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The effect of ferrite contents on the contact fatigue property of medium carbon alloy steels
Fatigue Abstracts represents the highest proportion of the experimental interlaboratory scatter. Many laboratories did not report any measure of bending and so could not be used in the initial analysis. However, a further interesting deduction from the models is that the entire BCR data-set can be encompassed within a scatter band based upon a bending criterion that is twice the allowable ASTM limit. Differences in the extent of scatter between materials at a given total strain range can be attributed to the gradient of the logarithmic plot of total strain range as a function of lifetime. Graphs, 5 ref. Geometry factors in corrosion fatigue crack propagation. Jakubowski, M. Fatigue Fract Eng Mater Struct (May 1993) 16 (5), 495-507 Fatigue crack growth rates for St41D medium-carbon steel in salt water at different but constant stress intensity factor ranges have been evaluated as a function of the crack length (as measured from the notch root) for cracks longer than so-called 'short' cracks. Equations describing the crack growth rate as a function of both the crack length and the stress intensity factor range have been obtained, and the effect of simulated infinite thickness of the specimens is discussed. The equations satisfactorily describe the numerous literature data for different steels, different specimens and different test conditions. Graphs, 30 ref. Numerical and experimental verification of a new model for fatigue life.
Svensson, T. and Holmgren, M. Fatigue Fract Eng Mater Struct (May 1993) 16 (5), 481-493 A new model for fatigue life prediction has been presented. The model is based on Palmgren-Miner's rule in combination with a level crossing analysis. Here an effort is made to verify the model, numerically and experimentally. Data from the literature and experimental data have been compared with fatigue life predictions made with the new model. The data have also been compared with traditional fatigue life estimations based on the rainflow count (RFC) method. The fatigue lives predicted by the new model often agree better with actual lives than predictions made with the RFC method. This is especially pronounced when the loading sequence is very irregular, i.e. when the sequence contains many small cycles superimposed on large cycles. The new method is both fast and simple to use. An SS2172 alloy steel is tested. Graphs, 17 ref. The effect of ferrite contents on the contact fatigue property of medium carbon
alloy steels. Huang, J.L., Zhu, Y.M. and Shao, E.Y. Wear (15 June 1993) 166 (1), 101-105 The subcritical quenching technique was used in large-size gear steels 45CrMnMo and 42CrMo to obtain ferrite and martensite compound structures with different ferrite contents. The effects of ferrite content on the contact fatigue properties of the two gear steels were investigated in systematic contact fatigue tests. The results show an obvious influence of ferrite content on the pitting lives of the tested steels. The pitting lives increase continuously with increasing ferrite content in the structures until they reach peak values with corresponding ferrite contents of 12 and 10% for 45CrMnMo steel and 42CrMo steel, respectively. Graphs, photomicrographs, 7 ref. Influence of stress ratio and loading condition on near-threshold fatigue crack
growth behaviour. Chen, D., Weiss, B., Stickler, R. and Wang, Z. J Mater Sci Technol (China) (Feb 1993) 9 (1), 47-52 Near-threshold fatigue crack propagation behaviour of a cold-worked copper tested with distinct fatigue testing systems under different stress ratios has been investigated. The emphasis was placed on the evaluation of crack closure effect as well as the effective fatigue threshold. It was found that the fatigue threshold for R = 0 is higher than those for R = - 1 and R = 0.4, for which almost the same threshold value was derived. Compared with the conventional closure evaluation method, the proposed new closure evaluation method can generally interpret the dependence of the fatigue threshold on stress ratio and loading condition; and leads to a higher and relatively constant effective fatigue threshold of approx 3 MPa m t/2 for the cold-worked Cu at different stress ratios and loading conditions. Graphs, 16 ref. Microstructure-mechanical property correlations in dual phase (et2/B2) titanium
alumluldes. Edelson, L. H. Diss Abstr lnt (Apt 1993) 53 (10)
The effects of thermomechanical processing on the microstructure, and tensile and fatigue properties of two a 2-base titanium aluminide alloys, super-a 2(Ti-25AI-10Nb-3.2V-1Mo, in at %) and a 2(Ti-24AI-11Nh), were studied. A literature review demonstrated how trends for mechanical properties and microstructure in the aluminides are paralleled in conventional Ti alloys. Asreceived super-a2 contained 50vo1% primary-a2(DO19) in a B2 (CsCIordered bcc) matrix. Annealing below 1000°C caused transformation of this B2 matrix, producing duplex microstructures. Ti-24AI-11Nb contained 90vo1% of primary-a2 and 10vo1% transformed B2. Increases in cooling rate from the [3-field produced transformed [3 microstructures in both alloys that ranged from coarse a 2 colonies, to fine a 2 basketweaves, to fully retained B2. Low-temperature (400°C) ageing of retained B2 produced a coarsened tweed of fine, non-co precipitates. Super a 2 tensile strengths were approximately twice the a2 for comparable microstructures. Solid-solution strengthening by vanadium and molybdenum accounts for most of this difference. Microstructural refinement also appears to be a factor. Basketweaves were much stronger than colony microstructures. The retained cubic phase was macroscopically brittle, but displayed coarsely spaced slip lines. The dualphase ct2B2 (as-received) microstructure exhibited superior elongation and stength approaching the basketweave. The ct2 improves ductility by homogenizing slip in the B2, thereby decreasing the strain incompatibilities as slip lines
converge or impinge on grain boundaries. The results are consistent with a B2 strength that exceeds the ct2. Fine precipitate structures wre macroscopically and microscopically brittle. Fatigue was studied in the super-a2. Load ratio effects were noted, with AKth of 1.95, 2.7 and 4.8 MPa m i for R = 0.75, 0.5 and 0.1, respectively. Closure, which was only noted at R = 0.1, does not account for the differences. AKth ranged from 4.5 in the as-received and duplex structures to 6.5 MPa m ~ in the coarse a 2 colony structure. ARhough closure was slightly higher in the colony structure, most of its improved fatigue resistance is derived from crack deflection, twisting and branching, which locally lower crack tip stresses. Fatigue in single crystal nickel superalloys. DeLuca, D.P. AD-A261 742/1/ XAB (1993) 6pp This programme investigates the seemingly unusual behaviour of single crystal airfoil materials. The fatigue initiation processes in single crystal materials are significantly more complicated and involved than fatigue initiation and subsequent behaviour of a (single) macrocrack in conventional, isotropic, materials. To understand these differences is the major goal of this project. Fatigue life of Sn-Pb-Bi solder having a low melting point. Taneda, M.,
Kaminishi, K., Motohiro, S. Soga, T. Yamaguchi Daigaku Kogakubu Kenkyu Hokoku (Memoirs of the Faculty of Engineering, Yamaguchi University) (Mar 1993) 43 (2), 7 - 1 3 ( i n Japanese) Strain-controlled torsional fatigue tests were carried out on 37Sn-45Pb-18Bi solder having a comparatively low melting point under two strain cycling frequencies of 0.01 and 1.0 Hz at 303 K. The type of specimen was a thinwalled cylinder. The following results were obtained. ( 1 ) T h e fatigue lives of the solder were a little lower than those of the 60Sn-40Pb solder shown in a previous paper in general. (2) The fatigue life and the plastic shearing strain range, which was found by a partition of the inelastic shearing strain range, could be correlated by the Coffin-Manson law for each cycling frequency. (3) The present test values of the 37Sn-45Pb-18Bi solder fatigue life nearly coincided with the values calculated by the method for the fatigue life evaluation in the previous paper. Consequently, the applicability of the method was verified. Graphs, photomicrographs, 9 ref. Effect of retained austenite and its stabilization on torsional flow hardening
behaviour of GCr15 steel. Huang, M.Z., Tan, Y.X., Zhang, F. and Bai, H.J. Iron and Steel (China) (Mar 1993) 28 (3), 50-52 The effect of retained austenite and its stabilization on torsional flow hardening and low cyclic torsional fatigue behaviour has been compared and analysed. Through the discussion on the coincidence between the results of contact fatigue experiment and the effect of austenite mentioned above, the cause of the increase of contact fatigue life which may be influenced by the stability of retained austenite could be revealed. That is, the stabilization of retained austenite can improve the inhomogeneity in deformation due to its more stable strain-hardening ability, so that the fracture strain of materials can be raised a great deal while not improving its strength and hardness. Graphs, 5 ref. Evaluation of fracture mechanics of ingot mould materials. Yu, G.L., Cui,
G.Z., Han, W.Y., Zheng, X.S. and Jin, J.Z. Iron and Steel (China) (Mar 1993) 28 (3), 26-29 (in Chinese) The concept of fracture mechanics is used to evaluate the fatigue crack propagation behaviours of various cast irons used for producing ingot moulds, and the crack propagation life is estimated. The results show that: (1) the crack propagation rate increases in the sequence of nodular iron, vermicular iron, and then grey iron, and this is coincident with the practical observation results of mould crack propation in situ; ( 2 ) t h e behaviours of crack propagation vary a lot with the different graphite morphologies of cast irons. Owing to flake graphite of grey iron linked together in eutectic colonies, fatigue cracks propagate continuously along graphite-matrix interfaces which are vertical to external stresses. As to the case of nodular iron, when the crack tip propagates near graphite nodules, the tip is blunted by ferrite around graphite nodules and the crack will be re-initiated. A fatigue crack propagation model for nodular iron is proposed. Graphs, 5 ref. A new method of constructing random fatigue spectrum. Ping, A., Wang,
D.J. and Xu, H. J Northeast Univ Technol (China) (Feb 1993) 14 (1), 64-68 (in Chinese)
Based on rainflow counting rules, a new method is put forward to construct a random fatigue spectrum. The spectrum constructed by the new method shows that it is not only identical with the statistical result measured by cyclic counting, but also available to remain unchanged the intrinsic characteristics of the history spectrum originally surveyed as much as possible. So, it is more actual in comparison with programme load spectra. Such a fatigue spectrum is proven basically equivalent to the damage conditions in that measured by means of an analysis made to load spectra of four vehicles. 45 and 16Mn steels and LYI2CZ aluminum-base alloy are discussed. 8 ref. Theoretical estimate for fatigue life of pistons in rock drill. Song, S.Z. J Northeast Univ Technol (China) (Feb 1993) 14 (1), 6-10 (in Chinese) Based on the contact stress theory by Hertz, the malfunctioning or failure mechanism of a piston in rock drill due to fatigue is discussed. It is found that a crevice source will take place in a depth of about one-half radius of contact circle under the initial compact surface, where the maximum shearing stress occurred. Main factors influencing the propagating rate of fatigue crevice arc discussed with an estimate method of piston fatigue life under
Fatigue, 1994, Vol 16, June 301
Svensson, T. and Holmgren, M. Fatigue Fract Eng Mater Struct (May 1993) 16 (5), 481-493 A new model for fatigue life prediction has been presented. The model is based on Palmgren-Miner's rule in combination with a level crossing analysis. Here an effort is made to verify the model, numerically and experimentally. Data from the literature and experimental data have been compared with fatigue life predictions made with the new model. The data have also been compared with traditional fatigue life estimations based on the rainflow count (RFC) method. The fatigue lives predicted by the new model often agree better with actual lives than predictions made with the RFC method. This is especially pronounced when the loading sequence is very irregular, i.e. when the sequence contains many small cycles superimposed on large cycles. The new method is both fast and simple to use. An SS2172 alloy steel is tested. Graphs, 17 ref. The effect of ferrite contents on the contact fatigue property of medium carbon
alloy steels. Huang, J.L., Zhu, Y.M. and Shao, E.Y. Wear (15 June 1993) 166 (1), 101-105 The subcritical quenching technique was used in large-size gear steels 45CrMnMo and 42CrMo to obtain ferrite and martensite compound structures with different ferrite contents. The effects of ferrite content on the contact fatigue properties of the two gear steels were investigated in systematic contact fatigue tests. The results show an obvious influence of ferrite content on the pitting lives of the tested steels. The pitting lives increase continuously with increasing ferrite content in the structures until they reach peak values with corresponding ferrite contents of 12 and 10% for 45CrMnMo steel and 42CrMo steel, respectively. Graphs, photomicrographs, 7 ref. Influence of stress ratio and loading condition on near-threshold fatigue crack
growth behaviour. Chen, D., Weiss, B., Stickler, R. and Wang, Z. J Mater Sci Technol (China) (Feb 1993) 9 (1), 47-52 Near-threshold fatigue crack propagation behaviour of a cold-worked copper tested with distinct fatigue testing systems under different stress ratios has been investigated. The emphasis was placed on the evaluation of crack closure effect as well as the effective fatigue threshold. It was found that the fatigue threshold for R = 0 is higher than those for R = - 1 and R = 0.4, for which almost the same threshold value was derived. Compared with the conventional closure evaluation method, the proposed new closure evaluation method can generally interpret the dependence of the fatigue threshold on stress ratio and loading condition; and leads to a higher and relatively constant effective fatigue threshold of approx 3 MPa m t/2 for the cold-worked Cu at different stress ratios and loading conditions. Graphs, 16 ref. Microstructure-mechanical property correlations in dual phase (et2/B2) titanium
alumluldes. Edelson, L. H. Diss Abstr lnt (Apt 1993) 53 (10)
The effects of thermomechanical processing on the microstructure, and tensile and fatigue properties of two a 2-base titanium aluminide alloys, super-a 2(Ti-25AI-10Nb-3.2V-1Mo, in at %) and a 2(Ti-24AI-11Nh), were studied. A literature review demonstrated how trends for mechanical properties and microstructure in the aluminides are paralleled in conventional Ti alloys. Asreceived super-a2 contained 50vo1% primary-a2(DO19) in a B2 (CsCIordered bcc) matrix. Annealing below 1000°C caused transformation of this B2 matrix, producing duplex microstructures. Ti-24AI-11Nb contained 90vo1% of primary-a2 and 10vo1% transformed B2. Increases in cooling rate from the [3-field produced transformed [3 microstructures in both alloys that ranged from coarse a 2 colonies, to fine a 2 basketweaves, to fully retained B2. Low-temperature (400°C) ageing of retained B2 produced a coarsened tweed of fine, non-co precipitates. Super a 2 tensile strengths were approximately twice the a2 for comparable microstructures. Solid-solution strengthening by vanadium and molybdenum accounts for most of this difference. Microstructural refinement also appears to be a factor. Basketweaves were much stronger than colony microstructures. The retained cubic phase was macroscopically brittle, but displayed coarsely spaced slip lines. The dualphase ct2B2 (as-received) microstructure exhibited superior elongation and stength approaching the basketweave. The ct2 improves ductility by homogenizing slip in the B2, thereby decreasing the strain incompatibilities as slip lines
converge or impinge on grain boundaries. The results are consistent with a B2 strength that exceeds the ct2. Fine precipitate structures wre macroscopically and microscopically brittle. Fatigue was studied in the super-a2. Load ratio effects were noted, with AKth of 1.95, 2.7 and 4.8 MPa m i for R = 0.75, 0.5 and 0.1, respectively. Closure, which was only noted at R = 0.1, does not account for the differences. AKth ranged from 4.5 in the as-received and duplex structures to 6.5 MPa m ~ in the coarse a 2 colony structure. ARhough closure was slightly higher in the colony structure, most of its improved fatigue resistance is derived from crack deflection, twisting and branching, which locally lower crack tip stresses. Fatigue in single crystal nickel superalloys. DeLuca, D.P. AD-A261 742/1/ XAB (1993) 6pp This programme investigates the seemingly unusual behaviour of single crystal airfoil materials. The fatigue initiation processes in single crystal materials are significantly more complicated and involved than fatigue initiation and subsequent behaviour of a (single) macrocrack in conventional, isotropic, materials. To understand these differences is the major goal of this project. Fatigue life of Sn-Pb-Bi solder having a low melting point. Taneda, M.,
Kaminishi, K., Motohiro, S. Soga, T. Yamaguchi Daigaku Kogakubu Kenkyu Hokoku (Memoirs of the Faculty of Engineering, Yamaguchi University) (Mar 1993) 43 (2), 7 - 1 3 ( i n Japanese) Strain-controlled torsional fatigue tests were carried out on 37Sn-45Pb-18Bi solder having a comparatively low melting point under two strain cycling frequencies of 0.01 and 1.0 Hz at 303 K. The type of specimen was a thinwalled cylinder. The following results were obtained. ( 1 ) T h e fatigue lives of the solder were a little lower than those of the 60Sn-40Pb solder shown in a previous paper in general. (2) The fatigue life and the plastic shearing strain range, which was found by a partition of the inelastic shearing strain range, could be correlated by the Coffin-Manson law for each cycling frequency. (3) The present test values of the 37Sn-45Pb-18Bi solder fatigue life nearly coincided with the values calculated by the method for the fatigue life evaluation in the previous paper. Consequently, the applicability of the method was verified. Graphs, photomicrographs, 9 ref. Effect of retained austenite and its stabilization on torsional flow hardening
behaviour of GCr15 steel. Huang, M.Z., Tan, Y.X., Zhang, F. and Bai, H.J. Iron and Steel (China) (Mar 1993) 28 (3), 50-52 The effect of retained austenite and its stabilization on torsional flow hardening and low cyclic torsional fatigue behaviour has been compared and analysed. Through the discussion on the coincidence between the results of contact fatigue experiment and the effect of austenite mentioned above, the cause of the increase of contact fatigue life which may be influenced by the stability of retained austenite could be revealed. That is, the stabilization of retained austenite can improve the inhomogeneity in deformation due to its more stable strain-hardening ability, so that the fracture strain of materials can be raised a great deal while not improving its strength and hardness. Graphs, 5 ref. Evaluation of fracture mechanics of ingot mould materials. Yu, G.L., Cui,
G.Z., Han, W.Y., Zheng, X.S. and Jin, J.Z. Iron and Steel (China) (Mar 1993) 28 (3), 26-29 (in Chinese) The concept of fracture mechanics is used to evaluate the fatigue crack propagation behaviours of various cast irons used for producing ingot moulds, and the crack propagation life is estimated. The results show that: (1) the crack propagation rate increases in the sequence of nodular iron, vermicular iron, and then grey iron, and this is coincident with the practical observation results of mould crack propation in situ; ( 2 ) t h e behaviours of crack propagation vary a lot with the different graphite morphologies of cast irons. Owing to flake graphite of grey iron linked together in eutectic colonies, fatigue cracks propagate continuously along graphite-matrix interfaces which are vertical to external stresses. As to the case of nodular iron, when the crack tip propagates near graphite nodules, the tip is blunted by ferrite around graphite nodules and the crack will be re-initiated. A fatigue crack propagation model for nodular iron is proposed. Graphs, 5 ref. A new method of constructing random fatigue spectrum. Ping, A., Wang,
D.J. and Xu, H. J Northeast Univ Technol (China) (Feb 1993) 14 (1), 64-68 (in Chinese)
Based on rainflow counting rules, a new method is put forward to construct a random fatigue spectrum. The spectrum constructed by the new method shows that it is not only identical with the statistical result measured by cyclic counting, but also available to remain unchanged the intrinsic characteristics of the history spectrum originally surveyed as much as possible. So, it is more actual in comparison with programme load spectra. Such a fatigue spectrum is proven basically equivalent to the damage conditions in that measured by means of an analysis made to load spectra of four vehicles. 45 and 16Mn steels and LYI2CZ aluminum-base alloy are discussed. 8 ref. Theoretical estimate for fatigue life of pistons in rock drill. Song, S.Z. J Northeast Univ Technol (China) (Feb 1993) 14 (1), 6-10 (in Chinese) Based on the contact stress theory by Hertz, the malfunctioning or failure mechanism of a piston in rock drill due to fatigue is discussed. It is found that a crevice source will take place in a depth of about one-half radius of contact circle under the initial compact surface, where the maximum shearing stress occurred. Main factors influencing the propagating rate of fatigue crevice arc discussed with an estimate method of piston fatigue life under
Fatigue, 1994, Vol 16, June 301