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Movement stress of bellows subjected to displacement loading of various kinds
Fatigue Abstracts surface in dry air, and the occurrence of various crack paths such as rolling plane delamination under unstable passivation potential. The difference between environmental crack closures under stable and unstable passivation conditions is discussed in terms of environment-assisted crack-tip damage processes. Graphs. photomicrographs, 16 ref.
Fatigue crack growth from two-dimensional surface defects Shuter, D.M. and Gearv, W. Fatigue Fraet. Eng. Mater. Struct. (1995) 18 (6), 6 5 3 ~ 5 9 The growth of semi-elliptical cracks emanating from single surface defects under cyclic bending loading conditions has been investigated. Experiments to determine crack shape development during fatigue have been conducted on specimens containing spark-machined starter defects of various shapes and sizes. The results appear to indicate that the size and shape of the initial starter defect only affects the developing crack shape until the crack depth is approx 20% of the specimen thickness; upon reaching this depth, all crack shapes (independent of initial size and shape) appear to be very similar. A mathematical model, based on the Newman and Raju stress intensity solution for semi-elliptical cracks, has been utilized to predict effectively the shape of the cracks developing from the various single starter defects with aspect (a/c) ratios as large as 3. Graphs, photomicrographs, 6 ref.
The low-cycle fatigue life prediction at medium temperature for a pressure vessel with large opening Guo, Y.-Z. and Zeng, Z.-J. Int. J. Pressure Vessels Piping (1995) 62 (2). 167-170 In this paper, according to experimental results from strain gauge measurements on a large opening in a pressure vessel and material properties at medium temperature, the fatigue crack initiation life and propagation life of the pressure vessel at the working temperature are evaluated. The results provide a convenient and reliable method for the low-cycle fatigue life prediction at medium temperature for pressure vessels with large openings. Graphs, 6 ref.
Movement stress of bellows subjected to displacement loading of various kinds Li, T., Luo, X. and Li, T.X. Int. J. Pressure Ve,s~els Piping (1995) 62 (21, 171-177 When a bellows is subjected to axial movement the maximum meriodional stress of each longitudinal line per convolution is the same, but there would be a great difference if lateral deflection or angular rotation were applied. The corresponding formulae for the last situation are deduced in this paper and testified by our experiment. These formulae are suitable to be used in engineering projects. This paper also points out that the maximum meridional stress is larger than the circumferential stress for each kind of displacement loading. The maximum meridional stress usually lies in the root of the convolution. These maximum stress points are usually the dangerous areas for bellows tbfigue failure. Graphs, 2 ref.
Fatigue crack growth and closure at high stress ratios Tsukuda, H., Ogiyama, H. and Shiraishi, T. Fatigue Fraet. Eng. Mater. Struct. (1995) 18 (4), 503-514 Fatigue crack growth tests have been carried out on a medium carbon structural steel over a wide range of stress ratios, i.e. from 0 to 0.7. All tests were conducted under constant-amplitude loading conditions corresponding to growth rates in the Paris regime. Crack closure behaviour was observed experimentally by a surface strain gauge technique, and numerically by a finite element analysis under plane stress condition. While the crack closure could not be detected by experimental measurements at stress ratios /> 0.5. the numerical results showed that closure occurred even at high stress ratios up to 0.7. The differences between experimentally and numerically determined crack opening levels were found for each stress ratio. A cause for these differences is discussed. In addition, two new types of crack tip parameters which have been proposed recently are evaluated by finite element analysis and their relevance to fatigue crack growth is discussed. It is concluded that fatigue crack growth rates are substantially determined by the effective stress intensity factor range, which is based on the crack closure concept. Graphs, 28 ref.
Propagation behaviour of short fatigue cracks in Q2N steel Wu, X.J. and Akid, R. Fatigue Fraet. Eng. Mater. Struet. (1995) 18 (4), 443-454 The work described in this paper characterizes short fatigue crack growth behaviour of Q2N steel having a complex microstructure and designated tbr pressure vessel and offshore structure applications. Short and long fatigue crack growth tests for this steel were conducted under three-point bend loading conditions. It was lound that in the initial stages of growth, short cracks propagate much faster than those of long cracks when correlated with the linear elastic fracture mechanics (LEFM) parameter AK. A period of crack growth retardation was observed at crack lengths of approx 50 I.Lm. The theory of the interaction between short cracks and grain boundaries fails to predict the occurrence of this deceleration minimum. A new short crack deceleration mechanism is proposed based on experimental observation. Observation of lhe characteristic behaviour of short cracks allowed the development of a short crack growth model based on microstructural fracture mechanics analyses. Photomicrographs, graphs, 30 ref.
421
Fatigue properties of austempered ductile cast iron at room and elevated temperatures Fukuyama, K., Hasegawa, N. and Inaba, K. J. Soc. Mater. Sci., Jpn. (1995) 44 (501), 776-781 (in Japanese) Rotating bending fatigue tests of smooth specimens were carried out using an austempered ductile cast iron (ADI, Fe-3.61C-2.09Si-0.66Cu-0.35Mn and Fe-3.66C-2.12Si~).58Cu~l.31Mn) in the temperature range between room temperature and 400°C. In order to clarify the fracture origin, the fracture surfaces were investigated by SEM. The amount of retained austenite was measured by X-ray diffraction method. The fatigue limit reached maximum at approx 300°C owing not only to the transformation of retained austenite but also to the cyclic strain ageing. The retained austenite transformed at 350400°C. Owing to the surface hardening by the transformation and strain ageing, most of the cracks caused at elevated temperatures initiated at the location of internal defects. Graphs, photomicrographs, 31 ref.
Fracture in high temperature fatigue of cast intermetallic compound TiAI Tsutsumi, M., Ohtani, R., Kitamura, T. Takano, S. and Ohshima, T. J. Soe. Mater. Sci., Jpn. (1995) 44 (501). 769-775 (in Japanese) The effects of total strain range and test temperature on the fatigue life of a cast intermetallic compound, Ti-34wt.% AL which possesses a lamellar structure, "), + ot 2, were investigated. The behaviours of initiation and propagation of small cracks were observed in the smooth bar specimens subjected to push-pull cyclic loading. The results observed are summarized as follows: (I) A small amount of inelastic strain is observed even in fatigue under high strain range up to 1%. The fatigue life is sensitive to the total strain range. (2) The fatigue life shows a positive temperature dependence. (3) Small cracks observed on/near the surface of specimens are classified into three types: Type A cracks, which initiate from defects introduced during casting process and form a main crack in fatigue < 1073 K; Type B cracks, which initiate along an interface of lamellae being parallel to the stress axis and are blocked by grain boundaries never to grow as a long crack; Type C cracks, which initiate from the cracking of the surface oxide layer and bring numerous fracture sites in the matrix > 1173 K. (4) Although the initiation and early propagation of Type A cracks show an eminent fluctuation caused by the distribution of casting defects and the orientation of lamellar structure, they are followed by a continuous propagation with an increase in crack length. Therefore, Type A cracks are typical of this material whereby the fatigue fracture is brought about at the early stage of life. Graphs, photomicrographs, 8 ref.
Fatigue design data and concepts of aluminium structures. 1II Takeuehi, K Kei Kinzoku Yosetsu (J. Light Met. WeM. Constr.) (1995) 33 {3), 37-45 The third in a series of fatigue property data for AI alloys is given. Fatigue test results and calculations are investigated. Tabulated fatigue data for various AI alloys are provided along with S N curves for welded joints of AI alloys. Graphs. 14 ref.
Fatigue crack initiation of Nb monocrystals and its mechanism during cyclic deformation Wu, J.S. and Lin, D.L. Aeta Metall. Sin. (China) (1995) 31 (2), Ag0-A96 Optical microscopy, SEM and TEM have been used to observe the morphological changes at the surface of fatigued Nb monocrystals and the saturated dislocation structure. It reveals that fatigue crack initiation is related to the deformation band at the specimen surface, and cracks initiate easily at the common fold area of the double deformation bands if the slip lines and deformation bands are parallel to each other. It is also found that the initiated cracks show the behaviour of cross-slips, and the steps due to cross-slips locate mostly in the vicinity of the initiated cracks. Based on our experimental results, a mechanism, which is the modification of the famous Mott model,is given to explain theoretically the initiation of fatigue cracks. In other words, the experimental results confirm the Mott model in general. Photomicrographs, 7 ref.
Initiation and propagation of short fatigue cracks in steel 45 Xu, H. and Wu, Z.X. Acta Metall. Sin. (China) (1995) 31 (2). A85-A89 The overall evolution for initiation and propagation of short fatigue cracks in smooth specimen of steel 45 was observed under optical microscope by using the replication technique. The short crack initiation life is < 10% of the failure one. According to the cracking rate, the growth of short cracks may separate into two stages, i.e. microcrack and physical crack, of which the characteristic values of crack size and the equations of growth rate to identify them are given. Graphs, 2 ref.
Mechanical properties and microstructures of two Ni~AI alloys Li, G., Wang, Z.G., Guo, J.T., Tan, M.H. and Shi, C.X. Acta Metall. Sin. (Chinal (1995) 31 (2), A64-A68 The microstmctures and mechanical properties of two polycrystalline alloys, an Ni~Al(0.6at.%B) alloy and an Ni3Al(l.0at.%B) alloy (Ni-24.2AI~).61B and Ni-23.74AI~).98B) are studied. The Ni3AI(O.6B) is a single-phase alloy whereas the Ni3AI(I.0B) consists of a few boride eutectics at the grain boundaries. Tensile tests and high-cycle fatigue tests at room temeprature are carried out in air. The results indicate that the fatigue resistance of the Ni3AI(0.6B) alloy is higher than that of the Ni~AI(1.0B) alloy, although the latter is much higher than the former in tensile strength. The characteristics
Fatigue crack growth from two-dimensional surface defects Shuter, D.M. and Gearv, W. Fatigue Fraet. Eng. Mater. Struct. (1995) 18 (6), 6 5 3 ~ 5 9 The growth of semi-elliptical cracks emanating from single surface defects under cyclic bending loading conditions has been investigated. Experiments to determine crack shape development during fatigue have been conducted on specimens containing spark-machined starter defects of various shapes and sizes. The results appear to indicate that the size and shape of the initial starter defect only affects the developing crack shape until the crack depth is approx 20% of the specimen thickness; upon reaching this depth, all crack shapes (independent of initial size and shape) appear to be very similar. A mathematical model, based on the Newman and Raju stress intensity solution for semi-elliptical cracks, has been utilized to predict effectively the shape of the cracks developing from the various single starter defects with aspect (a/c) ratios as large as 3. Graphs, photomicrographs, 6 ref.
The low-cycle fatigue life prediction at medium temperature for a pressure vessel with large opening Guo, Y.-Z. and Zeng, Z.-J. Int. J. Pressure Vessels Piping (1995) 62 (2). 167-170 In this paper, according to experimental results from strain gauge measurements on a large opening in a pressure vessel and material properties at medium temperature, the fatigue crack initiation life and propagation life of the pressure vessel at the working temperature are evaluated. The results provide a convenient and reliable method for the low-cycle fatigue life prediction at medium temperature for pressure vessels with large openings. Graphs, 6 ref.
Movement stress of bellows subjected to displacement loading of various kinds Li, T., Luo, X. and Li, T.X. Int. J. Pressure Ve,s~els Piping (1995) 62 (21, 171-177 When a bellows is subjected to axial movement the maximum meriodional stress of each longitudinal line per convolution is the same, but there would be a great difference if lateral deflection or angular rotation were applied. The corresponding formulae for the last situation are deduced in this paper and testified by our experiment. These formulae are suitable to be used in engineering projects. This paper also points out that the maximum meridional stress is larger than the circumferential stress for each kind of displacement loading. The maximum meridional stress usually lies in the root of the convolution. These maximum stress points are usually the dangerous areas for bellows tbfigue failure. Graphs, 2 ref.
Fatigue crack growth and closure at high stress ratios Tsukuda, H., Ogiyama, H. and Shiraishi, T. Fatigue Fraet. Eng. Mater. Struct. (1995) 18 (4), 503-514 Fatigue crack growth tests have been carried out on a medium carbon structural steel over a wide range of stress ratios, i.e. from 0 to 0.7. All tests were conducted under constant-amplitude loading conditions corresponding to growth rates in the Paris regime. Crack closure behaviour was observed experimentally by a surface strain gauge technique, and numerically by a finite element analysis under plane stress condition. While the crack closure could not be detected by experimental measurements at stress ratios /> 0.5. the numerical results showed that closure occurred even at high stress ratios up to 0.7. The differences between experimentally and numerically determined crack opening levels were found for each stress ratio. A cause for these differences is discussed. In addition, two new types of crack tip parameters which have been proposed recently are evaluated by finite element analysis and their relevance to fatigue crack growth is discussed. It is concluded that fatigue crack growth rates are substantially determined by the effective stress intensity factor range, which is based on the crack closure concept. Graphs, 28 ref.
Propagation behaviour of short fatigue cracks in Q2N steel Wu, X.J. and Akid, R. Fatigue Fraet. Eng. Mater. Struet. (1995) 18 (4), 443-454 The work described in this paper characterizes short fatigue crack growth behaviour of Q2N steel having a complex microstructure and designated tbr pressure vessel and offshore structure applications. Short and long fatigue crack growth tests for this steel were conducted under three-point bend loading conditions. It was lound that in the initial stages of growth, short cracks propagate much faster than those of long cracks when correlated with the linear elastic fracture mechanics (LEFM) parameter AK. A period of crack growth retardation was observed at crack lengths of approx 50 I.Lm. The theory of the interaction between short cracks and grain boundaries fails to predict the occurrence of this deceleration minimum. A new short crack deceleration mechanism is proposed based on experimental observation. Observation of lhe characteristic behaviour of short cracks allowed the development of a short crack growth model based on microstructural fracture mechanics analyses. Photomicrographs, graphs, 30 ref.
421
Fatigue properties of austempered ductile cast iron at room and elevated temperatures Fukuyama, K., Hasegawa, N. and Inaba, K. J. Soc. Mater. Sci., Jpn. (1995) 44 (501), 776-781 (in Japanese) Rotating bending fatigue tests of smooth specimens were carried out using an austempered ductile cast iron (ADI, Fe-3.61C-2.09Si-0.66Cu-0.35Mn and Fe-3.66C-2.12Si~).58Cu~l.31Mn) in the temperature range between room temperature and 400°C. In order to clarify the fracture origin, the fracture surfaces were investigated by SEM. The amount of retained austenite was measured by X-ray diffraction method. The fatigue limit reached maximum at approx 300°C owing not only to the transformation of retained austenite but also to the cyclic strain ageing. The retained austenite transformed at 350400°C. Owing to the surface hardening by the transformation and strain ageing, most of the cracks caused at elevated temperatures initiated at the location of internal defects. Graphs, photomicrographs, 31 ref.
Fracture in high temperature fatigue of cast intermetallic compound TiAI Tsutsumi, M., Ohtani, R., Kitamura, T. Takano, S. and Ohshima, T. J. Soe. Mater. Sci., Jpn. (1995) 44 (501). 769-775 (in Japanese) The effects of total strain range and test temperature on the fatigue life of a cast intermetallic compound, Ti-34wt.% AL which possesses a lamellar structure, "), + ot 2, were investigated. The behaviours of initiation and propagation of small cracks were observed in the smooth bar specimens subjected to push-pull cyclic loading. The results observed are summarized as follows: (I) A small amount of inelastic strain is observed even in fatigue under high strain range up to 1%. The fatigue life is sensitive to the total strain range. (2) The fatigue life shows a positive temperature dependence. (3) Small cracks observed on/near the surface of specimens are classified into three types: Type A cracks, which initiate from defects introduced during casting process and form a main crack in fatigue < 1073 K; Type B cracks, which initiate along an interface of lamellae being parallel to the stress axis and are blocked by grain boundaries never to grow as a long crack; Type C cracks, which initiate from the cracking of the surface oxide layer and bring numerous fracture sites in the matrix > 1173 K. (4) Although the initiation and early propagation of Type A cracks show an eminent fluctuation caused by the distribution of casting defects and the orientation of lamellar structure, they are followed by a continuous propagation with an increase in crack length. Therefore, Type A cracks are typical of this material whereby the fatigue fracture is brought about at the early stage of life. Graphs, photomicrographs, 8 ref.
Fatigue design data and concepts of aluminium structures. 1II Takeuehi, K Kei Kinzoku Yosetsu (J. Light Met. WeM. Constr.) (1995) 33 {3), 37-45 The third in a series of fatigue property data for AI alloys is given. Fatigue test results and calculations are investigated. Tabulated fatigue data for various AI alloys are provided along with S N curves for welded joints of AI alloys. Graphs. 14 ref.
Fatigue crack initiation of Nb monocrystals and its mechanism during cyclic deformation Wu, J.S. and Lin, D.L. Aeta Metall. Sin. (China) (1995) 31 (2), Ag0-A96 Optical microscopy, SEM and TEM have been used to observe the morphological changes at the surface of fatigued Nb monocrystals and the saturated dislocation structure. It reveals that fatigue crack initiation is related to the deformation band at the specimen surface, and cracks initiate easily at the common fold area of the double deformation bands if the slip lines and deformation bands are parallel to each other. It is also found that the initiated cracks show the behaviour of cross-slips, and the steps due to cross-slips locate mostly in the vicinity of the initiated cracks. Based on our experimental results, a mechanism, which is the modification of the famous Mott model,is given to explain theoretically the initiation of fatigue cracks. In other words, the experimental results confirm the Mott model in general. Photomicrographs, 7 ref.
Initiation and propagation of short fatigue cracks in steel 45 Xu, H. and Wu, Z.X. Acta Metall. Sin. (China) (1995) 31 (2). A85-A89 The overall evolution for initiation and propagation of short fatigue cracks in smooth specimen of steel 45 was observed under optical microscope by using the replication technique. The short crack initiation life is < 10% of the failure one. According to the cracking rate, the growth of short cracks may separate into two stages, i.e. microcrack and physical crack, of which the characteristic values of crack size and the equations of growth rate to identify them are given. Graphs, 2 ref.
Mechanical properties and microstructures of two Ni~AI alloys Li, G., Wang, Z.G., Guo, J.T., Tan, M.H. and Shi, C.X. Acta Metall. Sin. (Chinal (1995) 31 (2), A64-A68 The microstmctures and mechanical properties of two polycrystalline alloys, an Ni~Al(0.6at.%B) alloy and an Ni3Al(l.0at.%B) alloy (Ni-24.2AI~).61B and Ni-23.74AI~).98B) are studied. The Ni3AI(O.6B) is a single-phase alloy whereas the Ni3AI(I.0B) consists of a few boride eutectics at the grain boundaries. Tensile tests and high-cycle fatigue tests at room temeprature are carried out in air. The results indicate that the fatigue resistance of the Ni3AI(0.6B) alloy is higher than that of the Ni~AI(1.0B) alloy, although the latter is much higher than the former in tensile strength. The characteristics