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6061-T6 composite
This section contains abstracts of selected articles, technical reports, dissertations and patents concerned with fatigue. The abstracts are prepared in collaboration with Materials Information, a joint service of The Institute of Metals and ASM International. Readers wishing to obtain the full text of articles abstracted here should contact either: The Institute of Metals, 1 Carlton House Terrace, London SW1Y 5DB, UK, or: ASM International, Metals Park, OH 44073, USA (not International Journal of Fatigue). The fees charged for photocopying articles are £7.00 for the first ten pages and £3.00 per additional ten pages (UK office), or $10.00 for the first ten pages and $4.00 per additional ten pages (US office).
Composites Pries
o f cad)on-fibre-reinforced a l u m i n i u m laminates. Yang, F.-S.,
Lin, C.-T., Kao, P.-W. and Su, A.-C. China Steel Tech. Rap. Dec. 1990 (4), 180-186
A new hybrid composite (CARALL) consisting of thin layers of carbon-fibre/epoxy prepreg sandwiched between AI sheets has been developed. It has been shown that this class of materials offered • higher modulus, a higher tensile strength and a lower density as compared with 2024-1"3 alloy in the longitudinal direction. Owing to the large differences in thermal expansion coefficients among the constituents of CARALL laminates, thermal residual stresses may be introduced in the laminates after cooling down from the curing temperature. The thermal residual stresses were shown to increase with increasing thickness of the carbon-fibre/epoxy layer. Under tension-tension fatigue loading, these hybrid laminates showed superior fatigue crack propagation resistance, which might be attributed to the bridging effect imposed by the intact fibres in the crack wake. The resistance to fatigue crack propagation of this material can be further improved as compressive residual stresses are introduced in the AI layer by post-cure stretching the laminate in the plastic region of the AI alloy. Graphs. 7 refs.
Fatigue cracks initiated from several different microstructural features or defect types, but fatigue life did not vary significantly with the specific initiation site. As the fatigue crack advanced away from the fatigue crack initiation site, increasing numbers of SiC particles were fractured, in agreement with crack-tip process zone models. Graphs, photomicrographs. 33 refs. M a t r i x fatigue cracking in fibre composites. McMeeking, R.M. and Evans,
A.G. Mech. Mater Nov. 1990 9, (3), 217-227 A model is developed for fatigue growth of matrix cracks in metals (e.g., Ti-6AI-4V) reinforced with aligned continuous elastic fibres (e.g., SIC). The mechanics of elastic cracks bddged by frictionally constrained fibres is used to develop the model, which provides estimates of the tip value of the stress intensity factor amplitude, ~IKT1p. It is found that, when the applied load amplitude is held fixed during fatigue crack growth, AKTIp,and thus the rate of growth, approach an asymptotic value independent of the crack length. The residual strength after fatigue crack growth is also discussed. In some cases, the residual strength is unaffected by prior fatigue growth. But, in another regime, the matrix crack length allows fibres to begin breaking before the matrix crack grows. The strength is then inversely proportional to the square root of fatigue crack length. Graphs. 19 refs.
Fatigue crack propagation charaeterisffcs in Sk3j,/go61-T6 composite.
Kobayashi, T., Iwanari, H., Hakamata, S., Nfinoml, M. and Toda, H, J. Japan Inst. Met. Jan. 1991 55, (1), 72-78 (in Japanese) Research end development have produced AI matrix composites that ere excellent in specific strength and specific modulus, and applications of AI matrix components to the structural materials of the composites used in automobiles and aircraft are expected. However, there are few reports on the fatigue crack propagation characteristics, which are very important for the design of structural materials, since composites fracture in a complicated manner, suchss exfoliation between matrix and reinforcement or failure of reinforcements. Therefore, such properties and tensile strengths should be evaluated for the applications of AI matrix composites as structural materials especially from the viewpoint of the guarantee of better safety. The effect of the volume fraction of SiC particles on the fatigue crack propagation characteristics of 6061 AI alloys reinforced with SiC particles (SiCp/6061T6 composites) manufactured by powder metallurgy process was investigated. The following results were obtained. In a higher stress intensity range, unstable fatigue crack propagation was found as the threshold stress intensity range &Kchend AKeff.th increased with increasing content of SiC particles. However, &/~f. th was suggested to be solely a function of the mean SiC particle size and to be independent of the volume fraction. This implies that for near-threshold crack extension the maximum plastic zone size at the crack tip must exceed the mean SiC particle size. Graphs, photomicrographs. 24 refs.
Aluminium o x i d e fibre-reinforced a l u m i n i u m alloys: characterization of static and d y n a m i c properthm. Schulte, K., Trautmann, K.-H. and Girot,
F. Materialprufung Nov.-Dec. 1990 32, (11-12), 343-347
Metal matrix composites based on AI2 03 fibre reinforcements are gaining increasing attention for structural applications. An (t-AI2 03-fibre-(FP-flbre from Dupont) reinforced AI-2.5Li composite has been investigated. Tests were performed in the 0 ° and 90° directions. Transmission electron microscopy was performed to study the fibre/matrix interface. Precipitation-free areas were found around the fibres. However, within the matrix t-particles were present. For mechanical characterization, tensile and compressive tests were performed. To obtain sufficiently good results a special MMC-related test equipment was designed. Fatigue testing of the metal matrix composites showed that with fibre reinforcement a pronounced improvement of the fatigue behaviour can be achieved. Graphs, photomicrographs, 9 refs. Fatigue behaviour o f a 2 x x x series a l u m i n i u m alloy reinforced w i t h 15 vol.% 81Cp. Bonnen, J.J., Allison, J.E. and Jones, J.W. Metall. Trans. A M a y 1991 22A, (5), 1007-1019 The fatigue behaviour of a naturally aged powder metallurgy 2xxx series AI alloy (Alcoa MB85) and a composite made of this alloy with 15 vol.% SiCp has been investigated. The fatigue lives were determined using load-controlled axial testing of unnotched cylindrical samples. The influence of mean stress was determined at stress ratios of -1, 0.1 end 0.7. Mean stress had a significant influence on fatigue life, and this influence was consistent with that normally observed in metals. At each stress ratio, the incorporation of SiC reinforcement led to an increase in fatigue life at low and intermediate stresses. When considered on a strain-life basis, however, the composite materials had a somewhat inferior resistance to fatigue.
500
Fatigue behaviour of the SiCp/6061AI composite. Yu, W., Yuan, J. and
Wang, Z. Acts Metall. Sin. (China) Dec. 1990 26, (6), B428-B432 (in Chinese) The fatigue properties of a composite of 6061AI reinforced by 15 vol.% SiC particles sized to 10-2.5 I~m have been examined in comparison with those of 6061AI. The microprocess of fatigue crack initiation and propagation, as well as dislocation structure, have also been studied using SEM and TEM. For the composites reinforced by SiC particles of two different sizes, the fatigue strength of both at 107 cycles is 196 MPa, that is 25% greater than that of the matrix alloy. If the cycling life is below 107, the fatigue strength of the composite reinforced by coarse SiC particles is better than that of material reinforced by fine particles. The voids and microcracks initiated at and near the interface between SiCp and the matrix, where the higher density dislocations are presented, will propagate and link up to form the fatigue crack. There is important evidence that the dislocation channels where screw dislocations can travel are formed near the interface and corner regions of SiCp in the composite that is subjected to fatigue stress, demonstrating the relationship between fatigue crack initiation and dislocation movement in the SiC-particle-reinforced 6061AI composite. 7 refs. The influence of ageing on fatigue crack g r o w t h in SiC-particulate reinforced 8550 AI alloy. Knowles, D.M. and King, J.E. Acts Metall. Mater. M a y 1991 39, (5), 793-806 A study of the influence of SiC-paniculate reinforcement on ageing and subsequent fatigue crack growth resistance in a powder metallurgy 8090 AI alloy-SiC composite has been made. Macroscopic hardness measurements revealed that ageing at 170 °C in the composite is accelerated with respect to the unreinforced alloy, though TEM studies indicate that this does not result from the enhanced precipitation of S'. Fatigue crack growth rates in the naturally aged condition of the composite and unreinforcad matrix are similar at low to medium values of AK, but diverge above approximately 8 MPa ~/m owing to the lower fracture toughness of the composite. As a result of the presence of the reinforcement, planar slip in the composite is suppressed and fscetted crack growth is nut observed. Ageing at or above 170 °C has a deleterious effect on the fatigue crack growth. An increased ageing time decreases the roughness of the fracture path at higher growth rates. These effects are thought to arise from microstructurel changes occurring at or near to the SiC/matrix interfaces, providing sites for static-mode failure mechanisms to operate. This suggestion is supported by the observation that as ~K increases, the crack growth rates become dependent on Kmax, implying that the crack growth rate is strongly influenced by static modes. Graphs, photomicrographs. 30 refs. Fatigue behaviour of short-alumine-flbra-reinfor,-,ed AZ91 magnesium alloy metal m a t r i x c e m p o l i t e . Llorca, N., Bloyce, A. and Yue, T.M. Mater. Sci. Eng. A Mar. 1991 A13S, (1-2), 247-252 Magnesium alloy metal matrix composites (MMCs) have been produced by squeeze casting using AZ91 Mg alloy with ceramic reinforcements based on alumina (Saffil) fibre two-dimensional preforms. MMCs have been cast with 0.05, 0.16 and 0.25 volume fraction alumina reinforcements. Some tensile test results were obtained for the 0.25 volume fraction Seffil composite. The heat treatment widely used for AZ91 is unsuitable for the composite material where heating to 420 °C has changed
Int J Fatigue November 1991
Composites Pries
o f cad)on-fibre-reinforced a l u m i n i u m laminates. Yang, F.-S.,
Lin, C.-T., Kao, P.-W. and Su, A.-C. China Steel Tech. Rap. Dec. 1990 (4), 180-186
A new hybrid composite (CARALL) consisting of thin layers of carbon-fibre/epoxy prepreg sandwiched between AI sheets has been developed. It has been shown that this class of materials offered • higher modulus, a higher tensile strength and a lower density as compared with 2024-1"3 alloy in the longitudinal direction. Owing to the large differences in thermal expansion coefficients among the constituents of CARALL laminates, thermal residual stresses may be introduced in the laminates after cooling down from the curing temperature. The thermal residual stresses were shown to increase with increasing thickness of the carbon-fibre/epoxy layer. Under tension-tension fatigue loading, these hybrid laminates showed superior fatigue crack propagation resistance, which might be attributed to the bridging effect imposed by the intact fibres in the crack wake. The resistance to fatigue crack propagation of this material can be further improved as compressive residual stresses are introduced in the AI layer by post-cure stretching the laminate in the plastic region of the AI alloy. Graphs. 7 refs.
Fatigue cracks initiated from several different microstructural features or defect types, but fatigue life did not vary significantly with the specific initiation site. As the fatigue crack advanced away from the fatigue crack initiation site, increasing numbers of SiC particles were fractured, in agreement with crack-tip process zone models. Graphs, photomicrographs. 33 refs. M a t r i x fatigue cracking in fibre composites. McMeeking, R.M. and Evans,
A.G. Mech. Mater Nov. 1990 9, (3), 217-227 A model is developed for fatigue growth of matrix cracks in metals (e.g., Ti-6AI-4V) reinforced with aligned continuous elastic fibres (e.g., SIC). The mechanics of elastic cracks bddged by frictionally constrained fibres is used to develop the model, which provides estimates of the tip value of the stress intensity factor amplitude, ~IKT1p. It is found that, when the applied load amplitude is held fixed during fatigue crack growth, AKTIp,and thus the rate of growth, approach an asymptotic value independent of the crack length. The residual strength after fatigue crack growth is also discussed. In some cases, the residual strength is unaffected by prior fatigue growth. But, in another regime, the matrix crack length allows fibres to begin breaking before the matrix crack grows. The strength is then inversely proportional to the square root of fatigue crack length. Graphs. 19 refs.
Fatigue crack propagation charaeterisffcs in Sk3j,/go61-T6 composite.
Kobayashi, T., Iwanari, H., Hakamata, S., Nfinoml, M. and Toda, H, J. Japan Inst. Met. Jan. 1991 55, (1), 72-78 (in Japanese) Research end development have produced AI matrix composites that ere excellent in specific strength and specific modulus, and applications of AI matrix components to the structural materials of the composites used in automobiles and aircraft are expected. However, there are few reports on the fatigue crack propagation characteristics, which are very important for the design of structural materials, since composites fracture in a complicated manner, suchss exfoliation between matrix and reinforcement or failure of reinforcements. Therefore, such properties and tensile strengths should be evaluated for the applications of AI matrix composites as structural materials especially from the viewpoint of the guarantee of better safety. The effect of the volume fraction of SiC particles on the fatigue crack propagation characteristics of 6061 AI alloys reinforced with SiC particles (SiCp/6061T6 composites) manufactured by powder metallurgy process was investigated. The following results were obtained. In a higher stress intensity range, unstable fatigue crack propagation was found as the threshold stress intensity range &Kchend AKeff.th increased with increasing content of SiC particles. However, &/~f. th was suggested to be solely a function of the mean SiC particle size and to be independent of the volume fraction. This implies that for near-threshold crack extension the maximum plastic zone size at the crack tip must exceed the mean SiC particle size. Graphs, photomicrographs. 24 refs.
Aluminium o x i d e fibre-reinforced a l u m i n i u m alloys: characterization of static and d y n a m i c properthm. Schulte, K., Trautmann, K.-H. and Girot,
F. Materialprufung Nov.-Dec. 1990 32, (11-12), 343-347
Metal matrix composites based on AI2 03 fibre reinforcements are gaining increasing attention for structural applications. An (t-AI2 03-fibre-(FP-flbre from Dupont) reinforced AI-2.5Li composite has been investigated. Tests were performed in the 0 ° and 90° directions. Transmission electron microscopy was performed to study the fibre/matrix interface. Precipitation-free areas were found around the fibres. However, within the matrix t-particles were present. For mechanical characterization, tensile and compressive tests were performed. To obtain sufficiently good results a special MMC-related test equipment was designed. Fatigue testing of the metal matrix composites showed that with fibre reinforcement a pronounced improvement of the fatigue behaviour can be achieved. Graphs, photomicrographs, 9 refs. Fatigue behaviour o f a 2 x x x series a l u m i n i u m alloy reinforced w i t h 15 vol.% 81Cp. Bonnen, J.J., Allison, J.E. and Jones, J.W. Metall. Trans. A M a y 1991 22A, (5), 1007-1019 The fatigue behaviour of a naturally aged powder metallurgy 2xxx series AI alloy (Alcoa MB85) and a composite made of this alloy with 15 vol.% SiCp has been investigated. The fatigue lives were determined using load-controlled axial testing of unnotched cylindrical samples. The influence of mean stress was determined at stress ratios of -1, 0.1 end 0.7. Mean stress had a significant influence on fatigue life, and this influence was consistent with that normally observed in metals. At each stress ratio, the incorporation of SiC reinforcement led to an increase in fatigue life at low and intermediate stresses. When considered on a strain-life basis, however, the composite materials had a somewhat inferior resistance to fatigue.
500
Fatigue behaviour of the SiCp/6061AI composite. Yu, W., Yuan, J. and
Wang, Z. Acts Metall. Sin. (China) Dec. 1990 26, (6), B428-B432 (in Chinese) The fatigue properties of a composite of 6061AI reinforced by 15 vol.% SiC particles sized to 10-2.5 I~m have been examined in comparison with those of 6061AI. The microprocess of fatigue crack initiation and propagation, as well as dislocation structure, have also been studied using SEM and TEM. For the composites reinforced by SiC particles of two different sizes, the fatigue strength of both at 107 cycles is 196 MPa, that is 25% greater than that of the matrix alloy. If the cycling life is below 107, the fatigue strength of the composite reinforced by coarse SiC particles is better than that of material reinforced by fine particles. The voids and microcracks initiated at and near the interface between SiCp and the matrix, where the higher density dislocations are presented, will propagate and link up to form the fatigue crack. There is important evidence that the dislocation channels where screw dislocations can travel are formed near the interface and corner regions of SiCp in the composite that is subjected to fatigue stress, demonstrating the relationship between fatigue crack initiation and dislocation movement in the SiC-particle-reinforced 6061AI composite. 7 refs. The influence of ageing on fatigue crack g r o w t h in SiC-particulate reinforced 8550 AI alloy. Knowles, D.M. and King, J.E. Acts Metall. Mater. M a y 1991 39, (5), 793-806 A study of the influence of SiC-paniculate reinforcement on ageing and subsequent fatigue crack growth resistance in a powder metallurgy 8090 AI alloy-SiC composite has been made. Macroscopic hardness measurements revealed that ageing at 170 °C in the composite is accelerated with respect to the unreinforced alloy, though TEM studies indicate that this does not result from the enhanced precipitation of S'. Fatigue crack growth rates in the naturally aged condition of the composite and unreinforcad matrix are similar at low to medium values of AK, but diverge above approximately 8 MPa ~/m owing to the lower fracture toughness of the composite. As a result of the presence of the reinforcement, planar slip in the composite is suppressed and fscetted crack growth is nut observed. Ageing at or above 170 °C has a deleterious effect on the fatigue crack growth. An increased ageing time decreases the roughness of the fracture path at higher growth rates. These effects are thought to arise from microstructurel changes occurring at or near to the SiC/matrix interfaces, providing sites for static-mode failure mechanisms to operate. This suggestion is supported by the observation that as ~K increases, the crack growth rates become dependent on Kmax, implying that the crack growth rate is strongly influenced by static modes. Graphs, photomicrographs. 30 refs. Fatigue behaviour of short-alumine-flbra-reinfor,-,ed AZ91 magnesium alloy metal m a t r i x c e m p o l i t e . Llorca, N., Bloyce, A. and Yue, T.M. Mater. Sci. Eng. A Mar. 1991 A13S, (1-2), 247-252 Magnesium alloy metal matrix composites (MMCs) have been produced by squeeze casting using AZ91 Mg alloy with ceramic reinforcements based on alumina (Saffil) fibre two-dimensional preforms. MMCs have been cast with 0.05, 0.16 and 0.25 volume fraction alumina reinforcements. Some tensile test results were obtained for the 0.25 volume fraction Seffil composite. The heat treatment widely used for AZ91 is unsuitable for the composite material where heating to 420 °C has changed
Int J Fatigue November 1991