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Composites technology development in Italy
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Prepared by M. E. Adams and M. C. Hill
CERAMIC MA TRICES Effect of composition on the fracture strength of hot-presses silicon nitride Ovri, J. E. O. and Davies, T. J. Journal o f Materials Science Vol 23 No 5 (1988) pp 1817-1824 The effects of material composition and hot-pressing time and temperature on the densification of silicon nitride (Si3N4) were studied. Two compositions were used - Si3N4 with 5%(wt) MgO and Si3N4 with 2% MgO and 10% Y203. The densification rate was found to be dependent on the amount of liquid present. An optimum hot-pressing temperature was determined, above which a decrease in material quality was observed. The room temperature fracture strengths were found to be related to the amount and composition of the densifieation.
GENERAL Composites technology development in Italy Crivelli Visconti, I. Composites Science and Technology Vol 31, No 2 (1988) pp 81-85 A review paper which was first presented at a meeting of the European Composites Forum held in Cambridge, UK, in July 1987 is published as the Guest Editorial. The ~tate-of-the-art of the composites industry is presented in the context of the Italian industrial economy. The development of new technologies is seen as a powerful means of influencing industrial behaviour but scant attention is said to be officially paid to composites technology. No advanced reinforcing fibres are produced in Italy but there is large-scale development of polymers. The areas in which products made from composite materials have potential are discussed. Design and analysis of the crack rail shear spoctmen for Mode III interlaminar fracture ]Beeht, G. and Gillespie Jr, J. W. Composites Science and Technology Vol 31 No 2 (1988) I~P 143-157 The crack rail shear (CRS) specimen, a proposed test method to characterize the Mode III interlaminar fracture toughness of continuous fibre-reinforced composite materials, is described in detail. Based on the ASTM shear test specimen geometry, the CRS uses the two-rail shear test fixture and a Kapton film embedded in the specimen placed symmetrically about the mid-plane to provide starter cracks. An analytical model is also developed for verification of results. Results indicate that the CRS specimen is a viable Mode III test method. Interaction of boron fibres with aluminium melt during metallization Chernyshova, T. A., Tylkina, M. I. and Gevlich, S. O. Journal of Materials Science Vol 23 No 6 (1988) pp 1981-1984
COMPOSITES. JANUARY 1989
The interphase interaction on the fibre-melt interface boundary during metallization of boron fibres by aluminium is investigated. Boron fibres were coated by passing them through molten aluminium. Electron diffraction studies were then performed on fibres which had had their aluminium coating removed by chemical means to ascertain the chemical reactions that had taken place on the fibre surface. The strength of the fibres was calculated from bend tests on the fibres. The effects of contact time (with the molten aluminium) on strength, fibre mass and surface morphology is discussed.
K. Composites Science and Technology Vol 31 No 2 (1988) pp 111-120 The corrosion behaviour of carbon fibrereinforced aluminium composites that had been manufactured by the Na-K process was studied. The influence of distilled water and 3.5% NaCI solution were assessed using microscopic analysis. It was found that immersion in either medium for 14 days caused severe corrosion particularly at the interfaces. Exposure to air for an appreciable time also caused corrosion due to the formation of NaOH and KOH.
Prediction of mixed-mode cracking direction in random, short-fibre composite materials Tsai, L. W. and Zhang, S. Y. Composites Science and Technology Vol 31 No 2 (1988) pp 97-110 Several methods for predicting the cracking direction in the double-grooved tension/ shear specimen which gives mixed-mode cracking are examined in detail. Of the criteria discussed: strain energy density criterion; normal stress ratio criterion; strain energy density ratio criterion; extended Tsai-Hill criterion; and extended Norris criterion, the last three named have been derived by the authors. It is shown that the first named criterion is inapplicable but that the others give satisfactory agreement with experimental measurement, the latter three with a higher degree of accuracy. FEM is used to calculate stress distributions in the near-notch zone and allows prediction of the size of the zone in which the singular term is dominant.
Impact response of short **d**-alumina fibre/aluminium alloy metal matrix composites Friend, C. M. and Nixon, A. C. Journal of Materials Science Vol 23 No 6 (1988) pp 1967-1975 Instrumented impact testing was carried out on pseudorandomly orientated short ralumina fibre-reinforced aluminium alloy in order to determine their impact resistance. It is reported that the impact toughness of reinforced aluminium alloy is less than that of the unreinforced alloy. It is suggested that this is a result of the low composite failure strain and low crack propagation energy.
Strength and toughness of fibre composites Harris, B., Dorey, S. E. and Cooke, R. G. Composites Science and Technology Vol 31 No 2 (1988) pp 121-141 Laminates of different lay-ups using a variety of reinforcing fibres in differing matrix materials were tested to determine their tensile strength and fracture toughness. The results were compared with those obtained from the literature covering an even wider selection of composite types. The results led to the conclusion that there was a simple linear relationship between the strength of the material and the property referred to as the critical stress intensity factor, Kic. The implication is that all composites appear to behave as though they contain a defect of the order of 1 mm in length no matter what their structure or composition. The authors state that as this appears to be an unlikely possibility, the use of the concept Ktc has no meaning for composite materials due to their complex structure and cracking patterns.
METAL MA TRICES Corrosion behaviour of a carbon-aluminium composite Gu, J., Han, G. H., Sui, Q. W. and Yao, C.
Mechanical properties and microstructures of co-precipitation derived tetragonal Y203ZrO2-AI203 composites Rajendran, S., Swain, M. V. and Rossell, H. J. Journal o f Materials Science Vol 23 No 5 (1988) pp 1805-1812 The effects of processing variables (sintering temperature, alumina content and HIPing treatment) on the mechanical properties and material morphology of Y203-ZrO2-AI203 (Y-TZP-AI203) were studied. It was found that alumina improves material density and suppresses porosity development at high temperatures, HIPing substantially improves the material's strength and all materials were found to be durable in water. Microstructure and mechanical properties of AI203-Cr203-ZrO 2 composites Arahori, T. and Dow Whitney, E. Journal o f Materials Science Vol 23 No 5 (1988) pp 1615-1631 The mechanical properties (hardness, wear resistance and toughness) of alumina (A1203) may be enhanced by the addition of zirconia to give a zirconia toughened alumina (ZTA). This study used scanning electron microscopy (SEM). electron spectroscopy for chemical analysis (ESCA), X-ray diffraction (XRD), Vickers hardness testing and bend strength testing to ascertain the effects of ZrO 2 and Cr203 on alumina. It was reported that ZrO2 inhibited the grain growth of AIzO3-Cr203 and that a solid solution of A1203-Cr203 existed. Compositions yielding maximum hardness and toughness were established. The reasons for the materials behaviour are discussed.
93
te
twv
I
tesut
l
Prepared by M. E. Adams and M. C. Hill
CERAMIC MA TRICES Effect of composition on the fracture strength of hot-presses silicon nitride Ovri, J. E. O. and Davies, T. J. Journal o f Materials Science Vol 23 No 5 (1988) pp 1817-1824 The effects of material composition and hot-pressing time and temperature on the densification of silicon nitride (Si3N4) were studied. Two compositions were used - Si3N4 with 5%(wt) MgO and Si3N4 with 2% MgO and 10% Y203. The densification rate was found to be dependent on the amount of liquid present. An optimum hot-pressing temperature was determined, above which a decrease in material quality was observed. The room temperature fracture strengths were found to be related to the amount and composition of the densifieation.
GENERAL Composites technology development in Italy Crivelli Visconti, I. Composites Science and Technology Vol 31, No 2 (1988) pp 81-85 A review paper which was first presented at a meeting of the European Composites Forum held in Cambridge, UK, in July 1987 is published as the Guest Editorial. The ~tate-of-the-art of the composites industry is presented in the context of the Italian industrial economy. The development of new technologies is seen as a powerful means of influencing industrial behaviour but scant attention is said to be officially paid to composites technology. No advanced reinforcing fibres are produced in Italy but there is large-scale development of polymers. The areas in which products made from composite materials have potential are discussed. Design and analysis of the crack rail shear spoctmen for Mode III interlaminar fracture ]Beeht, G. and Gillespie Jr, J. W. Composites Science and Technology Vol 31 No 2 (1988) I~P 143-157 The crack rail shear (CRS) specimen, a proposed test method to characterize the Mode III interlaminar fracture toughness of continuous fibre-reinforced composite materials, is described in detail. Based on the ASTM shear test specimen geometry, the CRS uses the two-rail shear test fixture and a Kapton film embedded in the specimen placed symmetrically about the mid-plane to provide starter cracks. An analytical model is also developed for verification of results. Results indicate that the CRS specimen is a viable Mode III test method. Interaction of boron fibres with aluminium melt during metallization Chernyshova, T. A., Tylkina, M. I. and Gevlich, S. O. Journal of Materials Science Vol 23 No 6 (1988) pp 1981-1984
COMPOSITES. JANUARY 1989
The interphase interaction on the fibre-melt interface boundary during metallization of boron fibres by aluminium is investigated. Boron fibres were coated by passing them through molten aluminium. Electron diffraction studies were then performed on fibres which had had their aluminium coating removed by chemical means to ascertain the chemical reactions that had taken place on the fibre surface. The strength of the fibres was calculated from bend tests on the fibres. The effects of contact time (with the molten aluminium) on strength, fibre mass and surface morphology is discussed.
K. Composites Science and Technology Vol 31 No 2 (1988) pp 111-120 The corrosion behaviour of carbon fibrereinforced aluminium composites that had been manufactured by the Na-K process was studied. The influence of distilled water and 3.5% NaCI solution were assessed using microscopic analysis. It was found that immersion in either medium for 14 days caused severe corrosion particularly at the interfaces. Exposure to air for an appreciable time also caused corrosion due to the formation of NaOH and KOH.
Prediction of mixed-mode cracking direction in random, short-fibre composite materials Tsai, L. W. and Zhang, S. Y. Composites Science and Technology Vol 31 No 2 (1988) pp 97-110 Several methods for predicting the cracking direction in the double-grooved tension/ shear specimen which gives mixed-mode cracking are examined in detail. Of the criteria discussed: strain energy density criterion; normal stress ratio criterion; strain energy density ratio criterion; extended Tsai-Hill criterion; and extended Norris criterion, the last three named have been derived by the authors. It is shown that the first named criterion is inapplicable but that the others give satisfactory agreement with experimental measurement, the latter three with a higher degree of accuracy. FEM is used to calculate stress distributions in the near-notch zone and allows prediction of the size of the zone in which the singular term is dominant.
Impact response of short **d**-alumina fibre/aluminium alloy metal matrix composites Friend, C. M. and Nixon, A. C. Journal of Materials Science Vol 23 No 6 (1988) pp 1967-1975 Instrumented impact testing was carried out on pseudorandomly orientated short ralumina fibre-reinforced aluminium alloy in order to determine their impact resistance. It is reported that the impact toughness of reinforced aluminium alloy is less than that of the unreinforced alloy. It is suggested that this is a result of the low composite failure strain and low crack propagation energy.
Strength and toughness of fibre composites Harris, B., Dorey, S. E. and Cooke, R. G. Composites Science and Technology Vol 31 No 2 (1988) pp 121-141 Laminates of different lay-ups using a variety of reinforcing fibres in differing matrix materials were tested to determine their tensile strength and fracture toughness. The results were compared with those obtained from the literature covering an even wider selection of composite types. The results led to the conclusion that there was a simple linear relationship between the strength of the material and the property referred to as the critical stress intensity factor, Kic. The implication is that all composites appear to behave as though they contain a defect of the order of 1 mm in length no matter what their structure or composition. The authors state that as this appears to be an unlikely possibility, the use of the concept Ktc has no meaning for composite materials due to their complex structure and cracking patterns.
METAL MA TRICES Corrosion behaviour of a carbon-aluminium composite Gu, J., Han, G. H., Sui, Q. W. and Yao, C.
Mechanical properties and microstructures of co-precipitation derived tetragonal Y203ZrO2-AI203 composites Rajendran, S., Swain, M. V. and Rossell, H. J. Journal o f Materials Science Vol 23 No 5 (1988) pp 1805-1812 The effects of processing variables (sintering temperature, alumina content and HIPing treatment) on the mechanical properties and material morphology of Y203-ZrO2-AI203 (Y-TZP-AI203) were studied. It was found that alumina improves material density and suppresses porosity development at high temperatures, HIPing substantially improves the material's strength and all materials were found to be durable in water. Microstructure and mechanical properties of AI203-Cr203-ZrO 2 composites Arahori, T. and Dow Whitney, E. Journal o f Materials Science Vol 23 No 5 (1988) pp 1615-1631 The mechanical properties (hardness, wear resistance and toughness) of alumina (A1203) may be enhanced by the addition of zirconia to give a zirconia toughened alumina (ZTA). This study used scanning electron microscopy (SEM). electron spectroscopy for chemical analysis (ESCA), X-ray diffraction (XRD), Vickers hardness testing and bend strength testing to ascertain the effects of ZrO 2 and Cr203 on alumina. It was reported that ZrO2 inhibited the grain growth of AIzO3-Cr203 and that a solid solution of A1203-Cr203 existed. Compositions yielding maximum hardness and toughness were established. The reasons for the materials behaviour are discussed.
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