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Thermal-mechanical fatigue of MAR-M 509 superalloy. Comparison with low-cycle fatigue behaviour
found that the magnitude of the local cyclic strain distribution near the crack tip was varied by the applied cyclic load level and the material, but the shape of the local cyclic strain distribution near the crack tip was experimentally scarcely altered. The local cyclic strain field near the crack tip could be written as the following equation: &~eq(f,e) 3A f(~)r 1. A single parameter ~,A, which characterizes the local cyclic strain field near the crack tip, was proposed for the first time. The materials tested were a Ni-Cr alloy steel (JIS SNC631) and 2024-T6 AI. Graphs. 8 refs.
Fatigue processes in metals--role of aqueous environments. Sudarshan,
contribution together with time-dependent or environment*enhanced degradation. This complex phenomenon in Ti3AI is unlike that in Ni-based superalloys where crack growth was found to result from a linear combination of cycle- and timedependent contributions. Thus, the linear cumulative modelling technique is not applicable to the Ti3AI tested. Graphs. 20 refs.
The fatigue life of thick-walled autofrettaged cylinders with closed ends. Rees, D.W.A.
Fatigue Fract. Eng. Mater. Struct. 1991 14 {1), 5 1 - 6 8
The responses of a wide range of metals under the action of applied stresses and in environments spanning a complete range of aggressiveness, from the very inert to the aggressive, have been the subject of several investigations. Most of these studies have focused on mechanisms governing fatigue crack propagation and little attention has been paid to the effect of environment on fatigue crack initiation. A comprehensive understanding of the influence of aqueous environments has been hampered by the complexity of the problem, the difficulties in understanding the various micromechanisms governing crack initiation and crack propagation and by an absence of a truly interdisciplinary attack of the problem. Several of the fatigue crack initiation models are presented and the micromechanisms governing fatigue crack initiation are examined. The various processes that control the phenomenon of cracking including fatigue crack growth enhanced by aqueous environment are also highlighted. Some of the materials mentioned are AI-based alloys, Ti-based alloys and stainless steels. Graphs. 153 refs.
It is well known that the fatigue strength of a thick-walled cylinder is enhanced by autofrettage. However, this does not appear to have been explained using fracture mechanics. Two uncertainties arise when this is attempted. Firstly, the distribution of residual stress resulting from the autofrettage pressure must be estimated and, secondly, a realistic stress intensity factor for subsequent fatigue cracking must be defined. A number of available stress intensity solutions are modified with the predictions for the residual stress following an elastic-plastic autofrettage pressure in a closed cylinder of hardening material. A comparison with experiment has enabled the various approaches to be appraised. It is shown that the modified stress intensity factor of Bowie and Freese is most consistent with the propagation fatigue life observed in autofrettaged cylinders provided their solution is adapted to account for the propagation of a semielliptical crack front in the presence of residual stress. Other Ki estimates appear to lead to dangerously optimistic predictions particularly within the range of fluctuating pressure where failure occurs between 105 and 106 cycles. The contribution to fatigue failure from initiation cycles is expressed as a power function of the observed life for cyclic pressures in the region of the fatigue limit. Steel of type EN25 was tested. Graphs, photomicrographs. 33 refs.
Fatigue failure of gears of circular-arc tooth-profile. Atria, A.Y. and EI-
The propagation of non-coplanar semielliptical fatigue cracks, Soboyejo,
Bahloul, A . M . M .
W.O. and K n o t t , J.F.
T.S., Srivatsan, T.S. and Harvey, D.P., II Eng. Fract. Mech. 1990 36 (6), 8 2 7 - 9 5 2
J. Tribol. (Trans. ASME) July 1990 112 (3), 4 5 3 - 4 5 9
Fatigue Fract. Eng. Mater. Struct. 1991 14 (1), 3 7 - 4 9
Results and analysis of an experimental investigation carried out to study fatigue failures of a relatively new type of gearing having teeth with circular-arc profiles are presented, Twenty-one pairs of gears having different helix angles but with the same overlap ratio were tested in a power circulating gear test rig lubricated by oils of different viscosities, running at different speeds and transmitting powers, exerting a constant normal tooth load of 21 kN. Results show that fatigue cracks were initiated on the tooth surface at the start of the zone of single contact and propagated to the rear of the tooth until part of or all the tooth was broken. Curves representing the fatigue life and its changes with helix angle, the oil viscosity and speed are presented and discussed. The gears were made of the 4155MM and 4164MM~steels. Graphs. 12 refs.
The results of fatigue tests on specimens containing parallel offset and parallel collinear configurations of multiple non-coplanar cracks are presented. The fatigue growth of parallel collinear cracks is shown to be significantly affected by crack-tip shielding, and parallel offset cracks are shown to grow almost independently before their adjacent tips overlap. Subsequent growth in the region of ovedap results in coalescence, which begins when the deviating crack tips come into contact below the surfaces of the specimens. Simplified predictions of the propagation of offset non-coplanar semielliptical cracks are also presented and their implications for the prediction of fatigue lives in structures containing offset coplanar cracks are assessed. The pressure vessel steel Fe-0.18C-2.5Ni-l,5Cr-0,SMo was tested, Graphs, photomicrographs. 18 refs,
Fatigue of aluminium alloy 2024-T351 in humid and dry air. Voris, H.C.
Creep-fatigue crack growth and fractography of a Type 304 stainless steel at elevated temperature. Koterazawa, R. and Nosho, T.
and Jahn, M.-T. J. Mater. Sci. Nov. 1990 25 (11), 4 7 0 8 - 4 7 1 1 Reversed bending fatigue tests conducted on specimens of the AI alloy 2024-T351 in dry and humid air at stress levels of 248, 276, 290, 317 and 359 MPa showed that, at low stress amplitudes, humid air reduces the fatigue life by as much as 21 per cent. Microhardness tests showed that the reduction in fatigue life is primarily attributed to localized hydrogen-induced over-ageing. A SEM analysis and microhardness data were combined with previous studies to propose a mechanism for environmentally induced fatigue in the AI alloy 2024-T351 over a wide range of stress leveis. Graphs, photomicrographs. 12 refs.
Thermal-mechanical fatigue of MAR-M 509 superalloy. Comparison with low-cycle fatigue behaviour. Francois, M. and Remy, L Fatigue Fract. Eng. Mater. Struct. 1991 14 (1), 1 1 5 - 1 2 9 The thermal-mechanical fatigue behaviour of a cast cobalt-based superalloy, MARM 509, was investigated. Hollow smooth specimens were subjected to temperature cycling between 600-1050°C. The mechanical strain against temperature cycle shows a diamond shape with peak strains at intermediate temperatures. The stress-strain behaviour and fatigue life curves are reported. A significant part of the total life is spent in crack initiation. A comparison with isothermal low-cycle fatigue was made at the temperature where peak strains occurred. Isothermal lowcycle fatigue life to crack initiation was shown to give a conservative estimate of the thermal-mechanical fatigue life, provided extra strains arising from differences between the thermal expansion coefficients of the oxide scale on the surface and the base alloy were taken into account. Graphs, photomicrographs. 27 refs.
Fatigue Fract. Eng. Mater. Struct. 1991 14 (1), 1 - 9 The creep-fatigue crack growth behaviour of a Type 304 stainless steel under four types of reversed loading patterns (P-P, P-C. C-P and C-C) was investigated and the results are discussed in the light of fracture mechanics and fractography. The crack growth rate for all of the four types of loading was successfully correlated in terms of the cyclic integral range ,I J. It was unnecessary, for practical purposes, to divide "~J into a fatigue component, .IJf, and a creep component. -~Jc, as has been done elsewhere. The transition of the correlating fracture mechanics parameter from fatigue to creep was not necessarily associated with the fracture morphology. This was related to the longer transition hold time in morphology in C-C type loading compared with C-P type loading, and was attributed to recovery of grain boundary sliding during the compression hold in the C-C type loading. Graphs, photomicrographs. 15 refs.
Fatigue crack closure in kinked cracks and path of crack propagation. Mageed, A.M.A. and Pandey, R.K. int. J. Fract. Aug. 1990 44 (3), R39- R42 The occurrence of crack closure is believed to have a significant effect on the fatigue crack propagation path. The neglect of closure effects may lead to considerable error in the predicted path for kinked cracks especially for very small crack angles (~). The measurement of the crack opening stress intensity factor (Kop) was conducted in 2024-T3 alloy of 1.27 ~m thickness using a clip gauge technique by placing the gauge 1 mm behind the crack tip. The crack angles used were 15, 30, 45, and 60° with the loading axis beside the mode-I crack. The mode-i and -II components of the opening stress intensity factors in the kinked crack were evaluated. Graphs. 1 ref.
The fatigue crack growth behaviour of the Al-Cu-Li alloy Weldalite 049. Blankenship, C. P., Jr. and Starke, E. A., Jr. Fatigue Fract. Eng. Mater. Struct. 1991 14 (1), 1 0 3 - 1 1 4 The microstructure deformation behaviour and crack growth relationships have been examined for an AI-5Cu-I.3Li-0.4Mg-0.4Ag-O, lZr alloy. The TEM of deformed samples revealed that the T3 temper deformed via highly Iocafized planar slip owing to the presence of small, coherent precipitates (GP zones and ~,') while the T8 temper deformed homogeneously with Tr as the strengthening phase. Both constant Kmax and constant R (0.1) fatigue curves were generated for the T3 and T8 tempers in both the T-L and L-T orientations. The T3 temper exhibited high closure levels and an apparent intrinsic threshold of 2 MPa Vm. The T8 temper did not exhibit high closure levels, and the extrinsic threshold was determined to be 1.3 MPa "~ m. Weldalite-T3 has a strength comparable with 2024-T3 but has a higher resistance to fatigue crack growth, whereas Weldalite-T8 has a much higher strength and a comparable fatigue crack growth resistance to 2024-T8. Graphs, photomicrographs. 26 refs.
Crack growth in a titanium aluminide alloy under thermal mechanical cycling. Mall, S.,Nichofas, T., Pernot, J.J. and Burgess, D.G.
of superimposed high-frequency flutter on the fatigue life of a submarine hull steel. Khan, M Z . S . and Butch, I.A. Effect
Int. J. Fract. Aug 1990 44 (3), R35-R38 A new hull steel was subjected to small-amplitude high-frequency cyclic excursions superimposed on the basic, low-frequency cycle in air and seawater environments. The fatigue life in seawater is adversely affected by the superposition of the sinusoidal flutter particularly at high flutter frequencies. Tests in air show that the fatigue fife of the steel is insensitive to the flutter at the highest flutter frequency used, The steel was a low-alloy quenched and tempered type, given designation BIS 812 EVA (composition 0.12C-0.93Mn-I.INi-0.5Cr-0.4Mo with microadditions of Nb, Ti, V and B), with a nominal minimum yield stress of 690 MPa. Smooth hourglass-shaped specimens were machined with their long direction parallel to the rolling direction of the plate, In seawater tests, an environmental enclosure around the specimen was used. The basic waveform was a zero-to-tension trapezoidal waveform with a constant loading/unloading rate of 45 MPa s 1, a frequency of 0.015 Hz and an amplitude of 300 MPa. A high-frequency sinusoidal flutter was superimposed on the basic waveform with the flutter frequencies ranging between 30-1 Hz. Test specimens were examined by optical microscopy, scanning electron microscopy, and metallographically. Graphs. 5 refs.
Fatigue Fract. Eng. Mater. Struct. 1991 14 (1), 7.9-87 The fatigue crack growth behaviour in a titanium aluminide (Ti3AI) alloy under thermomechanical loading and under elevated temperature conditions was investigated. The thermal mechanical fatigue crack growth behaviour appears, in a general sense, to follow the same trends observed in similar data obtained in tests on Nibased superalloys. However, crack growth in Ti3AI appeared to be influenced by blunting of the crack tip because of creep in addition to a cycle-dependent
360
increase in hardening of 2024-T42 aluminium with fatigue stress amplitude. Kermanidis, Th.B., Pantetakis, S.P. and Pavlou, D.G. Theor. Appl. Fract. Mech. Sept. 1990 14 (1), 4 3 - 4 7
The fatigue lives of structural components and their subsequent failure behaviour are associated with the gradual damage of the material microstructure. A hierarchy
Int J Fatigue July 1991
Fatigue processes in metals--role of aqueous environments. Sudarshan,
contribution together with time-dependent or environment*enhanced degradation. This complex phenomenon in Ti3AI is unlike that in Ni-based superalloys where crack growth was found to result from a linear combination of cycle- and timedependent contributions. Thus, the linear cumulative modelling technique is not applicable to the Ti3AI tested. Graphs. 20 refs.
The fatigue life of thick-walled autofrettaged cylinders with closed ends. Rees, D.W.A.
Fatigue Fract. Eng. Mater. Struct. 1991 14 {1), 5 1 - 6 8
The responses of a wide range of metals under the action of applied stresses and in environments spanning a complete range of aggressiveness, from the very inert to the aggressive, have been the subject of several investigations. Most of these studies have focused on mechanisms governing fatigue crack propagation and little attention has been paid to the effect of environment on fatigue crack initiation. A comprehensive understanding of the influence of aqueous environments has been hampered by the complexity of the problem, the difficulties in understanding the various micromechanisms governing crack initiation and crack propagation and by an absence of a truly interdisciplinary attack of the problem. Several of the fatigue crack initiation models are presented and the micromechanisms governing fatigue crack initiation are examined. The various processes that control the phenomenon of cracking including fatigue crack growth enhanced by aqueous environment are also highlighted. Some of the materials mentioned are AI-based alloys, Ti-based alloys and stainless steels. Graphs. 153 refs.
It is well known that the fatigue strength of a thick-walled cylinder is enhanced by autofrettage. However, this does not appear to have been explained using fracture mechanics. Two uncertainties arise when this is attempted. Firstly, the distribution of residual stress resulting from the autofrettage pressure must be estimated and, secondly, a realistic stress intensity factor for subsequent fatigue cracking must be defined. A number of available stress intensity solutions are modified with the predictions for the residual stress following an elastic-plastic autofrettage pressure in a closed cylinder of hardening material. A comparison with experiment has enabled the various approaches to be appraised. It is shown that the modified stress intensity factor of Bowie and Freese is most consistent with the propagation fatigue life observed in autofrettaged cylinders provided their solution is adapted to account for the propagation of a semielliptical crack front in the presence of residual stress. Other Ki estimates appear to lead to dangerously optimistic predictions particularly within the range of fluctuating pressure where failure occurs between 105 and 106 cycles. The contribution to fatigue failure from initiation cycles is expressed as a power function of the observed life for cyclic pressures in the region of the fatigue limit. Steel of type EN25 was tested. Graphs, photomicrographs. 33 refs.
Fatigue failure of gears of circular-arc tooth-profile. Atria, A.Y. and EI-
The propagation of non-coplanar semielliptical fatigue cracks, Soboyejo,
Bahloul, A . M . M .
W.O. and K n o t t , J.F.
T.S., Srivatsan, T.S. and Harvey, D.P., II Eng. Fract. Mech. 1990 36 (6), 8 2 7 - 9 5 2
J. Tribol. (Trans. ASME) July 1990 112 (3), 4 5 3 - 4 5 9
Fatigue Fract. Eng. Mater. Struct. 1991 14 (1), 3 7 - 4 9
Results and analysis of an experimental investigation carried out to study fatigue failures of a relatively new type of gearing having teeth with circular-arc profiles are presented, Twenty-one pairs of gears having different helix angles but with the same overlap ratio were tested in a power circulating gear test rig lubricated by oils of different viscosities, running at different speeds and transmitting powers, exerting a constant normal tooth load of 21 kN. Results show that fatigue cracks were initiated on the tooth surface at the start of the zone of single contact and propagated to the rear of the tooth until part of or all the tooth was broken. Curves representing the fatigue life and its changes with helix angle, the oil viscosity and speed are presented and discussed. The gears were made of the 4155MM and 4164MM~steels. Graphs. 12 refs.
The results of fatigue tests on specimens containing parallel offset and parallel collinear configurations of multiple non-coplanar cracks are presented. The fatigue growth of parallel collinear cracks is shown to be significantly affected by crack-tip shielding, and parallel offset cracks are shown to grow almost independently before their adjacent tips overlap. Subsequent growth in the region of ovedap results in coalescence, which begins when the deviating crack tips come into contact below the surfaces of the specimens. Simplified predictions of the propagation of offset non-coplanar semielliptical cracks are also presented and their implications for the prediction of fatigue lives in structures containing offset coplanar cracks are assessed. The pressure vessel steel Fe-0.18C-2.5Ni-l,5Cr-0,SMo was tested, Graphs, photomicrographs. 18 refs,
Fatigue of aluminium alloy 2024-T351 in humid and dry air. Voris, H.C.
Creep-fatigue crack growth and fractography of a Type 304 stainless steel at elevated temperature. Koterazawa, R. and Nosho, T.
and Jahn, M.-T. J. Mater. Sci. Nov. 1990 25 (11), 4 7 0 8 - 4 7 1 1 Reversed bending fatigue tests conducted on specimens of the AI alloy 2024-T351 in dry and humid air at stress levels of 248, 276, 290, 317 and 359 MPa showed that, at low stress amplitudes, humid air reduces the fatigue life by as much as 21 per cent. Microhardness tests showed that the reduction in fatigue life is primarily attributed to localized hydrogen-induced over-ageing. A SEM analysis and microhardness data were combined with previous studies to propose a mechanism for environmentally induced fatigue in the AI alloy 2024-T351 over a wide range of stress leveis. Graphs, photomicrographs. 12 refs.
Thermal-mechanical fatigue of MAR-M 509 superalloy. Comparison with low-cycle fatigue behaviour. Francois, M. and Remy, L Fatigue Fract. Eng. Mater. Struct. 1991 14 (1), 1 1 5 - 1 2 9 The thermal-mechanical fatigue behaviour of a cast cobalt-based superalloy, MARM 509, was investigated. Hollow smooth specimens were subjected to temperature cycling between 600-1050°C. The mechanical strain against temperature cycle shows a diamond shape with peak strains at intermediate temperatures. The stress-strain behaviour and fatigue life curves are reported. A significant part of the total life is spent in crack initiation. A comparison with isothermal low-cycle fatigue was made at the temperature where peak strains occurred. Isothermal lowcycle fatigue life to crack initiation was shown to give a conservative estimate of the thermal-mechanical fatigue life, provided extra strains arising from differences between the thermal expansion coefficients of the oxide scale on the surface and the base alloy were taken into account. Graphs, photomicrographs. 27 refs.
Fatigue Fract. Eng. Mater. Struct. 1991 14 (1), 1 - 9 The creep-fatigue crack growth behaviour of a Type 304 stainless steel under four types of reversed loading patterns (P-P, P-C. C-P and C-C) was investigated and the results are discussed in the light of fracture mechanics and fractography. The crack growth rate for all of the four types of loading was successfully correlated in terms of the cyclic integral range ,I J. It was unnecessary, for practical purposes, to divide "~J into a fatigue component, .IJf, and a creep component. -~Jc, as has been done elsewhere. The transition of the correlating fracture mechanics parameter from fatigue to creep was not necessarily associated with the fracture morphology. This was related to the longer transition hold time in morphology in C-C type loading compared with C-P type loading, and was attributed to recovery of grain boundary sliding during the compression hold in the C-C type loading. Graphs, photomicrographs. 15 refs.
Fatigue crack closure in kinked cracks and path of crack propagation. Mageed, A.M.A. and Pandey, R.K. int. J. Fract. Aug. 1990 44 (3), R39- R42 The occurrence of crack closure is believed to have a significant effect on the fatigue crack propagation path. The neglect of closure effects may lead to considerable error in the predicted path for kinked cracks especially for very small crack angles (~). The measurement of the crack opening stress intensity factor (Kop) was conducted in 2024-T3 alloy of 1.27 ~m thickness using a clip gauge technique by placing the gauge 1 mm behind the crack tip. The crack angles used were 15, 30, 45, and 60° with the loading axis beside the mode-I crack. The mode-i and -II components of the opening stress intensity factors in the kinked crack were evaluated. Graphs. 1 ref.
The fatigue crack growth behaviour of the Al-Cu-Li alloy Weldalite 049. Blankenship, C. P., Jr. and Starke, E. A., Jr. Fatigue Fract. Eng. Mater. Struct. 1991 14 (1), 1 0 3 - 1 1 4 The microstructure deformation behaviour and crack growth relationships have been examined for an AI-5Cu-I.3Li-0.4Mg-0.4Ag-O, lZr alloy. The TEM of deformed samples revealed that the T3 temper deformed via highly Iocafized planar slip owing to the presence of small, coherent precipitates (GP zones and ~,') while the T8 temper deformed homogeneously with Tr as the strengthening phase. Both constant Kmax and constant R (0.1) fatigue curves were generated for the T3 and T8 tempers in both the T-L and L-T orientations. The T3 temper exhibited high closure levels and an apparent intrinsic threshold of 2 MPa Vm. The T8 temper did not exhibit high closure levels, and the extrinsic threshold was determined to be 1.3 MPa "~ m. Weldalite-T3 has a strength comparable with 2024-T3 but has a higher resistance to fatigue crack growth, whereas Weldalite-T8 has a much higher strength and a comparable fatigue crack growth resistance to 2024-T8. Graphs, photomicrographs. 26 refs.
Crack growth in a titanium aluminide alloy under thermal mechanical cycling. Mall, S.,Nichofas, T., Pernot, J.J. and Burgess, D.G.
of superimposed high-frequency flutter on the fatigue life of a submarine hull steel. Khan, M Z . S . and Butch, I.A. Effect
Int. J. Fract. Aug 1990 44 (3), R35-R38 A new hull steel was subjected to small-amplitude high-frequency cyclic excursions superimposed on the basic, low-frequency cycle in air and seawater environments. The fatigue life in seawater is adversely affected by the superposition of the sinusoidal flutter particularly at high flutter frequencies. Tests in air show that the fatigue fife of the steel is insensitive to the flutter at the highest flutter frequency used, The steel was a low-alloy quenched and tempered type, given designation BIS 812 EVA (composition 0.12C-0.93Mn-I.INi-0.5Cr-0.4Mo with microadditions of Nb, Ti, V and B), with a nominal minimum yield stress of 690 MPa. Smooth hourglass-shaped specimens were machined with their long direction parallel to the rolling direction of the plate, In seawater tests, an environmental enclosure around the specimen was used. The basic waveform was a zero-to-tension trapezoidal waveform with a constant loading/unloading rate of 45 MPa s 1, a frequency of 0.015 Hz and an amplitude of 300 MPa. A high-frequency sinusoidal flutter was superimposed on the basic waveform with the flutter frequencies ranging between 30-1 Hz. Test specimens were examined by optical microscopy, scanning electron microscopy, and metallographically. Graphs. 5 refs.
Fatigue Fract. Eng. Mater. Struct. 1991 14 (1), 7.9-87 The fatigue crack growth behaviour in a titanium aluminide (Ti3AI) alloy under thermomechanical loading and under elevated temperature conditions was investigated. The thermal mechanical fatigue crack growth behaviour appears, in a general sense, to follow the same trends observed in similar data obtained in tests on Nibased superalloys. However, crack growth in Ti3AI appeared to be influenced by blunting of the crack tip because of creep in addition to a cycle-dependent
360
increase in hardening of 2024-T42 aluminium with fatigue stress amplitude. Kermanidis, Th.B., Pantetakis, S.P. and Pavlou, D.G. Theor. Appl. Fract. Mech. Sept. 1990 14 (1), 4 3 - 4 7
The fatigue lives of structural components and their subsequent failure behaviour are associated with the gradual damage of the material microstructure. A hierarchy
Int J Fatigue July 1991