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Influence of dynamic strain aging on the near-threshold fatigue crack growth behavior of a single crystal nickel-based superalloy
Fatigue Abstracts number of cycles to failure and the sulphidizing attack at the external surface were concerned. In both materials, the creep-fatigue propagation was directly controlled by the environmental attack of the SO2-containing environment at the region ahead of the crack tip. Graphs, photomicrographs, spectra, 8 ref.
Wear-related fatigue in a wire rope failure. Schrems, K.K. ASTM J. Test. Eval. (Sept. 1994) 22 (5), 490-499 The fatigue failure of a non-rotating wire rope used on a skip hoist in an underground mine has been studied as part of the ongoing research by the US Bureau of Mines into haulage and materials-handling hazards in mines. Correlation of individual wire failures within two segments of the failed rope were used to gain an understanding of the progression of degradation leading to rope failure. Wire failures occurred predominantly at locations of wear between adjacent strands. These inter-strand wear sites are identifiable by a large reduction in diameter; however, reduction in area is not responsible for the location of failure. Fractography revealed crack initiation sites to be located opposite the characteristic wear site or at other less noticeable wear sites. The primary failure mechanism of individual wires within the rope is believed to be a function of contact stress at the inter-strand wear sites. Axially loading and unloading the rope produces high compressive stresses at the contact sites, which in turn produce large alternating tensile stresses on the opposite side of the wire. This mechanism has been termed contact-stress-accelerated fatigue. This mechanism and the affiliated wear pattern are both consequences of interstrand contact. Graphs, photomcrographs, 22 ref.
Failure analysis for bolt guide die and its strengthening and toughening. Xiao, JZ. and Zhu, X.Q. Heat Treat. Met. (China) (Aug. 1994) 204 (8), 35-36, 45 (in Chinese) The failure mechanism of a bolt guide die made of Crl2MoV steel is analysed. The failure of bolt guide dies results from fatigue of materials causing stress concentration at the comer of the die. To improve the toughness of the dies, the heat treatment process is adjusted. After strengthening and toughening, the life of bolt guide dies is prolonged by ten times. Photomicrographs, 3 ref.
Effects of aging on the tensile and fatigue behavior of the near-alpha Til l 0 0 at room temperature and 593°C. Madsen, A. and Ghonem, H. Mater. Sci. Eng. A (15 Apr. 1994) A177 (1-2), 63-73 Long-term ageing of Ti-1100 alloy at its intended service temperature of 593°C results in the formation of two types of precipitate. Ti3AI and (TiZr)tSi3. The effect of ageing times corresponding to the conditions of unaged, peak-aged (10,000 min), and over-aged (<60,000min) on tensile behaviour is studied at two test temperatures: room temperature and 593°C. Ageing produces an increase in yield strength and a decrease in ductility at both test temperatures. The decrease in ductility is much more pronounced at room temperature than at 593°C. Ageing also suppresses the appearance of serrations associated with dynamic strain ageing in the plastic portion of the tensile curve at 593°C. However, another feature of dynamic strain ageing, namely a lack of strain rate effect on yield, is not substantially changed by the ageing process. The effect of ageing on fatigue crack growth rates (FCGR) at room temperature and 593°C is also examined. Ageing increases FCGR at room temperature but produces a slight decrease in FCGR at 593°C. Photomicrographs, graphs, 27 ref.
Cyclic stress-strain response of polycrystalline nickel. Morrison, D.J. and Chopra, V. Mater. Sci. Eng. A (15 Apr. 1994) A177 (1-2), 29-42 Constant plastic strain amplitude fatigue experiments were conducted at room temperature on polycrystalline nickel (290/zm grain size) at plastic strain amplitudes from 2.5 x 10-5 to 2.5 x 10-3. Cyclic deformation behaviour was characterized by analysing the cyclic hardening response, evaluating the evolution of the shape of the hysteresis loop, and optical and transmission electron microscopy observations. The results indicate that the cyclic stress-strain (CSS) curve has a pronounced bulge or region of reduced slope extending from a plastic strain amplitude of approx 2 x 10-4 to 8 x 10-4. This region of reduced slope is caused by the localization of plastic strain in persistent slip bands (PSBs). It is also shown that plastic strain amplitude has little influence on the friction stress of cyclically saturated Ni; however, the back stress increases with increasing plastic strain amplitude. A comparison of the cyclic deformation characteristics of polycrystalline Ni with those of Cu indicates that these materials exhibit similar fundamental cyclic behaviour on both a macroscopic and a microscopic level. Photomicrographs, 52 ref.
275
data show that crack growth occurs along the { l l l } ( t y p e planes, and both the extrinsic near-threshold and fatigue threshold are temperature independent up to 800 °C. Graphs, photomicrographs, 19 ref.
An engineering assessment of fatigue crack growth of irregularly oriented multiple cracks. Tu, S.-T. and Dai, S.-H. Fatigue Fract. Eng. Mater. Struct. (Oct. 1994) 17 (10), 1235-1246 Knowledge of the behaviour of interacting and irregularly oriented multiple cracks is very limited. The recharacterization roles for such cracks are usually empirical. In order to provide more reasonable rules for an engineering assessment of fatigue growth of irregularly oriented multiple cracks, this paper first studies the mechanics of fatigue growth of two-dimensional non-coplanar cracks. Uniaxial and biaxial fatigue testing on specimens with various multiple cracks are then carried out. Possible errors in the assessment of the cracks using the current rules are discussed. An improved procedure for the fatigue life assessment is developed. 16MnR is mentioned. Graphs, photomicrographs, 21 ref.
A fatigue design parameter for spot welds. Swellam, M.H.; Banas, G. and Lawrence, F.V. Fatigue Fract. Eng. Mater. Struct. (Oct. 1994) 17 (10), 1197-1204 Mode I and mode II stress intensity factors for two half-spaces connected by a circular patch were used to develop a mixed-mode stress intensity factor (termed the stress index K~), which can correlate the fatigue life of all spot weld geometries, base metals, and specimen dimensions. Empirical corrections were applied to Broek's equivalent stress intensity factor (K~cq) to account for the weldment geometry (sheet thickness, nugget diameter, specimen width) and the effect of mean stress. The final expression (Ki), is a measure of the notch-root stress field in the location where crack initiation and early crack growth occur. The stress index (Ki) should be a useful tool for spot-weld fatigue design. Graphs, 14 ref.
Effect of cyclic stress amplitude and mean stress on high temperature fatigue life of Ni3AI (B) alloy. Li, G., Guo, J., Wang, Z., Li, 1t. and Shi, C. Acta Metall. Sin. (China) (18 Sept. 1994) 30 (9), A427-A430, (in Chinese) High-temperature fatigue properties of a polycrystalline Ni3AI (0.6 at %B) alloy (Ni-23.93AI-0.57B), being brittle at an elevated temperature, were studied. The tension-tension fatigue tests under controlled loading were carded out in air at 450 °C. By fixing the maximum values of tensile stress in all tests but changing the minimum values of tensile stress in various tests, the effect of cyclic stress amplitude or mean stress and their interaction on the damage of materials may be differentiated. The results of cyclic stress amplitude and mean stress vs fatigue life are plotted as an 'S' shape and interpreted preliminarily. Graphs, 5 ref.
Low cycle fatigue behavior of polycrystailine NI3AI alloys at ambient and elevated temperatures. Webb, G. and Antolovich, S.D. Metall. Mater. Trans. A (Nov. 1994) 25A (11), 2469-2476 The low-cycle fatigue (LCF) resistance of polycrystalline Ni3A1 has been evaluated at ambient, intermediate (300 °C), and elevated (600 °C) temperatures using strain rates of 10-2s-~ and lO-4s-L Testing was conducted on a binary and a Cr-containing alloy of similar stoichiometry and B content (hypostoichiometric, 200 wppm B). Test results were combined with electron microscope investigations in order to evaluate microstructural changes during LCF. At ambient and intermediate temperatures, the cyclic constitutive response of both alloys was similar, and the LCF behaviour was virtually rate-independent. Under these conditions, the alloys rapidly hardened and then gradually softened for the remainder of the life. Initial hardening resulted from the accumulation of dislocation debris within the deformed microstructure, whereas softening was related to localized disordering. For these experimental conditions, crack initiation resulted within persistent slip bands (PSBs). At the elevated temperature, diffusion-assisted deformation resulted in a rate-dependent constitutive response and crack-initiation characteristics. At the high strain rate (10-2s-~), continuous cyclic hardening resulted from the accumulation of dislocation debris. At the low strain rate (10-4s-~), the diffusion of dislocation debris to grain boundaries resulted in cyclic softening. The elevated-temperature LCF resistance was determined by the effect of the constitutive response on the driving force for environmental embrittiement. Chromium additions were observed to enhance LCF performance only under conditions where crack initiation is environmentally driven.
Influence of dynamic strain aging on the near-threshold fatigue crack growth behavior of a single crystal nickel-hased superalloy. Sengupta, A. and Putatunda, S.K. Scr. Metall. Mater. (1 Nov. 1994) 31 (9), 1163-1168
Short fatigue crack growth behaviour in a ferritic-hainitic steel. Hussain, K., Tauqir, A., Hashmi, F.H. and Khan, A.W. Metall. Mater. Trans. A (Nov. 1994) 25A (11), 2421-2425
The addition of rhenium to the superalloy CMSX increases its hot corrosion resistance and high-temperature creep properties. Owing to its potential as a gas turbine blade material, a better understanding of its fatigue crack growth rate and fatigue threshold are required. These properties were studied, along with the effects of dynamic strain ageing, in the temperature range 650-800 °C. Single crystals of CMSX-4 (CMSX with 3% Rh) were grown in the [001 ] orientation and heat treated to produce cuboidal precipitates with an average size of 0.5 p,m and a volume fraction of 70%. Tensile tests were performed in the range 260-1204°C at a strain rate of 0.005 min-' to yield and then at 0.05 rain-' to failure. A second series was tested at 0.1 min-L Compact tension tests were used for fatigue threshold and crack growth rate measurements. The
Short fatigue crack growth behaviour was studied in a fcrrite-balnite microstructure in C-Mn steel with respect to microstroctural variations. Specimens were subjecWAi to cyclic loading at three different stress levels: 559, 626, and 687 MPa. The crack propagation rates varied from 10-4 to 10-2 p,m cycle-I. Crack lengths were measured using a replication technique. The growth rates were systematically decreased at microstrotural heterogeneities up to a length of 3-4 grain diameters. A two-stage short fatigue crack growth model previously developed by Hussaln et al. was modified to predict the crack growth behaviour. The calculated values were within 10% error of the experimentally determined results. The model was then used to present the effect of grain boundaries on cracks propagating at constant rates. It was shown that the mode of presentation
Wear-related fatigue in a wire rope failure. Schrems, K.K. ASTM J. Test. Eval. (Sept. 1994) 22 (5), 490-499 The fatigue failure of a non-rotating wire rope used on a skip hoist in an underground mine has been studied as part of the ongoing research by the US Bureau of Mines into haulage and materials-handling hazards in mines. Correlation of individual wire failures within two segments of the failed rope were used to gain an understanding of the progression of degradation leading to rope failure. Wire failures occurred predominantly at locations of wear between adjacent strands. These inter-strand wear sites are identifiable by a large reduction in diameter; however, reduction in area is not responsible for the location of failure. Fractography revealed crack initiation sites to be located opposite the characteristic wear site or at other less noticeable wear sites. The primary failure mechanism of individual wires within the rope is believed to be a function of contact stress at the inter-strand wear sites. Axially loading and unloading the rope produces high compressive stresses at the contact sites, which in turn produce large alternating tensile stresses on the opposite side of the wire. This mechanism has been termed contact-stress-accelerated fatigue. This mechanism and the affiliated wear pattern are both consequences of interstrand contact. Graphs, photomcrographs, 22 ref.
Failure analysis for bolt guide die and its strengthening and toughening. Xiao, JZ. and Zhu, X.Q. Heat Treat. Met. (China) (Aug. 1994) 204 (8), 35-36, 45 (in Chinese) The failure mechanism of a bolt guide die made of Crl2MoV steel is analysed. The failure of bolt guide dies results from fatigue of materials causing stress concentration at the comer of the die. To improve the toughness of the dies, the heat treatment process is adjusted. After strengthening and toughening, the life of bolt guide dies is prolonged by ten times. Photomicrographs, 3 ref.
Effects of aging on the tensile and fatigue behavior of the near-alpha Til l 0 0 at room temperature and 593°C. Madsen, A. and Ghonem, H. Mater. Sci. Eng. A (15 Apr. 1994) A177 (1-2), 63-73 Long-term ageing of Ti-1100 alloy at its intended service temperature of 593°C results in the formation of two types of precipitate. Ti3AI and (TiZr)tSi3. The effect of ageing times corresponding to the conditions of unaged, peak-aged (10,000 min), and over-aged (<60,000min) on tensile behaviour is studied at two test temperatures: room temperature and 593°C. Ageing produces an increase in yield strength and a decrease in ductility at both test temperatures. The decrease in ductility is much more pronounced at room temperature than at 593°C. Ageing also suppresses the appearance of serrations associated with dynamic strain ageing in the plastic portion of the tensile curve at 593°C. However, another feature of dynamic strain ageing, namely a lack of strain rate effect on yield, is not substantially changed by the ageing process. The effect of ageing on fatigue crack growth rates (FCGR) at room temperature and 593°C is also examined. Ageing increases FCGR at room temperature but produces a slight decrease in FCGR at 593°C. Photomicrographs, graphs, 27 ref.
Cyclic stress-strain response of polycrystalline nickel. Morrison, D.J. and Chopra, V. Mater. Sci. Eng. A (15 Apr. 1994) A177 (1-2), 29-42 Constant plastic strain amplitude fatigue experiments were conducted at room temperature on polycrystalline nickel (290/zm grain size) at plastic strain amplitudes from 2.5 x 10-5 to 2.5 x 10-3. Cyclic deformation behaviour was characterized by analysing the cyclic hardening response, evaluating the evolution of the shape of the hysteresis loop, and optical and transmission electron microscopy observations. The results indicate that the cyclic stress-strain (CSS) curve has a pronounced bulge or region of reduced slope extending from a plastic strain amplitude of approx 2 x 10-4 to 8 x 10-4. This region of reduced slope is caused by the localization of plastic strain in persistent slip bands (PSBs). It is also shown that plastic strain amplitude has little influence on the friction stress of cyclically saturated Ni; however, the back stress increases with increasing plastic strain amplitude. A comparison of the cyclic deformation characteristics of polycrystalline Ni with those of Cu indicates that these materials exhibit similar fundamental cyclic behaviour on both a macroscopic and a microscopic level. Photomicrographs, 52 ref.
275
data show that crack growth occurs along the { l l l } ( t y p e planes, and both the extrinsic near-threshold and fatigue threshold are temperature independent up to 800 °C. Graphs, photomicrographs, 19 ref.
An engineering assessment of fatigue crack growth of irregularly oriented multiple cracks. Tu, S.-T. and Dai, S.-H. Fatigue Fract. Eng. Mater. Struct. (Oct. 1994) 17 (10), 1235-1246 Knowledge of the behaviour of interacting and irregularly oriented multiple cracks is very limited. The recharacterization roles for such cracks are usually empirical. In order to provide more reasonable rules for an engineering assessment of fatigue growth of irregularly oriented multiple cracks, this paper first studies the mechanics of fatigue growth of two-dimensional non-coplanar cracks. Uniaxial and biaxial fatigue testing on specimens with various multiple cracks are then carried out. Possible errors in the assessment of the cracks using the current rules are discussed. An improved procedure for the fatigue life assessment is developed. 16MnR is mentioned. Graphs, photomicrographs, 21 ref.
A fatigue design parameter for spot welds. Swellam, M.H.; Banas, G. and Lawrence, F.V. Fatigue Fract. Eng. Mater. Struct. (Oct. 1994) 17 (10), 1197-1204 Mode I and mode II stress intensity factors for two half-spaces connected by a circular patch were used to develop a mixed-mode stress intensity factor (termed the stress index K~), which can correlate the fatigue life of all spot weld geometries, base metals, and specimen dimensions. Empirical corrections were applied to Broek's equivalent stress intensity factor (K~cq) to account for the weldment geometry (sheet thickness, nugget diameter, specimen width) and the effect of mean stress. The final expression (Ki), is a measure of the notch-root stress field in the location where crack initiation and early crack growth occur. The stress index (Ki) should be a useful tool for spot-weld fatigue design. Graphs, 14 ref.
Effect of cyclic stress amplitude and mean stress on high temperature fatigue life of Ni3AI (B) alloy. Li, G., Guo, J., Wang, Z., Li, 1t. and Shi, C. Acta Metall. Sin. (China) (18 Sept. 1994) 30 (9), A427-A430, (in Chinese) High-temperature fatigue properties of a polycrystalline Ni3AI (0.6 at %B) alloy (Ni-23.93AI-0.57B), being brittle at an elevated temperature, were studied. The tension-tension fatigue tests under controlled loading were carded out in air at 450 °C. By fixing the maximum values of tensile stress in all tests but changing the minimum values of tensile stress in various tests, the effect of cyclic stress amplitude or mean stress and their interaction on the damage of materials may be differentiated. The results of cyclic stress amplitude and mean stress vs fatigue life are plotted as an 'S' shape and interpreted preliminarily. Graphs, 5 ref.
Low cycle fatigue behavior of polycrystailine NI3AI alloys at ambient and elevated temperatures. Webb, G. and Antolovich, S.D. Metall. Mater. Trans. A (Nov. 1994) 25A (11), 2469-2476 The low-cycle fatigue (LCF) resistance of polycrystalline Ni3A1 has been evaluated at ambient, intermediate (300 °C), and elevated (600 °C) temperatures using strain rates of 10-2s-~ and lO-4s-L Testing was conducted on a binary and a Cr-containing alloy of similar stoichiometry and B content (hypostoichiometric, 200 wppm B). Test results were combined with electron microscope investigations in order to evaluate microstructural changes during LCF. At ambient and intermediate temperatures, the cyclic constitutive response of both alloys was similar, and the LCF behaviour was virtually rate-independent. Under these conditions, the alloys rapidly hardened and then gradually softened for the remainder of the life. Initial hardening resulted from the accumulation of dislocation debris within the deformed microstructure, whereas softening was related to localized disordering. For these experimental conditions, crack initiation resulted within persistent slip bands (PSBs). At the elevated temperature, diffusion-assisted deformation resulted in a rate-dependent constitutive response and crack-initiation characteristics. At the high strain rate (10-2s-~), continuous cyclic hardening resulted from the accumulation of dislocation debris. At the low strain rate (10-4s-~), the diffusion of dislocation debris to grain boundaries resulted in cyclic softening. The elevated-temperature LCF resistance was determined by the effect of the constitutive response on the driving force for environmental embrittiement. Chromium additions were observed to enhance LCF performance only under conditions where crack initiation is environmentally driven.
Influence of dynamic strain aging on the near-threshold fatigue crack growth behavior of a single crystal nickel-hased superalloy. Sengupta, A. and Putatunda, S.K. Scr. Metall. Mater. (1 Nov. 1994) 31 (9), 1163-1168
Short fatigue crack growth behaviour in a ferritic-hainitic steel. Hussain, K., Tauqir, A., Hashmi, F.H. and Khan, A.W. Metall. Mater. Trans. A (Nov. 1994) 25A (11), 2421-2425
The addition of rhenium to the superalloy CMSX increases its hot corrosion resistance and high-temperature creep properties. Owing to its potential as a gas turbine blade material, a better understanding of its fatigue crack growth rate and fatigue threshold are required. These properties were studied, along with the effects of dynamic strain ageing, in the temperature range 650-800 °C. Single crystals of CMSX-4 (CMSX with 3% Rh) were grown in the [001 ] orientation and heat treated to produce cuboidal precipitates with an average size of 0.5 p,m and a volume fraction of 70%. Tensile tests were performed in the range 260-1204°C at a strain rate of 0.005 min-' to yield and then at 0.05 rain-' to failure. A second series was tested at 0.1 min-L Compact tension tests were used for fatigue threshold and crack growth rate measurements. The
Short fatigue crack growth behaviour was studied in a fcrrite-balnite microstructure in C-Mn steel with respect to microstroctural variations. Specimens were subjecWAi to cyclic loading at three different stress levels: 559, 626, and 687 MPa. The crack propagation rates varied from 10-4 to 10-2 p,m cycle-I. Crack lengths were measured using a replication technique. The growth rates were systematically decreased at microstrotural heterogeneities up to a length of 3-4 grain diameters. A two-stage short fatigue crack growth model previously developed by Hussaln et al. was modified to predict the crack growth behaviour. The calculated values were within 10% error of the experimentally determined results. The model was then used to present the effect of grain boundaries on cracks propagating at constant rates. It was shown that the mode of presentation