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The bonding of carbon fibres to epoxy resins as affected by the manufacturing and surface treatment processes
The damping characteristics of 2024-T3 and 6061-T4 aluminium, and unidirectional graphite/metal-matrix specimens with P55 and P100 fibres in 6061 aluminium and A291C magnesium matrices, were determined by recording the free decay response of a beamlike specimen in free fall. The tests were performed in vacuum to eliminate the effects of aerodynamic damping. The graphite/ aluminium composites were found to have a damping level slightly above the Zener prediction for the pure matrix. The graphite/ magnesium composite had higher d a m p i n g than could be attributed to the matrix alone, implying the presence of an additional loss mechanism, such as at the fibre/matrix interface. Mechanical properties of some silicon carbide reinforced aluminium composites Tsangarakis, N., Andrews, B.O. and Cavallaro, C. Journal of Composite Materials Vol 21 (May 1987) pp 481--492 The mechanical properties of particulate and continuous silicon carbide fibre-reinforced a l u m i n i u m composites have been investigated. The longitudinal strength of unidirectionally reinforced (47% volume fraction, Vf, of fibres) was 1273 MPa while the transverse strength was 76 MPa. The tensile strength of the (0,90)4 s and (02,90,0)s composites were reported at 679 and 864 MPa respectively. The tensile properties of the particulate composites (30% Vf) depended on the nature of the matrix. Additional results on the endurance limits, fracture toughness and fatigue crack growth rate for both composites are also presented. Tensile strength of fibres containing two types of flaws and its influence on the tensile behaviour of metal matrix composites Ochiai, S. and Osamura, K. Zeitschrift fftr Metallkunde Vol 78 No 7 (July 1987) pp 525-532 In this paper, the strength of fibres, in which two types of flaws co-exist, is investigated by employing a simple model enabling the fracture probability to be expressed by a bimodel Wiebull distribution function. The effect of gauge length, ratio of mixture of flaws and scatter in the size of flaws is considered in detail. The effect of the strength of such fibres on the tensile behaviour of the reinforced composite are studied by a computer simulation technique. The results of the simulation experiments are explained by consideration of the interfacial bonding conditions (good or poor), the critical length and scatter of links.
ORGANIC FIBRES Structural characteristics of polyacrylonitrile (PAN) fibres during oxidative stabilization Jiang, H., Wu, C., Zhang, A. and Yang, P. Composites Science and Technology Vol 29 No 1 (1987) pp 33-44 Structural changes in PAN fibres during oxidation in the temperature range 20°C and 300°C, in the relaxed condition and under tension, were investigated. The changes were examined by small-angle X-ray scattering, wide-angle X-ray scattering in situ, thermal Fourier transform infra-red spectroscopy, differential scanning calorimetry and thermomechanical analysis. The results indicate that
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below 180°C the changes are small; from 180°C to 240°C some chemical reactions occur but the back-bone remains; but above 240°C chemical reactions occur violently and a new planar trapezoidal structure is formed. Twist effect on the mechanical behaviour of Kevlar 29/epoxy strands Weinberg, A. and Schwartz, P. Journal of Materials Science Letters Vol 6 No 7 (July 1987) pp 832-834 The effect of twist on tensile strength and modulus is tested for dry Kevlar yarn and epoxy-impregnated yams. Twisting reduces the strength of impregnated yams, and increases the strength of dry yarns up to one twist/cm before causing a similar decrease. A decrease in modulus with twist is found for both types of sample.
RESIN MATRICES The 'abrasive wear behaviour of continuous fibre polymer composites Cirino, M., Pipes, ILK and Friedrich, K. Journal of Materials Science Vo122 (1987) pp 2481-2492 The results of an investigation on the wear performance of selected continuous fibre/ polymer composites under dry abrasive conditions have been reported. The effects of operation variables, apparent normal pressure, sliding velocity and apparent contact area were determined by measuring friction coefficients and wear rates. Basic wear mechanisms were identified in different orientations with each fibre material and matrix materials. The conclusion of the investigation led to the selection of a PEEK matrix reinforced with aramid fibres oriented normal to the contacting surface and carbon fibres oriented parallel to the contacting surface as an ideal low wear composite material. The anisotropic diffusion of water in Kevlarepoxy Aronhime, M.T., N e u m a n n , S. and Marom, G. Journal of Materials Science Vol 22 (1987) pp 2435-2446 The diffusion of water into unidirectional Kevlar fibre-reinforced epoxy resin has been investigated as a function of fibre orientation (and volume fraction in the case of 0 ° unidirectional laminates). The diffusivity was found to increase dramatically as the angle of orientation increased from 0 ° to 90°. The equilibrium weight gain of water (M~) for Kevlar fibres was found to be 4.9%. M~o of the composite increased with increasing volume fraction of fibres. It was found that the two diffusion coefficients - - D H along the fibre direction and D22 transverse to the fibre direction - - were dissimilar so that, as the volume fraction increased from 0.37 to 0.59, D I increased from 0.83 to 4.2 X 10- 12 m 2 s - ,1 whereas D22 decreased from 0.21 to 0.033 >( 10-12 m 2 s-1. The bonding of carbon fibres to epoxy resins as affected by the manufacturing and surface treatment processes Goldstein, B., Aronhime, M.T., Anvy, Y. and Marom, G. International Journal of Adhesion and Adhesives Vol 7 No 3 (July 1987) pp 135-139 The differences in bonding to epoxy resins, as measured by the interlaminar shear strength (ILSS), of three nominally similar carbon fibres were investigated. Fibres from a polyacrylo-
nitrile precursor from three separate batches which had nominally undergone the same manufacturing, surface treatment and finishing processes but which were reported by the manufacturer to yield different values of ILSS for a carbon fibre-reinforced epoxy composite were examined. They were designated: (a) good ILSS values; (b) moderate ILSS values; and (c) poor ILSS values. Two of the fibres (a) and (c) were found to have emerged from the m a n u facturing process essentially identical but subsequent surface treatments had been very different. Fibre b was found to have a more ordered structure and therefore to be less susceptible to surface treatment. Thus it is shown that variations in surface treatment of identical base fibres can dramatically affect the bonding properties, whereas the degree of order of the base fibre can have an important, although smaller, effect on the bonding, Characterization of the interfacial adhesion using tan delta Chua, P.S. SAMPE Quarterly Vol 18 No 3 (April 1987) pp 10-15 The dynamic mechanical properties of samples of glass fibre-reinforced polyester, varying only in the organosilane coating applied to the glass fibres, were determined. Tan 8, which is defined as the ratio between the energy loss and the applied energy, was determined in the dynamic mechanical analyser as the ratio between the flexural loss modulus and the flexural storage modulus and measured as a function of temperature. It was found that tan d at the Tg of the composite was affected by the type and amount of the organosilane coated on the fibre, the fibre diameter and the Vf. The implication is made that the quality of the interfacial adhesion can be characterized by the tan 8 at the Tg. A comparative study of the ballistic performance of glass reinforced plastic materials Vasudev, A. and Meehlman, M.J. SAMPE Quarterly Vol 18 No 4 (July 1987) pp 43-48 The two part study consisted of: 1) the selection and characterization of E and S-2 Glass ®woven roving prepregs suitable for thick ballistic laminate fabrication; and 2) a comparative evaluation of the ballistic performance of flat composite laminates ranging in thickness from 35.6 to 48.3 m m fabricated with the prepregs. E and S-2 glass woven roving reinforcements were prepregged with polyester, polyester interpenetrating network (IPN), vinylester and epoxy resins. A total of 14 different prepregs (2 E glass and 12 S-2 glass) from seven manufacturers were selected for evaluation. Two types of fibre finishes (epoxy-compatible and starch-oil) were chosen to vary the level of surface compatibility (bond strength) with the particular matrix resin chosen. Results indicate that polyester and vinyl ester matrices, incompatible fibre finish and higher laminate tensile strength would influence superior ballistic performance of thick laminates. The presence of a m o n o m e r of low volatility such as diallyl phthalate will result in a more practical resin system for thick laminate fabrication. At least six of the 14 prepregs studied were found to be suitable for thick laminate fabrication from the point of view of processability and ballistic performance. The presence of fire-retardant additives did not affect the ballistic performance of the polyester laminates. Crack growth characterization in a short fibre glass-epoxy composite Kumar, A.N., Pandey, R.K. and Nanda, A.
COMPOSITES
. JANUARY
1988
ORGANIC FIBRES Structural characteristics of polyacrylonitrile (PAN) fibres during oxidative stabilization Jiang, H., Wu, C., Zhang, A. and Yang, P. Composites Science and Technology Vol 29 No 1 (1987) pp 33-44 Structural changes in PAN fibres during oxidation in the temperature range 20°C and 300°C, in the relaxed condition and under tension, were investigated. The changes were examined by small-angle X-ray scattering, wide-angle X-ray scattering in situ, thermal Fourier transform infra-red spectroscopy, differential scanning calorimetry and thermomechanical analysis. The results indicate that
78
below 180°C the changes are small; from 180°C to 240°C some chemical reactions occur but the back-bone remains; but above 240°C chemical reactions occur violently and a new planar trapezoidal structure is formed. Twist effect on the mechanical behaviour of Kevlar 29/epoxy strands Weinberg, A. and Schwartz, P. Journal of Materials Science Letters Vol 6 No 7 (July 1987) pp 832-834 The effect of twist on tensile strength and modulus is tested for dry Kevlar yarn and epoxy-impregnated yams. Twisting reduces the strength of impregnated yams, and increases the strength of dry yarns up to one twist/cm before causing a similar decrease. A decrease in modulus with twist is found for both types of sample.
RESIN MATRICES The 'abrasive wear behaviour of continuous fibre polymer composites Cirino, M., Pipes, ILK and Friedrich, K. Journal of Materials Science Vo122 (1987) pp 2481-2492 The results of an investigation on the wear performance of selected continuous fibre/ polymer composites under dry abrasive conditions have been reported. The effects of operation variables, apparent normal pressure, sliding velocity and apparent contact area were determined by measuring friction coefficients and wear rates. Basic wear mechanisms were identified in different orientations with each fibre material and matrix materials. The conclusion of the investigation led to the selection of a PEEK matrix reinforced with aramid fibres oriented normal to the contacting surface and carbon fibres oriented parallel to the contacting surface as an ideal low wear composite material. The anisotropic diffusion of water in Kevlarepoxy Aronhime, M.T., N e u m a n n , S. and Marom, G. Journal of Materials Science Vol 22 (1987) pp 2435-2446 The diffusion of water into unidirectional Kevlar fibre-reinforced epoxy resin has been investigated as a function of fibre orientation (and volume fraction in the case of 0 ° unidirectional laminates). The diffusivity was found to increase dramatically as the angle of orientation increased from 0 ° to 90°. The equilibrium weight gain of water (M~) for Kevlar fibres was found to be 4.9%. M~o of the composite increased with increasing volume fraction of fibres. It was found that the two diffusion coefficients - - D H along the fibre direction and D22 transverse to the fibre direction - - were dissimilar so that, as the volume fraction increased from 0.37 to 0.59, D I increased from 0.83 to 4.2 X 10- 12 m 2 s - ,1 whereas D22 decreased from 0.21 to 0.033 >( 10-12 m 2 s-1. The bonding of carbon fibres to epoxy resins as affected by the manufacturing and surface treatment processes Goldstein, B., Aronhime, M.T., Anvy, Y. and Marom, G. International Journal of Adhesion and Adhesives Vol 7 No 3 (July 1987) pp 135-139 The differences in bonding to epoxy resins, as measured by the interlaminar shear strength (ILSS), of three nominally similar carbon fibres were investigated. Fibres from a polyacrylo-
nitrile precursor from three separate batches which had nominally undergone the same manufacturing, surface treatment and finishing processes but which were reported by the manufacturer to yield different values of ILSS for a carbon fibre-reinforced epoxy composite were examined. They were designated: (a) good ILSS values; (b) moderate ILSS values; and (c) poor ILSS values. Two of the fibres (a) and (c) were found to have emerged from the m a n u facturing process essentially identical but subsequent surface treatments had been very different. Fibre b was found to have a more ordered structure and therefore to be less susceptible to surface treatment. Thus it is shown that variations in surface treatment of identical base fibres can dramatically affect the bonding properties, whereas the degree of order of the base fibre can have an important, although smaller, effect on the bonding, Characterization of the interfacial adhesion using tan delta Chua, P.S. SAMPE Quarterly Vol 18 No 3 (April 1987) pp 10-15 The dynamic mechanical properties of samples of glass fibre-reinforced polyester, varying only in the organosilane coating applied to the glass fibres, were determined. Tan 8, which is defined as the ratio between the energy loss and the applied energy, was determined in the dynamic mechanical analyser as the ratio between the flexural loss modulus and the flexural storage modulus and measured as a function of temperature. It was found that tan d at the Tg of the composite was affected by the type and amount of the organosilane coated on the fibre, the fibre diameter and the Vf. The implication is made that the quality of the interfacial adhesion can be characterized by the tan 8 at the Tg. A comparative study of the ballistic performance of glass reinforced plastic materials Vasudev, A. and Meehlman, M.J. SAMPE Quarterly Vol 18 No 4 (July 1987) pp 43-48 The two part study consisted of: 1) the selection and characterization of E and S-2 Glass ®woven roving prepregs suitable for thick ballistic laminate fabrication; and 2) a comparative evaluation of the ballistic performance of flat composite laminates ranging in thickness from 35.6 to 48.3 m m fabricated with the prepregs. E and S-2 glass woven roving reinforcements were prepregged with polyester, polyester interpenetrating network (IPN), vinylester and epoxy resins. A total of 14 different prepregs (2 E glass and 12 S-2 glass) from seven manufacturers were selected for evaluation. Two types of fibre finishes (epoxy-compatible and starch-oil) were chosen to vary the level of surface compatibility (bond strength) with the particular matrix resin chosen. Results indicate that polyester and vinyl ester matrices, incompatible fibre finish and higher laminate tensile strength would influence superior ballistic performance of thick laminates. The presence of a m o n o m e r of low volatility such as diallyl phthalate will result in a more practical resin system for thick laminate fabrication. At least six of the 14 prepregs studied were found to be suitable for thick laminate fabrication from the point of view of processability and ballistic performance. The presence of fire-retardant additives did not affect the ballistic performance of the polyester laminates. Crack growth characterization in a short fibre glass-epoxy composite Kumar, A.N., Pandey, R.K. and Nanda, A.
COMPOSITES
. JANUARY
1988