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Fatigue crack growth automated testing method
An oxidation fatigue interaction dama creek rowth. Rezai-Aria, F. and Remy, Eng. Pr8cf. Mech. 1989 34, (2), 283-294
e model for thermal
B.
fatigue
Thermal fatigue of MAR-M509, a typical cast superallov for vanes in jet engines, was previously shown to involve mainly crack propagation which is strongly influenced bv oxidation. Crack orooaoation was so modelled using demeae eauetions which are based on local stredses iha volume element at the crack tip.-The.volume element at the crack tip wes taken as the secondary dendrite size, a materiel constant. Local stresses ahead of the crack were estimated from Tracev’s finite element analysis of plane strain small scale yielding which was adapted to a cyclic loading using Rice’s hypothesis. A fatigue damage equation was fitted to fatigue crack growth data measured et high frequency on CT specimens, which accounts for load ratio effects. High temperature oxidation of precrecked CT specimens induced embrittlement et medium temperatures ahead of the oxidized precreck. The critical stress to fracture was found to increase with increasing distance from the oxidized crack tip and to depend on oxygen diffusion end on interdendritic oxide depth, which can be easily measured by quentitetive metallography on oxidized specimens. Damage equations were then derived for isothermal fatigue end thermal fatigue crack growth; all the parameters involved were fitted to the experiments on virgin end pre-oxidized CT specimens. These equations were used to compute the isothermal fatigue life et 900 “C to 0.3 mm crack depth end the propagation rate of thermal fatigue cracks in wedge specimens and they were found to give reasonably good predictions in most cases. 31 refs. Stetisticel design of fatigue crack growth test programmer. G.C. and Hoeppner, D. W. ASTM J. Test. Eva/. Nov. 1988 16, (6). 508-515
Sal&v,
experimental design method for determining statistically significant differences in fatigue crack growth rate date due to the influence of various test conditions (factors) is presented. This method is based on a completely randomized factorial design end a three-way classification analysis of variance (ANOVA) procedure. Although the example presented is for fatigue crack growrh rate testing, this method is generic to any materiels test programme where comparisons of properties or behaviour are made. The procedure allows decisions regarding these comparisons to be based on statistical tests of significance. Steel SA533B-1 was tested. 18 refs. An
Fatigue crack growth from an artificial flaw. Taggart, R., Ramulu, M. and Jolly, T. Mater. Sci. Eng. A 1 Nov. 1989 A119, (l-2). 73-80 The crack growth characteristics of physically short cracks have been examined under cyclic load conditions. These short cracks were nucleated from artifice1 flaws that had been induced symmetrically in a keyhole-notched compact-type specimen of Al ellov 7075-l735. The fetioue crack arowth rate is shown to be a function of flaw dep&. A limit to short-crack behavioir is predicted in terms of flaw depth. A transition from short- to long-crack behaviour is observed for crack lengths between l.O-3.0mm. The effect of residual stresses created bv the introduction of the artificial flew is discussed. Fatigue crack morphology in terms of microstations end flew depth is also considered. 39 refs.
Crack initiation mechanisms in low cycle fatigue 7675 T6. Li, P., Marchand, N.J. and Ilschner, 13. Mater. Sci. Eng. A 1 Nov. 1989 Allg, (l-2). 41-50
of aiuminium
Influence of environmental variables and intermittent overloadin s on fatigue crack growth in on-boerd NGV cylinder steel. Bhuyan, G. 8, and Brezden, W. J. Int. J. Pressure Vessel Piping 1989 40, (2). 139- 149 Fatigue creek growth rates in the on-board compressed natural gas (CNG) steel cvlinder IAISI 4130X oredel were obtained in air end in the simulated natural oas environment. Effects if loading frequency (1.0, 0.1 end 0.01 Hz) on corrosion fatigue crack growth rates were investigated. The maximum crack growth rate in the modified solution was -60 times the rate in air. A maximum corrosion-assisted cracking rate of 2.0 x lo-’ m/s was obtained. Retardation of fatigue crack growth was observed after the overloadings, equivalent to the present requalification tests of the on-board steel CNG cylinders. Ratio of the experimentally determined overload effected zone to the cyclic plane strain plastic zone varied from 0.85-1.91. 7 refs. ($tAyip
fatigue strength of ductile cast irons through surface rolling. rB Karser, B. and Adelmann, J. Konsir. &ssen 1989 14, (11, 4-10 (in German)
Experimental test results are reported on two peerlitic cast irons containing 2.6 carbon, 1.4 Si end 3.4 C, 2.2 Si leg GGGGO,GGG65-02) respectively. They confirm the well-known fatigue properties of surface rolled parts. This roll strengthening procedure produced only minor increases in the fatigue strength of unnotched specimens, but had such a pronounced effect on notched specimens that the notch effect could be completely neutralized. Compared with steel,‘higher fatigue to tensile strength ratios were obtained, especially for smeller test bar diameters. The cast iron specimens had only minor responses to deviations from optimum rolling conditions, but the results showed a much larger well thickness effect on the strength characteristics when compared with steel. The enormous gain in fatigue strength of the notched bars was bought et the expense of incipient cracks at notch roots. These incipient cracks lowered the statistical strength reserve of the specimens to about double the fatigue strength. In surface rolling critical parts subjected to design/load peaks in service, adequate safety factors must be considered. 5 refs. Fatigue-creep life prediction of 2.26Cr-1Mo steel by inelastic analysis. Inoue, T., Igari, T., Okazaki, M., Sakane, M. and Tokimasa, K. Nucl. Eng. Des. June 1989 114, (3). 311-321 The life prediction methods under fatigue-creep interaction are covered by taking into account the plasticity-creep interaction described by the constitutive models in a previous publication. By specifying a normalized end tempered 2.25Cr-1Mo steel at 600 “C, uniexiel fatigue-creep tests under six patterns of strain waves ere performed. Adopting eight types of life estimation methods, two kinds of life prediction procedures are examined: one is a normal way, based on an experimentally obtained stress-strain hysteresis loop; the other is a way of employing the calculated stress-strain hysteresis loop by use of ten types of constitutive models. Predicted lives of the material are compared with observed failure lives, end dicussions on the evalution of the methods are included. 18 refs.
alloy
Testing and control
Fully reversed strain-controlled push-pull tests were performed on polycrystelline specimens of Al alloy 7075 T6 to investigate the influence of temperature end strain amplitude on the micromechanisms of cyclic plastic deformation end crack initiation. The tests were carried out between 20-260 “C in the strain range 0.&2.4%. Goldelated reolicas end scennina electron microscoov were used to detect crack initiation i& - 10 ;m) end microcrack growth. The re&ts showed the crack initiation life IN;) to be a fraction of the total life (Ntl. The ratios HIi% were found to be independent of the strain amplitude in ;he strain range investigated end to vary with temperature only. Transmission electron microscopy results indicated that the cyclic behaviour is controlled either by the evolution of the dislocation substructures at low temperature (with cycling) or by the changing morphology and distribution of the precipitates et elevated temperatures. The kinetics of dissolution and precipitation were shown to be influenced strongly by cyclic plastic strain. This entails that the results of precipitation kinetics studies cannot be used to rationalize the changes in precipitation morphology end distribution occurring in higher temperature, low cycle fatigue testing. Finally. the occurrence of any of the three fevoured sites for creek initiation is shown to correlate with the plastic-to-total strain ratio (Aq,/Att).
alone proved to be Conservative when compared with smooth specimen test results to such an extent that Neuber-generated notch stresses end strain amplitudes cannot accurately be compared with the mean date curves derived from the ASME Section III fatigue curves for carbon steels which are based on net section stress meas”rements. 37 refs.
Fatigue crack growth automated testing method. Hatch, P.W., Van DenAvyle, J.A. and Laing, J. Sandia National Laboratories Report No. DE89014352/XAB June 1989 PP 45 A computer controlled servo-hydraulic mechanical test system has been configured to conduct automated fatigue crack growth testing. This provides two major benefits: it allows continuous cycling of specimens without operator attention over evenings end weekends; end complex load histories, including random loading end spectrum loading, can be applied to the specimens to simulate cyclic loading of engineering structures. The software is written in MTS Multi-User Basic to control test machine output end acquire date et predetermined intervals. Compact tension specimens are cycled according to ASTM specification EE47-86. Fatigue crack growth is measured vie specimen compliance during the test using a compliance/crack length calibration determined earlier by visual crack length measurements. This set-up was used to measure crack growth rates in 6063 Al alloy for a variety of cyclic loadings, including spectrum loads. Date collected compared well with tests run manually.
21 rafs.
Stress cottcentrations and the Mott mechanism Jackson, P.J. Mater. Sci. Eng. A 1 Nov. 1989 A119, (l-2). l-6
in fatigue
failure.
The tensile stress across a persistent slip bend in a fatigued specimen is considered, It is demonstrated that the stress concentration produced by a fatigue crack promotes the circulation of screw dislocations around the crack end that the direction of circulation is such as to punch the crack deeper into the materiel prismatically. It is suggested that extrusions, intrusions end cracks are produced by the Mon mechanism, driven by stress concentrations. Examples of Cu are given. 27 refs.
Useof Nwber’srule to estimate the fati ue life of notched specimens of ASME SA 166-B steel pipin in 286 Y? air. Terrefl, J.8. Int. J. Pressure Vessels Piping P989 40, (11, 17-40 Fatigue strain-life tests were conducted on notched specimens of ASME SA 106-B piping steel et PWR operating temperatures (288°C). under completely reversed loading. Fatigue limits et 10’ cycles were estimated for smooth specimens to be 185 MPa (26.8 ksil et 24°C and 232 MPa (33.7 ksi) at 288°C. The higher fatigue strength observed at the PWR temperature is postulated to be caused by dynamic strain egeing processes. However, a reduction in fatigue strength in the low cycle fatigue regime was .observed in 288 “C air environment tests, which may indicate that the current ASME Section III design curve for carbon steels is non-conservative in its positioning. Notch strain histories were estimated for the notched specimen tests using various interpretations of Neuber’s rule. It was concluded that the use of the fatigue notch concentration factor (Kfl in the Neuber relation in conjunction with the uniexial cyclic stress-strain curve provided the best correlation of notched specimen fatigue date with results obtained from smooth specimen tests. The notched specimen strain-life results derived from the application of Neuber’s rule
Int J Fatigue July 1990
Fati ue of steels under combined stresses: application to steel 30 NCD 16. e roustey, C. and Lassere, S. fcole Nationale Superieure des Arts et Metiers de Paris Report No PB8922315WXAB Oct. 1988 pp 44 (in French) A new test programme was undertaken with the following objectives: to verify if a static torsion stress has no effect on other types of loads; to determine for these tests at different frequencies the flexion end torsion amplitudes which are acceptable when the average flexion value is not zero; to specify the utilization limits of the various critierie; to confirm or not the dimensioning method end, if this method proves itself to be viable, to seek a theoretical justification. In the first section, a review of the principal results obtained is presented. The second part concerns the new test programme; the validity of the bibliographic criteria end of the proposed method is discussed. A theoretical justificeion of the dimensioning method presented is proposed, as well as its conditions end its limits of utilization. Detection of bending fatigue life of steel by magnetic method. K., Yoshinaga, A., Nakano, M. and Okazaki, Y. Hihakai Kensa (J. ND/l Aug. 1989 36, (8). 671-676(in Japanese)
Endo,
Non-destructive detection of the progress of fatigue in steel at an early staae is important not only for prevention df fatigue fr&ture but also for St&y or the mechanism of the fatigue phenomenon. Onlv the ‘X-rev method’ is normallv used. The torsional fatigue-of &eel is studied b; means df the magnetic metjlod to establish the non-destructive method for detection of fatigue in an early stage. A method of reception end processing of the magnetic output signal, end relations between the processed magnetic date and the bending fatigue life are presented. The experimental results show that this magnetic method, using both the hysteresis end the harmonics of magnetic signal, is very useful in detecting the progress of bending fatigue in steel. 4 refs.
303
e model for thermal
B.
fatigue
Thermal fatigue of MAR-M509, a typical cast superallov for vanes in jet engines, was previously shown to involve mainly crack propagation which is strongly influenced bv oxidation. Crack orooaoation was so modelled using demeae eauetions which are based on local stredses iha volume element at the crack tip.-The.volume element at the crack tip wes taken as the secondary dendrite size, a materiel constant. Local stresses ahead of the crack were estimated from Tracev’s finite element analysis of plane strain small scale yielding which was adapted to a cyclic loading using Rice’s hypothesis. A fatigue damage equation was fitted to fatigue crack growth data measured et high frequency on CT specimens, which accounts for load ratio effects. High temperature oxidation of precrecked CT specimens induced embrittlement et medium temperatures ahead of the oxidized precreck. The critical stress to fracture was found to increase with increasing distance from the oxidized crack tip and to depend on oxygen diffusion end on interdendritic oxide depth, which can be easily measured by quentitetive metallography on oxidized specimens. Damage equations were then derived for isothermal fatigue end thermal fatigue crack growth; all the parameters involved were fitted to the experiments on virgin end pre-oxidized CT specimens. These equations were used to compute the isothermal fatigue life et 900 “C to 0.3 mm crack depth end the propagation rate of thermal fatigue cracks in wedge specimens and they were found to give reasonably good predictions in most cases. 31 refs. Stetisticel design of fatigue crack growth test programmer. G.C. and Hoeppner, D. W. ASTM J. Test. Eva/. Nov. 1988 16, (6). 508-515
Sal&v,
experimental design method for determining statistically significant differences in fatigue crack growth rate date due to the influence of various test conditions (factors) is presented. This method is based on a completely randomized factorial design end a three-way classification analysis of variance (ANOVA) procedure. Although the example presented is for fatigue crack growrh rate testing, this method is generic to any materiels test programme where comparisons of properties or behaviour are made. The procedure allows decisions regarding these comparisons to be based on statistical tests of significance. Steel SA533B-1 was tested. 18 refs. An
Fatigue crack growth from an artificial flaw. Taggart, R., Ramulu, M. and Jolly, T. Mater. Sci. Eng. A 1 Nov. 1989 A119, (l-2). 73-80 The crack growth characteristics of physically short cracks have been examined under cyclic load conditions. These short cracks were nucleated from artifice1 flaws that had been induced symmetrically in a keyhole-notched compact-type specimen of Al ellov 7075-l735. The fetioue crack arowth rate is shown to be a function of flaw dep&. A limit to short-crack behavioir is predicted in terms of flaw depth. A transition from short- to long-crack behaviour is observed for crack lengths between l.O-3.0mm. The effect of residual stresses created bv the introduction of the artificial flew is discussed. Fatigue crack morphology in terms of microstations end flew depth is also considered. 39 refs.
Crack initiation mechanisms in low cycle fatigue 7675 T6. Li, P., Marchand, N.J. and Ilschner, 13. Mater. Sci. Eng. A 1 Nov. 1989 Allg, (l-2). 41-50
of aiuminium
Influence of environmental variables and intermittent overloadin s on fatigue crack growth in on-boerd NGV cylinder steel. Bhuyan, G. 8, and Brezden, W. J. Int. J. Pressure Vessel Piping 1989 40, (2). 139- 149 Fatigue creek growth rates in the on-board compressed natural gas (CNG) steel cvlinder IAISI 4130X oredel were obtained in air end in the simulated natural oas environment. Effects if loading frequency (1.0, 0.1 end 0.01 Hz) on corrosion fatigue crack growth rates were investigated. The maximum crack growth rate in the modified solution was -60 times the rate in air. A maximum corrosion-assisted cracking rate of 2.0 x lo-’ m/s was obtained. Retardation of fatigue crack growth was observed after the overloadings, equivalent to the present requalification tests of the on-board steel CNG cylinders. Ratio of the experimentally determined overload effected zone to the cyclic plane strain plastic zone varied from 0.85-1.91. 7 refs. ($tAyip
fatigue strength of ductile cast irons through surface rolling. rB Karser, B. and Adelmann, J. Konsir. &ssen 1989 14, (11, 4-10 (in German)
Experimental test results are reported on two peerlitic cast irons containing 2.6 carbon, 1.4 Si end 3.4 C, 2.2 Si leg GGGGO,GGG65-02) respectively. They confirm the well-known fatigue properties of surface rolled parts. This roll strengthening procedure produced only minor increases in the fatigue strength of unnotched specimens, but had such a pronounced effect on notched specimens that the notch effect could be completely neutralized. Compared with steel,‘higher fatigue to tensile strength ratios were obtained, especially for smeller test bar diameters. The cast iron specimens had only minor responses to deviations from optimum rolling conditions, but the results showed a much larger well thickness effect on the strength characteristics when compared with steel. The enormous gain in fatigue strength of the notched bars was bought et the expense of incipient cracks at notch roots. These incipient cracks lowered the statistical strength reserve of the specimens to about double the fatigue strength. In surface rolling critical parts subjected to design/load peaks in service, adequate safety factors must be considered. 5 refs. Fatigue-creep life prediction of 2.26Cr-1Mo steel by inelastic analysis. Inoue, T., Igari, T., Okazaki, M., Sakane, M. and Tokimasa, K. Nucl. Eng. Des. June 1989 114, (3). 311-321 The life prediction methods under fatigue-creep interaction are covered by taking into account the plasticity-creep interaction described by the constitutive models in a previous publication. By specifying a normalized end tempered 2.25Cr-1Mo steel at 600 “C, uniexiel fatigue-creep tests under six patterns of strain waves ere performed. Adopting eight types of life estimation methods, two kinds of life prediction procedures are examined: one is a normal way, based on an experimentally obtained stress-strain hysteresis loop; the other is a way of employing the calculated stress-strain hysteresis loop by use of ten types of constitutive models. Predicted lives of the material are compared with observed failure lives, end dicussions on the evalution of the methods are included. 18 refs.
alloy
Testing and control
Fully reversed strain-controlled push-pull tests were performed on polycrystelline specimens of Al alloy 7075 T6 to investigate the influence of temperature end strain amplitude on the micromechanisms of cyclic plastic deformation end crack initiation. The tests were carried out between 20-260 “C in the strain range 0.&2.4%. Goldelated reolicas end scennina electron microscoov were used to detect crack initiation i& - 10 ;m) end microcrack growth. The re&ts showed the crack initiation life IN;) to be a fraction of the total life (Ntl. The ratios HIi% were found to be independent of the strain amplitude in ;he strain range investigated end to vary with temperature only. Transmission electron microscopy results indicated that the cyclic behaviour is controlled either by the evolution of the dislocation substructures at low temperature (with cycling) or by the changing morphology and distribution of the precipitates et elevated temperatures. The kinetics of dissolution and precipitation were shown to be influenced strongly by cyclic plastic strain. This entails that the results of precipitation kinetics studies cannot be used to rationalize the changes in precipitation morphology end distribution occurring in higher temperature, low cycle fatigue testing. Finally. the occurrence of any of the three fevoured sites for creek initiation is shown to correlate with the plastic-to-total strain ratio (Aq,/Att).
alone proved to be Conservative when compared with smooth specimen test results to such an extent that Neuber-generated notch stresses end strain amplitudes cannot accurately be compared with the mean date curves derived from the ASME Section III fatigue curves for carbon steels which are based on net section stress meas”rements. 37 refs.
Fatigue crack growth automated testing method. Hatch, P.W., Van DenAvyle, J.A. and Laing, J. Sandia National Laboratories Report No. DE89014352/XAB June 1989 PP 45 A computer controlled servo-hydraulic mechanical test system has been configured to conduct automated fatigue crack growth testing. This provides two major benefits: it allows continuous cycling of specimens without operator attention over evenings end weekends; end complex load histories, including random loading end spectrum loading, can be applied to the specimens to simulate cyclic loading of engineering structures. The software is written in MTS Multi-User Basic to control test machine output end acquire date et predetermined intervals. Compact tension specimens are cycled according to ASTM specification EE47-86. Fatigue crack growth is measured vie specimen compliance during the test using a compliance/crack length calibration determined earlier by visual crack length measurements. This set-up was used to measure crack growth rates in 6063 Al alloy for a variety of cyclic loadings, including spectrum loads. Date collected compared well with tests run manually.
21 rafs.
Stress cottcentrations and the Mott mechanism Jackson, P.J. Mater. Sci. Eng. A 1 Nov. 1989 A119, (l-2). l-6
in fatigue
failure.
The tensile stress across a persistent slip bend in a fatigued specimen is considered, It is demonstrated that the stress concentration produced by a fatigue crack promotes the circulation of screw dislocations around the crack end that the direction of circulation is such as to punch the crack deeper into the materiel prismatically. It is suggested that extrusions, intrusions end cracks are produced by the Mon mechanism, driven by stress concentrations. Examples of Cu are given. 27 refs.
Useof Nwber’srule to estimate the fati ue life of notched specimens of ASME SA 166-B steel pipin in 286 Y? air. Terrefl, J.8. Int. J. Pressure Vessels Piping P989 40, (11, 17-40 Fatigue strain-life tests were conducted on notched specimens of ASME SA 106-B piping steel et PWR operating temperatures (288°C). under completely reversed loading. Fatigue limits et 10’ cycles were estimated for smooth specimens to be 185 MPa (26.8 ksil et 24°C and 232 MPa (33.7 ksi) at 288°C. The higher fatigue strength observed at the PWR temperature is postulated to be caused by dynamic strain egeing processes. However, a reduction in fatigue strength in the low cycle fatigue regime was .observed in 288 “C air environment tests, which may indicate that the current ASME Section III design curve for carbon steels is non-conservative in its positioning. Notch strain histories were estimated for the notched specimen tests using various interpretations of Neuber’s rule. It was concluded that the use of the fatigue notch concentration factor (Kfl in the Neuber relation in conjunction with the uniexial cyclic stress-strain curve provided the best correlation of notched specimen fatigue date with results obtained from smooth specimen tests. The notched specimen strain-life results derived from the application of Neuber’s rule
Int J Fatigue July 1990
Fati ue of steels under combined stresses: application to steel 30 NCD 16. e roustey, C. and Lassere, S. fcole Nationale Superieure des Arts et Metiers de Paris Report No PB8922315WXAB Oct. 1988 pp 44 (in French) A new test programme was undertaken with the following objectives: to verify if a static torsion stress has no effect on other types of loads; to determine for these tests at different frequencies the flexion end torsion amplitudes which are acceptable when the average flexion value is not zero; to specify the utilization limits of the various critierie; to confirm or not the dimensioning method end, if this method proves itself to be viable, to seek a theoretical justification. In the first section, a review of the principal results obtained is presented. The second part concerns the new test programme; the validity of the bibliographic criteria end of the proposed method is discussed. A theoretical justificeion of the dimensioning method presented is proposed, as well as its conditions end its limits of utilization. Detection of bending fatigue life of steel by magnetic method. K., Yoshinaga, A., Nakano, M. and Okazaki, Y. Hihakai Kensa (J. ND/l Aug. 1989 36, (8). 671-676(in Japanese)
Endo,
Non-destructive detection of the progress of fatigue in steel at an early staae is important not only for prevention df fatigue fr&ture but also for St&y or the mechanism of the fatigue phenomenon. Onlv the ‘X-rev method’ is normallv used. The torsional fatigue-of &eel is studied b; means df the magnetic metjlod to establish the non-destructive method for detection of fatigue in an early stage. A method of reception end processing of the magnetic output signal, end relations between the processed magnetic date and the bending fatigue life are presented. The experimental results show that this magnetic method, using both the hysteresis end the harmonics of magnetic signal, is very useful in detecting the progress of bending fatigue in steel. 4 refs.
303