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A new prediction method of fatigue-creep interaction behaviour based on total strain energy for high-strength superalloy
increased cycles observed on Si-Mn dual-phase steel results from fine cell structures in the ferrite matrix of the soft phase. (2) The monotonous decrease in the X-ray half-value breadth observed on niobium precipitation-hardened steel results from sub-boundaries due to the rearrangement of the dislocations. Photomicrographs, Graphs. 26 refs.
A new prediction method of fatigue-creep interaction behaviour based on total strain energy for high-strength superalloy. Matsuda, N., Umezawa, S. and Miyata, H. J. Soc. Mater. Sci., Jpn. J u l y 1989 38, (430), 8 0 9 - 8 1 5 (in Japanese) A new life prediction method was proposed for high-strength materials under fatigue-creep interaction (FCI) based on their tensile total strain energy behaviour. The net tensile hysteresis energy is now being used to evaluate the FCI life in the frequency-modified damage function rule developed by W.J. Ostergren. For highstrength materials, however, this damage rule seems to require some modification to give good life assessment, because the elastic strain range is much larger than the inelastic strain range in the FCI behaviour of these materials. In the paper, straincontrolled tensile or compressive strain hold tests with F-F, F-S and S-F wave forms were performed for cast Rene 80. The total strain energy including a large elastic strain energy was defined, and the FCI life was obtained against this strain energy. Multiple-regression analysis was carried out to assess the relationship between strain energy and cycles to failure and was expressed numerically to improve life estimation accuracy. Finally, a frequency-modified total strain energy parameter was defined to evaluate the failure lives (Nf) of high-strength materials such as Rene 80 under the FCI condition. The total tensile strain energy (~W-~) and the time (~TT) under tensile stress loading were used to define this tensile strain energy parameter. A similar relation was also obtained between total strain energy (AWTT) and crack initiation life (Nc). 9 refs.
Low-cycle fatigue behaviour of structural materials at cryogenic temperature. Mizoguchi, T., Kataoka, T., Shimada, M. and Yamamoto, S. Kobe Res. Dev. J u l y 1989 38, (3), 9 3 - 9 6 (in Japanese) Studies have been made of the interrelations among temperature, strain rate, cyclic deformation and low-cycle fatigue lives of parent and welded austenitic steels. Strain rate significantly affects the appearance of serrations on stress-strain hysteresis loops, but does not affect the fatigue life unless a considerable rise in temperature occurs. In a constant total strain range, a cryogenic temperature gives a longer life than the ambient temperature. However, no temperature dependence is observed in plastic strain range against life, meaning that the dominant factor in cryogenic low-cycle fatigue is the plastic strain. Graphs. 11 refs.
Composite extruded aluminium-steel transition couplings and their dynamic strength. Gitter, R. Schweissen Schneiden J u l y 1989 41, (7), 3 2 3 - 3 2 7 (in G e r m a n ) Composite extrusion enables composite profiles to be produced, which can be used among other things as transition couplings between aluminium and steel. The production method is described and the potential applications are discussed. The dynamic strength tests performed in connection with the serviceability testing are dealt with in particular. (In English pp. E108-E109.) 2 refs.
Study of impact-fatigue behaviour of 35NCDV12 weepons-barrel steel and 7075-T6 sluminium alloy. Perrin, R. Etablissement Technique Central de I'Armement Report No PB90174228/XAB 3 July 1989 38 pp (in French) In order to approximate as closely as possible the working conditions of materials used in some equipment, an experimental device was built for repeated impact loading based on the principle of Hopkinson rods. Impact-fatigue life was determined for test pieces cut from 35NCDV12 steel and 7075 light alloy. Observed behaviours differ from those of other materials studied earlier, with no observed effect on the life of the material. Measurement of crack velocity for 2024 and 7075 shows that da/dN is higher under impact stress for the first, and that no difference exists for the second.
Study of the propagation of short fissures. Dabezies, B. Etablissement Technique Central de I'Armement Report No PB90178278/XAB 10 M a y 1989 65 pp (in French)
decreases, the grain boundary migration takes place. This is suggested from the fact that the grain boundary sliding and migration occur in alternative manners. Tension-tension fatigue tests were also carried out to confirm the suggestion. Stepped surface markings are formed by tension-tension stress, and convex or concave ones by tension-compression stress. This fact means that the direction of grain boundary sliding under tension is opposite to that under compression; grain boundary migration is induced by the strain near triple points of the grain boundary accumulated by grain boundary sliding, and grain boundary sliding during its migration is limited. Photomicrographs. 19 refs.
Fatigue resistance of pressure vessels in high-strength steels. Effect of some improvement techniques. Sys, A. Centre Recherches Scientifiques Techniques Industrie Fabrications Metalliques Report No N90-13799/3/XAB May 1989 26 pp Fatigue tests by external cyclic loading on nozzles in heavy pressurized vessel models have been performed. Twelve models were tested. They were manufactured under industrial conditions from a high tensile pipe material API X60. One third are reference specimens for which the fatigue strength was compared with that of those made from mild steels. To the other models tungsten-inert-gas (TIG) dressing and burr grinding techniques were applied to improve the fatigue resistance. During testing, computer-aided control measurements were applied to ensure the correct loading conditions. The fatigue properties of the higher tensile material in untreated conditions were found to be lower than those of mild steel. TIG dressing of a higher strength material always had a favourable effect on the fatigue properties compared with those of mild steels. With burr grinding the same fatigue properties as for mild steel can only be obtained in the low-cycle region. Effect o f precipitation hardening on rotary bendin!B fatigue strength of circumferential V-notched specimens, Kobayashl, M., Nagasaka, A., Kashihara, M., Ends, R. and Futamura, A. J. Soc. Mater. ScL, Jpn. July 1989 38, (430), 7 8 9 - 7 9 5 (in Japanese) The effect of precipitation hardening on rotary bending fatigue strength of circumferential V-notched specimens was investigated at room temperature by using two commercial steels, i.e. 18 Ni maraging steel and an austenitic heat resisting steel, JIS SUH38. The rotary bending fatigue tests were carried out on the assolution-treated, peak-aged and over-aged specimens. The fatigue limits of the smooth specimens as well as all of the notched specimens were not influenced by precipitation hardening in 18 Ni maraging steel. Non-propagating cracks were found in all the notched specimens having the stress concentration factor, (z, of 6.2 except the over-aged specimens. It was also found that the stress concentration factor at the branching point, (~0, is nearly four. In SUH38, the fatigue limits of the smooth specimen and the notched specimen with an ~ of 2.1 were found to increase with precipitation hardening, while the fatigue limit for the other notched specimens having ~ > 2.1 did not change in spite of precipitation hardening. The value of (~s was nearly equal to two in the as-solution-treated specimens and four in the other aged specimens. Furthermore, non-propagating cracks were more easily formed in SUH38 than in 18 Ni maraging steel and in the as-solution-treated specimens than in the aged specimens. Discussions were finally given on the fatigue limits by dividing them into the fatigue limit for crack initiation, ~wl and the fatigue limit for crack propagation, Crw2. The behaviour of non-propagating cracks was discussed on the basis of roughness-induced crack closure. Graphs, Photomicrographs. 20 refs.
Recent investigations on precipitation phenomena of aluminium alloys.
Murakami, Y. J. Jpn. Inst. Light Met. May 1989 39, (5), 364-377 (in Japanese)
Recent studies on precipitation in AI alloys are reviewed, especially regarding the initial segregation process in a supersaturated solid solution and the coarsening process of the precipitation phase. The precipitation hardening mechanism is explained and the strength of commercial AI alloys is summarized. Regarding the influence of the precipitate structure on the mechanical properties, recent information on refinement of grains by recrystallization, fracture toughness, fatigue, superplastic alloys, and stress corrosion cracking of 7000 series alloys is outlined. Graphs, Photomicrographs. 77 refs. licotion o f metallurgical characteristics to the industrial development ~tPaP 12% c h r o m i u m martensitic steel f o r pipelines. Vanderschaeghe, A., Lecoq, J. and Vigneron, G.
VGB Kraftvverkstechnik Aug. 1989 69, (8), 8 1 7 - 8 2 4 (in German)
Beginning with its initial firing, the inner surface of the barrel of a firearm develops a pattern of crazing comprising fissures whose length is between 350-400 p,m. Different studies bearing on the propagation by fatigue of defects of the dimensions have shown that the rate of fissuring, apparently greater than that of long fissures, can be explained by using the concepts of closing and of effective amplitude of the intensity of the constraint factor. The presence of beginning fissures on the microshrink cavities in a type 32CDV13 steel has provoked ruptures at levels of constraints lower than the endurance limit. However, defects 500 p,m long artificially produced in 35NCD16 behave like long fissures.
In the context of steam lines for high-output boilers, operating in the region of 560 °C with steam pressures of 200 bar, the properties of an X20 CrMoV12 1 steel, with 0.20% carbon and vanadium and molybdenum, to stabilize M2X carbides, were assessed. Anisothermic relaxation tests indicated the effectiveness of lowtemperature stress relief, and forgeability was determined in comparative tests. Lowcycle fatigue tests were carried out in the range 350-600 °C in tension-compression to show similar characteristics to a 9% chromium steel at 550 °C, Crack growth rate was measured at 20 °C and 550 °C in welded specimens. Industrial applications of the steel are listed. Graphs. 26 refs.
Small-crack growth and its influence in near a - t i t a n i u m alloys. Technical memo. Hardy, M.C. Royal Aerospace Establishment Technical M e m o AD-A216 838/3/XAB
Trial production and strength assessment o f t i t a n i u m alloy connecting
J u n e 1989 33 pp Small fatigue cracks are known to propagate at rates much greater than target cracks in the same material at an equivalent crack driving force. The review clarifies the small-crack problem and the reasons for its existence. Some recent models, incorporating large-scale plasticity, crack closure and microstructural dissimilitude, are introduced. Small-crack behaviour in near c(-Ti alloys is examined.
Quasi-in situ microscopy of surface markings on aluminium formed by fatigue at elevated t e m p e r a t u r e . Ohhashi, K.-I., Fukutomi, H. and Ends, T. J. Jpn. Inst. Light Met. M a y 1989 39, (5), 3 4 4 - 3 4 9 (in Japanese) Fatigue tests of 99.99% AI were conducted at 700 K under the ramp-shaped cyclic stress at 2.5 MPa amplitude and 0.001 Hz frequency. A new step on the surface is found in the course of an increase in the absolute value of cyclic stress by quasiin situ microscopy of surface markings. When the absolute value of applied stress
530
rods. Toyama, K. and Kuwayama, T. Sumitomo Met. Apr. 1989 41, (2), 7 5 - 8 0 (in Japanese)
In order to meet expectations for higher-powered compact engines for automobiles, a new titanium alloy connecting rod, whose specific strength is greater than that of steel, has been manufactured on a trial basis. A great weight saving can be achieved. The weight ratio of this new titanium connecting rod compared to steel is 65-80%. A full-size fatigue test and engine test were conducted to evaluate the durability of this titanium connecting rod. As a result, it was verified that this titanium connecting rod has sufficient fatigue strength for automobile usage. Graphs. 8 refs.
Development of high-strength I~-titanium alloys with excellent cold deformability. Takahashi, W., Maeda, T., Nagai, H. and Fukuda, T. Sumitomo Met. Apr. 1989 41, (2), 5 5 - 6 2 (in Japanese) Two types of ~-Ti alloys have been developed for automobile applications. First, a new ~-Ti alloy, Ti-20V-4AI-1Sn, has been developed for cold-forged products used for automobile parts, for example, valve retainers. This alloy possesses excellent
Int J Fatigue November 1990
A new prediction method of fatigue-creep interaction behaviour based on total strain energy for high-strength superalloy. Matsuda, N., Umezawa, S. and Miyata, H. J. Soc. Mater. Sci., Jpn. J u l y 1989 38, (430), 8 0 9 - 8 1 5 (in Japanese) A new life prediction method was proposed for high-strength materials under fatigue-creep interaction (FCI) based on their tensile total strain energy behaviour. The net tensile hysteresis energy is now being used to evaluate the FCI life in the frequency-modified damage function rule developed by W.J. Ostergren. For highstrength materials, however, this damage rule seems to require some modification to give good life assessment, because the elastic strain range is much larger than the inelastic strain range in the FCI behaviour of these materials. In the paper, straincontrolled tensile or compressive strain hold tests with F-F, F-S and S-F wave forms were performed for cast Rene 80. The total strain energy including a large elastic strain energy was defined, and the FCI life was obtained against this strain energy. Multiple-regression analysis was carried out to assess the relationship between strain energy and cycles to failure and was expressed numerically to improve life estimation accuracy. Finally, a frequency-modified total strain energy parameter was defined to evaluate the failure lives (Nf) of high-strength materials such as Rene 80 under the FCI condition. The total tensile strain energy (~W-~) and the time (~TT) under tensile stress loading were used to define this tensile strain energy parameter. A similar relation was also obtained between total strain energy (AWTT) and crack initiation life (Nc). 9 refs.
Low-cycle fatigue behaviour of structural materials at cryogenic temperature. Mizoguchi, T., Kataoka, T., Shimada, M. and Yamamoto, S. Kobe Res. Dev. J u l y 1989 38, (3), 9 3 - 9 6 (in Japanese) Studies have been made of the interrelations among temperature, strain rate, cyclic deformation and low-cycle fatigue lives of parent and welded austenitic steels. Strain rate significantly affects the appearance of serrations on stress-strain hysteresis loops, but does not affect the fatigue life unless a considerable rise in temperature occurs. In a constant total strain range, a cryogenic temperature gives a longer life than the ambient temperature. However, no temperature dependence is observed in plastic strain range against life, meaning that the dominant factor in cryogenic low-cycle fatigue is the plastic strain. Graphs. 11 refs.
Composite extruded aluminium-steel transition couplings and their dynamic strength. Gitter, R. Schweissen Schneiden J u l y 1989 41, (7), 3 2 3 - 3 2 7 (in G e r m a n ) Composite extrusion enables composite profiles to be produced, which can be used among other things as transition couplings between aluminium and steel. The production method is described and the potential applications are discussed. The dynamic strength tests performed in connection with the serviceability testing are dealt with in particular. (In English pp. E108-E109.) 2 refs.
Study of impact-fatigue behaviour of 35NCDV12 weepons-barrel steel and 7075-T6 sluminium alloy. Perrin, R. Etablissement Technique Central de I'Armement Report No PB90174228/XAB 3 July 1989 38 pp (in French) In order to approximate as closely as possible the working conditions of materials used in some equipment, an experimental device was built for repeated impact loading based on the principle of Hopkinson rods. Impact-fatigue life was determined for test pieces cut from 35NCDV12 steel and 7075 light alloy. Observed behaviours differ from those of other materials studied earlier, with no observed effect on the life of the material. Measurement of crack velocity for 2024 and 7075 shows that da/dN is higher under impact stress for the first, and that no difference exists for the second.
Study of the propagation of short fissures. Dabezies, B. Etablissement Technique Central de I'Armement Report No PB90178278/XAB 10 M a y 1989 65 pp (in French)
decreases, the grain boundary migration takes place. This is suggested from the fact that the grain boundary sliding and migration occur in alternative manners. Tension-tension fatigue tests were also carried out to confirm the suggestion. Stepped surface markings are formed by tension-tension stress, and convex or concave ones by tension-compression stress. This fact means that the direction of grain boundary sliding under tension is opposite to that under compression; grain boundary migration is induced by the strain near triple points of the grain boundary accumulated by grain boundary sliding, and grain boundary sliding during its migration is limited. Photomicrographs. 19 refs.
Fatigue resistance of pressure vessels in high-strength steels. Effect of some improvement techniques. Sys, A. Centre Recherches Scientifiques Techniques Industrie Fabrications Metalliques Report No N90-13799/3/XAB May 1989 26 pp Fatigue tests by external cyclic loading on nozzles in heavy pressurized vessel models have been performed. Twelve models were tested. They were manufactured under industrial conditions from a high tensile pipe material API X60. One third are reference specimens for which the fatigue strength was compared with that of those made from mild steels. To the other models tungsten-inert-gas (TIG) dressing and burr grinding techniques were applied to improve the fatigue resistance. During testing, computer-aided control measurements were applied to ensure the correct loading conditions. The fatigue properties of the higher tensile material in untreated conditions were found to be lower than those of mild steel. TIG dressing of a higher strength material always had a favourable effect on the fatigue properties compared with those of mild steels. With burr grinding the same fatigue properties as for mild steel can only be obtained in the low-cycle region. Effect o f precipitation hardening on rotary bendin!B fatigue strength of circumferential V-notched specimens, Kobayashl, M., Nagasaka, A., Kashihara, M., Ends, R. and Futamura, A. J. Soc. Mater. ScL, Jpn. July 1989 38, (430), 7 8 9 - 7 9 5 (in Japanese) The effect of precipitation hardening on rotary bending fatigue strength of circumferential V-notched specimens was investigated at room temperature by using two commercial steels, i.e. 18 Ni maraging steel and an austenitic heat resisting steel, JIS SUH38. The rotary bending fatigue tests were carried out on the assolution-treated, peak-aged and over-aged specimens. The fatigue limits of the smooth specimens as well as all of the notched specimens were not influenced by precipitation hardening in 18 Ni maraging steel. Non-propagating cracks were found in all the notched specimens having the stress concentration factor, (z, of 6.2 except the over-aged specimens. It was also found that the stress concentration factor at the branching point, (~0, is nearly four. In SUH38, the fatigue limits of the smooth specimen and the notched specimen with an ~ of 2.1 were found to increase with precipitation hardening, while the fatigue limit for the other notched specimens having ~ > 2.1 did not change in spite of precipitation hardening. The value of (~s was nearly equal to two in the as-solution-treated specimens and four in the other aged specimens. Furthermore, non-propagating cracks were more easily formed in SUH38 than in 18 Ni maraging steel and in the as-solution-treated specimens than in the aged specimens. Discussions were finally given on the fatigue limits by dividing them into the fatigue limit for crack initiation, ~wl and the fatigue limit for crack propagation, Crw2. The behaviour of non-propagating cracks was discussed on the basis of roughness-induced crack closure. Graphs, Photomicrographs. 20 refs.
Recent investigations on precipitation phenomena of aluminium alloys.
Murakami, Y. J. Jpn. Inst. Light Met. May 1989 39, (5), 364-377 (in Japanese)
Recent studies on precipitation in AI alloys are reviewed, especially regarding the initial segregation process in a supersaturated solid solution and the coarsening process of the precipitation phase. The precipitation hardening mechanism is explained and the strength of commercial AI alloys is summarized. Regarding the influence of the precipitate structure on the mechanical properties, recent information on refinement of grains by recrystallization, fracture toughness, fatigue, superplastic alloys, and stress corrosion cracking of 7000 series alloys is outlined. Graphs, Photomicrographs. 77 refs. licotion o f metallurgical characteristics to the industrial development ~tPaP 12% c h r o m i u m martensitic steel f o r pipelines. Vanderschaeghe, A., Lecoq, J. and Vigneron, G.
VGB Kraftvverkstechnik Aug. 1989 69, (8), 8 1 7 - 8 2 4 (in German)
Beginning with its initial firing, the inner surface of the barrel of a firearm develops a pattern of crazing comprising fissures whose length is between 350-400 p,m. Different studies bearing on the propagation by fatigue of defects of the dimensions have shown that the rate of fissuring, apparently greater than that of long fissures, can be explained by using the concepts of closing and of effective amplitude of the intensity of the constraint factor. The presence of beginning fissures on the microshrink cavities in a type 32CDV13 steel has provoked ruptures at levels of constraints lower than the endurance limit. However, defects 500 p,m long artificially produced in 35NCD16 behave like long fissures.
In the context of steam lines for high-output boilers, operating in the region of 560 °C with steam pressures of 200 bar, the properties of an X20 CrMoV12 1 steel, with 0.20% carbon and vanadium and molybdenum, to stabilize M2X carbides, were assessed. Anisothermic relaxation tests indicated the effectiveness of lowtemperature stress relief, and forgeability was determined in comparative tests. Lowcycle fatigue tests were carried out in the range 350-600 °C in tension-compression to show similar characteristics to a 9% chromium steel at 550 °C, Crack growth rate was measured at 20 °C and 550 °C in welded specimens. Industrial applications of the steel are listed. Graphs. 26 refs.
Small-crack growth and its influence in near a - t i t a n i u m alloys. Technical memo. Hardy, M.C. Royal Aerospace Establishment Technical M e m o AD-A216 838/3/XAB
Trial production and strength assessment o f t i t a n i u m alloy connecting
J u n e 1989 33 pp Small fatigue cracks are known to propagate at rates much greater than target cracks in the same material at an equivalent crack driving force. The review clarifies the small-crack problem and the reasons for its existence. Some recent models, incorporating large-scale plasticity, crack closure and microstructural dissimilitude, are introduced. Small-crack behaviour in near c(-Ti alloys is examined.
Quasi-in situ microscopy of surface markings on aluminium formed by fatigue at elevated t e m p e r a t u r e . Ohhashi, K.-I., Fukutomi, H. and Ends, T. J. Jpn. Inst. Light Met. M a y 1989 39, (5), 3 4 4 - 3 4 9 (in Japanese) Fatigue tests of 99.99% AI were conducted at 700 K under the ramp-shaped cyclic stress at 2.5 MPa amplitude and 0.001 Hz frequency. A new step on the surface is found in the course of an increase in the absolute value of cyclic stress by quasiin situ microscopy of surface markings. When the absolute value of applied stress
530
rods. Toyama, K. and Kuwayama, T. Sumitomo Met. Apr. 1989 41, (2), 7 5 - 8 0 (in Japanese)
In order to meet expectations for higher-powered compact engines for automobiles, a new titanium alloy connecting rod, whose specific strength is greater than that of steel, has been manufactured on a trial basis. A great weight saving can be achieved. The weight ratio of this new titanium connecting rod compared to steel is 65-80%. A full-size fatigue test and engine test were conducted to evaluate the durability of this titanium connecting rod. As a result, it was verified that this titanium connecting rod has sufficient fatigue strength for automobile usage. Graphs. 8 refs.
Development of high-strength I~-titanium alloys with excellent cold deformability. Takahashi, W., Maeda, T., Nagai, H. and Fukuda, T. Sumitomo Met. Apr. 1989 41, (2), 5 5 - 6 2 (in Japanese) Two types of ~-Ti alloys have been developed for automobile applications. First, a new ~-Ti alloy, Ti-20V-4AI-1Sn, has been developed for cold-forged products used for automobile parts, for example, valve retainers. This alloy possesses excellent
Int J Fatigue November 1990