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D.C. electrical conductivity of amorphous Si3N4-C composites prepared by chemical vapour deposition
Iittcatute Prepared by M.E. Adams, R.S. Bailey, M.J. Mulheron and J.W. Rock CA RBON FIBRES Behavior of an aramid fiber under uniform compression De Teresa, S.J., Farris, R.J. and Porter, R.S. Polymer Composites Vol 3 No 2 /April 1982) pp 5 7-58 A new method of applying small, uniform strains to organic fibres by shrinkage of the surrounding polymer matrix is described. ESCA studies of carbon fibres: Part 1. The chemical composition of a carbon fibre subsurface Waltersson, K. Fibre Science and Technology Vol 17No 4/December 1982) pp 289302 Courtaulds AS carbon fibres were studied by the ESCA technique after having been treated with a mixture of H 2 SO4 and HNO 3 to increase the amount of oxygen-containing groups on the fibre surface. Mole fractions of the elements present are given. It was found that with the ESCA technique it was possible to distinguish between contributions from the fibre subsurface and its overlayer. Results indicate that oxygen and carbon concentration gradients exist within the fibre subsurface.
CARBON MA TRICES D.C. electrical conductivity of amorphous Sis N 4 4: composites prepared by chemical vapour deposition Goto, T. and Hirai, T. Journal of Materials Science Vo118 (1983) pp 383-390 The preparation of amorphous Sis N 442 (Am CVD-(Si~ N 4 -C)) composites on graphite substrates is described. SiC14 , H2, NH~ and C3H s axe the source gases. The DC electrical conductivity was measured normal (or±) and parallel (all) to the substrate. Composites containing 0.2% wt C were noted as having a± of 101° times greater than those without carbon at 500°C. Crll was observed to be 10 to 30 times greater than e±at room temperature. Activation energies were measured, and results suggest that electricity is conducted through a carbon network in the amorphous SisN 4 matrix.
CEMENT MA TRICES Factors influencing the workabil/ty of steelfibre reinforced concrete. Part 2. Narayanan, R. and Palanjian, A.S. Concrete Vol 17 (February 1983) p 42 The authors demonstrate how the sand content of the mix affects the amount of fibre that can be incorporated. Increasing fibre content also increases the Vebe time. How fibre shape affects workability was also investigated using crimped, round and duoform fibres. Crimped fibres reduced the workability compared with the other two fibres, whose effects were similar. Incorporation of fibres also increased the compression
320
strength of the concrete, the percentage increase was found to be inversely dependent upon the water: cement ratio.
local strengths where required, and any shape is possible. Another process takes care of circular structures (Magnaswirl). The processes are predicted to be capable of producing skeletal preforms on a volume basis cheaper than using standard lay-up techniques.
GENERA L Analysis of composite bonded joints Rao, B.N., Rao, Y.V.K.S. and Yadagiri, S. Fibre Science and Technology Vol 17 No 2 /September 1982) pp 77-90 A special G-node isoparametric element is developed for the adhesive layer of a bonded joint and used for solving problems relating to differing types of joints and various adherend materials. This element, together with the 8-node isoparametric element used to model adherends, is shown to have an advantage in solving problems of joints with shaped adherends.
Analysis of the net tension failure mode in composite bolted joints York, J.L., Wilson, D.W. and Pipes, R.B. Journal of Reinforced Plastics and Composites Vol I (1982) p 141 The development of an analysis to predict the net tension strength of composite bolts is discussed. A two-dimensional plane-stress finite element analysis, employing quadrilateral elements with orthotropic material properties, was used to determine the stress state along the failure plane. The "point stress" failure criterion was used, and development of the failure criterion for a specific system involved determining two notch sensitive parameters. Strength predictions were compared with experimental data and showed good agreement. Composite flywheels with rim and hub Ikegami, K., Igakashi, J4. and Shiratori, E. International Journal of Mechanical Sciences Vo125 No 1 pp 59-69 The increase in moment of inertia and rotathag speed obtained by using a glass cloth laminate flywheel has been investigated. The reinforcement of the central hole with similar material is shown to give rise to improved speed of rotation. Attaching a rim to the hub serves to give a large moment of inertia, and is produced by winding carbon fibre around the disc. The optimum flywheel shape for high energy density is described. Composites get stronger with 3-D reinforcement Webrenberg II, R.H. Materials Engineering, (January 1983) pp 27-31 A new process (Magnaweave) is used to weave a skeletal preform of a composite into a required shape. Three-dimensionally reinforced composites are targetted for high performance applications, as they do not delaminate. All fibre types may be woven, as the process treats fibres gently, and more than one fibre type may be employed. Weave geometry may be tailored to provide
The creep of silicon carbide fibres Simon, G. and Bunsell, A.R. Journal of Materials Science Letters Vol 2 (1983) p 80 The properties and behaviour of single NicaIon (silicon carbide) fibres have been studied at temperatures of up to 16000C. A rapid decrease in strength was observed above 1000°C. Creep rate measurements showed that a two stage process was operative. The initial creep rate is found to be temperature dependent and the authors postulate that this is due to a recrystallization process. This stage lasted for 20 hours at all the temperatures investigated above 1000°C, and was followed by an increased creep rate stage involving defect migration until fracture. Double cantilever shear beam model of dynamic fracture in unidirectional fibre composites Lee, S.S., Williams, J.H. Jr and Kousiounelos, P.N. Fibre Science and Technology Vol 17 No 2/September 1982) pp 99-122 An analysis of a homogeneous orthotropic double cantilever shear beam model, used to study Mode I dynamic fracture in unidirectional fibre composites, is presented. The analysis follows that by Freund on isotropic specimens. The dominant quantity in the results is found to be the crack-tip bluntness parameter - a measure of the pre-propagation energy in excess of the pre-propagation energy for a sharp crack. The results have yet to be verified experimentally.
Effect of fibre misalignment on the elastic properties of oriented discontinuous fibre composites Berthelot, J.M. Fibre Science and Technology Vol 17No 1/July 1982) pp 25-39 The development of a theory to evaluate elastic properties of a unidirectional fibre composite with misaligned discontinuous fibres is presented. A comparison is made with experimental results. The data shows that a misallgnment of -+10 ° reduces Young's longitudinal modulus by about 3%, indicathag that fibre lengths must be large enough to have a modulus comparable with that of continuous composites. An experimental and theoretical study of crack propagation in crossply fibre composites Sun, G., Kolsky, H. and Pipkin, A.C. Engineering Fracture Mechanics Vol 17 (1983) p 349 It was observed that the direction of crack propagation in rectangular double cantilever beam specimens, was dependent upon the
COMPOSITES. JULY 1983
CARBON MA TRICES D.C. electrical conductivity of amorphous Sis N 4 4: composites prepared by chemical vapour deposition Goto, T. and Hirai, T. Journal of Materials Science Vo118 (1983) pp 383-390 The preparation of amorphous Sis N 442 (Am CVD-(Si~ N 4 -C)) composites on graphite substrates is described. SiC14 , H2, NH~ and C3H s axe the source gases. The DC electrical conductivity was measured normal (or±) and parallel (all) to the substrate. Composites containing 0.2% wt C were noted as having a± of 101° times greater than those without carbon at 500°C. Crll was observed to be 10 to 30 times greater than e±at room temperature. Activation energies were measured, and results suggest that electricity is conducted through a carbon network in the amorphous SisN 4 matrix.
CEMENT MA TRICES Factors influencing the workabil/ty of steelfibre reinforced concrete. Part 2. Narayanan, R. and Palanjian, A.S. Concrete Vol 17 (February 1983) p 42 The authors demonstrate how the sand content of the mix affects the amount of fibre that can be incorporated. Increasing fibre content also increases the Vebe time. How fibre shape affects workability was also investigated using crimped, round and duoform fibres. Crimped fibres reduced the workability compared with the other two fibres, whose effects were similar. Incorporation of fibres also increased the compression
320
strength of the concrete, the percentage increase was found to be inversely dependent upon the water: cement ratio.
local strengths where required, and any shape is possible. Another process takes care of circular structures (Magnaswirl). The processes are predicted to be capable of producing skeletal preforms on a volume basis cheaper than using standard lay-up techniques.
GENERA L Analysis of composite bonded joints Rao, B.N., Rao, Y.V.K.S. and Yadagiri, S. Fibre Science and Technology Vol 17 No 2 /September 1982) pp 77-90 A special G-node isoparametric element is developed for the adhesive layer of a bonded joint and used for solving problems relating to differing types of joints and various adherend materials. This element, together with the 8-node isoparametric element used to model adherends, is shown to have an advantage in solving problems of joints with shaped adherends.
Analysis of the net tension failure mode in composite bolted joints York, J.L., Wilson, D.W. and Pipes, R.B. Journal of Reinforced Plastics and Composites Vol I (1982) p 141 The development of an analysis to predict the net tension strength of composite bolts is discussed. A two-dimensional plane-stress finite element analysis, employing quadrilateral elements with orthotropic material properties, was used to determine the stress state along the failure plane. The "point stress" failure criterion was used, and development of the failure criterion for a specific system involved determining two notch sensitive parameters. Strength predictions were compared with experimental data and showed good agreement. Composite flywheels with rim and hub Ikegami, K., Igakashi, J4. and Shiratori, E. International Journal of Mechanical Sciences Vo125 No 1 pp 59-69 The increase in moment of inertia and rotathag speed obtained by using a glass cloth laminate flywheel has been investigated. The reinforcement of the central hole with similar material is shown to give rise to improved speed of rotation. Attaching a rim to the hub serves to give a large moment of inertia, and is produced by winding carbon fibre around the disc. The optimum flywheel shape for high energy density is described. Composites get stronger with 3-D reinforcement Webrenberg II, R.H. Materials Engineering, (January 1983) pp 27-31 A new process (Magnaweave) is used to weave a skeletal preform of a composite into a required shape. Three-dimensionally reinforced composites are targetted for high performance applications, as they do not delaminate. All fibre types may be woven, as the process treats fibres gently, and more than one fibre type may be employed. Weave geometry may be tailored to provide
The creep of silicon carbide fibres Simon, G. and Bunsell, A.R. Journal of Materials Science Letters Vol 2 (1983) p 80 The properties and behaviour of single NicaIon (silicon carbide) fibres have been studied at temperatures of up to 16000C. A rapid decrease in strength was observed above 1000°C. Creep rate measurements showed that a two stage process was operative. The initial creep rate is found to be temperature dependent and the authors postulate that this is due to a recrystallization process. This stage lasted for 20 hours at all the temperatures investigated above 1000°C, and was followed by an increased creep rate stage involving defect migration until fracture. Double cantilever shear beam model of dynamic fracture in unidirectional fibre composites Lee, S.S., Williams, J.H. Jr and Kousiounelos, P.N. Fibre Science and Technology Vol 17 No 2/September 1982) pp 99-122 An analysis of a homogeneous orthotropic double cantilever shear beam model, used to study Mode I dynamic fracture in unidirectional fibre composites, is presented. The analysis follows that by Freund on isotropic specimens. The dominant quantity in the results is found to be the crack-tip bluntness parameter - a measure of the pre-propagation energy in excess of the pre-propagation energy for a sharp crack. The results have yet to be verified experimentally.
Effect of fibre misalignment on the elastic properties of oriented discontinuous fibre composites Berthelot, J.M. Fibre Science and Technology Vol 17No 1/July 1982) pp 25-39 The development of a theory to evaluate elastic properties of a unidirectional fibre composite with misaligned discontinuous fibres is presented. A comparison is made with experimental results. The data shows that a misallgnment of -+10 ° reduces Young's longitudinal modulus by about 3%, indicathag that fibre lengths must be large enough to have a modulus comparable with that of continuous composites. An experimental and theoretical study of crack propagation in crossply fibre composites Sun, G., Kolsky, H. and Pipkin, A.C. Engineering Fracture Mechanics Vol 17 (1983) p 349 It was observed that the direction of crack propagation in rectangular double cantilever beam specimens, was dependent upon the
COMPOSITES. JULY 1983