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Silicon carbide whiskers from rice husk: role of catalysts
and microstructural analyses allow a comparison of the different composites to be made. It is seen that the mean grain size evolved differs according to the preparative route. When the mean grain size is very small, little influence of transformation toughening is observed. A large increase in rupture strength is observed without a noticeable improvement in toughness. Silicon carbide whiskers from rice husk: role of catalysts Patel, M. and Karer, A. Journal of Materials Science Letters Vol 8 No 8 (1989) pp 955-956 This letter describes the production of SiC whiskers from rice husks without the use of added catalysts. The formation of these whiskers is explained by the catalytic effect of some trace element impurities present in the rice husk. The letter compares and contrasts the surface morphology and thermal properties of whiskers produced with and without the use of added catalysts. The tensile failure of brittle matrix composites reinforced with unidirectional continuous fibres Davidge, R. W. and Briggs, A. Journal of Materials Science Vol 24 No 8 (1989) pp 2815-2819 The strength values obtained from tests on ceramic composites are dependent on the test method and specimen size. This communication shows that measured strength differences between bend and tensile tests can be understood in terms of the statistical distribution of the strengths of individual fibres.
GENERAL An acoustic emission technique for measuring fiber fragment length distributions in the single-fiber-composite test Netravali, A. N., Topoleski, L. T. T., Sachse, W. H. and Phoenix, S. L. Composites Science and Technology Vol35 No 1 (1989)pp 13-29 The development of an acoustic emission technique for locating the positions of breaks in the fibre, and hence the length distribution of the fibre fragments, in the single-fibre composite test is reported. The technique was applied to E-glass fibres in two epoxy blends, differing in tensile modulus, and the results were compared with those using optical techniques. Good agreement was obtained for interfacial shear strength values measured by acoustic and optical means, particularly for the case of the resin with the higher modulus. Continuous micro-indenter push-through technique for measuring interfacial shear strength of fiber composites Netravali, A. N., Stone, D., Ruoff, S. and Topoleski, L. T. T. Composites Science and Technology Voi34 No 4 (1989) pp 289-303 The apparatus used for the continuous push-through, micro-indentation technique is described and its use for determining the interfacial shear strength of E-glass fibres, with and without an epoxy-compatible silane coupling agent, embedded perpendicular to the plane of thin polished specimens of epoxy matrix is reported. Average shear strength values are shown to be in good agreement with those obtained from the single fibre composite test. Fibres with the coupling agent are shown to have over 60% higher bond strengths than those without. However, it is
pointed out that for the case of fibres without coupling agent, the bond strength cannot be explained by considering only a mechanical interlock mechanism. Craze yielding and fracture mechanisms in PE/PS/PE laminated films. Part 2 Zhu, C. X., Umemoto, S., Okui, N. and Saki, T. Journal of Materials Science Vol 24 No 8 (1989) pp 2787-2793 In this paper, the second in a series of publications, the yielding mechanism of polystyrene (PS) in PE/PS/PE laminated films is studied. By employing an ultrasonic immersion technique to measure the change in PS layer thickness during post yield deformation, crazing is shown to be the basic mechanism of toughening in all laminated films. The aspects of crazes and cracks developed in both bulk and laminated PS samples are compared by optical microscopy. Crazes formed in PS layers in the laminated films are slender and regular compared with the short and lenticular crazes found in bulk PS films. Craze tip advance is measured and related to variations in the stress concentration effect at the craze tip caused by the strain hardening of PE supporting the craze. Diffusion of moisture into two-phase polymers. Part 1 Jacobs, P. M. and Jones, P. R. Journal of Materials Science Vol 24 No 7 (1989) pp 2331-2336 The moisture absorption of a thermoplastic elastomer consisting of a segregated polystyrene glassy phase in a rubber matrix at 96% relative humidity is monitored. A n analytical model to describe the diffusion process is developed and applied for the two phase resin system, allowing a value for the volume fraction of dense phase to be estimated. Dynamic behaviour of delamination and transverse cracks in fibre reinforced laminate composites Awal, M. A., Kundu, T. and Joshi, S. P. Engineering Fracture Mechanics Vo133 No 5 (1989) pp 753-764 This paper develops a numerical method for the study of the dynamic behaviour of delamination and transverse cracks in laminated fibre reinforced composite plates of finite dimensions. The plate surfaces are subjected to a dynamic anti plane shear stress field. Through a numerical analysis a versatile functional is developed which can handle delaminafion and tranverse cracks with any orientation in multilayered laminates.
dislocation and a welded surface crack has been analysed using the conformational mapping technique, to obtain the complex potential, stress field, stress intensity factor, crack extension force, strain energy and i mage force on the dislocation. The general result of this investigations is then reduced to 4 special cases. Some of which are in good agreement with those derived in previous reports. Extended X-ray absorption fine structure of interfaces of layered structures Barrera, E. V., Heald, S. M. and Marcus, H. L. Materials Science and Engineering Vol A l l 7 (1989) pp 45-49 This paper describes the use of extended X-ray absorption fine structure spectroscopy to characterize the atomic ordering of impurity level elements in the in situ condition at the interface of AI-Ga and AI-As layered structures produced by molecular beam epitaxy. Impact resistance and energy absorption mechanisms in hybrid composites Jang, B. A., Chen, L. C., Wang, C. Z., Lin, H. T. and Zee, R. H. Composites Science and Technology Vo134 No 4 (1989) pp 305-335 A n extensive programme to investigate the response of hybrid composites to low-velocity impact loading is reported. Energy absorbing mechanisms of laminates were studied, primarily, by the instrumented falling dart impact testing technique. The impact properties of various single-fibre woven fabric samples, with or without resin impregnation, were used when interpreting the impact response of hybrids. The fibres included: polyethylene, graphite, aramid, nylon, polyester and glass; an epoxy resin matrix was used throughout. Among many conclusions it is shown that polyethylene, polyester and nylon fibres, when combined with epoxy resin, will absorb large amounts of energy prior to failure and can be used in hybrids to improve the impact resistance of the composite. It is also shown that stacking sequence in hybrid laminates plays a critical role in controlling plastic deformation and dclamination.
Effect of shear deformation on bending of bimodular composite-material plates Gordaninejad, F. Composite Structures Vol 12 (1989) pp 162-170 The effect of shear deformation on bimodular fibrous composite plates is studied by comparing results obtained using first-order and higher shear deformation plate theories. The finite-element analysis for in-plane and outof-plane deformations of plates constructed of aramid rubber and polyester rubber are presented.
Influence of statistical fiber strength distribution on matrix cracking in fibre composites Cox, B. N., Marshall, D. B. and Thoulcss, M. D. Acta Metallurgica Vol 37 No 7 (1989) pp 1933-1943 Matrix cracking is analysed for brittle matrix composites containing fibres with statistically distributed strengths. The analysis defines the influence of the shape parameter, of the strength distribution, on the matrix cracking stress and also the condition for transition between catastrophic and non catstrophic failure mechanisms. Analytical solutions are obtained for steady-state cracks, numerically for non steady-state. It is found by comparing the results with analyses for single-valued fibre strengths that the steady-state matrix cracking stress is not strongly influenced by the shape parameter, however the transition condition is more sensitive.
Elastic interaction between screw dislocations and a welded surface crack in composite materials Shiue, S. T., Hu, C. T. and Lee, S. Engineering Fracture Mechanics Vo133 No 5 pp 697-706 In this paper, the interaction between a screw
In-situ composite cure monitoring using infrared transmitting optical fibers Young, P. R., Druy, M. A., Stevenson, W. A. and Compton, D. A. C. S A M P E Journal Vo125 No 2 (March/April 1989) pp I 1-16 The use of an embedded optical fibre to sense and transmit infrared spectra during the
COMPOSITES
. JANUARY
1990
91
GENERAL An acoustic emission technique for measuring fiber fragment length distributions in the single-fiber-composite test Netravali, A. N., Topoleski, L. T. T., Sachse, W. H. and Phoenix, S. L. Composites Science and Technology Vol35 No 1 (1989)pp 13-29 The development of an acoustic emission technique for locating the positions of breaks in the fibre, and hence the length distribution of the fibre fragments, in the single-fibre composite test is reported. The technique was applied to E-glass fibres in two epoxy blends, differing in tensile modulus, and the results were compared with those using optical techniques. Good agreement was obtained for interfacial shear strength values measured by acoustic and optical means, particularly for the case of the resin with the higher modulus. Continuous micro-indenter push-through technique for measuring interfacial shear strength of fiber composites Netravali, A. N., Stone, D., Ruoff, S. and Topoleski, L. T. T. Composites Science and Technology Voi34 No 4 (1989) pp 289-303 The apparatus used for the continuous push-through, micro-indentation technique is described and its use for determining the interfacial shear strength of E-glass fibres, with and without an epoxy-compatible silane coupling agent, embedded perpendicular to the plane of thin polished specimens of epoxy matrix is reported. Average shear strength values are shown to be in good agreement with those obtained from the single fibre composite test. Fibres with the coupling agent are shown to have over 60% higher bond strengths than those without. However, it is
pointed out that for the case of fibres without coupling agent, the bond strength cannot be explained by considering only a mechanical interlock mechanism. Craze yielding and fracture mechanisms in PE/PS/PE laminated films. Part 2 Zhu, C. X., Umemoto, S., Okui, N. and Saki, T. Journal of Materials Science Vol 24 No 8 (1989) pp 2787-2793 In this paper, the second in a series of publications, the yielding mechanism of polystyrene (PS) in PE/PS/PE laminated films is studied. By employing an ultrasonic immersion technique to measure the change in PS layer thickness during post yield deformation, crazing is shown to be the basic mechanism of toughening in all laminated films. The aspects of crazes and cracks developed in both bulk and laminated PS samples are compared by optical microscopy. Crazes formed in PS layers in the laminated films are slender and regular compared with the short and lenticular crazes found in bulk PS films. Craze tip advance is measured and related to variations in the stress concentration effect at the craze tip caused by the strain hardening of PE supporting the craze. Diffusion of moisture into two-phase polymers. Part 1 Jacobs, P. M. and Jones, P. R. Journal of Materials Science Vol 24 No 7 (1989) pp 2331-2336 The moisture absorption of a thermoplastic elastomer consisting of a segregated polystyrene glassy phase in a rubber matrix at 96% relative humidity is monitored. A n analytical model to describe the diffusion process is developed and applied for the two phase resin system, allowing a value for the volume fraction of dense phase to be estimated. Dynamic behaviour of delamination and transverse cracks in fibre reinforced laminate composites Awal, M. A., Kundu, T. and Joshi, S. P. Engineering Fracture Mechanics Vo133 No 5 (1989) pp 753-764 This paper develops a numerical method for the study of the dynamic behaviour of delamination and transverse cracks in laminated fibre reinforced composite plates of finite dimensions. The plate surfaces are subjected to a dynamic anti plane shear stress field. Through a numerical analysis a versatile functional is developed which can handle delaminafion and tranverse cracks with any orientation in multilayered laminates.
dislocation and a welded surface crack has been analysed using the conformational mapping technique, to obtain the complex potential, stress field, stress intensity factor, crack extension force, strain energy and i mage force on the dislocation. The general result of this investigations is then reduced to 4 special cases. Some of which are in good agreement with those derived in previous reports. Extended X-ray absorption fine structure of interfaces of layered structures Barrera, E. V., Heald, S. M. and Marcus, H. L. Materials Science and Engineering Vol A l l 7 (1989) pp 45-49 This paper describes the use of extended X-ray absorption fine structure spectroscopy to characterize the atomic ordering of impurity level elements in the in situ condition at the interface of AI-Ga and AI-As layered structures produced by molecular beam epitaxy. Impact resistance and energy absorption mechanisms in hybrid composites Jang, B. A., Chen, L. C., Wang, C. Z., Lin, H. T. and Zee, R. H. Composites Science and Technology Vo134 No 4 (1989) pp 305-335 A n extensive programme to investigate the response of hybrid composites to low-velocity impact loading is reported. Energy absorbing mechanisms of laminates were studied, primarily, by the instrumented falling dart impact testing technique. The impact properties of various single-fibre woven fabric samples, with or without resin impregnation, were used when interpreting the impact response of hybrids. The fibres included: polyethylene, graphite, aramid, nylon, polyester and glass; an epoxy resin matrix was used throughout. Among many conclusions it is shown that polyethylene, polyester and nylon fibres, when combined with epoxy resin, will absorb large amounts of energy prior to failure and can be used in hybrids to improve the impact resistance of the composite. It is also shown that stacking sequence in hybrid laminates plays a critical role in controlling plastic deformation and dclamination.
Effect of shear deformation on bending of bimodular composite-material plates Gordaninejad, F. Composite Structures Vol 12 (1989) pp 162-170 The effect of shear deformation on bimodular fibrous composite plates is studied by comparing results obtained using first-order and higher shear deformation plate theories. The finite-element analysis for in-plane and outof-plane deformations of plates constructed of aramid rubber and polyester rubber are presented.
Influence of statistical fiber strength distribution on matrix cracking in fibre composites Cox, B. N., Marshall, D. B. and Thoulcss, M. D. Acta Metallurgica Vol 37 No 7 (1989) pp 1933-1943 Matrix cracking is analysed for brittle matrix composites containing fibres with statistically distributed strengths. The analysis defines the influence of the shape parameter, of the strength distribution, on the matrix cracking stress and also the condition for transition between catastrophic and non catstrophic failure mechanisms. Analytical solutions are obtained for steady-state cracks, numerically for non steady-state. It is found by comparing the results with analyses for single-valued fibre strengths that the steady-state matrix cracking stress is not strongly influenced by the shape parameter, however the transition condition is more sensitive.
Elastic interaction between screw dislocations and a welded surface crack in composite materials Shiue, S. T., Hu, C. T. and Lee, S. Engineering Fracture Mechanics Vo133 No 5 pp 697-706 In this paper, the interaction between a screw
In-situ composite cure monitoring using infrared transmitting optical fibers Young, P. R., Druy, M. A., Stevenson, W. A. and Compton, D. A. C. S A M P E Journal Vo125 No 2 (March/April 1989) pp I 1-16 The use of an embedded optical fibre to sense and transmit infrared spectra during the
COMPOSITES
. JANUARY
1990
91