resin interface: evaluation of experimental parameters

chosen to encompass a range of mechanical responses. Under small deformations it is considered that classical lamination theory is adequate to describe their linear elastic behaviour. Three analytical approaches are examined to model non linear elastic behaviour. An incremental method based on the superposition of infinitesimal deformations is shown to be a good approximation, whilst theories based on Eularian or Lagrangian systems are considered to be more powerful. Finally the paper discusses areas requiring greater understanding to enable the tailoring of flexible composite properties for engineering applications. Fracture surface roughness as a gauge of fracture toughness: aluminium-particulate SiC composites Davidson, D. L. Journal o f Materials Science Vol 24 (1989) pp 681-687 The influence of manufacturing and processing variables on the fracture toughness of a particulate SiC reinforced aluminium alloy has been determined. This was achieved by mechanically alloying and conventionally casting material, varying particle size, volume fraction and matrix composition and heat treatment. Samples were tested in compact tension for fracture toughness and a quantitative metallography technique used to determine fracture surface profiles. Results indicate surface roughness ratios to be well described by fractel dimensions in fast fracture zones. However, these observations do not correlate with fracture toughness measurements. An explanation is proposed based on the work done in the plastic zone of the crack during propagation. Honeycomb cure modelling Chiao, L. and Borris, P. W. S A M P E Quarterly Vol 22 No l (October 1988) pp 33-37 A model for the cure of honeycomb core materials is presented. Use of the model for curing aramid paper honeycomb coated with phenolic resin has resulted in a cure schedule with shorter cure times at higher temperatures, reducing the ramp/hold processing times by 50%. The resultant core is shown to have equivalent mechanical properties to cores produced by standard cure procedures. Implosive consolidation of polymer ceramic powder composites Muhanna, A. H. and Blazynski, T. Z. Composites and Science Technology Vol 33 No 2 (1988) pp 121-133 Compacts of PVC-ceramic powders were formed by a direct implosive method and their morphology, density and compressive strength examined. It is shown that compacts of PVC-silica and PVC-alumina of high strength and density with potential for use in demanding wear and lubrication conditions can be formed by this method. Industrial development of composite materials: towards a functional appraisal Willinger, M. Composites Science and Technology Vol 34 No 1 (1989) pp 53-71 This paper, first presented at the European Composites Forum held in Cambridge, UK, July 1987, analyses economic aspects of the development of composite materials. Design philosophies (matrix, structural, and functional designs) are reviewed. The distribution of composite materials in complex

COMPOSITES. SEPTEMBER 1989

systems (eg aircraft and cars) is identified and the technological consequences of this diffusion are discussed. Finally, future producer/user relationships are proposed. A low-frequency axial oscillation technique for composite material damping measurement Lin, C. H. and Plunkett, R. Journal o f Composite Materials Vol 23 No 1 (January 1989) pp 92-105 Material damping measurements are made using strain vs strain hysteresis loops during low-amplitude sinusoidal axial loading of an aluminium tube coated with a transverse carbon/epoxy layer over part of its length. Specimen preparation and experimental techniques are described in detail. The loss factor is obtained from the hysteresis loop area, using the ratio of axial stiffnesses of the individual layers and the phase difference between the strain in the coated and un-coated regions. The loss factor is found to be relatively insensitive to frequency (<15% change from 0.05Hz to 10Hz) and mean strain (<7% change from -1000 to 1100 ~tc at 1 Hz) over the ranges investigated. The measurement of fracture energy in aligned composites Barlow, C. Y. and Windle, A. H. Composites Science and Technology Vol 33 No 2 (1988) pp I35-150 A test, developed to measure the minimum fracture energy in materials with a welldefined direction of weakness, is described. In essence, a razor blade is held normal to the specimen block so that it can be driven into the sample and the device is mounted on a tensometer; specimen dimensions and crack length are measured in situ. Results obtained using this test are shown to agree well with those from conventional tests. It is shown that the test is well suited to measurements on uniaxially aligned fibre composites. Microbond method for determination of the shear strength of a fiber/resin interface: evaluation of experimental parameters Gaur, U. and Miller, B. Composites Science and Technology I/o134 No I (1989) pp 35-51 The effect of various experimental parameters (embedment area, initial tension, loading rate, droplet-droplet shearing) on the interfacial shear strengths as determined by the microbond pull-out test were investigated for four different fibre/resin combinations. Kevlar, glass and carbon fibres, each embedded in the same epoxy resin, were tested. The results indicate that the force exerted on the fibre/matrix interface is predominantly a shearing force. It is suggested that the shear strength distributions obtained by this test are real variations in bond strength (not due to experimental error) indicating differences in the fibre surfaces. It is also shown that the interfacial shear strengths obtained by the microbond technique are higher than bond strength values obtained by other methods. Micromechanical analysis of the strength of unidirectional fiber composites Aboudi, J. Composites Science and Technology Vo133 No 2 (1988) pp 79-96 A micromechanical analysis for the prediction of ultimate stresses of unidirectional fibre composites under complex loading

systems is presented. It is used to predict the off-axis strength of six types of laminae: boron/epoxy, graphite/polyimide, graphite/ epoxy, aramid/epoxy, glass/epoxy and boron/aluminium and the results are shown to be in good agreement with known measured results for these systems. Applications of the theory to incorporate compressive loadings and thermal stresses are discussed. Mode I and mode II stress intensity factors for interfacial cracks in bi-material media Hamoush, S. A. and Ahmad, S. H. Engineering Fracture Mechanics Vol 33 No 3 (1989) pp 421-428 This analysis considers the case of a mixedmode interface crack between two dissimilar isotropic materials, for example, in composite laminates. The total strain energy release rate is first evaluated using a crack closure integral approach. The mode I and II contributions are then separated by imposing solutions for two independent states of equilibrium, from which the mode I and mode II stress intensity factors are obtained. The procedure is then combined with a finite element analysis. The present numerical values of the stress intensity factors are compared with exact analytical solutions (from literature) for stress intensity factor with increasing crack length. The authors find good agreement between the analyses and conclude that their method is simple and easy to apply. Optimum design of variable composite flywheel Georgian. J. C. Journal o f Composite Materials Vol 23 No 1 (January 1989) pp 2-10 In this paper, the design of a composite flywheel is optimised by considering the maximum energy density of the flywheel from equations of motion and compatibility for rotating discs. A low density, high strength composite with a low modulus is required for the centre part of the wheel on the basis of a constant stress design criterion whilst the outer part requires a constant thickness of material of high density, strength and modulus. Using property data from the literature for orthotropic 0/90/45 composites, a maximum energy density is obtained with a boron/epoxy rim and graphite/epoxy for the centre part of the wheel. The authors suggest that further improvements in energy density would be obtained using a composite material of lower density and higher strength for the centre portion. A predictive model for particulate-filled composite materials Part 1. Hard particles Guild, F. J. and Young, R. J. Journal o f Materials Science Vol 24 (1989) pp 298-306 Particulate-reinforced polymers are rapidly developing as an engineering material, but understanding of their mechanical behaviour is lacking. This study proposes a model capable of predicting composite properties from those of the constituent materials and is based on a combination of finite element analysis and spatial statistical ideas. As a result real filler distributions may he taken into account, unlike previous attempts which have assumed simple cubic packing. Composite predictions of stiffness and stress around the interface for systems containing hard

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