite fibre/epoxy composites are made. It is shown that, using these mathematical expressions, the term Ft2 can be determined from a combination of strains at failure and the elastic constants of the materials. Further work is proposed. The distribution of interparticle distance and its application in finite-element modelling of composite materials Davy, P. J. and Guild, F. J. Proceedings of

the Royal Society of London A418 (1988) pp 95-112 The overall linear elastic behaviour of a composite material is predicted by incorporating the local geometric properties of a random Gibbs hard-core model into finite element analysis of the stress and strain surrounding a single filler sphere. The distribution of interparticle distance based on a Voronoi tesselation was found. The distribution was then used as input for a finite element analysis. Statistical analysis provided close bounds for overall elastic properties. Reasonable agreement was found with experimental data. The effect of impurities on the properties of superconductive composites Bashkirov, Yu. A.. Golub, A. A. and Grimalski, O. U. Journal of Physics D:

Applied Physics Vol 21 No 4 (1988) pp 622-627 In this paper the proximity effect in superconducting composites is analysed and the dependence of the superconducting characteristics of the superconductor - normal matrix system on the distance to the phase boundary is established. It is shown that the increase in the coefficient of electron diffusion in the non-superconducting region near the NS boundary results in depression of the superconductivity in the superconducting elements of the composite. The effect of the interface/interphase of fibre composite properties Piggott, M. R. Polymer Composites Vol 8 No

5 (October 1987) pp 291-297 The problems of preparing a composite material with a complaint matrix which reflects the high strength and modulus of the reinforcing fibres are addressed. Emphasis is placed upon the interphase between fibres and matrix, and the effect of an interphase of lower shear modulus than the matrix in a composite of very short aligned carbon fibres in an epoxy resin is discussed in detail. The results indicate the need for further systematic experiments. (Paper presented at 'Composites 86', Canada) Effects of neutron irradiation on the critical current of bronze processed multifilamentary Nb3Sn super-conducting composites The influence of fast neutron irradiation on critical current. I,., and its strain dependence

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in a bronze processed multi-filamentary Nb3Sn superconducting composite has been investigated. The results suggest that the scaling law for change in dose holds over a certain range of neutron dose. The strain sensitivity of Ic is only slightly affected by irradiation, but is significantly altered by annealing after irradiation. Elastic load transfer from partially embedded axially loaded fibre to matrix Chun-hway Haveh Journal of Materials

Science Letters Vol 7 No 5 (1988) pp 497-499 Simple solutions are derived for the elastic load transfer from a partially embedded fibre into the matrix upon axial loading of the fibre. The results are shown to be insensitive to the fibre aspect ratio when the ratio of the embedded length of fibre to fibre radius is greater than 5. It is shown that the maximum interfacial shear stress developed increases with increasing volume fraction of fibres and decreases in the ratio of fibre to matrix stiffness. An extensometer for fracture mechanics testing of thin composite laminates Barbieri, M. and Corvi, A. Engineering

Fracture Mechanics Vol 30 No 1 (1988) pp 1-4 A lightweight extensometer designed and calibrated by the authors has been described. The extensometer is used without knife edges and being highly deformable does not rigidify when used on low stiffness specimens. In situ fracture tests in the scanning electron microscope Roulin-Moloney, A. C., Cudr6-Mauroux, N. and Kausch, H. H. Polymer Composites Vol

8 No 5 (October 1987) pp 324-330 The experimental set-up for conducting fracture tests on composite materials in the SEM is described. It is shown that this technique for following fracture in situ has potential for studying mechanisms of fracture, providing particular care is taken in interpreting the results. It is suggested that the method should be used as a supplement to more extensive programmes. (Paper presented at 'Composites' 86, Canada). On laminate configurations for simultaneous failure Fukunaga, H. and Chou, T. W. Journal of

Composite 271-286

Materials

Vol 22 (1988) pp

In this paper loading conditions and laminate configurations for simultaneous failure of all laminae in a laminate are derived under in-plane loads. The optimal laminate configuration giving the highest fracture strength for graphite-epoxy composites for a given loading condition are presented. It is shown that the laminate configurations for simultaneous failure are optimal only for a special loading condition. Magnetoresistors based on magnetic composite materials Arivoli, T., Ramkumar, K. and Satym, M.

Journal of Physics D: Applied Physics Vo121 No 4 (1988) pp 636-640 This paper outlines the fabrication and characteristic properties of a magnetoresistor based on a magnet composite material. The device exhibits a magnetoresistance comparable to that of conventional magnetoresistors but can be manufactured using very low

cost technology. The theoretical analysis of the magnetoresistance characteristics of the device is also described. Measurement of small angle fiber misalignments in continuous fiber composites Yurgartis, S. W. Composites Science and

Technology Vol 30 No 4 (1987) pp 279-293 A technique for measuring the volume fraction distribution of the fibre misalignment angle about the mean fibre direction in composites is discussed and described. The technique uses a digitized table interfaced to a microcomputer to make measurements from micrographs of sections of cylindrical samples of composite materials. The method is applied to APC-2 in prepreg, unidirectional, and (0,90) laminate form and the results indicate that the distribution of the fibres in the prepreg is axially symmetric but changes upon lamination, the changes depending upon the stacking sequence. The mechanism of pore formation and the influence of pore size on the reducibility of Fe2Oa-CaCO3 composites Standish, N. and Yang, Y. H. Journal of

Materials Science Letters Vol 7 No 5 (1988) pp 542-544 The mechanism of pore formation and reducibility of composites of Fe203-CaCO3 has been investigated using thermogravimetric and metallographic techniques. Various possible factors which might influence the final pore structure were investigated, including heating pattern, initial porosity of pore samples, and particle size of the raw materials. It was found that the pores were formed at the position of the CaCO3 particles and the size of these pores as proportional to the size of the original CaCO3 particles. Reduction tests showed that the reducibility increased with decreasing CaCO3 particle size and was associated with increasing total surface area. Thi~ mechanisms of prepreg conformance Gutowski, T. G. and Bonhomme, L. Journal

of Composite Materials Vol 22 (1988) pp 204-223 This paper deals with the mechanics of prepreg conformance to a substrate. Using mathematical models and experimental data, two types of behaviour were identified for graphite epoxy prepregs, namely pressure driven lay-up behaviour and surface tension driven lay-up behaviour. For both cases an upper bound on the lay-up speed was observed. The reasons for two different behaviours are discussed. Modified eigen functions for transversely isotropic composite with applications to stress analysis of a broken fiber Jin, Y. and Ting, T. C. T. Journal of

Composite Materials 224-244

Vol 22 (1988) pp

The series solution for a case where a singular point is not on the axis of symmetry is applied to a transversely isotropic composite. Under circumstances where 6 (the order of singularity) as well as 6+K, where K is a positive integer, are eigen values, a modified solution is required and this is presented in the paper. Numerical examples are presented for the stresses associated with the singular terms around the singular points which are created by a broken fibre and interface delamination.

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Protective coatings for composite tubes in space applications Dursch, H. W. and Hendricks, C. L. S A M P E Quarterly Vol 19 No 1 (October 1987) pp 14-18 Protective coatings for a high-strength graphite fibre reinforced epoxy resin tubular structure for a manned space station were evaluated. Coatings assessed included: anodized AI foil; AI foil sputter-coated with AI and SIO2; electroplated Ni (with and without SiO2 coatings) and inorganic sol gel solutions. The coatings were applied to the graphite/epoxy tubes and then subjected to simulated low earth orbit environments. Both phosphoric and chromic acid anodized AI foil were shown to possess very good durability to LEO environment and also exhibited good adhesion to the tubes. A radical proposal for in-plane shear testing of fibrous composite laminates Hart-Smith, L. J. S A M P E Quarterly Vol 19 No 1 (October 1987) pp 7-13 A proposal that: the in-plane shear testing of fibrous composite laminates should be replaced by the much simpler axial tensile (and compressive) testing of a laminate with the complementary fibre pattern, is presented. Thus, the in-plane shear strength of a _+ 45 ° laminate would be established as nominally half the tensile strength of a 0o/90° laminate. Points in favour of the proposal, which is essentially related to a carbon fibre/epoxy resin composite, are discussed. It is suggested that if the proposal were accepted then there could be standardization on a simple, reliable, and reproducible test coupon for in-plane shear testing of all fibre-dominated composite laminates. Survey of current status and future trends in reinforced plastics composites Vu-Khanh, T. Polymer Composites Vol 8 No 6 (December 1987) pp 363-370 The markets, and their rate of growth, for reinforced plastics are reviewed. Future markets, applications, and matrix materials for advanced composites and high volume composites are discussed. The hurdles which will have to be overcome before new composites are commercially viable are also detailed. (Paper presented at 'Composites 86', Canada) Thermo-acoustic emission from a damaged composite Sato, N., Kurauchi, T. and Kamigaito, O. Sarape Journal Vol 23 No 5 (September/ October 1987) pp 48-52 It is demonstrated that the thermo-acoustic emission (the acoustic emission from a material when it is subjected to a thermal cycle) for a delaminated, failed or fatiguedamaged carbon fibre-reinforced epoxy resin is greater than that from the undamaged composite. The 'thermo-AE' is therefore offered as a NDT method for detecting damage in composite materials. Three-dimensional analysis of an arbitrary shared pressurized crack traversing a bimaterial interface Lee, T. S., Advani, S. H. and Lee, J. K. Engineering Fracture Mechanics Vo130 No 2 (1988) pp 191-209 A method for analysing the fracture responses of an arbitrarily shaped planar crack traversing a perfectly bonded bi-material

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interface is presented. The analysis is based on the derivation of two-dimensional singular integral equations for two welded elastic half-spaces which are used to characterize the opening displacement of the threedimensional crack. For the case of an elliptical crack in a homogeneous medium the computed results agree favourably with reported analytical solutions while the limiting cases show asymptotic agreement with results obtained for two dimensional problems. The toughness of a composite containing short britttle fibres Wells, J. K. and Beaumont, P. W. R. Journal o f Materials Science Vo123 (1988) pp 1274-1278 A new model for predicting the cumulative probability distribution of fibre pull-out lengths for a composite containing short brittle fibres is presented. Combined with models of energy dissipation mechanisms, it is used to predict increasing toughness with increasing fibre length, finally attaining a constant value. Good agreement is found between theory and experiment. Validation of mixture equations for dielectricmagnetic composites Musal, H. M., Hahn, H. D. and Bush, G. G. Journal o f Applied Physics Vol 63 No 8 (1988) pp 3768-3770 This paper reviews the assumptions and characteristics of a number of 'mixture equations' relating the effective microscopic electromagnetic properties of a composite material to the intrinsic microscopic electromagnetic properties of its constituents. The validity of these equations was tested by comparing measured and predicted values of dielectric constant and magnetic permeability for a series of well characterized dielectric-magnetic composite samples comprised of ferrite particles in an epoxy binder. The correlation between the predicted and measured values are shown and the regimes where large disparties between the predictions of the various equations occur are emphasised. Van der Pauw measurement of metal fibre orientation in a plastic-metal composite Kinsler, M., Murick, L. V. and Patton, J. Journal o f Materials Science Vol23 (1988) pp 1411-1415 The resistive anisotropy of stainless steel fibres in an ABS matrix has been studied as a function of moulding geometry using Van der Pauw's technique. Results obtained correspond to pictures produced by X-ray measurements. Resistivity was also measured by the more common two probe method. These agreed well with Van der Pauw data (95% confidence). Wave propagation in fibre reinforced composites for oblique incidence Kline, R. A. Journal o f Composite Materials Vol 22 (1988) pp 287-303 A simplified method for analysing reflectionrefraction phenomena in transversely isotropic materials for arbitrary angles of incidence is developed for non-destructive testing purposes. This approach is expected to be used in a scanning mode to map out local variations in moduli. As well as providing rapid visual identification of substandard regions it is expected to provide a quantitive measure of all pertinent elastic moduli.

Zero thickness quarter point crack tip finite element for modelling an interface between two materials Tarazi, S. S. and Mandel, J. Engineering Fracture Mechanics Vol 30 No 1 (1988) pp 37-48 A special five noded, quadratic, zero width singular interface finite element is developed for modelling the interface between fibres and the matrix material at the crack tip of an interface crack in a composite material. The element is shown to have the theoretical 1/~'~ singularity in the stress field at the crack tip and can be used with the quarter point singular element developed by Barsoum. Numerical results were found to be in close agreement (under biaxial tension).

METAL MA TRICES Dielectric behaviour of barium titanatepolyvinylidene fluoride composite Murabidhar, C. and Pillai, P. K. C. Journal o f Materials Science Vol 23 No 3 (1988) pp 1071-1076 The dielectric behaviour of barium titanate (BaTiO3) and polyvinylidene fluoride (PVDF) has been studied. The PVDF has a significant effect on the dielectric properties below 50 wt% BaTiO3 but this becomes insignificant at high weight fractions of BaTiO3. This finding is confirmed by X-ray diffraction studies. Elevated temperature fracture resistance of a SiC whisker reinforced/polycrystalline AI203 matrix composite Jenkins, M. G., Kobayashi, A. S., White, K. W. and Bradt, R. C. Engineering Fracture Mechanics Vol 30 No 4 (1988) pp 505-515 The fracture resistance of a 25% SiC whisker/Al203 matrix composite (HA9S) using chevron-notched and straight-notched, 3-point bend specimens has been determined over the temperature range 20-1400°C. Crack mouth opening displacement (CMOD) was monitored using a laser interferrometric strain gauge. The crack growth resistance curves were determined from previously established relationships between the CMOD compliance, effective crack length, and the load point displacement. Fracture toughness testing of metal matrix composites Tsangarakis, N., Nuves, J. and Slepetz, J. M. Engineering Fracture Mechanics Vol 30 No 5 (1988) pp 565-577 A variety of specimen configurations was used to determine the fracture toughness of various metal matrix composites. A further consideration of the ASTM E399 test procedure as a standard method for the determination of fracture toughness is suggested. Influence of high temperature exposure on the properties of alumina short fibre reinforced AA6061 alloy Suganuma, K., Okamoto, T., Hayami, T., Oku, Y. and Suzuki, N. Journal o f Materials Science Vol 23 (1988)pp 1317-1323 The influence .of exposure to high temperatures on AA6061 alloy matrix composites containing 15% volume alumina short fibres, in terms of the microstructure and strength has been examined below the liquidus of

COMPOSITES. NOVEMBER 1988

alloy matrices. Above 853K, the fracture strength was significantly decreased. This was accompanied by a decrease in the concentration of magnesium following precipitation as a spiral on the alumina fibre surface. Vacuum treatment facilitated the vaporisation of magnesium from the specimen surface. The use of the brazing method at short intervals and lower temperatures is recommended for joining to composites

Influences of interfacial bonding strength and scatter of fibre strength on tensile behaviour of unidirectional metal-matrix composites Ochiai, S. and Osamura, K. Journal of Materials Science Vol 23 No 3 (1988) pp 886-893 By means of the Monte-Carlo simulation technique using two dimensional model composites, the authors have studied the tensile behaviour of unidirectional metalmatrix composites whose matrix has a relatively low yield stress compared to the strength of the fibres. The results indicate that the strength of the composite increases with increasing bond strength when the scatter of fibre strength is large. The fracture mode changes from non-cumulative to cumulative with increasing scatter in fibre strength and the fracture surface becomes irregular when the bond strength is low and the scatter in fibre strength is large. The mechanical and electrical properties of ZrO2-Na[~"-AI203 Sheng, Y., Sarkar, P. and Nicholson, P. S. Journal o f Materials Science Vol 23 No 3 (1988) pp 958-967 The fracture toughness, Young's modulus and bending strength of ZrOz-NaI3"-AI203 composites are shown to increase with increasing ZrO content. For composites with a low ZrO2 content, surface grinding was found to be an effective way of increasing the strength. A study of the ionic conductivity of samples containing 15% (by volume) of ZrO2 indicated an ionic specific resistivity of 9 l]cm at 300°C. Metal matrix composite microwave packaging components Thaw, C., Minet, R., Zemany, J. and Zweben, C. S A M P E Journal Vol 23 No 6 (November/December 1987) pp 40-42 Metal matrix composites were investigated as replacement materials for conventional metallic materials to meet the stringent requirements for microwave circuit packaging. Candidate materials were selected for material property requirements such as modulus, coefficient of thermal expansion, thermal conductivity and density. Results of tests carried out on the two materials selected: silicon carbide particle-reinforced aluminium and pitch-based graphite fibrereinforced aluminium are presented and their suitability for the packaging materials discussed. Microstructural development of a ZrO2Na~' '-AI203 composite Sheng, Y. and Nicholson, P. S. Journal o f Material Science Vol 23 No 3 (1988) pp 982-986 The development of microstructure in ZrO2NaI3"-AI20 3 composite containing 15% (by volume) ZrO2 has been studied, The ZrO2 inhibits abnormal grain growth of the NaI3"AI20 3 grains which are modified to follow a

C O M P O S I T E S . NOVEMBER 1988

cubic time law. Direct particle coalescence was found to be the basic growth mechanism for the ZrO2.

Some observations on the matrix microstructure of aluminium-silicon alloy-graphite particle composites Das, S., Prasad, S. V., Rohagi, P. K. and Ramachandran, T. R. Metallurgical Transactions A, Vol 19A (May 1988) pp 1365-1367 A study has been made of the solidification behaviour of a near eutectic aluminiumsilicon alloy (BS: LM13) matrix containing 3 wt% graphite particles in order to understand how the eutectic silicon gets modified in the presence of dispersed graphite particles. The study indicated that when these particles are close to each other or the primary aluminium dendrite boundaries, the shape and size of the silicon is modified. It is proposed that the mechanism is that of physical constraint to the anisotropic growth of silicon.

RESIN MA TRICES The automation of the lay-up and consolidation of PEEK/graphite fiber composites Colton, J. S. et al. S A M P E Journal Vol 23 No 5 (September~October 1987) pp 19-25 Processes in the fabrication of graphite fibre/PEEK composites which may be performed by automated methods are discussed. Two lay-up processes, one for producing discrete components and the other for continuous operation, are described in detail. An automated method for achieving consolidation of the graphite fibre/PEEK composite using radiant infrared quartz tube heating was also investigated. All three processes are shown to be technically feasible.

Debonding and friction at fibre-polymer interfaces. I: Criteria for failing and sliding Piggott, M. R. Composites Science and Technology Vol 30 No 4 (1987) pp 295-306 Tests to measure certain interface or interphase effects in composite materials are critically reviewed. The significance of the results obtained from the single fibre pull-out test, single fibre 'composite' test, microdebond technique, and microcompression technique are discussed in detail. It is shown that the fibre pull-out test can provide both debonding energies and data on friction after debonding. This leads to the suggestion that the governing criterion for interface failure in carbon fibre-reinforced epoxies and glass fibre-reinforced epoxies and polyester resins is based on energy rather than stress. The delamination behaviour of carbon fiber reinforced PPS Davies, P., Benzeggagh, M. L. and de Charentenay, F. X. S A M P E Quarterly Vol 19 No 1 (October 1987) pp 19-24 The delamination behaviour of unidirectional carbon fibre-reinforced polyphenylene sulphide under different loadings was studied and compared with that of two carbon fibre-reinforced epoxy resins. The influence of: the type of loading (Mode I and Mode II); the annealing of specimens; the specimens geometry; and the temperature are described and discussed; as are the test methods. It is suggested that a test method designed to avoid fibre bridging would yield more satisfactory results.

Compressive response of Kevlar/epoxy composites Yeh, J. R. and Teply, J. L. Journal of Composite Materials Vol 22 (1988) pp 245-257 The longitudinal compressive response and failure mechanism of unidirectional Kevlar/ epoxy composites have been studied. A mathematical model is developed using the principle of minimum potential energy. The model was used to predict the effects of local fibre misalignment and non-linear shear deformation of the matrix. Comparison with experimental results showed reasonable agreement. It is shown that the compressive strength of Kevlar/epoxy composites is dominated by local shear failure.

Dynamic mechanical analysis of some randomly-oriented viscoelastic short-fiber composites Vallianos, C. Composites Science and Technology Vo130 No 4 (1987) pp 239-250 Static tensile and dynamic mechanical behaviour of tanned leather fibre-reinforced ethylene-vinyl acetate copolymers were investigated. Two copolymers, one containing 14% and the other 28% vinyl acetate, were used as matrix material with short fibres, randomly oriented, as reinforcement. The effect of fibre content on Young's modulus and the viscoelastic properties was measured over distinct fibre volume fractions, ranging from 0.0 to 0.6. Dynamic measurements were carried out at a frequency of 11 Hz and at temperatures from -80°C to 90°C. It is shown that the mechanical behaviour of these materials could be predicted by mathematical models incorporating, parametrically, the Puck equations for unidirectional laminae. These models coupled with the Hashin correspondence principle could also describe the complete viscoelastic response.

Damage tolerance in graphite-epoxy composite: comprehensive monitoring method Tanson, M. and Roy, C. Polymer Composites Vol 8 No 5 (October 1987) pp 352-357 A model, based on the statistical theory of strength and the mechanical redistribution of stresses between plies of a damaged laminate, from which the minimum expected lifetime of a graphite/epoxy structure under cyclic loading conditions may be calculated is presented. The results of tests on coupons of the unidirectional laminates, using acoustic emission to monitor internal damage during cyclic loading, agree well with the model. (Paper presented at 'Composites 86", Canada)

Dynamic mechanical analysis studies of the interphase Chua, P. S. Polymer Composites Vol 8 No 5 (October 1987) pp 308-313 The results of dynamic mechanical tests carried out along the fibre direction of unidirectional glass fibre-reinforced polyester are discussed. Organosilanes were used to coat the glass fibres and specimens were prepared by filament winding. The loss tangent (tan 6) at the glass transition temperature of the composite was determined and compared with interfacial shear strength. It is indicated that the quality of the interphase can be characterized by the tan 6 at the Tg. Good interfacial adhesion, associ-

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ated by low energy dissipation, exhibited low tan 8 at the T s of the glass fibre-reinforced polyester. (Paper presented at 'Composites' 86, Canada) The effect of fibre-matrix adhesion on the fatigue fracture of glass-fiber-reinforced poly(vinyl chloride) Nguyen, P. X. and Moet, A. Polymer Composites Vol 8 No 5 (October 1987) pp 298-307 The effects of fibre weight fraction, applied stress level, and the use of a silane coupling agent on the fatigue crack propagation in an injection-moulded glass fibre-reinforced PVC were examined. It is shown that, in the case of composites reinforced with fibres treated with a coupling agent, the fatigue lifetime and fracture toughness increased with fibre weight fraction. Composites not including a coupling agent exhibited the highest fracture toughness at 10 wt% fibre but a shorter fatigue life. A crack layer approach was used to characterize toughness and lifetime in terms of damage mechanisms. (Paper presented at 'Composites 86', Canada) Electrical conductivity of polyethylene carbon-fibre composites mixed with carbon black Balta Calleja, F. J., Bayer, R. K. and Ezquerra, T. A. Journal of Materials Science Vol 23 (1988) pp 1411-1415 The paper presents the results of a study on the change in electrical conductivity of polyethylene composites with mixtures of carbon fibres and carbon black. The resulting structures are shown to be affected by the mixing process. The results are discussed in the light of various electrical models. Electrical properties of exfoliated-graphite filled polyester based composites Foy, J. V. and Lindt, J. T. Polymer Composites Vol 8 No 6 (December 1987) pp 419-426 The method of incorporating exfoliated graphite particles (graphite particles expanded by heating to an accordion shape 7 × I mm) into an unsaturated polyester matrix is described, it is shown that the resultant composite is electrically conductive and of good mechanical integrity with EMI shielding effectiveness. (Paper presented at 'Composites 86', Canada) Excellent flexural properties of aminimidecured epoxy resin as a matrix for micadispersed polymer composites Inubushi, S., Ikeda, T., Tazuke, S., Satoh, T., Terada, Y. and Kumagai, Y. Journal of Materials Science Vol 23 No 4 (1988) pp 1182-1188 The flexural strength and modulus of aminimide-cured epoxy matrix have been compared with a conventional epoxy resin, both containing a range of volume fraction (Vf) of mica flakes. A steady increase in the flexural modulus .with Vf was found for the aminimide cured epoxy. Intact mica flakes without surface treatment imparted a substantial reinforcing effect on the flexural strength of the aminimide cured resin. Fracture toughness of unidirectional graphite fibre reinforced/epoxy composite in mode II (forward shear) using a thin tubular specimen.

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Giarre, G. S., Herold, A., Edwards, V. and Newcomb, R. R. Engineering Fracture Mechanics Vol 30 No 4 (1988) pp 531-545 The torsion tube method was used to find K~ic of a graphite fibre- reinforced/epoxy composite. It was found that the crack growth resistance at instability and the initial strain energy release rate were independent of the initial crack in the range of crack length investigated. Gnc by the torsion tube method was found to be 42% greater compared to the end cracked beam method. It is concluded that the thin tubular torsion method is more accurate. Gnc for graphite reinforced epoxy was found to be half of the glass fibre reinforced epoxy composites for similar volume fractions of fibre. High temperature liquid crysatalline copolyester composites. Part h A review and new data for the self-reinforced matrix phase Frayer, P. D. Polymer Composites Vol 8 No 6 (December 1987) pp 379-395 As an introduction to a project investigating fibre-reinforced thermotropic liquid crystalline polymers (TLCP) where the matrix material may be self-reinforced, the structure-processing-morphology-property relationships of TLCPs are reviewed and described in detail (162 references) (Paper presented at 'Composites 86', Canada) High temperature polyimide blends Burkes, H. D. and St Clair, T. L. SAMPE Quarterly Vo119 No I (October 1987) pp 1-6 Melt viscosities of various polyimide blends, which had been successfully used as matrix resins for composite materials, were investigated. Blends of LARC-TPI (Langley Research Centre Thermoplastic Polyimide) and PISO2 (polyimidesulphone, previously shown to have the processability of a polysulphone and the solvent resistance of a polyimide) were prepared in the ratios, 1:2, 1:1, and 2:1. It was found that the blend with one part LARC-TPI to two parts PISO2 had the highest viscosity at all strain rates, and afforded composites of high quality and mechanical performance but, all blends should be useful as composite matrices. Influence of cure cycle upon selected physical properties of a vinyl ester resin Sandalls, P. L., Yates, B., Baggott, R., Kanellopoulos, V. N., Wostenholm, G. H. and Stevenson, B. J. Journal of Materials Science Vol 23 (1988) pp 1443-1452 The influence of variations in the cure cycle of a vinyl ester resin upon selected properties such as flexural and tensile strengths, moduli, thermal expansion, density and hygrothermal properties of the resin and composites specimens have been examined, it is concluded that an alternative, more economic curing cycle can be defined by detailed observations of volumetric changes during cure without significant changes in physical properties. Influence of fibre characteristics on polyolefin reinforced composites under limited cyclic loading Keer, J. G. International Journal of Cement Composites and Lightweight Concrete Vol 9 No 3 (August 1987) pp 145-156 The behaviour of three types of polyolefinreinforced cement under limited cyclic loading is described. The reinforcing fibres were continuous fibres forming part of a fibre

network produced by opening up a fibrillated drawn film of polyolefin and were impreg n a t e d with a h i g h - s t r e n g t h , superplasticized cement. Three different polyolefin films were used: a rough textured; and a smooth textured polypropylene film; and a polyethylene film. The differences observed in the behaviour of the composites are related to the differences in the tensile stress/strain behaviour of these films. Mechanical and acoustic emission response of unidirectional and cross-plied GRP laminates Henrat, P., Vautrin, A. and Harris, B. Composites Science and Technology Vol 30 No 4 (1987) pp 263-277 An attempt to show that a joint analysis of in-plane macroscopic strains and A E amplitude distributions (plotted on logarithmic scales) can be used to characterize the onset of damage mechanisms is described. Damage accumulation in unidirectional and cross-ply (0, 90)2 s and (90, 0)2s GRP subjected to monotonic uniaxial tensile tests and their in-plane mechanical behaviour were continuously monitored by A E and triaxial strain gauge techniques. It was found that the chief A E features, such as continuous emissions or high logarithmic emission rates, were associated with changes in longitudinal and transverse in-plane mechanical response. Miernmechanisms of interlaminar fracture and fatigue Russell, A. J. Polymer Composites Vol 8 No 5 (October 1987) pp 342-351 The interlaminar fracture and fatigue properties of AS/3501-6 graphite/epoxy are discussed from a mechanistic point of view. Particular emphasis is placed on the interaction between loading mode and the local geometry of the interlaminar zone, and on how this affects the stresses close to the crack tip and the resulting failure path. Delamination growth under Mode I loading is shown to depend on the likelihood of fibre bridging occurring and on how effective these bridged fibres are at diverting strain energy away from the crack tip. The Mode II behaviour is controlled by both the work required to shear the fibres from the matrix and the ease with which tensile failure of the matrix between the fibres can occur. (Author's abstract) (Paper presented at 'Composites 86', Canada). Optothermal analysis of polymer composites Krapez, J. C., Cielo, P., Maldague, X. and Utracki, L. A. Polymer Composites Vol 8 No 6 (December 1987) pp 396-407 Applications of optothermal techniques (using radiative heating and temperature monitoring by infrared sensors) to the nondestructive testing of fibre-reinforced polymers are discussed. Thermographic techniques with extended surface heating may be used for the NDT of carbon fibre-reinforced plastic laminates and image-processing methods are shown to enhance the visibility of subsurface defects. Spot-heating thermographic methods have been developed which will characterize properties such as fibre concentration, orientation and distribution in fibre-reinforced thermosets and thermoplastics. It is also shown that thermography can provide information on fibre orientation not only at the surface but also at deeper layers below the surface. (Paper presented at 'Composites 86', Canada)

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Panel discussion: Thermoplastics vs thermosets in advanced composites Utracki, L. A. Polymer Composites Vol 8 No 6 (December 1987) pp 437-440 A resum6 of the contributions made by all the speakers in a panel discussion on the comparative advantages of thermoplastic or thermoset matrices in advanced composites and the future applications of these materials is presented. The discussion took place at the conference 'Composites 86' held in Canada on 25-26 November 1986, organized by the National Research Council of Canada, Industrial Materials Research Institute. Parameters determining the strength and toughness of particulate-filled epoxy composites Roulin-Moloney, A. C., Cantwell, W. J. and Kausch, H. H. Polymer Composites Vol 8 No 5 (October 1987) The effects of filler volume fraction, particle size, aspect ratio, modulus and strength of filler, resin/filler adhesion, and toughness of the matrix on the stiffness, strength and toughness of particulate-filled epoxy resins, typically used in high voltage insulators, have been evaluated. Failure mechanisms were determined by examining SEMs of the fracture surfaces of filled rubber-modified epoxies. Sub-critical crack, characterized by resin/particle debonding, is seen to initiate cracks which continue to grow until the size is reached after which sudden failure occurs. Calculations based on this mechanism allow the prediction of long-term strength with sufficient accuracy for engineering design. (Paper presented at 'Composites 86', Canada) Particulate metallic glass composite magnetostricters for interferrometric magnetometry Brugel, D., Gibbs, M. R. J. and Squire, P. T. Journal o f Applied Physics Vol 63 No 8 (1988) pp 4249-4251 This paper discusses the use of a particulate metallic glass (Metaglas-2605 SC) embedded in an epoxy resin binder (GY250/HY837) as a candidate material in the production of sensor heads for fibre optic interferrometric magnetometers. Measurements are presented on magnetization and magnetostriction of this material in the quasi-DC regime. The dynamic behaviour when used as magnetic field sensors is also described. Percolation phenomena in polymer/carbon composites Hsu, W. Y., Hottje, W. G. and Barkley, J. R. Journal of Materials Science Letters Vol 7 No 5 (1988) pp 459-461 The transition between the insulating and conducting states of various carbon/polymer composites have been studied. The percolation threshold, fc, determined from conductivity data obtained from the resistance and dielectric dissipation, was found to vary between 5 and 25% by volume of carbon depending on the polymer and carbon type. The results indicate that fc is critically dependent on dispersion conditions, the carbon structure and morphology, and the surface energy of the polymer and carbon. Critical exponents from the resistivity of conductive samples (t = 1.9) and the dielectric constant of insulative samples (s =

COMPOSITES. NOVEMBER 1988

0.8) agree well with experimental values obtained for other systems and with theoretical predictions. Values of the critical exponent from the loss factor of insulative samples were, however, substantially smaller than expected for an ideal composite or perfect conductor and insulator. PMR polyimide compositions for improved performance at 371°C Vannucci, R. D. S A M P E Quarterly Vol 19 No 1 (October 1987) pp 31-36 Higher molecular weight PMR resin formulations were investigated as candidate resins for matrices for composite materials for use at high temperatures. Neat resin mouldings were prepared from various monomer reactants and screened for their thermo-oxidative stability at 371°C under both ambient and four atmospheres air pressure (to simulate conditions in an engine zone). It was found that one PMR-II resin composition had potential for use under these conditions. It is also shown that resins of formulated molecular weight have enhanced oxidative stability at 371°C but require higher cure pressures to yield high quality laminates. Preparation and radiation-resistance evaluation of glass fibre composites having various epoxy matrices Egusa, S., Udagawa, A., Hashimoto, O., Ono, T., Yamamoto, Y. and Sonoda, K. Journal o f Materials Science Letters Vol 7 No 5 (1988) pp 503-505 The effect of radiation dosage on the strength, at room temperature and at 77 K, of E-glass fabric composites with five different epoxy resin matrices has been examined. The results support the conclusion that the strength of the composite is only slightly changed by irradiation when the failure strength of the matrix is higher than that of the fibre. Where the failure strength of the matrix is equal to or less than that of the fibre, the strength of the composite decreases with increasing radiation dosage due to the radiation-induced decrease in matrix failure strain. This is supported by the observation that the dose dependence of the strength of a composite is almost independent of the fibre volume fraction. Strain-controlled torsional test method for screening the performance of composite materials at cryogenic temperatures Kaser, M. G. Journal of Materials Science Letters Vo123 No 3 (1988) pp 830-834 This paper outlines a strain-controlled, torsional test method designed to provide a method for assessing the influence of component and environmental parameters on the performance of fibre-reinforced organic matrix composite materials at temperatures from 295 to 4K. The system uses inexpensive, easily constructed rod-shaped specimens and provides quantitative information on the torsional strength and modulus. Torsional buckling analysis and damage tolerance of graphite epoxy shafts Bauchau, O. A., Krafchack, T. M. and Hayes, J. F. Journal o f Composite Materials Vo122 (1988) pp 258-270 A preliminary study dealing with residual strength of tubes with holes has been

underatken. Experimentally measured torsional buckling loads on graphite epoxy shafts have been compared with theoretical predictions based on a model which includes elastic coupling effects and transverse shearing deformations. Good agreement was found between experimental results and the theoretical predictions. Toughened blends of poly(butylene terephthalate) and BPA polycarbonate. Part 1. Morphology Hobbs, S. Y., Dekkers, M. E. J. and Watkins, V. H. Journal o f Materials Science Vol 23 (1988) pp 1219-1224 The morphologies of melt blends of poly(butylene terephthalate) (PBT) and bisphenol-A (BPA) polycarbonate toughened with a core/shell impact modifier have been characterized using transmission and scanning electron microscopy. The distribution of various blend components have been examined by selective staining. The effect of thermal history on morphology is also investigated. Evidence is presented for partial melt miscibility of BPA polycarbonate and PBT and rate dependent segregation during cooling. Toughened blends of poly(butylene teraphthalate) and BPA polycarbonate. Part 2. Toughening mechanisms Dekkers, M. E. J., Hobbs, S. Y. and Watkins, V. H. Journal of Materials Science Vol 23 (1988) pp 1225-1230 The toughening mechanisms of blends of poly(butylene terephthalate) (PBT) and bisphenoI-A (BPA) polycarbonate with a core/ shell impact modifier have been studied. Shear deformation was found to be the major toughening mechanism for both PBT and PBT/BPA polycarbonate blends. The low temperature impact toughness of toughened PBT/BPA polycarbonate blends was significantly greater that that of toughened PBT and this is attributed to the partial miscibilty of BPA polycarbonate with PBT, with the BPA polycarbonate residing in the amorphous interlamellar regions of PBT spherulites facilitating interlamellar slip. Weldline integrity of reinforced plastics: effect of filler shape Fisa, B., Dufour, J. and Vu-Khanh, T. Polymer Composites Vol 8 No 6 (December 1987) pp 408-417 Weldlines such as occur in injection moulded products where two separate melt streams join either in multi-gated moulds or as a consequence of flow around inserts and which give rise to weaknesses in the finished products were invetsigated. A large number of polypropylene moulded products of different shapes reinforced with fillers of comparatively large size, in varying shapes (glass spheres, fibres, or flakes) were examined qualitatively. It was found that in weldlines formed by head-on meeting of two melt fronts with no subsequent flow, fibres and flakes are orientated perpendicular to the flow, producing weak weldlines. Redesigning moulds so that the melt front expands laterally after the weldline is formed is" suggested. (Paper presented at 'Composites 86', Canada)

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