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Hysteresis loop shape in fatigue of CuZn alloys
On the fatigue life o f MSO NIL rolling bearings.
Harris, T. A., Skiller, J. and Spitzer, R. F. Tribol. Trans. (Oct. 1992) 35 (4) 731-737 Based upon the test results, it appears that bearings manufactured from casehardened MS0 NiL steel can provide significantly greater rolling contact fatigue life than bearings manufactured front through-hardened MS0 steel. Moreover, M50 NiL bearings endursnce-tested under conditions of heavy tensile hoop stresses showed no tendency towards raceway spelling or Cracking through, whereas bearings fabricated from through-hardened MS0 exhibited both tendencies. For the conditions tested, especially the very heavy tensile hoop stress condition, the MSO SuperNiL steel showed no difference in endurance as compared with M50NiL. It may be that use of M50 SuperNiL, with its increased amount of compressive residual stress, may only be required for bearings that must undergo very high speeds with attendant heavy press fits and high internal centrifugal stresses. On the other hand, the extra amount of compressive rssidual stress can provide an additional margin of reliability in rolling contact fatigue endurance in critical applications. Recent research on the behaviour and design o f steel silo hoppers and trensition junctfons.
Tang, J. G, and Rotter, J. M. J. Construct. Steel Res. (1992) 23 ( 1 - 3 ) 313-343 Recent research on the beheviour and design of conical steel hoppers end transition junctions in both uniformly supported and column-supported circular steel silos is summarized. The hopper in a steel silo supports the majority of the weight of the stored bulk solid end can fail in several different modes including membrane yielding and meridional rupture. The junction between the hopper, the cylinder and the skirt is termed the transition junction. It is subject to a large circumferential compression which arises from the meridional tension in the hopper, and is therefore often strengthened by e ring. The transition junction can fail by elastic or plastic buckling of the ring or by plastic collapse of the hopper/cylinder/skirt/ring junction. A comprehensive picture of the behaviour and design of hoppers and transition junctions in a uniformly supported silo is presented, and several important design aspects of hoppers and transition junctions in column,supported silos are discussed. Graphs, 45 ref. Fatigue small crack g r o w t h in a single crystal nickel-base superelloy at elevated temperature~
Okazaki, M., Imai, T., Satoh, T. and Nohmi, S. J. Soc. Mater. ScL Jpn (Aug. 1992) 41 (467) 1261-1267 (in Japanese) Strain-controlled low-cycle fatigue tests were carried out on a single crystal Ni-base superelloy, CMSX-2, under a strain ratio of zero at 873 K in air. The CMSX-2 showed higher fatigue strength, compared with some other kinds of polycrystelline Ni-base supersiloys or with a directionsily solidified superelloy, CM247LC-DS. The fatigue small crack growth behaviour was also investigated by using a replication technique. The small crack growth rate increased proportionally with increasing crack length on the macroscopic level. On the microscopic level, however, they were significantly affected by the microstructure. From the microscopic observations of the crack path, fracture surface and deformation around the crack tip, it was found that the small cracks propagated in the -/phase matrix on {100) cubic planes, accompanied with negligible deformation of "y' phases, when the crack length was short enough. As the crack became longer, on the other hand, the crack propagation planes were converted onto {111) slip planes. In this stage, the crack rapidly grew by the slip plane decohesion mechanism, cutting the ~t' phases. The above transition of crack propagation plane occurred when the stress intensity factor range reached a critical value. Based on the foregoing results, the differences in the small crack growth rate and the fatigue strength between CMSX-2 and CM247LC-DS are also discussed. Graphs, photomicrographs, 8 refs. Effect of hydrogen-charging on the fatigue crack propagation behavior of T i - 1 3 V - 1 1 C r - 3 A I alloy.
R = 0.05. High AK~hvalues ere obtained by obvious crack-closing ability caused by high roughness of the fractured surfaces. Graphs, photomicrographs, 7 ref.
Burst phenomena in fatigue o f 70-30 s-brims at r o o m temperature.
Hu, X., Margolin, H., Duan, X. and Nourbakhsh, S. Mater. Sci. Eng. A (1 Oct. 1992) A157 (2) 181-194 Strain bursts in 70-30 (=-brass were studied under both strain control and load control. Jn strain control, the influence of strain amplitude and strain rate on the frequency of strain bursts were determined. Burst frequency passed through • maximum as the first cycle plaatic-r6solveq shear strain, increased, while burst frequency decreased with increased strain rate for • given strain amplitude. Strain bursts were mainly associated with new slip which formed immediately adjacent to the previously operating slip. A model wee proposed that incorporated Zn diffusion to mobile dislocations during those periods in • fatigue cycle where they are essentially immobile, ie during elastic loading and unloading. In load control, there are two types of strain burst: large strain bursts associated with load increases, and small strain bursts occurring without load increases. The operative mechanism for load-control strain bursts was considered to be the same as the mechanism producing increased strain under cyclic creep conditions where loading is continually interrupted. For comparison purposes, the burst behaviour was also examined for pure Cu under strain control. No Strain bursts were found. Graphs, photomicrographs, 20 ref.
Hysteresis loop shape in fatigue o f C u - Z n alloys.
Hu, X., Margolin, H., Duan, X. and Nourbakhsh, S. Mater. ScL Eng. A (1 Oct. 1992) A157 (2) 169-180 Hysteresis loop shapes in 70Cu-30Zn, 75Cu-25Zn and 80Cu-20Zn alloys were studied as s function of strain amplitude and holding stress during load interruptions. Three loop shapes, designated as I, II end Ill, were found. The strain amplitude at which transition from Shape I to Shape U and Shape II to Shape III occurs, decreases with decreasing Zn content. The characteristic shapes of these loops were considered to arise from Zn segregation to dislocations and from Bauechinger stress beheviour as a function of half-cycle strain. Holding during cycling produced anisotropic loop shapes. The magnitudes of these distortions increased with holding time, eventually producing burst and yielding behaviour. Explanations for anisotropic loop shapes were also based on Zn segregation to dislocations end on changes in Bausshinger stress as a function of half-cycle strain. Graphs, 32 ref.
Observations o f slip patterns on the surface o f fatigued gold using the scanning tunnelling microscope.
Grosskreutz, J. C., Bowles, C. Q. and Wahab, A. A. J. Mater. ScL (1 Nov. 1992) 27 (21) 5756-5764 Observations of fatigue-induced slip patterns on the surface of polycryatelline Au (+99.9°/=) using the scanning tunnelling microscope (STM) ere presented. The samples were cycled in four-point bending between 0 and 0.0025 strain for 250 and 2500 cycles. STM observations of the sample fatigued for 250 cycles revealed broad slip bands 0.38-0.69 i~m wide containing narrow slip bands 0.015--0.123 p.m wide and fine slip lines 0.006 i~m wide. The depth of these features is 20-57 nm for broad slip bands, 3-7 nm for narrow slip bands, and approx 2-4 nm for fine slip lines. The sample fatigued for 2500 cycles showed similar values for the width of the slip bands and slip lines, except that their depth was increased by a factor of between two and four times for the narrow slip bands and the fine slip lines. Apparent persistent slip bands (PSBs) spaced 2.4 p,m, 300-500 nm deep were also observed. These results demonstrate that STM is • significant new tool for observing and distinguishing various types of fatigue-induced surface slip patterns on suitably prepared samples. The vertical resolution obtained with STM is vastly superior to current SEM and TEM methods. Photomicrographs, 9 ref.
Nakasa, K., Horita, M. and Satoh, H. J. Soc. Mater. Sci. Jpn (Aug. 1992) 41 (467) 1248-1254 (in Japanese) To investigate the influence of hydrogen on the fatigue crack propagation behaviour of ~-Ti alloy, two types of fatigue tests were carried out. One was the fatigue test in air on the H-precharged specimens, where the charging was carried out in H2SO4 aqueous solution electrolytically under a current density ic of 1000 A m -;z for 260 ks. Another was the fatigue test under electrolytic H-charging in H2SO4aqueous solution at i c = 1000 or 3000 A m -2. Both test results were compared with the result obtained from the fatigue tests of the non-charged specimen in air. The fatigue crack propagation rate da/dN of the precharged specimen was much larger than the da/dN of the non-charged specimen in all the range of stress intensity factor, &K. The crack propagation rate da/dN under H charging was larger than the da/ dN of the non-charged specimen only when ~K was < 15 MPa m ~z and da/dN was much smaller than that of the precharged specimen. The fatigue fracture surface of the specimens which were H-charged by both methods revealed cleavage fracture, which corresponded to the decrease in cohesive strength of the cleavage plane of B-phase by the dissolution of H atoms. Diffraction patterns, graphs, photomicrographs, 12 ref.
Investigations into the fatigue beheviour of Chs-joints subjested t o spectrum loading.
Mang, F. and Bucak, O. Proc. Conf. Testing o f Metals for Structures, Naples, Italy, 29-31 May 1990, pp 273-284 A large number of constant-amplitude tests on the fatigue behaviour of hollow section structures, especially of their joints, are now available. These investigations resulted in the development of a draft for Eurocode 3 and in the publication of • compilation of Wohler curves (S-N lines}. A few teats have been carried out with hollow-cection joints under service fatigue load (block or random) in the scope of the European Offshore Programmes and some national research activities. In these teats, either a modified load spectrum from the region of the North Sea or fictitious load spectra and those from the field of crane construction were applied to one type of joint and one or two variations of joint dimensions. First systematic investigations of hollow section joints (St 37) under load spectrum have been carried out in Karlsruhe. The report, dealing with this topic, is given.
Energatlcal theories on fatigue life prediction.
Tong, X. Chinese J. Met. Sci. Technol. (Aug. 1992) 8 (4) 266-272 (in Chinese) Current developments in fatigue life prediction methods have bean systematically reviewed. In consideration of the irreversibility of energy dissipation during fatigue damage process, the main factors for fatigue damage estimation and localized equivalence as well as simulation models have been established. A frame of energybased fatigue life prediction method has been proposed, and the procedure in application to a prectJceJ structure component has been described. Graphs. 31 ref. Fatigue crack propagation in plain carbon dual-phase steel.
Lea, T. and Lin, G. Chinese J. MeL Sci, Technol, (Aug. 1992) 8 (4) 249-254 (in Chinese)
The effect of volume fraction VM and carbon content (%C)M of martensita was studied on the fatigue crack propagation behaviour of plain C martensite plus ferrite M + F dual-phase 10, 20, and 35 steels. The experimental results show that the &Kth decreases and da/dn increases with increasing VM and (%C)M at • load ratio
Int J Fatigue November 1993
T r e a t m e n t of R-ratio effects in the fatigue design of eluminium components.
Kosteas, D. Proc. Conf. Testing o f Metals for Structures, Naples, Italy, 29-31 May 1990, pp 257-272 Scant and incomplete experimental evidence, especially on full-size structural components, has inhibited a widely acceptable and quantitative statement on the effect of R-rstio variations on fatigue strength. Before the background of accumulating experimental data with the AI beam fatigue-testing program at TUM end new comprehensive data on small specimens made available to evaluation lately, an attempt has been undertaken to account for such effects in the European recommendations for fatigue design of AI structures (7010 and 6005 AI alloys). Data are described from four different sources, the respective results are compared and the procedure up to the final proposal for design followed, which is based on whether or not there is knowledge about the stress situation - and especially about residual stresses - in the component. In the first case, higher allowable fatigue design stresses may be used.
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Harris, T. A., Skiller, J. and Spitzer, R. F. Tribol. Trans. (Oct. 1992) 35 (4) 731-737 Based upon the test results, it appears that bearings manufactured from casehardened MS0 NiL steel can provide significantly greater rolling contact fatigue life than bearings manufactured front through-hardened MS0 steel. Moreover, M50 NiL bearings endursnce-tested under conditions of heavy tensile hoop stresses showed no tendency towards raceway spelling or Cracking through, whereas bearings fabricated from through-hardened MS0 exhibited both tendencies. For the conditions tested, especially the very heavy tensile hoop stress condition, the MSO SuperNiL steel showed no difference in endurance as compared with M50NiL. It may be that use of M50 SuperNiL, with its increased amount of compressive residual stress, may only be required for bearings that must undergo very high speeds with attendant heavy press fits and high internal centrifugal stresses. On the other hand, the extra amount of compressive rssidual stress can provide an additional margin of reliability in rolling contact fatigue endurance in critical applications. Recent research on the behaviour and design o f steel silo hoppers and trensition junctfons.
Tang, J. G, and Rotter, J. M. J. Construct. Steel Res. (1992) 23 ( 1 - 3 ) 313-343 Recent research on the beheviour and design of conical steel hoppers end transition junctions in both uniformly supported and column-supported circular steel silos is summarized. The hopper in a steel silo supports the majority of the weight of the stored bulk solid end can fail in several different modes including membrane yielding and meridional rupture. The junction between the hopper, the cylinder and the skirt is termed the transition junction. It is subject to a large circumferential compression which arises from the meridional tension in the hopper, and is therefore often strengthened by e ring. The transition junction can fail by elastic or plastic buckling of the ring or by plastic collapse of the hopper/cylinder/skirt/ring junction. A comprehensive picture of the behaviour and design of hoppers and transition junctions in a uniformly supported silo is presented, and several important design aspects of hoppers and transition junctions in column,supported silos are discussed. Graphs, 45 ref. Fatigue small crack g r o w t h in a single crystal nickel-base superelloy at elevated temperature~
Okazaki, M., Imai, T., Satoh, T. and Nohmi, S. J. Soc. Mater. ScL Jpn (Aug. 1992) 41 (467) 1261-1267 (in Japanese) Strain-controlled low-cycle fatigue tests were carried out on a single crystal Ni-base superelloy, CMSX-2, under a strain ratio of zero at 873 K in air. The CMSX-2 showed higher fatigue strength, compared with some other kinds of polycrystelline Ni-base supersiloys or with a directionsily solidified superelloy, CM247LC-DS. The fatigue small crack growth behaviour was also investigated by using a replication technique. The small crack growth rate increased proportionally with increasing crack length on the macroscopic level. On the microscopic level, however, they were significantly affected by the microstructure. From the microscopic observations of the crack path, fracture surface and deformation around the crack tip, it was found that the small cracks propagated in the -/phase matrix on {100) cubic planes, accompanied with negligible deformation of "y' phases, when the crack length was short enough. As the crack became longer, on the other hand, the crack propagation planes were converted onto {111) slip planes. In this stage, the crack rapidly grew by the slip plane decohesion mechanism, cutting the ~t' phases. The above transition of crack propagation plane occurred when the stress intensity factor range reached a critical value. Based on the foregoing results, the differences in the small crack growth rate and the fatigue strength between CMSX-2 and CM247LC-DS are also discussed. Graphs, photomicrographs, 8 refs. Effect of hydrogen-charging on the fatigue crack propagation behavior of T i - 1 3 V - 1 1 C r - 3 A I alloy.
R = 0.05. High AK~hvalues ere obtained by obvious crack-closing ability caused by high roughness of the fractured surfaces. Graphs, photomicrographs, 7 ref.
Burst phenomena in fatigue o f 70-30 s-brims at r o o m temperature.
Hu, X., Margolin, H., Duan, X. and Nourbakhsh, S. Mater. Sci. Eng. A (1 Oct. 1992) A157 (2) 181-194 Strain bursts in 70-30 (=-brass were studied under both strain control and load control. Jn strain control, the influence of strain amplitude and strain rate on the frequency of strain bursts were determined. Burst frequency passed through • maximum as the first cycle plaatic-r6solveq shear strain, increased, while burst frequency decreased with increased strain rate for • given strain amplitude. Strain bursts were mainly associated with new slip which formed immediately adjacent to the previously operating slip. A model wee proposed that incorporated Zn diffusion to mobile dislocations during those periods in • fatigue cycle where they are essentially immobile, ie during elastic loading and unloading. In load control, there are two types of strain burst: large strain bursts associated with load increases, and small strain bursts occurring without load increases. The operative mechanism for load-control strain bursts was considered to be the same as the mechanism producing increased strain under cyclic creep conditions where loading is continually interrupted. For comparison purposes, the burst behaviour was also examined for pure Cu under strain control. No Strain bursts were found. Graphs, photomicrographs, 20 ref.
Hysteresis loop shape in fatigue o f C u - Z n alloys.
Hu, X., Margolin, H., Duan, X. and Nourbakhsh, S. Mater. ScL Eng. A (1 Oct. 1992) A157 (2) 169-180 Hysteresis loop shapes in 70Cu-30Zn, 75Cu-25Zn and 80Cu-20Zn alloys were studied as s function of strain amplitude and holding stress during load interruptions. Three loop shapes, designated as I, II end Ill, were found. The strain amplitude at which transition from Shape I to Shape U and Shape II to Shape III occurs, decreases with decreasing Zn content. The characteristic shapes of these loops were considered to arise from Zn segregation to dislocations and from Bauechinger stress beheviour as a function of half-cycle strain. Holding during cycling produced anisotropic loop shapes. The magnitudes of these distortions increased with holding time, eventually producing burst and yielding behaviour. Explanations for anisotropic loop shapes were also based on Zn segregation to dislocations end on changes in Bausshinger stress as a function of half-cycle strain. Graphs, 32 ref.
Observations o f slip patterns on the surface o f fatigued gold using the scanning tunnelling microscope.
Grosskreutz, J. C., Bowles, C. Q. and Wahab, A. A. J. Mater. ScL (1 Nov. 1992) 27 (21) 5756-5764 Observations of fatigue-induced slip patterns on the surface of polycryatelline Au (+99.9°/=) using the scanning tunnelling microscope (STM) ere presented. The samples were cycled in four-point bending between 0 and 0.0025 strain for 250 and 2500 cycles. STM observations of the sample fatigued for 250 cycles revealed broad slip bands 0.38-0.69 i~m wide containing narrow slip bands 0.015--0.123 p.m wide and fine slip lines 0.006 i~m wide. The depth of these features is 20-57 nm for broad slip bands, 3-7 nm for narrow slip bands, and approx 2-4 nm for fine slip lines. The sample fatigued for 2500 cycles showed similar values for the width of the slip bands and slip lines, except that their depth was increased by a factor of between two and four times for the narrow slip bands and the fine slip lines. Apparent persistent slip bands (PSBs) spaced 2.4 p,m, 300-500 nm deep were also observed. These results demonstrate that STM is • significant new tool for observing and distinguishing various types of fatigue-induced surface slip patterns on suitably prepared samples. The vertical resolution obtained with STM is vastly superior to current SEM and TEM methods. Photomicrographs, 9 ref.
Nakasa, K., Horita, M. and Satoh, H. J. Soc. Mater. Sci. Jpn (Aug. 1992) 41 (467) 1248-1254 (in Japanese) To investigate the influence of hydrogen on the fatigue crack propagation behaviour of ~-Ti alloy, two types of fatigue tests were carried out. One was the fatigue test in air on the H-precharged specimens, where the charging was carried out in H2SO4 aqueous solution electrolytically under a current density ic of 1000 A m -;z for 260 ks. Another was the fatigue test under electrolytic H-charging in H2SO4aqueous solution at i c = 1000 or 3000 A m -2. Both test results were compared with the result obtained from the fatigue tests of the non-charged specimen in air. The fatigue crack propagation rate da/dN of the precharged specimen was much larger than the da/dN of the non-charged specimen in all the range of stress intensity factor, &K. The crack propagation rate da/dN under H charging was larger than the da/ dN of the non-charged specimen only when ~K was < 15 MPa m ~z and da/dN was much smaller than that of the precharged specimen. The fatigue fracture surface of the specimens which were H-charged by both methods revealed cleavage fracture, which corresponded to the decrease in cohesive strength of the cleavage plane of B-phase by the dissolution of H atoms. Diffraction patterns, graphs, photomicrographs, 12 ref.
Investigations into the fatigue beheviour of Chs-joints subjested t o spectrum loading.
Mang, F. and Bucak, O. Proc. Conf. Testing o f Metals for Structures, Naples, Italy, 29-31 May 1990, pp 273-284 A large number of constant-amplitude tests on the fatigue behaviour of hollow section structures, especially of their joints, are now available. These investigations resulted in the development of a draft for Eurocode 3 and in the publication of • compilation of Wohler curves (S-N lines}. A few teats have been carried out with hollow-cection joints under service fatigue load (block or random) in the scope of the European Offshore Programmes and some national research activities. In these teats, either a modified load spectrum from the region of the North Sea or fictitious load spectra and those from the field of crane construction were applied to one type of joint and one or two variations of joint dimensions. First systematic investigations of hollow section joints (St 37) under load spectrum have been carried out in Karlsruhe. The report, dealing with this topic, is given.
Energatlcal theories on fatigue life prediction.
Tong, X. Chinese J. Met. Sci. Technol. (Aug. 1992) 8 (4) 266-272 (in Chinese) Current developments in fatigue life prediction methods have bean systematically reviewed. In consideration of the irreversibility of energy dissipation during fatigue damage process, the main factors for fatigue damage estimation and localized equivalence as well as simulation models have been established. A frame of energybased fatigue life prediction method has been proposed, and the procedure in application to a prectJceJ structure component has been described. Graphs. 31 ref. Fatigue crack propagation in plain carbon dual-phase steel.
Lea, T. and Lin, G. Chinese J. MeL Sci, Technol, (Aug. 1992) 8 (4) 249-254 (in Chinese)
The effect of volume fraction VM and carbon content (%C)M of martensita was studied on the fatigue crack propagation behaviour of plain C martensite plus ferrite M + F dual-phase 10, 20, and 35 steels. The experimental results show that the &Kth decreases and da/dn increases with increasing VM and (%C)M at • load ratio
Int J Fatigue November 1993
T r e a t m e n t of R-ratio effects in the fatigue design of eluminium components.
Kosteas, D. Proc. Conf. Testing o f Metals for Structures, Naples, Italy, 29-31 May 1990, pp 257-272 Scant and incomplete experimental evidence, especially on full-size structural components, has inhibited a widely acceptable and quantitative statement on the effect of R-rstio variations on fatigue strength. Before the background of accumulating experimental data with the AI beam fatigue-testing program at TUM end new comprehensive data on small specimens made available to evaluation lately, an attempt has been undertaken to account for such effects in the European recommendations for fatigue design of AI structures (7010 and 6005 AI alloys). Data are described from four different sources, the respective results are compared and the procedure up to the final proposal for design followed, which is based on whether or not there is knowledge about the stress situation - and especially about residual stresses - in the component. In the first case, higher allowable fatigue design stresses may be used.
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