there is currently little literature concerning carbon ceramic systems. This paper reports on the preparation of a porous carbon clay composite and investigates the resultant properties: electrical conductivity, porosity, mechanical strength and thermal stability in air. Pellets were prepared containing a range of carbon contents between 0 and 23 wt %, and clay minerals. The porosity of fixed specimens was as high as 50-65 % with compressive strength values varying between 130 and 400 kg cm -1. Themogranimetric analysis (TGA) indicates a good resistance to o x i d a t i o n and electrical conductivity increases with carbon content up to 20 wt %. A modified version of the model developed by Scarisbrick has been compared with electrical conductivity measurements with good agreement. Toughness determination for fibre reinforced concrete Wang, Y. and Backer, S. The International Journal o f Cement Composites" and Lightweight Concrete Vol 11 No I (February 1989) pp 11-19 Methods currently used to evaluate the toughness of fibre-reinforced concrete are critically reviewed and a new toughness index is proposed. Based on the secant compliance criterion it may be easily determined from a given load/displacement curve. When applied to a wide range of idealized test curves, it is shown to give a better description of the toughness behaviour of FRC than other methods. It is proposed for use in toughness comparison and quality control with the provision that it is used for comparisons among results obtained under the same test conditions.
flexural strength by three-point bend and fracture toughness by SEN beam specimens. A higher sintering temperature is found to give a stronger whisker/matrix interfacial bond strength due to chemical reaction and the presence of residual thermal stresses. The authors suggest that suppressing the formation of a eutectic reaction phase at the whisker/matrix interface could lead to a greater contribution to improved toughness from a whisker pull-out mechanism. Interface structure and matrix crystallization in SiC (Nicalon)-Pyrex composites Murty, V. S. R. and Lewis, M. H. J. Materials Science Letters 5 (1989) pp 571-572 Observations on the microstructure of the matrix and interface are reported for a hot-pressed glass/ceramic composite containing a random dispersion of chopped SiC fibres in a Pyrex matrix. TEM and XRD studies show that the Pyrex partially crystallizes as the cristobalite form of Si02 in increasing proportions with increasing hot-pressing temperature. It is suggested that crystallization is promoted at the SiC-glass interfaces either by local modification of the glass composition or by heterogeneous nucleation on fibre surfaces. Control of the thermal processing cycle is important in developing non-cohesive interfaces which do not clamp fibres during cooling and to retain a glassy matrix structure, since the high relative thermal expansion coefficient of the cristobalite (compared to the matrix glass and fibres) leads to microcracking which adversely affects the composite mechanical properties.
CERAMIC FIBRES The effect of whisker length on the mechanical properties of alumina-SiC whisker composites Baek, Y. K. and Kim, C. H. J. Mater Sci Vol 24 (1989) pp 1589-1593 The good mechanical and thermal properties of alumina/SiC whisker composites make them attractive candidates for applications such as cutting tools and advanced heat engines. This study assesses the strength changes of alumina 20 vol % SiC whisker composites fabricated by hot pressing, for a number of whisker lengths. Measurement values of flexural strength and fracture toughness were found to increase with increasing whisker length with corresponding changes in fracture surface ie longer whiskers exhibiting longer pullout lengths. Strength measurements were compared to those calculated using a modified Fukuda model with good agreement for specimens containing longer whiskers. Fabrication and properties of hot-pressed SiC whisker-reinforced TiBz and TiC composites Kamiya, A., Nakano, K. and Kondoh, A. J. Materials Science Letters 5 (1989) pp 566-568 The fabrication route by sintering and hotpressing of powders is described for producing composites of TiB 2 and TiC reinforced with SiC whiskers. The dependence of matrix grain size and composite mechanical properties on Vf is evaluated by measurements of
COMPOSITES. NOVEMBER 1989
An analysis of shear failure mechanisms for compression loaded [_+ 0]s laminates Stuart, M. J. Journal o f Composite Materials, Vo123 (March 1989) pp 251-263 The interlaminar shear failure due to short wavelength initial imperfections and inplane matrix shearing failure have been analysed in [+ 0]~ laminates under uniaxial compression loading. The non-linear analysis for plies with short wavelength initial imperfections is used to determine laminate displacements, stresses and interlaminar stresses. A failure criterion for compression loaded [_+ 0]~ laminates is introduced. Calculation of the wave propagation in composite materials using the Lamb wave concept Noiret, D. and Roger, J. Journal of Composite Materials Vo123 (Feb 1989) pp 195-206 Simple theoretical calculations have been made on the propagation of a steady wave for plates made of unidirectional reinforced plastics, following the Lamb wave concept. The agreement between experimental data and the calculation was good. Further work will take into account thickness effects and more intricate stacking sequences.
A cell for the manufacture of composite components by filament winding Elliman, D. G., Sorenti, P., Brown, L., Shearing, M., Middleton, V. and Owen, M. J. Advanced Manufacturing Engineering Vol 1 No 1 (October 1988) pp 15-20 A manufacturing cell for the production of
composite components of complex geometry by filament winding is described. The development of a filament winding machine and purpose-built controller is described, together with the design of a robot-assisted cell. The manufacturing process is supported by the computer-aided design of filament paths to give the desired component properties. The operation of the cell is simulated by using a graphics work-station, and the final programme down-loaded to the cell for production. (Authors' abstract) Characterization of thermoplastic composites for processing Muzzy, J., Norpoth, L. and Varughese, B. S A M P E Quarterly Vol 25 No 1 (January/ February 1989) pp 23-29 The development of models simulating the behaviour of fibre-reinforced thermoplastic resins during processing is discussed. The paper focusses on which material properties need to be resolved to implement a process simulation and how these properties can be measured for the materials being used. The consolidation step in the preparation of laminates from APC-2 prepreg is examined in detail and it is shown that the proposed model, in which all parameters are measurable, appears to be appropriate. Electron radiation effects on Mode II interlaminar fracture toughness of GFRP and CFRP composites Takeda, N., Tohdoh, M. and Takahashi, K. S A M P E Quarterly Vol 20 No 2 (January 1989) pp 27-32 Mode II interlaminar fracture toughness was measured by end-notched flexure tests carried out on samples of fibre-reinforced epoxy laminates. The results of tests carried out on glass fibre cloth and carbon fibre cloth reinforced epoxy are reported. Samples were electron irradiated at room temperature prior to testing. For the glass fibre-reinforced samples, a significant decrease in Gnc because of irradiation was found which was attributed to debonding between fibres and matrix as well as resin degradation. For the carbon fibre-reinforced samples only a slight degradation of the resin was found and no degradation due to the fibre/resin interface was seen.
Exact solutions for the transient response of symmetric cross-ply laminates using a higberorder plate theory Khdeir, A. A. and Reddy, J. N. Composites Science and Technology Vol 34 No 3 (1989) pp 205-224 Exact solutions for the transient response of symmetric cross-ply rectangular composite laminates were obtained using a third-order laminate plate theory. Two alternative approaches were used: the method of orthogonality of principal modes; and the state variable approach. The laminate with simply supported boundary conditions was subjected to either a uniform or sinusoidal dynamic load at the upper surface. Comparison of numerical solutions for various loadings indicated that classical plate theory gives results that are significantly different from first-order and higher-order theories. An experimental investigation into the strength of angle-ply GRP tubes under a high rate of loading AI-Salehi, F. A. R., AI-Hassani, S. T. S. and