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Investigation of high temperature deformation behaviour of a SiC whisker reinforced 6061 aluminium composite
laminae, due to the applied axial loads. In the second case, the delamination is such that both laminae feel the existence of a spring distribution along the length of the delamination. Strain energy release rates of an interfacial crack between two anisotropic solids under uniform axial strain Manoharan, M.G. and Sun, C.T. Composites
Science and Technology Vol 39 No 2 (1990) pp 99-116 Results are compared from analytical and finite element investigations of Modes I, II and III strain energy release rates for a crack lying along the interface of two dissimilar anisotropic elastic solids subjected to a uniaxial strain. The authors show that the strain energy release rates do not converge to definite values because of the violent, oscillatory, crack-tip stress behaviour. However, the total strain energy release rate is well defined. A method for separating the effective strain energy release rates for the three fracture modes is suggested. Vibrational analysis of a double-layer compusite structure Hoilaway, L. and Farhat, A.M. Composite
Structures Vo116 No 4 (1990) pp 283-304 A double-layer skeletal structure manufactured by puitrusion was analysed under dynamic loading in this paper. Both analytical and experimental techniques were used in the analysis and a discussion was presented. It was stated that, provided great care was taken in modelling the analytical system, and the mechanical properties of the material system were accurately determined, the two methods of analysis gave good agreement.
METAL MA TRICES An analysis of high-temperature behaviour of AA2124/SiC whisker composites Schueller, R.D. and Wawner, F.E. Compos-
ites Science and Technology Vol 40 ~1o 2 (1991) pp 213-223 An analysis is presented of commercial hot rolled and extruded AA2124/SiC whisker composites. Tensile and shear tests were carried out on these materials at various temperatures to develop a better understanding of the failure mechanisms involved at high temperatures. It is reported that the loss in strength of aluminium composites with increasing temperature is mainly caused by a decrease in matrix shear strength. Precipitation kinetics contribute to this loss in shear strength through the resolution of precipitates at higher temperatures. This information is necessary in the development of aluminium-based composites with hightemperature capabilities. Casting and extrusion characteristics of an A l - Z n - M g alloy composite containing TiO 2 dispersions Balasubramanian, P.K., Rao, P.S., Pal, B.C., Satyanarayana, K.G. and Rohatgi, P.K. Composites Science and Technology Vol
3 7 N o 3 (1990) pp 245-259 Liquid metallurgy and rheocasting techniques were used to produce an AI-Zn-Mg wrought alloy composite of 5wt% TiO 2 particulate reinforcement of average size 0.37 ~tm. These composites were then subject
to solid, semi-solid and semi-liquid extrusion with evaluation of mechanical properties and microstructures at various conditions. Agglomerates were shown to form and processing which dispersed these gave improved mechanical properties. Compatibility between SiC filaments and aluminium in the K2ZrF 6 wetting process and its effect on filament strength Schamm, S., Le Petitcorps, Y. and Naslain,
R. Composites Science and Technology Vol 4 0 N o 2 (1991) pp 193-211 In this paper the various steps of the KaZrF 6 process, which is used to enhance the wettability of SiC (or C) fibres by molten aluminium, on the strength of the reinforcement is studied on model materials. Groups of 45 uncoated CVD filaments (100 ~tm in diameter) were subjected to three treatments representative of the process: (1) coating with a KzZrF6 layer of variable thickness; (2) annealing of the coated filaments at 650°C in sealed tubes and quenching; and (3) embedding the coated filaments in aluminium by hot pressing. After each step, the filaments were extracted chemically and subjected to tensile testing. The uxs data were treated by a two-dimensional Weibull function. Steps 1 and 2 were found not to significantly modify the filament strength~However, step 3 causes a more significant strength loss due to the formation of AI4C3. Composite ferrous powder metallurgy structures: Mechanical properties and stress analysis Ahmed, M.N., Vedula, M. and Koczak, M.J.
Metallurgical Transactions A Vol 21A No 11 (1990) pp 2943-2955 The mechanics of macrocomposites formed via powder metallurgy (PM) were considered for duplex and triplex layered structures as a function of the properties and the geometries of their constituent layers. Residual stresses were considered in the analysis. Using a rule of mixtures method, the yield strengths and residual stresses obtained correlated well with experimental results. The effects of volume fraction and modulus variations were discussed. The effects of hot rolling on AA2124 15 v/o SiC whisker composites Schuller, R.D. and Wawner, F.E. Journal o f
Composite Materials Vol 24 No 10 (1990) pp 1060-1076 Rolled sheet of AA212425 vol% SiC underwent mechanical testing and microstructural examination in an as-rolled state and after heat treatment. The rolling was found to reduce the tensile strength and the heat treatment restore it. The study showed this to be due to ovcrageing as opposed to the production and healing of voids. The heat treatment was shown to restore the composite's strength by dissolving the large precipitates. High temperature interactions of refractory metal matrices with selected ceramic reinforcements Joshi, A., Hu, H.S., Jesion, L., Stephens, J.J. and Wadsworth, J. Metallurgical Trans-
actions A VoI 21A No 11 (1990)pp 2829-2837 High temperature interdiffusion and reactions between metals and ceramics are of interest in the selection and design of high
temperature metal-matrix composites. Interfacial reactions were studied for Nb and Ta deposited on polished Al20 3 and SiC substrates. These were vacuum annealed for various times at between 800 and 1200°C. The interfaces were studied by optical microscopy, SEM, TEM and Auger electron microscopy (AES). SiC had reacted forming intermetallics of various compositions, activation energies were obtained for these. Al20 3 experienced only minor reactions with either of the refractory metals and consequently could be used as a diffusion barrier layer. The infiltration of aluminium into silicon carbide compacts Maxwell, P.B., Martins, G.P., Olson, D.L. and Edwards, G.R. Metallurgical Transac-
tions B Vo121B No 3 (1990) pp 475-485 Liquid metal processing to discontinuously reinforced metal-matrix composites is potentially more economically viable than other routes. The non-wetting nature of ceramics is the limiting factor that leads to agglomeration of ceramic particles mixed with liquid metal, incomplete infiltration, poor interfacial bonding and voids at interfaces. In this paper an infiltration model is presented based on the physical properties of the liquid and the preform. This indicates the infiltration rate is dependent on: (a) the pore radius in the compact; (b) the liquid's viscosity and density; (c) the surface tension and/or contact angle; and (d) the applied pressure. The model is compared with experimental results obtained from infiltrating silicon carbide compacts with pure aluminium, aluminium 1 wt% silicon and aluminium 1 wt% magnesium. The model was able to predict the threshold pressure, below which infiltration will not occur, and the infiltration rate. It was found that there was an incubation period after the threshold pressure was exceeded before infiltration began that was not predicted by the model. The mechanism responsible for this may be an oxide scavenging reaction or a capillary-driven compensate which covers the particles. Investigation of high temperature deformation behaviour of a SiC whisker reinforced 6061 aluminium composite Xiong, Z., Geng, L. and Yao, C.K. Compos-
ites Science and Technology Vol 39 No 2 (1990) pp 117-125 Studies of the high temperature compressive behaviour of silicon carbide whiskerreinforced 6061 aluminium alloy composite are described. The experimental results show that the value of compressive deformation that causes sample cracking of the SiC/ 6061A1 composite increases with increasing temperature and decreases with increasing deformation rate. The authors explain a peak in the compression stress/strain curves in terms of the rotation of the SiC whiskers rather than as a sign of recrystallization of the AI alloy matrix. Mechanical characterization of SCS-6/Ti--6-4 metal matrix composite Sun, C.T., Can, J.L., Sha, G.T. and Koop, W.E. Journal o f Composite Materials Vo124
No 10 (1990) pp 1029-1059 SCS-6/Ti-6--4 metal-matrix composite specimens were tested in off-axis tension. The elastic-plastic properties were characterized with a one-parameter plasticity model.
COMPOSITES. M A Y 1991
249
Science and Technology Vol 39 No 2 (1990) pp 99-116 Results are compared from analytical and finite element investigations of Modes I, II and III strain energy release rates for a crack lying along the interface of two dissimilar anisotropic elastic solids subjected to a uniaxial strain. The authors show that the strain energy release rates do not converge to definite values because of the violent, oscillatory, crack-tip stress behaviour. However, the total strain energy release rate is well defined. A method for separating the effective strain energy release rates for the three fracture modes is suggested. Vibrational analysis of a double-layer compusite structure Hoilaway, L. and Farhat, A.M. Composite
Structures Vo116 No 4 (1990) pp 283-304 A double-layer skeletal structure manufactured by puitrusion was analysed under dynamic loading in this paper. Both analytical and experimental techniques were used in the analysis and a discussion was presented. It was stated that, provided great care was taken in modelling the analytical system, and the mechanical properties of the material system were accurately determined, the two methods of analysis gave good agreement.
METAL MA TRICES An analysis of high-temperature behaviour of AA2124/SiC whisker composites Schueller, R.D. and Wawner, F.E. Compos-
ites Science and Technology Vol 40 ~1o 2 (1991) pp 213-223 An analysis is presented of commercial hot rolled and extruded AA2124/SiC whisker composites. Tensile and shear tests were carried out on these materials at various temperatures to develop a better understanding of the failure mechanisms involved at high temperatures. It is reported that the loss in strength of aluminium composites with increasing temperature is mainly caused by a decrease in matrix shear strength. Precipitation kinetics contribute to this loss in shear strength through the resolution of precipitates at higher temperatures. This information is necessary in the development of aluminium-based composites with hightemperature capabilities. Casting and extrusion characteristics of an A l - Z n - M g alloy composite containing TiO 2 dispersions Balasubramanian, P.K., Rao, P.S., Pal, B.C., Satyanarayana, K.G. and Rohatgi, P.K. Composites Science and Technology Vol
3 7 N o 3 (1990) pp 245-259 Liquid metallurgy and rheocasting techniques were used to produce an AI-Zn-Mg wrought alloy composite of 5wt% TiO 2 particulate reinforcement of average size 0.37 ~tm. These composites were then subject
to solid, semi-solid and semi-liquid extrusion with evaluation of mechanical properties and microstructures at various conditions. Agglomerates were shown to form and processing which dispersed these gave improved mechanical properties. Compatibility between SiC filaments and aluminium in the K2ZrF 6 wetting process and its effect on filament strength Schamm, S., Le Petitcorps, Y. and Naslain,
R. Composites Science and Technology Vol 4 0 N o 2 (1991) pp 193-211 In this paper the various steps of the KaZrF 6 process, which is used to enhance the wettability of SiC (or C) fibres by molten aluminium, on the strength of the reinforcement is studied on model materials. Groups of 45 uncoated CVD filaments (100 ~tm in diameter) were subjected to three treatments representative of the process: (1) coating with a KzZrF6 layer of variable thickness; (2) annealing of the coated filaments at 650°C in sealed tubes and quenching; and (3) embedding the coated filaments in aluminium by hot pressing. After each step, the filaments were extracted chemically and subjected to tensile testing. The uxs data were treated by a two-dimensional Weibull function. Steps 1 and 2 were found not to significantly modify the filament strength~However, step 3 causes a more significant strength loss due to the formation of AI4C3. Composite ferrous powder metallurgy structures: Mechanical properties and stress analysis Ahmed, M.N., Vedula, M. and Koczak, M.J.
Metallurgical Transactions A Vol 21A No 11 (1990) pp 2943-2955 The mechanics of macrocomposites formed via powder metallurgy (PM) were considered for duplex and triplex layered structures as a function of the properties and the geometries of their constituent layers. Residual stresses were considered in the analysis. Using a rule of mixtures method, the yield strengths and residual stresses obtained correlated well with experimental results. The effects of volume fraction and modulus variations were discussed. The effects of hot rolling on AA2124 15 v/o SiC whisker composites Schuller, R.D. and Wawner, F.E. Journal o f
Composite Materials Vol 24 No 10 (1990) pp 1060-1076 Rolled sheet of AA212425 vol% SiC underwent mechanical testing and microstructural examination in an as-rolled state and after heat treatment. The rolling was found to reduce the tensile strength and the heat treatment restore it. The study showed this to be due to ovcrageing as opposed to the production and healing of voids. The heat treatment was shown to restore the composite's strength by dissolving the large precipitates. High temperature interactions of refractory metal matrices with selected ceramic reinforcements Joshi, A., Hu, H.S., Jesion, L., Stephens, J.J. and Wadsworth, J. Metallurgical Trans-
actions A VoI 21A No 11 (1990)pp 2829-2837 High temperature interdiffusion and reactions between metals and ceramics are of interest in the selection and design of high
temperature metal-matrix composites. Interfacial reactions were studied for Nb and Ta deposited on polished Al20 3 and SiC substrates. These were vacuum annealed for various times at between 800 and 1200°C. The interfaces were studied by optical microscopy, SEM, TEM and Auger electron microscopy (AES). SiC had reacted forming intermetallics of various compositions, activation energies were obtained for these. Al20 3 experienced only minor reactions with either of the refractory metals and consequently could be used as a diffusion barrier layer. The infiltration of aluminium into silicon carbide compacts Maxwell, P.B., Martins, G.P., Olson, D.L. and Edwards, G.R. Metallurgical Transac-
tions B Vo121B No 3 (1990) pp 475-485 Liquid metal processing to discontinuously reinforced metal-matrix composites is potentially more economically viable than other routes. The non-wetting nature of ceramics is the limiting factor that leads to agglomeration of ceramic particles mixed with liquid metal, incomplete infiltration, poor interfacial bonding and voids at interfaces. In this paper an infiltration model is presented based on the physical properties of the liquid and the preform. This indicates the infiltration rate is dependent on: (a) the pore radius in the compact; (b) the liquid's viscosity and density; (c) the surface tension and/or contact angle; and (d) the applied pressure. The model is compared with experimental results obtained from infiltrating silicon carbide compacts with pure aluminium, aluminium 1 wt% silicon and aluminium 1 wt% magnesium. The model was able to predict the threshold pressure, below which infiltration will not occur, and the infiltration rate. It was found that there was an incubation period after the threshold pressure was exceeded before infiltration began that was not predicted by the model. The mechanism responsible for this may be an oxide scavenging reaction or a capillary-driven compensate which covers the particles. Investigation of high temperature deformation behaviour of a SiC whisker reinforced 6061 aluminium composite Xiong, Z., Geng, L. and Yao, C.K. Compos-
ites Science and Technology Vol 39 No 2 (1990) pp 117-125 Studies of the high temperature compressive behaviour of silicon carbide whiskerreinforced 6061 aluminium alloy composite are described. The experimental results show that the value of compressive deformation that causes sample cracking of the SiC/ 6061A1 composite increases with increasing temperature and decreases with increasing deformation rate. The authors explain a peak in the compression stress/strain curves in terms of the rotation of the SiC whiskers rather than as a sign of recrystallization of the AI alloy matrix. Mechanical characterization of SCS-6/Ti--6-4 metal matrix composite Sun, C.T., Can, J.L., Sha, G.T. and Koop, W.E. Journal o f Composite Materials Vo124
No 10 (1990) pp 1029-1059 SCS-6/Ti-6--4 metal-matrix composite specimens were tested in off-axis tension. The elastic-plastic properties were characterized with a one-parameter plasticity model.
COMPOSITES. M A Y 1991
249