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Fatigue strength of friction welded joints of AZ31 magnesium alloy
376
Abstracts
oxidation in the presence of H20 and CO2, they show some fatigue stress reduction. Silicon, manganese and chromium penetrate into the boundaries of austenite granules and enhance the heat treatment capabilities. An alternative to conventional case harding is shot peening, in which hard cast steel granular particles or cut steel wire parts are blasted against the working surface being treated. Other methods are hard shot peening and plasma hardening. These techniques are explained, with relevant illustrations and performance characteristics. Graphs, photomicrographs, 62 ref. Fatigue strength of friction welded joints of AZ31 magnesium alloy. Asahina, 7",. Katoh, K. and Tokisue. 14. J. J, Inst. Light Met. (Mar 1994) 44 (3), 147-151 (in Japanese) AZ31 magnesium alloy was friction welded using a brake-type friction welding machine under optimum welding conditions, such as PI= 50 MPa, tl = 5 s, P2= 100 MPa, and tz = 5 s. The fatigue tests were conducted by Ono's rotary bending tester for smooth and notched specimens and a Shenck-type repeated torsion fatigue tester for smooth specimens. In the rotary bending tests on the smooth specimens, both the fatigue strength and the fatigue ratio of the welded joints are lower than those of the base metal, irrespective of the number of cycles. The fatigue limit of the welded joint is 81.4% of that of the base metal. The fatigue strength of the welded joints with a notch at the weld interface is slightly lower than that of the base metal. The fatigue limit of the welded joint is 93. 1% of that of the base metal. The notched speciments show fatigue limit values lower than those of the smooth specimens for both base metal and welded joints. In repeated torsion fatigue tests, the fatigue strength of welded joints at a given endurance decreased in an almost linear manner with increasing number of cycles. The fatigue limit of the welded joints is 95.8% of that of the base metal. Without exception, the smooth specimens fractured at the weld interface, regardless of the method of test. For a given fatigue test, the smooth specimens of welded joints show nearly identical macro- and microfractorgraphs, independent of the number of cycles to failure. Graphs, photomicrographs, 10 ref. Microstructure-fatigue crack growth rate correlation in multipass submerged arc C - M n steel weld deposit. Ghosh. P.K.. Nagesh Babu, P. and Gupta. P.C. ISIJ Int. (1994) 34 (3), 280-284 All-weld blocks of C-Mn steel were prepared by multipass submerged are weld deposits, using different welding currents (500-750 A) and speeds (40-60 cm rain ~), filler wire of 4 mm diameter and a basic bonded type of flux. The dendrite content of the weld blocks was estimated by a quantitative metallography technique. The fatigue crack growth rate of the weld in the LT direction of the block was evaluated by using C-T specimens, and correlated with the area fraction of dendrite (Dr) of the matrix. The increase in dendrite content of the matrix was found to reduce the crack growth rate by influencing significantly the material constant C and exponent m of the Paris law, da/dN = c(AKm, where a is the crack length, N is the number of loading cycles and AK is the stress intensity factor range. The modification of C and m with Df was found to provide a satisfactory basis for evaluation of the fatigue crack growth rate of multipass C-Mn steel weld deposits with a given dendrite content. Graphs, photomicrographs, 5 ref. On improving the fatigue life of U-form bellows. Subramanian. G. and Raghunandan, C. J, Mater. Pprocess. Technol. (Feb. 1994) 41 (1), 105-114 Fatigue failure invariably occurs at the root in hydroformed bellows (austenitic stainless steels), as the hydroforming process does not cold-work the root region and raise the yield point there, as it does in other regions. Both elastic and plastic analyses confirm this by predicting that the yield criterion is first satisfied in the root region during deflection. On the other hand, the roll-forming process imparts a substantial amount of cold work to the root of the bellows. A judicious combination of hydroforming and roll-forming processes is examined here, therefore, as a viable alternative (as opposed to individual routes) for enhancing the fatigue life of austenitic steel bellows for low-pressure, low-temperature applications. This combination process has the added merit that bellows with extra-deep convolutions can be formed as replacements to costlier diaphram-type bellows, and for applications having space restrictions. While testing the bellows for fatigue, it is noted that corrugations do not share the total movement equally; this phenomenon appears to he a major cause for the scatter in values obtained in life tests. Investigation reveals that a correlation exists between this unequal sharing of movement of fatigue life. Based on these observations a new nondestructive stretch test is proposed with which original life estimates can be refined. Graphs, 6 ref, Correlation of fatigue crack growth rate at different stress ratios for quenched and tempered steels and other alloys. Robertson, I.M. Fatigue Fract. Eng. Mater. Struct. (Mar. 1994) 17 (3) 327-338 Measurements of the effect of stress ratio on the constant-amplitude fatigue crack growth rates in four quenched and tempered steels in the Paris regime arc reported. These data and publiscd data for other alloys (including lowerstrength steels and non-ferrous alloys) are evaluated, and a correlation function suitable for practical fatigue life calculations is derived. In addition to stress intensity factor range and stress ratio, other significant parameters are the yield stress of the material and its thickness. For the four steels on which new measurements were made, the degree of dependence of the crack growth rate on stress ratio may be related to sensitivity to environmental conditions. Graphs, 24 ref.
Fatigue crack growth in nickel-based superalloys at 500-700°C. If. Directaged Alloy 718. Lynch, S.P., Radtke, T.C., Wicks. B.J. and Bvrnes, R.T. Fatigue Fract. Eng. Mater. Struct. (Mar. 1994) 17 13), 313-32,~ The effects of cyclic frequency, hold time, and stress-intensity factor range (AK) on rates of fatigue crack growth in air at 500°C and 7(XI°C have been studied for the directed-age version of the nickel-based superalloy 718, The main effects were similar to those observed for Waspaloy (Part l), namely: (i) small effects of cyclic frequency and hold time at 500°C, (ii) higher rates of crack growth at lower cyclic frequencies at high AK at 7(gl°C, and (iii) lower rates of crack growth at low AK (and higher AK thresholds) for longer hold times at 700°C, For DA 718~ there was no increase in crack growth rates with increasing hold times ((I-60 s) at high AK at 700°C (unlike the large increases reported for standard processed Alloy 718). Metallographic and fractographic observations showed that crack growth was predominantly transgranular at 500°C. and predominantly intergranular at 700°C except at 2 Hz at high AK. The precise intergranular crack path, extent of branching, and fracture-surface appearance depended on AK, waveform and cycle period. The mechanisms responsible for the observed effects, and possible explanations for the different behaviour of DA 718 and standard processed Alloy 718, arc discussed. Graphs, photomicrographs, 21 ref. Fatigue crack growth in nickel-based superalloys at 500-700°C. 1. Waspaloy. Lynch, S.P., Radtke, T.C., Wicks, B.J. and Byrnes, R.T. Fatigue Fract. Eng. Mater. Struct. (Mar. 1994) 17 (3). 297-311 The effects of cyclic frequency, hold time, and stress-intensity factor range (AK) on rates of fatigue crack growth in air at 500-700°C have been studied for Waspaloy-a nickel-based supcralloy used for gas-turbine engine discs. The main effects observed were: (i) higher rates of crack growth for lower cyclic frequencies at high AK at 600 and 700°C, and (ii) lower rates of crack growth at low AK (and higher AK thresholds) for longer hold times at 700°C, compared with those at a baseline frequency of 2 Hz. Metallographic and fractographic observations suggested that the effects of cyclic frequency and hold time could be rationalized in terms of the competing effects of enhancement of cracking due to creep and inhibition of cracking caused by oxide-induced crack closure, fracture-surface roughness-induced crack closure, and crack-branching/deflection. Possible mechanisms for promoting intergranular and transgranular cracking at low cyclic frequencies or long hold times are discussed. Graphs, photomicrographs. 32 ref. The fatigue resistance of peened 7050-T7451 aluminum alloy. Sharp, P.K., Clayton, J.Q. and Clark, G. Fatigue Fract. Eng. Mater. Struct. (Mar. 1994) 17 (3), 243-252 Metal and glass-bead peening treatments, widely used throughout the aircraft industry to enhance the fatigue performance of many steels and titanium alloys, are not being routinely applied to high-strength aluminium-alloy components. This paper describes the effects of peening on the fatigue life of 7050 AI alloy material, which is representative of alloys used for many components in modern military aircraft. Using simulated service loading, two proposed peening/re-peening procedures were evaluated and compared with both the original peened surface and a simple hand-polished surface. The results show that optimization of peening parameters to reduce surface damage can provide a substantial improvement in fatigue life over both the original peening treatment and the polished surface treatment; however, poor control of peening procedures, or unnecessary "overpeening'. can lead to a relatively poor fatigue life. For re-peened surfaces, a procedure incorporating a polishing step, designed to repair any damage from the severe peening applied initially, gave the best fatigue performance. Results are discussed in relation to the stability of the residual surface stresses under fatigue loading, the surface roughness, and the number and types of defects introduced by the peening treatments. Photomicrographs, graphs, 13 ref. Corrosion-fatigue behavior of Ti-75 titanium alloy. Meng, L.. Huan. H. and Li. Z.C. Xivou Jimhu Cailiao yu Gongchenq (Rare Metal Materials and Engineering) IJ(me 1994) 23 (3), 40-44 (in Chinese) The unit of liquor automatic cycle is introduced, which is for the experiment of the corrosion-fatigue properties of Ti-75 titanium alloy. The fatigue limits determined in air and 3.5 wt% NaCI aqueous solution at room temperature at 1 × 107 cycles arc 392 and 431 MPa respectively. The results indicate that the corrosion fatigue properties of Ti-75 alloy increase by a factor of 29% (in air) and 26% (in 3.5 wt% NaCl aqueous solution), as compared with TA5 alloy. The improvements of the properties above are related to the microstructure of Ti-75 alloy. Graphs, photomicrographs, 6 ref. Experimental study of contact fatigue damage of ZQSnI0-1 discs. Lian. X.J. and Fu. Y. C. Mater. Mech. Eng. (China) (June 1994) 18 (3), 51-52 (in Chinese) By experimental research on a disc machine, the damage mechanism of bronze ZQSnl0-1 is analysed. The damage curves of ZQSnI0-1 discs under different loads are given. Graphs, photomicrographs, 2 ref. Fracture analysis of the infinitely variable speed twist shaft. P~m, S.L. and Mao, Z. Q, Mater. Mech, Eng. (China) (June 1994) 18 (3), 48-5(/ (in Chinese) The reasons for the fracture of an infinitely variable speed twist shaft (made of 60Si2Mn steel), which is used in a spinning wheel, arc analysed. The primary reason for lowering the fatigue life is decarburization. After developing
Abstracts
oxidation in the presence of H20 and CO2, they show some fatigue stress reduction. Silicon, manganese and chromium penetrate into the boundaries of austenite granules and enhance the heat treatment capabilities. An alternative to conventional case harding is shot peening, in which hard cast steel granular particles or cut steel wire parts are blasted against the working surface being treated. Other methods are hard shot peening and plasma hardening. These techniques are explained, with relevant illustrations and performance characteristics. Graphs, photomicrographs, 62 ref. Fatigue strength of friction welded joints of AZ31 magnesium alloy. Asahina, 7",. Katoh, K. and Tokisue. 14. J. J, Inst. Light Met. (Mar 1994) 44 (3), 147-151 (in Japanese) AZ31 magnesium alloy was friction welded using a brake-type friction welding machine under optimum welding conditions, such as PI= 50 MPa, tl = 5 s, P2= 100 MPa, and tz = 5 s. The fatigue tests were conducted by Ono's rotary bending tester for smooth and notched specimens and a Shenck-type repeated torsion fatigue tester for smooth specimens. In the rotary bending tests on the smooth specimens, both the fatigue strength and the fatigue ratio of the welded joints are lower than those of the base metal, irrespective of the number of cycles. The fatigue limit of the welded joint is 81.4% of that of the base metal. The fatigue strength of the welded joints with a notch at the weld interface is slightly lower than that of the base metal. The fatigue limit of the welded joint is 93. 1% of that of the base metal. The notched speciments show fatigue limit values lower than those of the smooth specimens for both base metal and welded joints. In repeated torsion fatigue tests, the fatigue strength of welded joints at a given endurance decreased in an almost linear manner with increasing number of cycles. The fatigue limit of the welded joints is 95.8% of that of the base metal. Without exception, the smooth specimens fractured at the weld interface, regardless of the method of test. For a given fatigue test, the smooth specimens of welded joints show nearly identical macro- and microfractorgraphs, independent of the number of cycles to failure. Graphs, photomicrographs, 10 ref. Microstructure-fatigue crack growth rate correlation in multipass submerged arc C - M n steel weld deposit. Ghosh. P.K.. Nagesh Babu, P. and Gupta. P.C. ISIJ Int. (1994) 34 (3), 280-284 All-weld blocks of C-Mn steel were prepared by multipass submerged are weld deposits, using different welding currents (500-750 A) and speeds (40-60 cm rain ~), filler wire of 4 mm diameter and a basic bonded type of flux. The dendrite content of the weld blocks was estimated by a quantitative metallography technique. The fatigue crack growth rate of the weld in the LT direction of the block was evaluated by using C-T specimens, and correlated with the area fraction of dendrite (Dr) of the matrix. The increase in dendrite content of the matrix was found to reduce the crack growth rate by influencing significantly the material constant C and exponent m of the Paris law, da/dN = c(AKm, where a is the crack length, N is the number of loading cycles and AK is the stress intensity factor range. The modification of C and m with Df was found to provide a satisfactory basis for evaluation of the fatigue crack growth rate of multipass C-Mn steel weld deposits with a given dendrite content. Graphs, photomicrographs, 5 ref. On improving the fatigue life of U-form bellows. Subramanian. G. and Raghunandan, C. J, Mater. Pprocess. Technol. (Feb. 1994) 41 (1), 105-114 Fatigue failure invariably occurs at the root in hydroformed bellows (austenitic stainless steels), as the hydroforming process does not cold-work the root region and raise the yield point there, as it does in other regions. Both elastic and plastic analyses confirm this by predicting that the yield criterion is first satisfied in the root region during deflection. On the other hand, the roll-forming process imparts a substantial amount of cold work to the root of the bellows. A judicious combination of hydroforming and roll-forming processes is examined here, therefore, as a viable alternative (as opposed to individual routes) for enhancing the fatigue life of austenitic steel bellows for low-pressure, low-temperature applications. This combination process has the added merit that bellows with extra-deep convolutions can be formed as replacements to costlier diaphram-type bellows, and for applications having space restrictions. While testing the bellows for fatigue, it is noted that corrugations do not share the total movement equally; this phenomenon appears to he a major cause for the scatter in values obtained in life tests. Investigation reveals that a correlation exists between this unequal sharing of movement of fatigue life. Based on these observations a new nondestructive stretch test is proposed with which original life estimates can be refined. Graphs, 6 ref, Correlation of fatigue crack growth rate at different stress ratios for quenched and tempered steels and other alloys. Robertson, I.M. Fatigue Fract. Eng. Mater. Struct. (Mar. 1994) 17 (3) 327-338 Measurements of the effect of stress ratio on the constant-amplitude fatigue crack growth rates in four quenched and tempered steels in the Paris regime arc reported. These data and publiscd data for other alloys (including lowerstrength steels and non-ferrous alloys) are evaluated, and a correlation function suitable for practical fatigue life calculations is derived. In addition to stress intensity factor range and stress ratio, other significant parameters are the yield stress of the material and its thickness. For the four steels on which new measurements were made, the degree of dependence of the crack growth rate on stress ratio may be related to sensitivity to environmental conditions. Graphs, 24 ref.
Fatigue crack growth in nickel-based superalloys at 500-700°C. If. Directaged Alloy 718. Lynch, S.P., Radtke, T.C., Wicks. B.J. and Bvrnes, R.T. Fatigue Fract. Eng. Mater. Struct. (Mar. 1994) 17 13), 313-32,~ The effects of cyclic frequency, hold time, and stress-intensity factor range (AK) on rates of fatigue crack growth in air at 500°C and 7(XI°C have been studied for the directed-age version of the nickel-based superalloy 718, The main effects were similar to those observed for Waspaloy (Part l), namely: (i) small effects of cyclic frequency and hold time at 500°C, (ii) higher rates of crack growth at lower cyclic frequencies at high AK at 7(gl°C, and (iii) lower rates of crack growth at low AK (and higher AK thresholds) for longer hold times at 700°C, For DA 718~ there was no increase in crack growth rates with increasing hold times ((I-60 s) at high AK at 700°C (unlike the large increases reported for standard processed Alloy 718). Metallographic and fractographic observations showed that crack growth was predominantly transgranular at 500°C. and predominantly intergranular at 700°C except at 2 Hz at high AK. The precise intergranular crack path, extent of branching, and fracture-surface appearance depended on AK, waveform and cycle period. The mechanisms responsible for the observed effects, and possible explanations for the different behaviour of DA 718 and standard processed Alloy 718, arc discussed. Graphs, photomicrographs, 21 ref. Fatigue crack growth in nickel-based superalloys at 500-700°C. 1. Waspaloy. Lynch, S.P., Radtke, T.C., Wicks, B.J. and Byrnes, R.T. Fatigue Fract. Eng. Mater. Struct. (Mar. 1994) 17 (3). 297-311 The effects of cyclic frequency, hold time, and stress-intensity factor range (AK) on rates of fatigue crack growth in air at 500-700°C have been studied for Waspaloy-a nickel-based supcralloy used for gas-turbine engine discs. The main effects observed were: (i) higher rates of crack growth for lower cyclic frequencies at high AK at 600 and 700°C, and (ii) lower rates of crack growth at low AK (and higher AK thresholds) for longer hold times at 700°C, compared with those at a baseline frequency of 2 Hz. Metallographic and fractographic observations suggested that the effects of cyclic frequency and hold time could be rationalized in terms of the competing effects of enhancement of cracking due to creep and inhibition of cracking caused by oxide-induced crack closure, fracture-surface roughness-induced crack closure, and crack-branching/deflection. Possible mechanisms for promoting intergranular and transgranular cracking at low cyclic frequencies or long hold times are discussed. Graphs, photomicrographs. 32 ref. The fatigue resistance of peened 7050-T7451 aluminum alloy. Sharp, P.K., Clayton, J.Q. and Clark, G. Fatigue Fract. Eng. Mater. Struct. (Mar. 1994) 17 (3), 243-252 Metal and glass-bead peening treatments, widely used throughout the aircraft industry to enhance the fatigue performance of many steels and titanium alloys, are not being routinely applied to high-strength aluminium-alloy components. This paper describes the effects of peening on the fatigue life of 7050 AI alloy material, which is representative of alloys used for many components in modern military aircraft. Using simulated service loading, two proposed peening/re-peening procedures were evaluated and compared with both the original peened surface and a simple hand-polished surface. The results show that optimization of peening parameters to reduce surface damage can provide a substantial improvement in fatigue life over both the original peening treatment and the polished surface treatment; however, poor control of peening procedures, or unnecessary "overpeening'. can lead to a relatively poor fatigue life. For re-peened surfaces, a procedure incorporating a polishing step, designed to repair any damage from the severe peening applied initially, gave the best fatigue performance. Results are discussed in relation to the stability of the residual surface stresses under fatigue loading, the surface roughness, and the number and types of defects introduced by the peening treatments. Photomicrographs, graphs, 13 ref. Corrosion-fatigue behavior of Ti-75 titanium alloy. Meng, L.. Huan. H. and Li. Z.C. Xivou Jimhu Cailiao yu Gongchenq (Rare Metal Materials and Engineering) IJ(me 1994) 23 (3), 40-44 (in Chinese) The unit of liquor automatic cycle is introduced, which is for the experiment of the corrosion-fatigue properties of Ti-75 titanium alloy. The fatigue limits determined in air and 3.5 wt% NaCI aqueous solution at room temperature at 1 × 107 cycles arc 392 and 431 MPa respectively. The results indicate that the corrosion fatigue properties of Ti-75 alloy increase by a factor of 29% (in air) and 26% (in 3.5 wt% NaCl aqueous solution), as compared with TA5 alloy. The improvements of the properties above are related to the microstructure of Ti-75 alloy. Graphs, photomicrographs, 6 ref. Experimental study of contact fatigue damage of ZQSnI0-1 discs. Lian. X.J. and Fu. Y. C. Mater. Mech. Eng. (China) (June 1994) 18 (3), 51-52 (in Chinese) By experimental research on a disc machine, the damage mechanism of bronze ZQSnl0-1 is analysed. The damage curves of ZQSnI0-1 discs under different loads are given. Graphs, photomicrographs, 2 ref. Fracture analysis of the infinitely variable speed twist shaft. P~m, S.L. and Mao, Z. Q, Mater. Mech, Eng. (China) (June 1994) 18 (3), 48-5(/ (in Chinese) The reasons for the fracture of an infinitely variable speed twist shaft (made of 60Si2Mn steel), which is used in a spinning wheel, arc analysed. The primary reason for lowering the fatigue life is decarburization. After developing