METAL MATRICES Creep rupture of a silicon carbide reinforced aluminium composite Nieh, T.G. Metallurgical Transactions Vol 15-.4 (January 1984) p 139 The steady state creep properties of aluminium reinforced with SiC in the form of both whiskers and particles are investigated in constant stress creep tests in air in the temperature range 230-370°C. The creep strength of the composite is greater than that of the A1 matrix, and the steady state creep rate is found to depend strongly on temperature and applied stress. The form of the SiC reinforcement affects the creep strength; the whisker form shows markedly superior creep resistance over the particulate form, reflecting their relative strengths and load-bearing capabilities. Fracture surfaces examined by SEM show that failure is by coalescence of voids within the matrix, beginning at the AI/SiC interface.
High temperature strength of oxide dispersion strengthened uluminium Clauer, A.H. and Hansen, N. Acta Metallurgica Vol 32 (1984) pp 269-278 Measurements of the tensile flow stress of dispersion strengthened A1/A120 3 were made as a function of temperature a n d volume fraction. An initial decrease in the flow stress was observed for temperatures between 77 and 195 K, thereafter it was found to be independent of temperature except at high volume fractions of A120 3. Creep rate measurements indicated the presence of a threshold stress, below which creep or plastic flow was not apparent. This threshold value was found to be relatively independent of tepaperature once above 0.5-0.6 T M. from microscopical examination the authors concluded that the A120 3 particles modify the substructure of the materials by producing a coarse dislocation network.
Squeeze casting of carbon fibre--tin alloy composites Geldedoos, D.G. and Karasek, K.R. Journal of Materials Science Letters Vol 3 (1984) pp 232238 Composites are prepared by squeeze casting, involving infiltration of chopped nickel-coated carbon fibres with a liquid tin alloy (ASTM B23/2), and solidifying under pressure. The 8 p m diameter fibres have a 0.5 p m thick coating. Dogbone-shaped tensile specimens are tested, showing an improvement in strength over the matrix alloy. SEM examination of fracture, surfaces of the composite with Vf = 0.31 show good uniform infiltration with two-dimensional fibre alignment; fracture is dominated by failure at the fibre/Ni and Ni/ matrix interfaces. An increase in composite strength can be gained by improvement of the fibre/Ni interface by better dissolution of Ni into the matrix. Thermal diffusivity in in-situ composites Ostenson, J.E., Finnemore, D.K., Verhoeven, J.D., G!bson, E.D. a n d Shanks, H.1L Journal of Applied Physics Vol 55 No 1 (January 1984) pp 278-279 In this work, the suitability of Cu-20 weight % Nb metal/metal composites for use in high strength structural components requiring high thermal conductivities is evaluated in terms of thermal and electrical transport properties in
the temperature range 0-400°C. The alloys are prepared by consumable arc casting, with fine Nb filaments randomly dispersed in a Cu matrix. The results show that for a given Nb dendrite spacing, the rule of mixtures predicts the thermal diffusivity well. Thermal conductivity processes are dominated by p h o n o n scattering rather than boundary scattering. These composites appear attractive as structural members owing to their high strength and thermal coefficients.
RESIN MATRICES The butt-fusion welding of PVDF and its composites Part 2. The reinforcement and welding of PVDF with short carbon fibres Andrews, J.R.F. and Bevis, M. Journal of Materials Science 1Iol 19 (1984) pp 653-671 Injection moulded PVDF (polyvinyledeneflouride) reinforced with 15% of short carbon fibres was prepared, and its mechanical properties investigated. Various compounding and moulding parameters were changed including fibre length, injection temperature, mould geometry a n d fibre finish. The authors were particularly interested in how the material welded to itself. They found that simple butt welding was not successful, especially if the .improved strength and stiffness properties of the material are to be utilized. Problems due to off-axis fibres in the weld were partially solved by using unreinforced material in the weld. However to fully utilize the properties of the material, the authors conclude that end profding or a spigot and socket system would have to be used for jointed ends.
Conductive polycarbonate-cnrbon composites Baltfi Celleja~ FJ., Ezquerra, T.A., Rueda, D.R. and Alonso-L6pez, J. Jol~rnal of Materials Science Letters Vol 3 (1984) pp 165-168 Conductivity measurements of films of polycarbonate filled with several concentrations of carbon black were made at atmospheric pressure in directions parallel and perpendicular to the film surface. At a critical concentration of approximately 90%, the conductivity (~) is" increased by more than 12 orders of magnitude and a saturation effect is observed. The value of tr parallel to the surface is about two orders of magnitude greater than that perpendicular to the surface. At concentrations above the transition region, both of these cr values depend on film thicknesses smaller than 400 pro. The behaviour is explained on the basis of a sufficiently developed network of carbon particles which aid charge transport through the matrix. Current-field characteristics show a decrease in o(perpendicular) with increasing temperature, explained by the thermal expansion coefficient of the polymer. Crack propagation in a glass particle-filled epoxy resin Part 1. Effect of particle volume fraction and size Spanoudakis, J. and Young, RJ. Journal of Materials Science Vol 19 (1984) pp 473-486 A double torsion beam test was used to investigate the effect of strain rate, volume fraction and particle size on the fracture behaviour of glass bead-reinforced epoxy composites. The strain rate had a similar effect on K Ic as found in epoxy resins alone--K Ic decreased with increasing strain rate. Both G IC
and K Ic were found to increase with volume fraction, although at high volume fractions the relationship became complicated. Crack growth in these materials could best be explained in terms of crack pinning. However, comparison of the results with the theories of Lange and Evans produced poor agreement. Much better agreement was obtained using a critical crack opening criteria to describe crack growth.
Crack propagation in a glass particle-filler epoxy resin Part 2. Effect of particle-matrix adhesion Spanoudakis, J. and Young, R.J. Journal of Materials Science Vol 19 (1984)pp 487-496 The effect of the strength of the glass/matrix interface on the fracture behaviour of glass bead-reinforced epoxy composites has been investigated using a double torsion beam technique. Whereas the strength of the interfacial bond had little effect on the fracture toughness, K IC, of the composite, it did effect the fracture energy, G IC- This was found to be due to the drop in the Young's modulus of a poorly bonded composite compared with that of a well-bonded composite.
Deformation design for short-fibre-reinforced thermoplastics M c C a m m o n d , D. and North, P.A. Polymer Composites Vol 5 No 1 (January 1984) pp 72-80 Using the Halpin-Tsai laminate analogy, stiffness matrices at various locations in four short glass fibre-reinforced thermoplastic mouldings are predicted. The resulting anisotropy and inhomogeneity are compared with quasiisotropic values. Predictions are based on actual material structure as obtained from contact microradiographs. The response of the materials to tensile, flexural and shear loads is studied, as is load deformation behaviour in plate bending and twisting. It is concluded that, in the absence of a predictive approach to fibre orientation in these materials, the quasiisotropic stiffness data provide an acceptable means of performing deformation design analysis. The effect of a coating on the thermo-oxidative stability of Celion 6000 graphite fiber/PMR 15 polyimide composites Hurwitz, F.I. and Whittenberger, J.D. Composites Technology Review Vol 5 No 4 (Winter 1983) pp 109-114 The thermo-oxidative stability in air at 316°C of unidirectional Celion 6000/PMR 15 composite panels was investigated. Both uncoated panels and panels coated on one side or both sides with kitchen-grade a l u m i n i u m foil were studied; weight loss and materialograpl~ic techniques were used to assess microstructural damage. It was found that an oxidation resistant coating increased the resistance of the composite to the cracking and matrix degradation usually observed in a high-temperature reactive environment. The effect of edge stresses on the failure of (0 °, 45 °, 90 °) CFRP laminates Curtis, P.T. Journal of Materials Science Vol 19 (1984) pp 167-182 Four laminate geometries were investigated: [0~, -t-45°, 90°]s, 10~, 90°, +45°]s, [5:45 °, 0~, 90°]s and [5:45 °, 90°, 0~ls. The edge strains developed during tensile loading were measured using 1 m m strain gauges bonded to the specimens edge, and orientated in the z direction. Specimen damage was monitored using acoustic emission,
COMPOSITES . JULY 1984