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Bearings produced by sintering metal powders with solid lubricants
aluminium coated fibres oxidised at a rate similar to the uncoated type below 500°C, oxidation was slower at temperatures above this. Oxidation was found to be more rapid for PAN based fibres than for rayon based fibres and more rapid for low modulus than high modulus fibre. (70/3[42)
Bearings produced by sintering metal powders with solid lubricants GALLO, A. and DE JORIO, I. Powder Metallurgy, Vol 13, No 25, pp 67 - 70 (Spring 1970) Composite bearing materials were prepared from Fe, Cu and bronze with small volume fractions of solid lubricants by powder metallurgy. The coefficient of friction and wear of these composites were measured. Comparison was made between boron nitride, graphite and MoS2 as the lubricants. The boron nitride gave unsatisfactory wear behaviour and the materials containing MoS~_ exhibited the best properties. It was concluded that the lubricant should form a continuous layer between the metal surfaces and not merely have a low coefficient of friction. (70•3/43)
The observation of the fracture path in WC-Co cemented carbides using a newly developed replica method with an electron microscope HARA, A., NISHIKAWA, T. and YAZU, S. Planseeberichte fftr Pulvermetallurgie Vol 18, No 1, pp 2 8 - 4 3 (March 1970) Observation of the fracture surface of WC-Co cemented carbide alloys was made before and after etching the surface to remove cobalt. In this way it was claimed to be possible to determine the nature of the fracture path. It was concluded from the study that for fine grained alloys the fracture path is either between the WC grains or through the Co phase. In a coarsegrained alloy a smaller proportion of the fracture is through the WC grains than has previously been reported. (70[3/44)
Strengthening of copper with tantalum (continuous) filaments IQBAL AHMAD and BARRANCO, J.M. Metallurgical Transactions, Vol 1, No 4, pp 985 - 995 (April 1970) Composites of Cu reinforced with continuous Ta filaments (0.003in
3] 8
COMPOSITESSeptember 1970
diameter) were produced by an infiltration technique. The elastic modulus, UTS and yield strength of the composites were measured and found to be linear functions of the volume fraction of the filaments (up to 38 vol%). The filaments elongated continuously up to the failure of the composite, without any random fracture in the filaments. It was found that the UTS of the composite could be successfully predicted using an expression involving the UTS of the filaments in isolation, the volume fraction of the filaments and the stress in the matrix at the fracture strain of the composite. (70/3/45)
Metal-ceramic reinforced electric contacts MAREK, B. A., SUKHIKH, L. L. and TEODOROVICH, O. K. Soviet Powder Metallurgy No 2, p l l 7 [February 1969) The preparation is described of electric contact materials made of directionally arranged fibres of W wire (diameter 0"3 and 0"5mm) in Cu or Ag. The materials were prepared b o t h by a liquid impregnation method and an explosion forming method. In the former, the W wires were coated with 0 " 2 - 0-3mm Ni layers to improve bonding between the W and liquid metal. In the latter the wires were coated with the required proportion of Cu or Ag and then explosively pressed. The resulting billet was worked mechanically. Both methods produced pore-free microstructures and the electrical conductivities were 20 to 25% higher than for similar alloys prepared b y powder metallurgy. The explosively formed composite was harder than the infiltrated alloy. (70/3•46)
Interaction of the elements of a composite material reinforced with fibre UMANSKII, E. S. Soviet Powder Metallurgy No 1, p 80 (January 1969) A theoretical analysis is made of the stress distribution in the fibres and matrix of a composite material, reinforced with uni-directional fibres, subjected to a uni-axial tensile stress. With the assumption that only elastic elongation occurs and that only frictional forces exist between the two phases, the stress distribution is derived as a function of the content of fibres and the elastic properties of the phases. (70/3/47)
Resin matrices Flame resistant properties of a modified Ppo composite ABOLINS, V. Plastics design and engineering, Vol 10, No 5, pp 14 - 17 (May 1970) The details are given of a new modified polyphenylene oxide resin combining a self extinguishing property with glass fibre reinforcement while retaining good structural and electrical characteristics. Contrary to expectation the flame resistance of resins is frequently lowered b y the addition of glass fibres, especially if 'sized' glass is used. The mechanical and electrical properties of the GRP tested are not altered much by the fire retardant additives. (70/4/80)
Surface fracture in injection moulding of filled polymers BALLMAN, R. L., KRUSE, R. L. and TAGGART, W. P. Polymer Eng and Sci, Vol 10, No 3, p 154, (May 1970) Work on surface fracture during injection moulding which sometimes occurs at the mould surface is described. Polystyrene filled with glass beads was used and an analysis made by means of a force balance at the fracture site in the flowing polymer. Results suggest that fracture will occur more readily with increasing viscosity and shear rate and with decreasing interfacial strength, coefficient of wall friction and melt elasticity and this appears to be borne out quantitatively by experiment. (70/4/81)
The effect of hydrostatic pressure on the fibre-matrix bond in a steel - resin model composite BOWDEN, P. B. J o f Mat Science, Vol 5, No 6; pp 517 - 520 (June 1970) A simple technique is used to measure shear strength of the fibre-matrix bond and frictional stress after that bond has been broken as a function of hydrostatic pressure applied to the composite model. Data are presented for a steel wire pulled from an e p o x y resin matrix which suggest that, at applied pressures of 1 0 - 20Nmm -2, the bond shear strength corresponds closely to the resin shear yield stress as measured by a p l a n e - s t r a i n compression test. Deviation from this agreement at pressures of 10Nmm -2 are explained in terms of the nucleation of stress concentrating shear cracks which could be suppressed by an increase in pressure. These results imply that
Bearings produced by sintering metal powders with solid lubricants GALLO, A. and DE JORIO, I. Powder Metallurgy, Vol 13, No 25, pp 67 - 70 (Spring 1970) Composite bearing materials were prepared from Fe, Cu and bronze with small volume fractions of solid lubricants by powder metallurgy. The coefficient of friction and wear of these composites were measured. Comparison was made between boron nitride, graphite and MoS2 as the lubricants. The boron nitride gave unsatisfactory wear behaviour and the materials containing MoS~_ exhibited the best properties. It was concluded that the lubricant should form a continuous layer between the metal surfaces and not merely have a low coefficient of friction. (70•3/43)
The observation of the fracture path in WC-Co cemented carbides using a newly developed replica method with an electron microscope HARA, A., NISHIKAWA, T. and YAZU, S. Planseeberichte fftr Pulvermetallurgie Vol 18, No 1, pp 2 8 - 4 3 (March 1970) Observation of the fracture surface of WC-Co cemented carbide alloys was made before and after etching the surface to remove cobalt. In this way it was claimed to be possible to determine the nature of the fracture path. It was concluded from the study that for fine grained alloys the fracture path is either between the WC grains or through the Co phase. In a coarsegrained alloy a smaller proportion of the fracture is through the WC grains than has previously been reported. (70[3/44)
Strengthening of copper with tantalum (continuous) filaments IQBAL AHMAD and BARRANCO, J.M. Metallurgical Transactions, Vol 1, No 4, pp 985 - 995 (April 1970) Composites of Cu reinforced with continuous Ta filaments (0.003in
3] 8
COMPOSITESSeptember 1970
diameter) were produced by an infiltration technique. The elastic modulus, UTS and yield strength of the composites were measured and found to be linear functions of the volume fraction of the filaments (up to 38 vol%). The filaments elongated continuously up to the failure of the composite, without any random fracture in the filaments. It was found that the UTS of the composite could be successfully predicted using an expression involving the UTS of the filaments in isolation, the volume fraction of the filaments and the stress in the matrix at the fracture strain of the composite. (70/3/45)
Metal-ceramic reinforced electric contacts MAREK, B. A., SUKHIKH, L. L. and TEODOROVICH, O. K. Soviet Powder Metallurgy No 2, p l l 7 [February 1969) The preparation is described of electric contact materials made of directionally arranged fibres of W wire (diameter 0"3 and 0"5mm) in Cu or Ag. The materials were prepared b o t h by a liquid impregnation method and an explosion forming method. In the former, the W wires were coated with 0 " 2 - 0-3mm Ni layers to improve bonding between the W and liquid metal. In the latter the wires were coated with the required proportion of Cu or Ag and then explosively pressed. The resulting billet was worked mechanically. Both methods produced pore-free microstructures and the electrical conductivities were 20 to 25% higher than for similar alloys prepared b y powder metallurgy. The explosively formed composite was harder than the infiltrated alloy. (70/3•46)
Interaction of the elements of a composite material reinforced with fibre UMANSKII, E. S. Soviet Powder Metallurgy No 1, p 80 (January 1969) A theoretical analysis is made of the stress distribution in the fibres and matrix of a composite material, reinforced with uni-directional fibres, subjected to a uni-axial tensile stress. With the assumption that only elastic elongation occurs and that only frictional forces exist between the two phases, the stress distribution is derived as a function of the content of fibres and the elastic properties of the phases. (70/3/47)
Resin matrices Flame resistant properties of a modified Ppo composite ABOLINS, V. Plastics design and engineering, Vol 10, No 5, pp 14 - 17 (May 1970) The details are given of a new modified polyphenylene oxide resin combining a self extinguishing property with glass fibre reinforcement while retaining good structural and electrical characteristics. Contrary to expectation the flame resistance of resins is frequently lowered b y the addition of glass fibres, especially if 'sized' glass is used. The mechanical and electrical properties of the GRP tested are not altered much by the fire retardant additives. (70/4/80)
Surface fracture in injection moulding of filled polymers BALLMAN, R. L., KRUSE, R. L. and TAGGART, W. P. Polymer Eng and Sci, Vol 10, No 3, p 154, (May 1970) Work on surface fracture during injection moulding which sometimes occurs at the mould surface is described. Polystyrene filled with glass beads was used and an analysis made by means of a force balance at the fracture site in the flowing polymer. Results suggest that fracture will occur more readily with increasing viscosity and shear rate and with decreasing interfacial strength, coefficient of wall friction and melt elasticity and this appears to be borne out quantitatively by experiment. (70/4/81)
The effect of hydrostatic pressure on the fibre-matrix bond in a steel - resin model composite BOWDEN, P. B. J o f Mat Science, Vol 5, No 6; pp 517 - 520 (June 1970) A simple technique is used to measure shear strength of the fibre-matrix bond and frictional stress after that bond has been broken as a function of hydrostatic pressure applied to the composite model. Data are presented for a steel wire pulled from an e p o x y resin matrix which suggest that, at applied pressures of 1 0 - 20Nmm -2, the bond shear strength corresponds closely to the resin shear yield stress as measured by a p l a n e - s t r a i n compression test. Deviation from this agreement at pressures of 10Nmm -2 are explained in terms of the nucleation of stress concentrating shear cracks which could be suppressed by an increase in pressure. These results imply that