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Surface pitting fatigue life of non-involute, low-contact-ratio gears
A Crystallographic M o d e l f o r t h e Tensile end Fatigue Response for Rene N 4 at 982 °C. Shah, M. Y. and Stouffer, D. C. J. Appl. Mech. (Trans. ASME) Mar. 1990 57, (1), 25-31 An anisotropic constitutive model based on crystallographic slip theory was formulated for Ni-bese single-crystal superalloys. The current equations include both drag stress and back stress state variables to model the local inelastic flow. Specially designed experiments have been conducted to evaluate the existence of back stress in single crystals. The results showed that the back stress of reverse inelastic flow on the unloading stress is orientation dependent, and a back stress state variable in the inelastic flow equation is necessary for predicting an elastic behaviour. Model correlations and predictions of experimental data are presented for the single-crystal superalloy Rene N4 at 982 °C. Graphs. 30 refs.
Surface Pitting Fatigue Life o f N o n - i n v o l u t e , Low-Contact-Ratio Gears.
Townsend, D. P. NASA Lewis Research Center Report No NASA TM-I03116 1990 8 pp Spur gear endurance tests were conducted to investigate the surface pitting fatigue life of non-involute gears with low numbers of teeth and low contact ratios for use in advanced applications. The results were compared with those for a standard involute design with a low number of teeth. The gear pitch diameter was 6.89 cm with 12 teeth on both gear designs. Test conditions were an oil inlet temperature of 320 K, an oil outlet temperature of 350 K, a maximum Hertz stress of 1.49 GPa, and a speed of 10000 rpm. The following results were obtained: the non-involute gear had a surface pitting fatigue life approximately 1.6 times that of the standard involute gear of a similar design; the surface pitting fatigue life of the 3.43-pitch AISI 8620 non-involute gear was approximately equal to the surface pitting fatigue life of an 8-pitch, 28-tooth AISI 9310 gear at the same load but at a considerably higher maximum Hertz stress. Graphs, photomicrographs. 7 refs. R n i t e - E l e m e n t E l a s t i c - P l a s t i c - C r e e p and Cyclic Life Analysis of a C o w l Up. Arya, V. K., Melis, M. E. and Ha/ford, G. R. NASA Lewis Research Center Report No NASA TM-I02342 1990 11 pp Results are presented of elastic, elastic-plastic, and elastic-plastic-creep analyses of a test-rig component of an actively cooled Cu cowl lip. A cowl lip is part of the leading edge of an engine inlet of proposed hypersonic aircraft and is subject to severe thermal Ioadings and gradients during flight. Values of stresses calculsted by elastic analysis are well above the yield strength of the cowl lip material. Such values are highly unrealistic and thus elastic stress analyses are inappropriate. The inelastic (elastic-plastic and elastic-plastic-creep) analyses produce more reasonable and acceptable stress and strain distributions in the component. Finally, using the results from these analyses, predictions are made for the cyclic crack initiation life of a cowl lip. A comparison of predicted cyclic lives shows the cyclic life prediction from the elastic-plastic-creep analysis to be the lowest and, hence, most realistic. Graphs. 14 refs.
spots. (3) When installed convexly upwards with single-spot initiation, a larger tensile load permits larger areas of the rapid fracture regions. Graphs, photomicrographs. 4 refs.
J., •Helesic, o H. and Obrtlik, pScr.lak,Metall. C K. l Mater.
i
c
Strain Localization in Copper Single Crystals and Polycrystals. Feb. 1990 24, (2), 4 1 5 - 4 1 9
Constant plastic strain amplitude testing of Cu single crystals and polycrystals with a detailed record of hysteresis loop shape changes and correlation with surface observations led to the following conclusions. The loop shape parameter VH can be used to detect the start of cyclic strain localization in both single crystals and polycrystals. The localization continues until the plastic strain is fully transferred to the PSBs and the plastic strain amplitude in the matrix is close to zero, a point that corresponds to the local maximum of VH. The cyclic slip localization is the reason for stress amplitude saturation in strain-controlled cycling. Secondary slip in PSBs leads to hardening of existing PSBs, in turn resulting in the final drop in VH and softening for low plastic strain amplitudes. Graphs, photomicrographs. 11 refs.
STM and Surface Analytical Study of the Effect of Environment on Fatigue Crack Initiation in Silver Single Crystals. I, Surface Chemical Effects. Venkataraman, G., Sriram, T. S., Fine, M. E. and Chung, Y. W. Scr. Metall. Mater. Feb. 1990 24, (2), 2 7 3 - 2 7 8 Fatigue crack initiation studies were performed on pure Ag single crystals oriented for slip using a scanning tunnelling microscope to detect fatigue cracks. It was found that the fatigue process has a crack nucleation stage which is strongly accelerated in an oxygen environment. Dissociative chemisorption of strongly bound O on the exposed slip steps is responsible. The effect of thermally activated dislocation processes is less pronounced than that of the environment. There was evidence of penetration of chemisorbed O into slip bands. 17 refs.
STM and Surface Analytical S t u d y o f t h e Effect o f Environment on Fati~lue Crack Initiation in Silver Single crystals. II, Effects of Oxygen Partml Pressure. Sriram, T. S., Fine, M. E. and Chung, Y. W. Scr. Metal/. Mater. Feb. 1990 24, (2), 2 7 9 - 2 8 4 Silver single crystals of 99.999% purity were grown using the horizontal zone technique. It was found that fatigue cracks do not grow from zero iength, but are formed by a nucleation process. Strong absorption of ambient 0 on the slip steps is responsible. The effect of O on fatigue crack initiation becomes important above approx. 10 3 Pa of O. Oxygen is incorporated into slip bands during fatigue. The extent of incorporation is dependent on 0 pressure. Graphs, photomicrographs. 13 refs.
Influence of Lubrication on Pitting and Micropitting Resistance of Gears. Winter, H. and Oster, P. Gear Technol. M a r . - A p r . 1990 7, (2), 1 6 - 2 3
Fatigue Crack Initiation and S m a l l Crack G r o w t h in Several A i r f r a m e Alloys. Swain, M. H., Newman, J. C., Phillips, E. P. and Everett, R. A. NASA Langley Research Center Report No N90-18746/9/XAB Jan. 1990 8 pp
Pitting of cese-carburized gears is a form of fatigue damage. Therefore, pitting endurance has to be determined by running tests and displaying the results as S-N curves. Because this procedure is time consuming, a short time test was developed to determine the influence of lubricants doped with different additives on pitting resistance. The tests have shown that lubricants doped with S-P additives (sulphur-phosphorus) show a higher micropitting resistance than lubricants doped with ZDP additive. The round robin tests were run on 16MnCr5 and 42CrMo4 steel. Graphs. photomicrographs. 10 refs.
The growth of naturally-initiated small cracks under a variety of constant-amplitude and variable-amplitude load sequences is examined for several airframe materials: the conventional AI alloys, 2024-T3 and 7075-T6, the AI-Li alloy, 2090-T8E41, and the 4340 steel. Loading conditions investigated include constant-amplitude loading at R=0.5, 0, -1 and - 2 and the variable-amplitude sequences FALSTAFF, MiniTWlST and FELIX/28. Crack growth was measured at the root of the semicircular edge notches using acetate replicas. Crack growth rates are compared, on a stress intensity factor basis, to those for large cracks to evaluate the extent of the small crack affect in each alloy. In addition, the various alloys are compared on a crack initiation and crack growth morphology basis.
Selecting Materials f o r Fatigue Resistance. Adv. Mater. Process. J u n e 1990 137, (6), 3 9 - 4 1 , 102-103 Fatigue fractures are said to account for nearly 80% of failures in engineering components. Regardless of the material specified, the possibility of fatigue failure can be reduced via careful design and manufacturing practices. A review of fatigue resistance covered metals, polymers, and ceramics. Fatigue is one of the major causes of fracture in metals, and it is likely that fatigue also plays an important part in the failure of plastics. It is not clear whether conventional fatigue actually occurs in ceramic materials; however, failure over time does occur in brittle ceramic materials, despite the absence of the crack-tip plasticity inherent in materials showing fatigue failure, Graphs.
Damage in t h e Steel Ck45N b y Fatigue Loading with Variable Amplitudes. Walla, J., Bomas, H. and Mayr, P. Hart.-Tech. Mitt. J a n . - F e b . 1990 45, (1), 3 0 - 3 7 (in German) The fatigue life, mechanical behaviour and microstructure of Ck45N steel specimens were investigated under variable-amplitude fatigue loading. The results show that the fatigue life decreases with an increase in the irregularity of the sequence of load amplitudes. This observation cannot be explained by the mechanical behaviour of the material or by the development of the dislocation cell structure, which is almost independent of the load sequence. In additional investigations it was found that dislocation cell structures formed during high-amplitude loading are irreversible and stable in subsequent fatigue with lower amplitudes and make no contribution to fatigue damage. Graphs, photomicrographs. 7 refs. Fatigue Fractured Surface of Component Wire for Steel Wire Ropes.
Ueda, K. and Fujinaka, Y. J. Min. Mater. Process. Inst. Jpn. Jan. 1990 106, (1), 2 9 - 3 3 (in Japanese) Fatigue of component wire for steel wire ropes under tension and bending has been studied. This paper describes the results of fatigue tests of a steel wire which has a natural curling, and discusses the results of observations of the fracture face of the specimen. The relation beWveen the S-N diagram and the fracture face is also discussed. The following were found. (1) The degree of symmetry of fracture faces depends on both the residual stress and the curvature of the specimen before installation. (2) The degree of flatness of the fatigue fracture face and the shape of the S-N diagram are considerably influenced by the number of crack initiation
Int J Fatigue March 1991
Solution of the Fokker-Planck-Kolmogorov Equation in Stochastic Modelling of Fatigue Crack Propagation. Wu, W.-F. and Huang, T.-H. J. Chin. Inst. Eng. Jan. 1990 13, (1), 2 5 - 3 3 Based on linear fracture mechanics concepts and random process theory, several stochastic models of fatigue crack propagation have been proposed in recent years. One of the models randomizes the fatigue crack propagation equation by employing a random pulse train and applying a stochastic average technique to treat the dynamic fatigue crack propagation as a Markov process. The probabilistic structure of a Markov diffusion process is governed by a Fokker-Planck-Kolmogorov equation. Therefore, time and the probability distribution function of the random time at which a given crack size is reached are treated as solutions of the Fokker-Ptanck-Kolmogorov equation associated with the Markov process. Analytical solutions are found for these quantities and numerical examples for AI 2024 are given. The results are compared with some experimentally obtained data. Graphs. 19 refs. F ~ i g u e of Mar-M247. I. Experiments. Boismier, D. A. and Sehitoglu, H~:!i',~ J. Eng. Mater. T e c h n o ~ r a n s ASME) Jan. 1990 112, (1), 6 8 - 7 9
Thermo-Mechanicel
Isothermal fatigue tests, and out-of-phase and in-phase thermo-mechanical fatigue tests were performed on Mar-M247 Ni-based superalloy. The experiments were conducted in the temperature range 500-871 °C. Results indicate that the lives differ with strain-temperature phasing and with strain rate. The results of out-of-phase thermo-mechanicel tests correspond well with strain-life data of isothermal tests conducted at the peak temperature (871 °C). However, the in-phase thermomechanical results differed depending on the strain amplitude. Significant surface and crack tip oxidation and "y' depletion have been observed based on matallographic and Auger spectroscopic analyses. These changes were measured as a function of time. The environment-induced changes significantly influenced the fatigue lives in isothermal and out-of-phase thermo-mechanicat fatigue cases. In these cases tranagranular cracking was observed. Grain boundary crack nucleation and grain boundary crack growth dominated the in-phase thermo-mechanical fatigue cases. Based on these observations the requirements for a life prediction model are outlined. The life prediction model and the predictions are given in part I1. Graphs, photomicrographs. 42 refs.
189
Surface Pitting Fatigue Life o f N o n - i n v o l u t e , Low-Contact-Ratio Gears.
Townsend, D. P. NASA Lewis Research Center Report No NASA TM-I03116 1990 8 pp Spur gear endurance tests were conducted to investigate the surface pitting fatigue life of non-involute gears with low numbers of teeth and low contact ratios for use in advanced applications. The results were compared with those for a standard involute design with a low number of teeth. The gear pitch diameter was 6.89 cm with 12 teeth on both gear designs. Test conditions were an oil inlet temperature of 320 K, an oil outlet temperature of 350 K, a maximum Hertz stress of 1.49 GPa, and a speed of 10000 rpm. The following results were obtained: the non-involute gear had a surface pitting fatigue life approximately 1.6 times that of the standard involute gear of a similar design; the surface pitting fatigue life of the 3.43-pitch AISI 8620 non-involute gear was approximately equal to the surface pitting fatigue life of an 8-pitch, 28-tooth AISI 9310 gear at the same load but at a considerably higher maximum Hertz stress. Graphs, photomicrographs. 7 refs. R n i t e - E l e m e n t E l a s t i c - P l a s t i c - C r e e p and Cyclic Life Analysis of a C o w l Up. Arya, V. K., Melis, M. E. and Ha/ford, G. R. NASA Lewis Research Center Report No NASA TM-I02342 1990 11 pp Results are presented of elastic, elastic-plastic, and elastic-plastic-creep analyses of a test-rig component of an actively cooled Cu cowl lip. A cowl lip is part of the leading edge of an engine inlet of proposed hypersonic aircraft and is subject to severe thermal Ioadings and gradients during flight. Values of stresses calculsted by elastic analysis are well above the yield strength of the cowl lip material. Such values are highly unrealistic and thus elastic stress analyses are inappropriate. The inelastic (elastic-plastic and elastic-plastic-creep) analyses produce more reasonable and acceptable stress and strain distributions in the component. Finally, using the results from these analyses, predictions are made for the cyclic crack initiation life of a cowl lip. A comparison of predicted cyclic lives shows the cyclic life prediction from the elastic-plastic-creep analysis to be the lowest and, hence, most realistic. Graphs. 14 refs.
spots. (3) When installed convexly upwards with single-spot initiation, a larger tensile load permits larger areas of the rapid fracture regions. Graphs, photomicrographs. 4 refs.
J., •Helesic, o H. and Obrtlik, pScr.lak,Metall. C K. l Mater.
i
c
Strain Localization in Copper Single Crystals and Polycrystals. Feb. 1990 24, (2), 4 1 5 - 4 1 9
Constant plastic strain amplitude testing of Cu single crystals and polycrystals with a detailed record of hysteresis loop shape changes and correlation with surface observations led to the following conclusions. The loop shape parameter VH can be used to detect the start of cyclic strain localization in both single crystals and polycrystals. The localization continues until the plastic strain is fully transferred to the PSBs and the plastic strain amplitude in the matrix is close to zero, a point that corresponds to the local maximum of VH. The cyclic slip localization is the reason for stress amplitude saturation in strain-controlled cycling. Secondary slip in PSBs leads to hardening of existing PSBs, in turn resulting in the final drop in VH and softening for low plastic strain amplitudes. Graphs, photomicrographs. 11 refs.
STM and Surface Analytical Study of the Effect of Environment on Fatigue Crack Initiation in Silver Single Crystals. I, Surface Chemical Effects. Venkataraman, G., Sriram, T. S., Fine, M. E. and Chung, Y. W. Scr. Metall. Mater. Feb. 1990 24, (2), 2 7 3 - 2 7 8 Fatigue crack initiation studies were performed on pure Ag single crystals oriented for slip using a scanning tunnelling microscope to detect fatigue cracks. It was found that the fatigue process has a crack nucleation stage which is strongly accelerated in an oxygen environment. Dissociative chemisorption of strongly bound O on the exposed slip steps is responsible. The effect of thermally activated dislocation processes is less pronounced than that of the environment. There was evidence of penetration of chemisorbed O into slip bands. 17 refs.
STM and Surface Analytical S t u d y o f t h e Effect o f Environment on Fati~lue Crack Initiation in Silver Single crystals. II, Effects of Oxygen Partml Pressure. Sriram, T. S., Fine, M. E. and Chung, Y. W. Scr. Metal/. Mater. Feb. 1990 24, (2), 2 7 9 - 2 8 4 Silver single crystals of 99.999% purity were grown using the horizontal zone technique. It was found that fatigue cracks do not grow from zero iength, but are formed by a nucleation process. Strong absorption of ambient 0 on the slip steps is responsible. The effect of O on fatigue crack initiation becomes important above approx. 10 3 Pa of O. Oxygen is incorporated into slip bands during fatigue. The extent of incorporation is dependent on 0 pressure. Graphs, photomicrographs. 13 refs.
Influence of Lubrication on Pitting and Micropitting Resistance of Gears. Winter, H. and Oster, P. Gear Technol. M a r . - A p r . 1990 7, (2), 1 6 - 2 3
Fatigue Crack Initiation and S m a l l Crack G r o w t h in Several A i r f r a m e Alloys. Swain, M. H., Newman, J. C., Phillips, E. P. and Everett, R. A. NASA Langley Research Center Report No N90-18746/9/XAB Jan. 1990 8 pp
Pitting of cese-carburized gears is a form of fatigue damage. Therefore, pitting endurance has to be determined by running tests and displaying the results as S-N curves. Because this procedure is time consuming, a short time test was developed to determine the influence of lubricants doped with different additives on pitting resistance. The tests have shown that lubricants doped with S-P additives (sulphur-phosphorus) show a higher micropitting resistance than lubricants doped with ZDP additive. The round robin tests were run on 16MnCr5 and 42CrMo4 steel. Graphs. photomicrographs. 10 refs.
The growth of naturally-initiated small cracks under a variety of constant-amplitude and variable-amplitude load sequences is examined for several airframe materials: the conventional AI alloys, 2024-T3 and 7075-T6, the AI-Li alloy, 2090-T8E41, and the 4340 steel. Loading conditions investigated include constant-amplitude loading at R=0.5, 0, -1 and - 2 and the variable-amplitude sequences FALSTAFF, MiniTWlST and FELIX/28. Crack growth was measured at the root of the semicircular edge notches using acetate replicas. Crack growth rates are compared, on a stress intensity factor basis, to those for large cracks to evaluate the extent of the small crack affect in each alloy. In addition, the various alloys are compared on a crack initiation and crack growth morphology basis.
Selecting Materials f o r Fatigue Resistance. Adv. Mater. Process. J u n e 1990 137, (6), 3 9 - 4 1 , 102-103 Fatigue fractures are said to account for nearly 80% of failures in engineering components. Regardless of the material specified, the possibility of fatigue failure can be reduced via careful design and manufacturing practices. A review of fatigue resistance covered metals, polymers, and ceramics. Fatigue is one of the major causes of fracture in metals, and it is likely that fatigue also plays an important part in the failure of plastics. It is not clear whether conventional fatigue actually occurs in ceramic materials; however, failure over time does occur in brittle ceramic materials, despite the absence of the crack-tip plasticity inherent in materials showing fatigue failure, Graphs.
Damage in t h e Steel Ck45N b y Fatigue Loading with Variable Amplitudes. Walla, J., Bomas, H. and Mayr, P. Hart.-Tech. Mitt. J a n . - F e b . 1990 45, (1), 3 0 - 3 7 (in German) The fatigue life, mechanical behaviour and microstructure of Ck45N steel specimens were investigated under variable-amplitude fatigue loading. The results show that the fatigue life decreases with an increase in the irregularity of the sequence of load amplitudes. This observation cannot be explained by the mechanical behaviour of the material or by the development of the dislocation cell structure, which is almost independent of the load sequence. In additional investigations it was found that dislocation cell structures formed during high-amplitude loading are irreversible and stable in subsequent fatigue with lower amplitudes and make no contribution to fatigue damage. Graphs, photomicrographs. 7 refs. Fatigue Fractured Surface of Component Wire for Steel Wire Ropes.
Ueda, K. and Fujinaka, Y. J. Min. Mater. Process. Inst. Jpn. Jan. 1990 106, (1), 2 9 - 3 3 (in Japanese) Fatigue of component wire for steel wire ropes under tension and bending has been studied. This paper describes the results of fatigue tests of a steel wire which has a natural curling, and discusses the results of observations of the fracture face of the specimen. The relation beWveen the S-N diagram and the fracture face is also discussed. The following were found. (1) The degree of symmetry of fracture faces depends on both the residual stress and the curvature of the specimen before installation. (2) The degree of flatness of the fatigue fracture face and the shape of the S-N diagram are considerably influenced by the number of crack initiation
Int J Fatigue March 1991
Solution of the Fokker-Planck-Kolmogorov Equation in Stochastic Modelling of Fatigue Crack Propagation. Wu, W.-F. and Huang, T.-H. J. Chin. Inst. Eng. Jan. 1990 13, (1), 2 5 - 3 3 Based on linear fracture mechanics concepts and random process theory, several stochastic models of fatigue crack propagation have been proposed in recent years. One of the models randomizes the fatigue crack propagation equation by employing a random pulse train and applying a stochastic average technique to treat the dynamic fatigue crack propagation as a Markov process. The probabilistic structure of a Markov diffusion process is governed by a Fokker-Planck-Kolmogorov equation. Therefore, time and the probability distribution function of the random time at which a given crack size is reached are treated as solutions of the Fokker-Ptanck-Kolmogorov equation associated with the Markov process. Analytical solutions are found for these quantities and numerical examples for AI 2024 are given. The results are compared with some experimentally obtained data. Graphs. 19 refs. F ~ i g u e of Mar-M247. I. Experiments. Boismier, D. A. and Sehitoglu, H~:!i',~ J. Eng. Mater. T e c h n o ~ r a n s ASME) Jan. 1990 112, (1), 6 8 - 7 9
Thermo-Mechanicel
Isothermal fatigue tests, and out-of-phase and in-phase thermo-mechanical fatigue tests were performed on Mar-M247 Ni-based superalloy. The experiments were conducted in the temperature range 500-871 °C. Results indicate that the lives differ with strain-temperature phasing and with strain rate. The results of out-of-phase thermo-mechanicel tests correspond well with strain-life data of isothermal tests conducted at the peak temperature (871 °C). However, the in-phase thermomechanical results differed depending on the strain amplitude. Significant surface and crack tip oxidation and "y' depletion have been observed based on matallographic and Auger spectroscopic analyses. These changes were measured as a function of time. The environment-induced changes significantly influenced the fatigue lives in isothermal and out-of-phase thermo-mechanicat fatigue cases. In these cases tranagranular cracking was observed. Grain boundary crack nucleation and grain boundary crack growth dominated the in-phase thermo-mechanical fatigue cases. Based on these observations the requirements for a life prediction model are outlined. The life prediction model and the predictions are given in part I1. Graphs, photomicrographs. 42 refs.
189