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Fracture and fatigue crack propagation properties of hardened 52100 steel
representing different fractions of the ultimate strength of the material. A toughening mechanism is postulated that accounts for the interaction between the advancing crack front and the duplex microatructure which includes finely oriented manganese sulphide (MnS) stringers encapsulated in the ferrlte phase. Graphs, photomicrographs. 10 refL
Specific strain w o r k as both failure criterion end material damage
measure. Zuchowski, R. Res Mech. 1989 27, (4), 309-322
The difference between values of specific strain work needed for rupturing (at room temperature) the virgin specimen and that previously subjected to a loading process until a specified cycle number is reached is accepted as a material damage. A failure criterion and damage rule based on this concept are proposed. These assumptions were verified during the investigation in uniaxial and plane stress state in the conditions of thermal cycling, creep and fatigue, it was found that the proposed failure criterion is independent of stress, temperature, feilure mechanism and type of stress state, thus the suggested failure criterion was experimentally confirmed. The analysis of the results obtained showed that the growth of damage for a greater part of the loading range may be described (for a given material) with one equation, independently of stress, temperature, failure mechanism and type of stress state. This was proved by variance analysis. Materials studied were: carbon steel (40), and three auatenitic stainless steels (H23N18, H23N13, 50N17G17). Graphs. 15 refe.
nucleation and propagation have been studied in several kinds of gaseous environments. The variety of gaseous environments included Ar and oxygen, both dry and fully saturated with water vapour. This study of the effect of environment revealed that the environment is not the key factor in determining the crack nucleation mode. However, the mechanisms of crack propagation and fatigue life do depend on the environment. The main effect is due to O. Water vapour did not show a significant effect on its own. The presence of O increased the rate of propagation of cracks and, hence, reduced the fatigue life. Graphs, photomicrographs. 26 refs. Intormctallic alloys based on , / t i t a n i u m eluminide. Kim, Y.-W. JOM July 1989 41, (7), 24-30 Titanium aluminide alloys based on TiAI have an excellent potential to become one of the most important aerospace materials because of their low densiW, high melting temperature, good elevated-temperature strength end modulus retention, high resistance to oxidation and hydrogen absorption, and excellent creep properties. The chief obstruction to their application is poor ductility at low to intermediate temperatures that results in low fracture toughness end a fast fstigue-creck growth rate. During the last several veers, a great deal of effort has been made to improve these ductile properties. These endeevours have mat with some success through chemistry modification and microatructure control. Graphs, photomicrographs, phase diagrams. 61 refs.
High strain fatigue crack g r o w t h in nickel-heee alloys. Marchand, N. J.
and Pelloux, R. M. Res Mech. 1989 27, (4), 285-308 The application of different fracture mechanics data correlation parameters to the prediction of the isothermal fatigue crack propagation life of turbine engine hot section materials was evaluated. Both conventional linear and non-linesr fracture mechanics analyses were considered. Isothermal fatigue crock propagation tests were performed in Haatelioy-X and B-1900 + Hf materials at 400 and 925°C under elastic and fully plastic conditions. The fatigue crack growth data were reduced using the stress intensity factor, the strain intensity factor and the cyclic J-integral, None of these three parameters correlated the data successfully. The parameter which showed the best correlation was the modified stress intensity factor (M~) computed from the load, the closing bending moment caused by the change of compliance with crack length, and the effective opening stress. The resulting correlations were rationalized by the fact that fracture in Hastelloy-X and B-1900 + Hf is atress-beesd rather than strein-beesd. The main effect of an increasing strain range is to lower the opening stress. The compressive closure stresses at high strain ranges are explained in terms of the residual tensile stresses which are left in the wake of the growing crack. Graphs. 42 refs. On the orientation of cyclic-slip-induced intergranuler fatigue cracks in face-centred cubic m e t a l ~ Christ, H.-J. Mater. Sci. Eng. A Sept. 1989 A l 1 7 , (1-2), L25-L29 Cyclic deformation of FCC metals leads to intergrenular cracks even at low plastic strain amplitudes. Experimental observations indicate that most of these cracks are formed by the action of persistent slip bands against grain boundaries st the surface. Theoretical considerations are presented, allowing an estimate of the dependence of the crack frequency distribution (with respect to characteristic angles) on the environment and the magnitude of the plastic strain range ~,~¢. The theoretical results are compared with experimental observations on crack initiation carried out on polycryataliine Cu fatigued in air and in vacuum at different ~Ept. Graphs. 14 refs. Control o f intergrenuler fatigue cracking by slip h o m o g e n e i t y in copper: I. Effect of grain size. Liang, F.-L. andLaird, C. Mater. Sci. Eng. A Sept. 1989 A l 1 7 , (1-2), 95-102 Recent studies of long-life fatigue in polycrystslhne Cu have shown fractures to initiate primarily st grain boundaries. This is considered surprising in the light of early work where crack nucleation in persistent slip bands seemed to be the rule. To investigate the causes of this beheviour, studies have been carried out on polycrystalline Cu with emphasis on the following factors: grain size (Part I), method of starting the test, frequency and mode of test control (Part II). The results show that the cyclic plasticity is the controlling factor in grain boundary initiation and propagation of fatigue cracks. It was found that transgrsnular cracking can be produced by factors which promote strain Iocalizatton, and reducing the grain size of the specimens in constant-amplitude tests is one of them. In small-grain-sized metals, most of the applied plastic strain is concentrated in a few persistent slip bands, some of which develop into cracks with continued cycling. Use of coarsegrained structures causes strain homogenization and, therefore, intergranular cracking. For coarse-greined Cu, a step is gradually built up at a sensitive grain boundary as a result of the 'homogeneous' cyclic slip, at whtch point the cracking occurs in the same manner as proposed by Kim and Lard for high strain fatigue. Graphs, photomicrographs. 24 refs. Control of intergrenular fatigue cracking by slip h o m o g e n e i t y in copper: II. Effect of loading mode. Liang, F.-L. and Laird, C. Mater. Sci. Eng. A Sept. 1989 A l 1 7 , (1-2), 103-113 To investigate the causes of grain boundary crack nucleation in the region of low amplitude fatigue, studies have been carried out on polycrystalline Cu with emphasis on the factors of method of starting the test and mode of test control, The results show that grain boundary nucleation and propagation of fatigue cracks depend on the slip homogeneity. Those tests conducted in load or strain control, even at low amplitudes, homogenize the deformation and cause grain boundary failure. Tests started by ramp loading emphasize localized strain, persistent slip band formation and thus transgranular cracking. Trensgrsnular cracking can occur by either reducing the grain size of the specimens in constant-amplitude tests or by conducting the tests using a ramp-loading program. The conditions under which the early tests (1940s-1960s) were run emphasize such factors and explain the early transgranular results. Photomicrographs. 34 refs. The effect of e n v i r o n m e n t on the mechanism of fatigue crack initiation and propagation in polymltatalline copper. Liang, F.-L. and Laird, C. Mater. Sci. Eng. A Sept. 1989 A l 1 7 , (1-2), 83-93 To investigate the mechanisms of intergranular crack nucleation in the high cycle fatigue of oxygen-free high conductivity polycrystslline Cu, the details of crack
Int J Fatigue May 1990
The structure end properties of • gless-bottle mould made of SMRI-87 alloy cast iron. Li, C.-L Heat Treat. Met. (China) 1989 (2), 28-32 (in Chinese) The optimization of the material for a glass-bottle mould is studied. The test results show that using SMRI-87 alloy cast iron as the mould material improves the microstructure, mechanical properties, the anti-oxidation and hot fatigue resistance. An operation teat shows the service life of the mould is prolonged remarkably. Photomicrographs. 9 refe.
Creep end fatigue of • single-crystal (Dissertation). Bates, P. Diss. Abstr. Int. June 1989 49, (12), 331 pp
nickel
base
superalloy.
The introduction of single-crystal casting techniques has led to the development of existing Ni-beee superalloys to produce materials with optimum mechanical properties in the single-crystal condition. As single crystals are known to be anisotropic, a study is needed to determine the general mechanical properties of these materials, and determine the effects of crystal orientation upon them. A study has been carried out to identify the effect of orientation end temperature on the creep and fatigue properties of a single-crystal superslloy, SRR 99. Creep testing and crystal rotation experiments have been made on SRR 99 and an earlier developed alloy, SRR 9. Fatigue experiments st elevated temperatures have been carried out on both notched and un-notched specimens of alloy SRR 99. To aid in this analysis, several analytical techniques have been employed including Laue X-rey orientation analysis, measurement of strain by photographic methods and microstructursl examination. Crystal rotation experiments have indicated that shear of ~/' precipitates by {111}(112) slip systems is operative during primary creep deformation at temperatures of 750 and 850°C. The effect of orientation variation obtained by standard casting practices was not found to be significant. Creep rupture was found to be associated with multiple crack initiation from microporee. Fatigue crack inittation in un-notched specimens was found to be related to microporosity and microstructurel defects. Failure was predominantly by crystallographic crack growth on {111} planes. The use of linear elastic fracture mechanics to describe fatigue crack propagation in alloy SRR 99 was found to be acceptable at temperatures up to 850°C. Variation of temperature, frequency and crystal orientation was found to have only moderate effect upon crack propagation rates. Fracture and fatigue crack propagation pmpertiac o f hardened 52100
steel. Beswick, J. M. Metall. Trans. A Oct. 1989 20A, (10), 1961-1973
Good toughness in hardened 52100 bali bearing steel is important to prevent premature fracture during mounting or service of bearing elements. Steel cleanliness, residual Cu content, and carbon content effects have been investigated in relation to fracture mechanics properties, and it was observed that only the C content has any relevance for the range of compositions investigated. The effect of hardening and tempering temperatures for conventional furnace-hardening tecllniques on toughness was mvestigated, the Kic being generally much less sensitive to these parameters than blunt notch toughness testing. Cold deformation of the material prior to martensitic hardening significantly increased the blunt notch toughness. Thermal grain refinmg treatments did not give the same improved blunt notch toughness as observed for prior cold deformation. Short austenitization cycles (10 s) for martensittc hardening resulted in microstructures with high retained austenite contents. This microstructure resulted in higher fracture toughness and retardation of the crack growth rates, the mechanism being associated with transformation toughening in the plastic zone. Inductive tempering of martensitic-hardened 52100 was observed to result in similar blunt notch toughneeses as compared to furnace tempered material of the same hardness. A poor correlation between fracture toughness and blunt notch toughness was observed, particularly for the unstable structures, ie microstructures with high levels of retained austsnite. Fracture toughness does not represent the intrinsic toughness of high-C martensite with related high contents of retained austenlte. Graphs, photomicrographs. 37 refs.
On the cyclic J-integral applied to fatigue cracking. Chow, C. L. and Lu, T.J. Int. J. Fract. July 1989 40, (3), R53-R59 When extensive irreverstbie deformations occur ahead of the crack tip and and the small scale yielding (SSY) condition is violated, linear elastic fracture mechanics (LEFM) characterization of fatigue crack growth (FCG) breaks down and other parameters pertaining to elastic-plastic fracture mechanics which have potential abilities in characterizing fatigue crack growth beheviours must be used. The parameters ~,J and &Jowl can be used in FCG studies, &J being the better of the two. These defined parameters are used for characterizing steel, AI alloys, PVC, and PMMA to yield a master FCG diagram. Graphs. 20 refs.
227
Specific strain w o r k as both failure criterion end material damage
measure. Zuchowski, R. Res Mech. 1989 27, (4), 309-322
The difference between values of specific strain work needed for rupturing (at room temperature) the virgin specimen and that previously subjected to a loading process until a specified cycle number is reached is accepted as a material damage. A failure criterion and damage rule based on this concept are proposed. These assumptions were verified during the investigation in uniaxial and plane stress state in the conditions of thermal cycling, creep and fatigue, it was found that the proposed failure criterion is independent of stress, temperature, feilure mechanism and type of stress state, thus the suggested failure criterion was experimentally confirmed. The analysis of the results obtained showed that the growth of damage for a greater part of the loading range may be described (for a given material) with one equation, independently of stress, temperature, failure mechanism and type of stress state. This was proved by variance analysis. Materials studied were: carbon steel (40), and three auatenitic stainless steels (H23N18, H23N13, 50N17G17). Graphs. 15 refe.
nucleation and propagation have been studied in several kinds of gaseous environments. The variety of gaseous environments included Ar and oxygen, both dry and fully saturated with water vapour. This study of the effect of environment revealed that the environment is not the key factor in determining the crack nucleation mode. However, the mechanisms of crack propagation and fatigue life do depend on the environment. The main effect is due to O. Water vapour did not show a significant effect on its own. The presence of O increased the rate of propagation of cracks and, hence, reduced the fatigue life. Graphs, photomicrographs. 26 refs. Intormctallic alloys based on , / t i t a n i u m eluminide. Kim, Y.-W. JOM July 1989 41, (7), 24-30 Titanium aluminide alloys based on TiAI have an excellent potential to become one of the most important aerospace materials because of their low densiW, high melting temperature, good elevated-temperature strength end modulus retention, high resistance to oxidation and hydrogen absorption, and excellent creep properties. The chief obstruction to their application is poor ductility at low to intermediate temperatures that results in low fracture toughness end a fast fstigue-creck growth rate. During the last several veers, a great deal of effort has been made to improve these ductile properties. These endeevours have mat with some success through chemistry modification and microatructure control. Graphs, photomicrographs, phase diagrams. 61 refs.
High strain fatigue crack g r o w t h in nickel-heee alloys. Marchand, N. J.
and Pelloux, R. M. Res Mech. 1989 27, (4), 285-308 The application of different fracture mechanics data correlation parameters to the prediction of the isothermal fatigue crack propagation life of turbine engine hot section materials was evaluated. Both conventional linear and non-linesr fracture mechanics analyses were considered. Isothermal fatigue crock propagation tests were performed in Haatelioy-X and B-1900 + Hf materials at 400 and 925°C under elastic and fully plastic conditions. The fatigue crack growth data were reduced using the stress intensity factor, the strain intensity factor and the cyclic J-integral, None of these three parameters correlated the data successfully. The parameter which showed the best correlation was the modified stress intensity factor (M~) computed from the load, the closing bending moment caused by the change of compliance with crack length, and the effective opening stress. The resulting correlations were rationalized by the fact that fracture in Hastelloy-X and B-1900 + Hf is atress-beesd rather than strein-beesd. The main effect of an increasing strain range is to lower the opening stress. The compressive closure stresses at high strain ranges are explained in terms of the residual tensile stresses which are left in the wake of the growing crack. Graphs. 42 refs. On the orientation of cyclic-slip-induced intergranuler fatigue cracks in face-centred cubic m e t a l ~ Christ, H.-J. Mater. Sci. Eng. A Sept. 1989 A l 1 7 , (1-2), L25-L29 Cyclic deformation of FCC metals leads to intergrenular cracks even at low plastic strain amplitudes. Experimental observations indicate that most of these cracks are formed by the action of persistent slip bands against grain boundaries st the surface. Theoretical considerations are presented, allowing an estimate of the dependence of the crack frequency distribution (with respect to characteristic angles) on the environment and the magnitude of the plastic strain range ~,~¢. The theoretical results are compared with experimental observations on crack initiation carried out on polycryataliine Cu fatigued in air and in vacuum at different ~Ept. Graphs. 14 refs. Control o f intergrenuler fatigue cracking by slip h o m o g e n e i t y in copper: I. Effect of grain size. Liang, F.-L. andLaird, C. Mater. Sci. Eng. A Sept. 1989 A l 1 7 , (1-2), 95-102 Recent studies of long-life fatigue in polycrystslhne Cu have shown fractures to initiate primarily st grain boundaries. This is considered surprising in the light of early work where crack nucleation in persistent slip bands seemed to be the rule. To investigate the causes of this beheviour, studies have been carried out on polycrystalline Cu with emphasis on the following factors: grain size (Part I), method of starting the test, frequency and mode of test control (Part II). The results show that the cyclic plasticity is the controlling factor in grain boundary initiation and propagation of fatigue cracks. It was found that transgrsnular cracking can be produced by factors which promote strain Iocalizatton, and reducing the grain size of the specimens in constant-amplitude tests is one of them. In small-grain-sized metals, most of the applied plastic strain is concentrated in a few persistent slip bands, some of which develop into cracks with continued cycling. Use of coarsegrained structures causes strain homogenization and, therefore, intergranular cracking. For coarse-greined Cu, a step is gradually built up at a sensitive grain boundary as a result of the 'homogeneous' cyclic slip, at whtch point the cracking occurs in the same manner as proposed by Kim and Lard for high strain fatigue. Graphs, photomicrographs. 24 refs. Control of intergrenular fatigue cracking by slip h o m o g e n e i t y in copper: II. Effect of loading mode. Liang, F.-L. and Laird, C. Mater. Sci. Eng. A Sept. 1989 A l 1 7 , (1-2), 103-113 To investigate the causes of grain boundary crack nucleation in the region of low amplitude fatigue, studies have been carried out on polycrystalline Cu with emphasis on the factors of method of starting the test and mode of test control, The results show that grain boundary nucleation and propagation of fatigue cracks depend on the slip homogeneity. Those tests conducted in load or strain control, even at low amplitudes, homogenize the deformation and cause grain boundary failure. Tests started by ramp loading emphasize localized strain, persistent slip band formation and thus transgranular cracking. Trensgrsnular cracking can occur by either reducing the grain size of the specimens in constant-amplitude tests or by conducting the tests using a ramp-loading program. The conditions under which the early tests (1940s-1960s) were run emphasize such factors and explain the early transgranular results. Photomicrographs. 34 refs. The effect of e n v i r o n m e n t on the mechanism of fatigue crack initiation and propagation in polymltatalline copper. Liang, F.-L. and Laird, C. Mater. Sci. Eng. A Sept. 1989 A l 1 7 , (1-2), 83-93 To investigate the mechanisms of intergranular crack nucleation in the high cycle fatigue of oxygen-free high conductivity polycrystslline Cu, the details of crack
Int J Fatigue May 1990
The structure end properties of • gless-bottle mould made of SMRI-87 alloy cast iron. Li, C.-L Heat Treat. Met. (China) 1989 (2), 28-32 (in Chinese) The optimization of the material for a glass-bottle mould is studied. The test results show that using SMRI-87 alloy cast iron as the mould material improves the microstructure, mechanical properties, the anti-oxidation and hot fatigue resistance. An operation teat shows the service life of the mould is prolonged remarkably. Photomicrographs. 9 refe.
Creep end fatigue of • single-crystal (Dissertation). Bates, P. Diss. Abstr. Int. June 1989 49, (12), 331 pp
nickel
base
superalloy.
The introduction of single-crystal casting techniques has led to the development of existing Ni-beee superalloys to produce materials with optimum mechanical properties in the single-crystal condition. As single crystals are known to be anisotropic, a study is needed to determine the general mechanical properties of these materials, and determine the effects of crystal orientation upon them. A study has been carried out to identify the effect of orientation end temperature on the creep and fatigue properties of a single-crystal superslloy, SRR 99. Creep testing and crystal rotation experiments have been made on SRR 99 and an earlier developed alloy, SRR 9. Fatigue experiments st elevated temperatures have been carried out on both notched and un-notched specimens of alloy SRR 99. To aid in this analysis, several analytical techniques have been employed including Laue X-rey orientation analysis, measurement of strain by photographic methods and microstructursl examination. Crystal rotation experiments have indicated that shear of ~/' precipitates by {111}(112) slip systems is operative during primary creep deformation at temperatures of 750 and 850°C. The effect of orientation variation obtained by standard casting practices was not found to be significant. Creep rupture was found to be associated with multiple crack initiation from microporee. Fatigue crack inittation in un-notched specimens was found to be related to microporosity and microstructurel defects. Failure was predominantly by crystallographic crack growth on {111} planes. The use of linear elastic fracture mechanics to describe fatigue crack propagation in alloy SRR 99 was found to be acceptable at temperatures up to 850°C. Variation of temperature, frequency and crystal orientation was found to have only moderate effect upon crack propagation rates. Fracture and fatigue crack propagation pmpertiac o f hardened 52100
steel. Beswick, J. M. Metall. Trans. A Oct. 1989 20A, (10), 1961-1973
Good toughness in hardened 52100 bali bearing steel is important to prevent premature fracture during mounting or service of bearing elements. Steel cleanliness, residual Cu content, and carbon content effects have been investigated in relation to fracture mechanics properties, and it was observed that only the C content has any relevance for the range of compositions investigated. The effect of hardening and tempering temperatures for conventional furnace-hardening tecllniques on toughness was mvestigated, the Kic being generally much less sensitive to these parameters than blunt notch toughness testing. Cold deformation of the material prior to martensitic hardening significantly increased the blunt notch toughness. Thermal grain refinmg treatments did not give the same improved blunt notch toughness as observed for prior cold deformation. Short austenitization cycles (10 s) for martensittc hardening resulted in microstructures with high retained austenite contents. This microstructure resulted in higher fracture toughness and retardation of the crack growth rates, the mechanism being associated with transformation toughening in the plastic zone. Inductive tempering of martensitic-hardened 52100 was observed to result in similar blunt notch toughneeses as compared to furnace tempered material of the same hardness. A poor correlation between fracture toughness and blunt notch toughness was observed, particularly for the unstable structures, ie microstructures with high levels of retained austsnite. Fracture toughness does not represent the intrinsic toughness of high-C martensite with related high contents of retained austenlte. Graphs, photomicrographs. 37 refs.
On the cyclic J-integral applied to fatigue cracking. Chow, C. L. and Lu, T.J. Int. J. Fract. July 1989 40, (3), R53-R59 When extensive irreverstbie deformations occur ahead of the crack tip and and the small scale yielding (SSY) condition is violated, linear elastic fracture mechanics (LEFM) characterization of fatigue crack growth (FCG) breaks down and other parameters pertaining to elastic-plastic fracture mechanics which have potential abilities in characterizing fatigue crack growth beheviours must be used. The parameters ~,J and &Jowl can be used in FCG studies, &J being the better of the two. These defined parameters are used for characterizing steel, AI alloys, PVC, and PMMA to yield a master FCG diagram. Graphs. 20 refs.
227