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Derivation of design curves for the elevated-temperature fatigue endurance of type 316 stainless steels
the results for other materials, such as low-carbon steel. On the other hand, the predicted lifetimes are consistent with experimental results. This suggests the J integral as a mechanics parameter for characterizing the thermal fatigue strength of grey cast iron. The mechanics model and calculation method developed here are efficient. A parameter &Wt was proposed from an energy aspect to characterize the capacity of crack propagation. The isothermal fatigue life is the same as the thermal fatigue life for identical &Wt values. 7 refs.
Mechanical properties of austempered ductile iron. lio, Y., Yoshino, S. and Ogino, Y. Kubota Tech. Rep. Apr. 1988 (20), 1-6 (in Japanese) Non-alloyed austempered ductile iron with less than 10 mm wall thickness was studied. The relationship between austempering treatment and the mechanical properties against the various total carbon contents was investigated. Total C was changed to three marks, 2.5, 3.0 and 3.6%. In order to get the effect of the total C contents accurately, purified Fe (obtained by lowering Mn, phosphorus and minor elements) was used as a raw material. The maximum tensile strength was obtained at 2.5% of the total C, and maximum elongation, impact value and fatigue strength were obtained at 3% of the total C. 2 refs.
Radiographic line width and surface rupture density as wear criteria. Schilh'ng, A., Reinhold, C., Stemmler, D. and Wuttke, W. Schmierungstechnik 1989 20, (3), 86-88 (in German) The relation between wear-induced surface damage, determined by scanning electron microscopy and lattice strain measured as line width, is demonstrated by taking high-cycle fatigue wear as an example. The stochasticity of straining and real structural development are discussed as causes of the lattice strain variations, which are dependent upon the number of cycles. In addition, the removal of heavily deformed zones of materials is discussed. 13 refs,
Notch effect on fatigue and creep/fatigue interaction properties of GH132 disc superalloy. Xio, X., Chen, G. and Jiang, H. J. Univ. Sci. Technol. Beijing 1989 11, (2), 130-135 (in Chinese) The iron-base disc superalloy GH132 is susceptible to LCF notch sensitivity, though it has no stress rupture notch sensitivity at elevated temperature. The creep/fatigue interaction lives to fracture of GH132 for notch and smooth specimens both exhibit 'nose' curves with maximum lives to fr3cture. In the regime above the 'nose', the alloy is susceptible to notch sensitivity. Below and near the 'nose' regime, lives to fracture of notch specimens are longer than in smooth specimens. For turbine disc alloy development it is necessary both to raise the strength and to improve the ductility. 3 refs.
High-strength steel plates for offshore platform for deep and cold sea. Bessyo, K., Arimochi, K,, Tsukamoto, M., Konda, N. and Fujimoto, M. Sumitomo Search Nov. 1988 (37), 13-28 New explorations for offshore oil and gas fields are tending to move from shallow seas to deep and cold seas. Therefore, platforms are becoming very large and heavy, and the adoption of HT60 steel plates in place of conventional HTS0 steel plates is being explored as a way to reduce the total weight of the structure, HT60 steel plates with superior low-temperature toughness properties have been developed using the quench-tempering and DAC (dynamic accelerated cooling) processes. The base metal properties, weLdability, welded joint properties, fracture toughness and fatigue properties of these newly developed steel plates were investigated. The results showed superior properties for all test items. It was confirmed that these new steel plates could be applied to structures in deep and cold sea fields with welding procedures equivalent to those of conventional normalized HT50 steels. L o w cycle fatigue damage in turboengine discs. Guedou, J. Y. and
Honnorat, Y. Mater. Tech. (Paris) Jan.-Feb. 1989 77, (1-2), 49-56 (in French) In modern turboengines, discs are the most critical parts due to the high thermal and mechanical Ioadings they are subjected to. The damage processes of these parts are correlated to engine working cycles, generating low-frequency and highamplitude cyclic loads: the life of discs is therefore mainly limited by low-cycle fatigue, possibly associated with environmental effects (time, temperature) and high-frequency low-amplitude cycles superimposition (due to interference in rotating machines). Disc design is based on laboratory test results, which permits the quantification of damage models used in calculations, The reliability of those methods, as well as the accurate knowledge of physical damaging mechanisms in disc alloys, makes it possible to give 'safe lives' to those parts, which are however checked by spin pit tests on modules or whole engines. Nevertheless, the recent trend towards 'damage tolerance concepts', in which material defects are taken into account, need more intensive studies of crack propagation and damage mechanics, including complex phenomena such as spectrum fatigue. Therefore, the improvement of more and more sophisticated laboratory mechanical tests (short crack propagation, thermomechanical fatigue, complex fatigue) seems mandatory to meet those requirements. 15 refs.
High strength, high carbon grey irons containing vanadium and their resistance to thermal fatigue cracking. Dawson, J. V. and Sage, A. M. Foundry Trade J. Int. June 1989 12, (2), 36, 38, 48 The development of high strength, high-C grey irons containing V is described. It is suggested that the higher thermal conductivity arising from the increased C content can provide enhanced heat dissipation, especially in those cases where castings are subjected to rapid thermal cycfing. Amongst possible applications are heavy-duty brake drums and discs. 4 refs.
Fatigue crack propagation in AI-Sn bearing alloys. Busby, A, K. and Martin, J. W. Mater. Sci. Technol. July 1989 5, (7), 689-698 Fatigue crack propagation has been studied in a series of AI-Sn bearing alloys as a function of microstructure and environment at stress intensity ratios R of 0.7 and 0.1. Fatigue thresho]ds of Sn-containing alloys increased with a reduction in content
74
and in continuity of the Sn-phase in laboratory air. This is interpreted in terms of crack closure, crack growth along the AI/Sn interface, and crack tip blunting mechanisms. Mechanisms that retard fatigue crack growth through the AI phase leg by an increase in the reversibility of slip or by an increase in the size of the reverse plastic zone) were found to increase fatigue thresholds. When tested in dry air, the AI/Sn interface shows reduced embrittlement. The consequence of this for fatigue thresholds is complex: at R = 0.7, fatigue thresholds increase with a decrease in Sn content, while the thresholds are constant at R - 0.1. 10 refs.
Investigation of die stresses and die deflections in forging axisymmetric parts. Hirt, G. and Allan, T. Steel Res. 1989 60, (6), 255-262 In this study, two examples were investigated. The first was cold coining of a thin circular disc where the effect of elastic die deflections upon the tolerances of the formed part was evaluated, in the second example, the die stresses and die deflections were estimated for the upper die in hot closed-die forging of a flangeshaft type part. The predicted results in the first example showed good agreement with experimental data. Thus, it was illustrated that the methods used and discussed in this study are reliable to estimate die stresses and deflections. It is expected that additional work is necessary to develop a practical procedure for predicting the failure and fatigue life of cold and hot forging dies. 16 refs.
Micromechanisms governing fatigue behaviour of lithium-containing a l u m i n i u m alloys. Srivatsan, 7. S. and Coyne, Jr, E. J. Mater. Sci. Technol. June 1989 5, (6), 548-555 The emergence of Li-containing AI alloys as potential light metals for aircraft structures has engendered an unprecedented widespread interest aimed at improving their mechanical properties and studying their cyclic fatigue characteristics. The phenomenon of fatigue is environment sensitive and the alternating moisture conditions experienced by this candidate airframe material can be a handicap when designing for enhanced fatigue resistance. In this paper the fatigue properties, deformation characteristics and cyclic stress response of the commercial AI-Li-Cu-Mn and the experimental AI-Li-Mn and AI-Li-Cu-Mg-Zr alloys cycled to failure are compared over a range of plastic strain amplitudes in various environments, spanning the inert to the very aggressive. Abnormal plastic strain-fatigue life behaviour was observed for all the alloy systems and is attributed to differences in the distribution of deformation as a function of plastic strain amplitude and to change in the relative amounts of intergranular and transgranular fracture as a function of strain amplitude. Cyclic deformation was also observed to produce softening in the three alloys for most of their fatigue life. The softening is due to progressive loss of ordering contributions to hardening and is a mechanical and not an environmental effect. 43 refs.
Structure and properties of A I - L i - - C u - M g - Z r alloy AA 2091 in sheet form. Smith, P. F. Mater. Sci. Technol. June 1989 5, (6), 533-641 The structure and properties of AI-Li-Cu-Mo-Zr alloy AA 2091 in sheet form have been studied. Static and dynamic behaviour of material aged to the 'damage tolerant' category has been found to be at least equivalent to current BS L109 (AA2024-T3) sheet while re-solution heat treatment did not appear to degrade properties. In contrast, although static strength parameters of stretched material aged to the 'medium strength' category were comparable to those of BS L157 (AA2014-T6), re-solution heat treatment effected a noticeable decrease, with a failure to achieve 0.2% PS levels. Mechanical properties and subsequent fracture behaviour were correlated with submicrostructure throughout the investigation. 23 refs.
Code rules for fatigue analysis of crack-like discontinuities and small cracks, Roche, R. L. Int. J. Pressure Vessels Piping 1989 37, (1-4), 201-218 Practical application of code rules for preventing fatigue crack initiation in geometrical discontinuities having the appearance of cracks is discussed. Attention is given to the RCC-MR specific rules for fatigue analysis of crack-like discontinuities. These rules are based on the 'd-concept', that is to say that the strain range is computed at some finite distance d below the surface, this distance d being characteristic of the material. This strain range and the conventional fatigue design curves are then utilized as usual for fatigue analysis. Experimental validation of these rules is discussed and several examples of practical application are given. In addition it is shown this rule can be applied to avoid fatigue crack initiation from small cracks. Steel 316L is included in the analysis. Graphs. 32 refs.
Derivation of design curves for the elevated-temperature fatigue endurance of type 316 stainless steels. Wood, D. S., Wynn, J. and Williamson, K. Int. J. Pressure Vessels Piping 1989 37, (1-4), 171-188 Elevated4emperature low-cycle continuous cycling fatigue data on type 316 steel have been collected and statistically analysed using a multiple linear regression method. Average fatigue curves between 102-105 cycles have been produced over the temperature range RT-650 °C. The data curves have been translated into design curves and compared with published fatigue design curves in ASME Code Case N47 and the French RCC-MR design code. At 550 °C and low strain range, a condition very relevant to some fast reactor structures, it is shown that the existing codes are too conservative. Graphs. 23 refs. Simplified elastoplastic f a t i g u e analysis. Autrusson, B., Acker, D. and
Hoffmann, A. Int. J. Pressure Vessels Piping 1989 37, (1-4), 157-169 In design by analysis, the rules to avoid unacceptable fatigue damage require the true local strain range to be determined conservatively. A review of simplified methods to estimate the local strain range by the Ke factor and also of experimental results is presented. For each test, the results are the maximum strain range in the notch. In addition, those results have been compared with predictions. The results vary greatly, depending on the tests, because the simplified rules are established for particular cases and then generalized afterwards. Finally, a simplified elastoplastic method based on finite element codes is tested. The calculated strains are very
Int J Fatigue January 1990
Mechanical properties of austempered ductile iron. lio, Y., Yoshino, S. and Ogino, Y. Kubota Tech. Rep. Apr. 1988 (20), 1-6 (in Japanese) Non-alloyed austempered ductile iron with less than 10 mm wall thickness was studied. The relationship between austempering treatment and the mechanical properties against the various total carbon contents was investigated. Total C was changed to three marks, 2.5, 3.0 and 3.6%. In order to get the effect of the total C contents accurately, purified Fe (obtained by lowering Mn, phosphorus and minor elements) was used as a raw material. The maximum tensile strength was obtained at 2.5% of the total C, and maximum elongation, impact value and fatigue strength were obtained at 3% of the total C. 2 refs.
Radiographic line width and surface rupture density as wear criteria. Schilh'ng, A., Reinhold, C., Stemmler, D. and Wuttke, W. Schmierungstechnik 1989 20, (3), 86-88 (in German) The relation between wear-induced surface damage, determined by scanning electron microscopy and lattice strain measured as line width, is demonstrated by taking high-cycle fatigue wear as an example. The stochasticity of straining and real structural development are discussed as causes of the lattice strain variations, which are dependent upon the number of cycles. In addition, the removal of heavily deformed zones of materials is discussed. 13 refs,
Notch effect on fatigue and creep/fatigue interaction properties of GH132 disc superalloy. Xio, X., Chen, G. and Jiang, H. J. Univ. Sci. Technol. Beijing 1989 11, (2), 130-135 (in Chinese) The iron-base disc superalloy GH132 is susceptible to LCF notch sensitivity, though it has no stress rupture notch sensitivity at elevated temperature. The creep/fatigue interaction lives to fracture of GH132 for notch and smooth specimens both exhibit 'nose' curves with maximum lives to fr3cture. In the regime above the 'nose', the alloy is susceptible to notch sensitivity. Below and near the 'nose' regime, lives to fracture of notch specimens are longer than in smooth specimens. For turbine disc alloy development it is necessary both to raise the strength and to improve the ductility. 3 refs.
High-strength steel plates for offshore platform for deep and cold sea. Bessyo, K., Arimochi, K,, Tsukamoto, M., Konda, N. and Fujimoto, M. Sumitomo Search Nov. 1988 (37), 13-28 New explorations for offshore oil and gas fields are tending to move from shallow seas to deep and cold seas. Therefore, platforms are becoming very large and heavy, and the adoption of HT60 steel plates in place of conventional HTS0 steel plates is being explored as a way to reduce the total weight of the structure, HT60 steel plates with superior low-temperature toughness properties have been developed using the quench-tempering and DAC (dynamic accelerated cooling) processes. The base metal properties, weLdability, welded joint properties, fracture toughness and fatigue properties of these newly developed steel plates were investigated. The results showed superior properties for all test items. It was confirmed that these new steel plates could be applied to structures in deep and cold sea fields with welding procedures equivalent to those of conventional normalized HT50 steels. L o w cycle fatigue damage in turboengine discs. Guedou, J. Y. and
Honnorat, Y. Mater. Tech. (Paris) Jan.-Feb. 1989 77, (1-2), 49-56 (in French) In modern turboengines, discs are the most critical parts due to the high thermal and mechanical Ioadings they are subjected to. The damage processes of these parts are correlated to engine working cycles, generating low-frequency and highamplitude cyclic loads: the life of discs is therefore mainly limited by low-cycle fatigue, possibly associated with environmental effects (time, temperature) and high-frequency low-amplitude cycles superimposition (due to interference in rotating machines). Disc design is based on laboratory test results, which permits the quantification of damage models used in calculations, The reliability of those methods, as well as the accurate knowledge of physical damaging mechanisms in disc alloys, makes it possible to give 'safe lives' to those parts, which are however checked by spin pit tests on modules or whole engines. Nevertheless, the recent trend towards 'damage tolerance concepts', in which material defects are taken into account, need more intensive studies of crack propagation and damage mechanics, including complex phenomena such as spectrum fatigue. Therefore, the improvement of more and more sophisticated laboratory mechanical tests (short crack propagation, thermomechanical fatigue, complex fatigue) seems mandatory to meet those requirements. 15 refs.
High strength, high carbon grey irons containing vanadium and their resistance to thermal fatigue cracking. Dawson, J. V. and Sage, A. M. Foundry Trade J. Int. June 1989 12, (2), 36, 38, 48 The development of high strength, high-C grey irons containing V is described. It is suggested that the higher thermal conductivity arising from the increased C content can provide enhanced heat dissipation, especially in those cases where castings are subjected to rapid thermal cycfing. Amongst possible applications are heavy-duty brake drums and discs. 4 refs.
Fatigue crack propagation in AI-Sn bearing alloys. Busby, A, K. and Martin, J. W. Mater. Sci. Technol. July 1989 5, (7), 689-698 Fatigue crack propagation has been studied in a series of AI-Sn bearing alloys as a function of microstructure and environment at stress intensity ratios R of 0.7 and 0.1. Fatigue thresho]ds of Sn-containing alloys increased with a reduction in content
74
and in continuity of the Sn-phase in laboratory air. This is interpreted in terms of crack closure, crack growth along the AI/Sn interface, and crack tip blunting mechanisms. Mechanisms that retard fatigue crack growth through the AI phase leg by an increase in the reversibility of slip or by an increase in the size of the reverse plastic zone) were found to increase fatigue thresholds. When tested in dry air, the AI/Sn interface shows reduced embrittlement. The consequence of this for fatigue thresholds is complex: at R = 0.7, fatigue thresholds increase with a decrease in Sn content, while the thresholds are constant at R - 0.1. 10 refs.
Investigation of die stresses and die deflections in forging axisymmetric parts. Hirt, G. and Allan, T. Steel Res. 1989 60, (6), 255-262 In this study, two examples were investigated. The first was cold coining of a thin circular disc where the effect of elastic die deflections upon the tolerances of the formed part was evaluated, in the second example, the die stresses and die deflections were estimated for the upper die in hot closed-die forging of a flangeshaft type part. The predicted results in the first example showed good agreement with experimental data. Thus, it was illustrated that the methods used and discussed in this study are reliable to estimate die stresses and deflections. It is expected that additional work is necessary to develop a practical procedure for predicting the failure and fatigue life of cold and hot forging dies. 16 refs.
Micromechanisms governing fatigue behaviour of lithium-containing a l u m i n i u m alloys. Srivatsan, 7. S. and Coyne, Jr, E. J. Mater. Sci. Technol. June 1989 5, (6), 548-555 The emergence of Li-containing AI alloys as potential light metals for aircraft structures has engendered an unprecedented widespread interest aimed at improving their mechanical properties and studying their cyclic fatigue characteristics. The phenomenon of fatigue is environment sensitive and the alternating moisture conditions experienced by this candidate airframe material can be a handicap when designing for enhanced fatigue resistance. In this paper the fatigue properties, deformation characteristics and cyclic stress response of the commercial AI-Li-Cu-Mn and the experimental AI-Li-Mn and AI-Li-Cu-Mg-Zr alloys cycled to failure are compared over a range of plastic strain amplitudes in various environments, spanning the inert to the very aggressive. Abnormal plastic strain-fatigue life behaviour was observed for all the alloy systems and is attributed to differences in the distribution of deformation as a function of plastic strain amplitude and to change in the relative amounts of intergranular and transgranular fracture as a function of strain amplitude. Cyclic deformation was also observed to produce softening in the three alloys for most of their fatigue life. The softening is due to progressive loss of ordering contributions to hardening and is a mechanical and not an environmental effect. 43 refs.
Structure and properties of A I - L i - - C u - M g - Z r alloy AA 2091 in sheet form. Smith, P. F. Mater. Sci. Technol. June 1989 5, (6), 533-641 The structure and properties of AI-Li-Cu-Mo-Zr alloy AA 2091 in sheet form have been studied. Static and dynamic behaviour of material aged to the 'damage tolerant' category has been found to be at least equivalent to current BS L109 (AA2024-T3) sheet while re-solution heat treatment did not appear to degrade properties. In contrast, although static strength parameters of stretched material aged to the 'medium strength' category were comparable to those of BS L157 (AA2014-T6), re-solution heat treatment effected a noticeable decrease, with a failure to achieve 0.2% PS levels. Mechanical properties and subsequent fracture behaviour were correlated with submicrostructure throughout the investigation. 23 refs.
Code rules for fatigue analysis of crack-like discontinuities and small cracks, Roche, R. L. Int. J. Pressure Vessels Piping 1989 37, (1-4), 201-218 Practical application of code rules for preventing fatigue crack initiation in geometrical discontinuities having the appearance of cracks is discussed. Attention is given to the RCC-MR specific rules for fatigue analysis of crack-like discontinuities. These rules are based on the 'd-concept', that is to say that the strain range is computed at some finite distance d below the surface, this distance d being characteristic of the material. This strain range and the conventional fatigue design curves are then utilized as usual for fatigue analysis. Experimental validation of these rules is discussed and several examples of practical application are given. In addition it is shown this rule can be applied to avoid fatigue crack initiation from small cracks. Steel 316L is included in the analysis. Graphs. 32 refs.
Derivation of design curves for the elevated-temperature fatigue endurance of type 316 stainless steels. Wood, D. S., Wynn, J. and Williamson, K. Int. J. Pressure Vessels Piping 1989 37, (1-4), 171-188 Elevated4emperature low-cycle continuous cycling fatigue data on type 316 steel have been collected and statistically analysed using a multiple linear regression method. Average fatigue curves between 102-105 cycles have been produced over the temperature range RT-650 °C. The data curves have been translated into design curves and compared with published fatigue design curves in ASME Code Case N47 and the French RCC-MR design code. At 550 °C and low strain range, a condition very relevant to some fast reactor structures, it is shown that the existing codes are too conservative. Graphs. 23 refs. Simplified elastoplastic f a t i g u e analysis. Autrusson, B., Acker, D. and
Hoffmann, A. Int. J. Pressure Vessels Piping 1989 37, (1-4), 157-169 In design by analysis, the rules to avoid unacceptable fatigue damage require the true local strain range to be determined conservatively. A review of simplified methods to estimate the local strain range by the Ke factor and also of experimental results is presented. For each test, the results are the maximum strain range in the notch. In addition, those results have been compared with predictions. The results vary greatly, depending on the tests, because the simplified rules are established for particular cases and then generalized afterwards. Finally, a simplified elastoplastic method based on finite element codes is tested. The calculated strains are very
Int J Fatigue January 1990