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Effect of geometric changes on fatigue strength of welded joints
crack growth in the plates has been related to the crystallographic texture. The texture, due to its strong influence on the slip behaviour and plastic zone size, induces different amounts of roughness-induced closure and slip reversibility, thereby producing the observed anisotropY of the fatigue crack growth properties.
u 0 H. H. N o • ~mith, and Michel,•D. J. J. NucL Mater.
c
ni~radietion effects on fatigue crack propagation in alloy 718 at June 1987 148, (1), 109-112
High-temperature structural components in nuclear energy systems experience cyclic or combined cyclic-static loading during irradiation. Studies have shown that the Ni-based precipitation-hardened Alloy 718 is sensitive to heat treatment and heat-to-heat processing variations. Fluences of 0.5-3.0 dpa fast neutron irradiation at 427 °C produced a small decrease in crack propagation rate compared with unirradiated results. A 1 rain hold period in the fatigue cycle significantly increased the crack propagation rate of Alloy 718 at 427 °C. Specimens irradiated to 16-18 dpa at 650 °C showed significantly increased fatigue crack propagation (FCP) rates during cyclic and 1 rain hold time Ioedings. Test specimens were irradiated at 650 ~+5 °C to calculated fast neutron fluences of 6,2 and 7.0 × 1022 n/cmz, > 0.1 MeV. The crack propagation rate increased by a factor of two with cyclic loading and by a factor of ten with 1 min hold time Ioedings. The mode of crack propagation at 650 °C was found to be primarily transgrenular with a crystallographic cleavage character believed to be {100}, The crack propagation rates for unirradiated continuous cycling tests were nearly four times higher in the current test than in previous tests. The test temperature of 650 °C is in excess of the final ageing temperature of the modified heat treatment. This is considered to contribute to the partial dissolution of y" precipitate microstructure leading to higher FCP rates. The differences observed in the crack propagation rates of both heats of Alloy 718 were primarily the result of the influence of different heat treatments. Graphs, photomicrographs. 10 refs.
Contact fatigue resistance of a n e w F e - M n overlaying alloy. Zhang, P.,
Xu, B., klan, W. and Cai, Q. Hanjie Xuebao (Trans. China Weld. Inst.) Sept. 1988 9, (3), 188-194 (in Chinese) The contact fatigue resistance of several overlaying alloys was compared by roiling-sliding tests, and a new Fe-Mn alloy showed the best resistance among the different alloys, The service life of this alloy was found to be a maximum under the condition of ~i = 1560MPa. The mechanism of the good contact fatigue resistance of the alloy was investigated. It is considered that the strain-induced martensitic transformation from ~tto ~' and the precipitation of MaC carbide particles increase the strength of the material effectively, and impede the continuous plastic deformation. As the huge reserve of toughness in the austenite surrounding the martensite can decrease the propagation rate of cracks, the service life is increased. One of the advantages of this overlaying alloy is that the heat treatment for the overlaid surface can be saved because the strength needed can be obviated in the running-in process through effective work-hardening. 13 refs.
Effect of geometric changes on fatigue strength of w e l d e d joints. Kiuchi,
A., Ohtani, O. and Takeuchi, H. Kobe Res. Dev. July 1988 38, (3), 22-25 (in Japanese)
The effect of geometric changes on fatigue strength of welded joints has been investigsted analytically and experimentally. The fatigue strength was found to depend on attachment size (L) and main plate thickness (B). The analytical investigation led to the formulation of equations predicting the fatigue strength for given values of B and L. The predicted fatigue strength agreed well with experimental results. 5 refs.
influence of specimen size on fatigue crack initiation of welded HY100
High-temperature properties of ferritic spheroidal graphite cast iron. Lui, T. S. and Chao, C. G. J. Mater. ScL July 1989 24, (7), 2503-2507
The behaviour of fracture mode and intermediate temperature embrittlement of ferritic spheroidal graphite cast iron is influenced by many factors. From the experimental results, intermediate temperature embrittlement can be considered to be dominated by dynamic strain ageing and the triaxial stress field developed in the ferrite matrix amongst the graphite particles. To understand the effect of dynamic strain ageing on high-temperature properties, tensile properties, push-pull lowcycle fatigue properties, rotary bending fatigue properties and creep-rupture properties were investigated from room temperature to 500 °C, It was found that all the properties investigated were influenced by dynamic strain ageing. The intermediate temperature embrittlement of ferritic spheroidal graphite cast iron found in different load conditions is reported. Graphs, photomicrographs. 14 refs. Cyclic deformation pehsviour o f s Cu-1.5 mess% Fe alloy w i t h precipitate iron particles. Kato, M., Nishimura, A., Matsuyama, 7". and Horie, H. Mater. ScL Eng. A M a y 1989 111, 17-25 Three different specimens of Cu-1.5 mass% Fe alloy polycrystals were cyclically deformed: solution-treated specimens (specimens S), aged specimens with coherent "y-Feprecipitate particles (specimens G) and aged, deformed and annealed specimens with incoherent ~-Fe particles (specimens A). In both total-strain-controlled and stress-controlled tests, specimen G had the longest fatigue life. Transmission electron microscopic observation revealed that the formation of dipolar walls or fatigue cells was considerably delayed in specimen G compared with specimens S and A. The deformation-induced ~-~ transformation in the Fe particles in specimen G occurred in the very early stage of cyclic deformation, and the transformation induced the formation of tangled dislocations around the particles. It is concluded that the coexistence of the transformed ~-Fe particles and the tangled dislocations is very effective in preventing the rearrangement of dislocations during cyclic deformation. Graphs, photomicrographs. 29 refs, The phase t r a n s f o r m a t i o n and fatigue characteristics by thermal cycles at / i - N I - u u snspe m e m o r y alloys. Lee, O. Y., Chun, B. S., Nam, K. J.
and Cho, K. H. J. Korean Inst. Met. 1989 27, (2), 103-112 (in Korean)
Martensitic transformation and effects of thermal fatigue cycles on the transformation temperature and shape recovery of Ti-Ni-Cu alloys were investigated by means of electrical resistance measurement, thermal fatigue tests end transmission electron microscopy. Thermo-mechanical treatment at 600 °C for 1 h after cold rolling showed the best shape recovery effect irrespective of Cu concentration. Substitution of a small amount of Cu for Ni in the equistomic composition of Ti-Ni showed the following results: Ms temperature of the Ti-N~-Cu alloy increased slightly with the increase of Cu content: the range of transformation temperature for TisoNJ4oCufa alloy (ie TMf_Af)was reduced to 7 °C. After stress relief treatment at 750 °C for 1 h, the TisoNi4sCus alloy showed a good two-way memory effect. Change of the Ms temperature was observed to a certain number of thermal cycles, and it became nearly constant after a critical number of thermal fatigue cycles. Graphs, photomicrographs. 18 refs.
Joining A study of the fatigue strength of incomplete penetration butt welds.
Li, R. and Zhang, X. Hanjie Xuebao (Trans. China Weld. /nst.) June 1988 9, (2), 119-124 (in
Chinese)
One-side-welded butt welds are widely used in welded structures. The results of tests conducted on Iow-C steel bug welds containing incomplete penetration defects under fluctuating tensile stress are given. As the incomplete penetration defects generally occur at the surface of weld in the case of one-side-welded butt welds, the loss of fatigue strength is more severe compared with that of double-sidewelded butt welds of the same defect ratio. Inclusions existing in the tip of incomplete penetration may intensify the stress concentration in the stress concentration zone. This further lowers the fatigue strength. 4 refs.
Int J Fatigue January 1990
steel. Technical memo. Kreuzer, W, Defence Research Establishment Atlantic Report No AD-A 196 219/O/XAB Jan. 1988
The assumption of a statistical distribution of the flaws in a component leads to a prediction of a correlation between crack initiation life and the size of a fatigue loaded part. The influence of the specimen size on the fatigue crack initiation behaviour was analysed for two series of welded HY100 steel plates of different widths. The weldments were prepared with E12018M2 electrodes, The prediction of the number of cycles to crack initiation and of the allowable stresses for samples of a different size agreed well with the experimental results.
Fracture toughness of steel weldments containing lack of penetration
defects, (Dissertation). Byaruhanga, J. K. Diss. Abstr. Int. M a y 1988 48, (11)
The fracture resistance of weldments containing flaws in the as-welded state was studied. The major considerations which prompted this investigation were: (a) the suspicion that the use of standard notches to generate fracture toughness data for assessing real flaws in weldments might be unduly pessimistic; and (b) the fact that workmanship codes and specifications seldom distinguish between welding processes and procedures when nominating allowable defects in weldrnents. Therefore, the major aims were the investigation of the possibility of fracture toughness testing using real defects such as )ack of penetration as opposed to machined and fatigue cracked notches, the effects of welding process and procedure on fracture toughness, and the effects of factors such as notch geometry and angular distortion on the fracture toughness of weldments. The results of these investigations revealed the following: (i) lack of penetration defects and fatigue cracks gave similar fracture resistance values over a range of temperatures; (ii) specimens with shallow notches gave better fracture resistance values than those with standard notches; (iii) different welding processes and procedures gave different fracture resistance data; and I)v) specimens made with a restraining weld had better resistance to fracture than those allowed to distort during welding. The maior implications include: since lack of penetration defects and fatigue cracks gave similar fracture resistance values, the simpler lack of penetration defect could be used to generate fracture toughness data for the assessment of a range of welded structures using fracture mechanics. The fracture resistance of weldments is dependent on notch geometry since the results showed that the critical crack tip opening displacement for shallow notches was much greater than that for deep notches. The fracture resistance of weldments is dependent on the welding process and procedure, a factor not covered in workmanship codes. The reduction of angular distortion in weldments leads to significantly improved fracture resistance.
Mechanical properties Fatigue/creep interaction fracture map at various temperstums. Zhang, H., ~u, Z. and Chen, G. Acta Metal/. Sin, (China) Dec. 1988 24, ('6), A439-A442 lin Chinese) The relative ratio of fatigue resistance to creep resistance of materials varies with test temperature. As the temperature decreases, the creep resistance, since it is a thermal activation process, becomes relatively larger than the fatigue resistance. The fatigue damage therefore becomes predominant, and results in expansion of the fatigue fracture region (F region) and shrinkage, or even complete elimination of the creep fracture region (C region). This phenomenon could be understood on the basis of an integrated model of competitive and cumulative models of fatigue/ creep interaction. A material parameter, Q, can be used to estimate the temperature at which the creep fracture region is completely depressed. 5 refs. cTI~.ormsl fatigue and fracture mechanics analysis o f grey cast iron. Guo,
and Zhou, W. Acta Metal/. Sin. (China) Dec. 1988 24, (6), A419-A425 (in Chinese) The in-phase and out-of-phase thermal fatigue and the C-P type and P-C type isothermal fatigue of grey cast iron were experimentally studied. The fatigue life was evaluated analytically by using the elastic-plastic fracture mechanics method (mainly J integral). The results of experiments and calculations showed that the life times of in-phase and C-P type fatigue are longer than those of out-of-phase end P-C type fatigue respectively within the same strain range. This is in contrast to
73
u 0 H. H. N o • ~mith, and Michel,•D. J. J. NucL Mater.
c
ni~radietion effects on fatigue crack propagation in alloy 718 at June 1987 148, (1), 109-112
High-temperature structural components in nuclear energy systems experience cyclic or combined cyclic-static loading during irradiation. Studies have shown that the Ni-based precipitation-hardened Alloy 718 is sensitive to heat treatment and heat-to-heat processing variations. Fluences of 0.5-3.0 dpa fast neutron irradiation at 427 °C produced a small decrease in crack propagation rate compared with unirradiated results. A 1 rain hold period in the fatigue cycle significantly increased the crack propagation rate of Alloy 718 at 427 °C. Specimens irradiated to 16-18 dpa at 650 °C showed significantly increased fatigue crack propagation (FCP) rates during cyclic and 1 rain hold time Ioedings. Test specimens were irradiated at 650 ~+5 °C to calculated fast neutron fluences of 6,2 and 7.0 × 1022 n/cmz, > 0.1 MeV. The crack propagation rate increased by a factor of two with cyclic loading and by a factor of ten with 1 min hold time Ioedings. The mode of crack propagation at 650 °C was found to be primarily transgrenular with a crystallographic cleavage character believed to be {100}, The crack propagation rates for unirradiated continuous cycling tests were nearly four times higher in the current test than in previous tests. The test temperature of 650 °C is in excess of the final ageing temperature of the modified heat treatment. This is considered to contribute to the partial dissolution of y" precipitate microstructure leading to higher FCP rates. The differences observed in the crack propagation rates of both heats of Alloy 718 were primarily the result of the influence of different heat treatments. Graphs, photomicrographs. 10 refs.
Contact fatigue resistance of a n e w F e - M n overlaying alloy. Zhang, P.,
Xu, B., klan, W. and Cai, Q. Hanjie Xuebao (Trans. China Weld. Inst.) Sept. 1988 9, (3), 188-194 (in Chinese) The contact fatigue resistance of several overlaying alloys was compared by roiling-sliding tests, and a new Fe-Mn alloy showed the best resistance among the different alloys, The service life of this alloy was found to be a maximum under the condition of ~i = 1560MPa. The mechanism of the good contact fatigue resistance of the alloy was investigated. It is considered that the strain-induced martensitic transformation from ~tto ~' and the precipitation of MaC carbide particles increase the strength of the material effectively, and impede the continuous plastic deformation. As the huge reserve of toughness in the austenite surrounding the martensite can decrease the propagation rate of cracks, the service life is increased. One of the advantages of this overlaying alloy is that the heat treatment for the overlaid surface can be saved because the strength needed can be obviated in the running-in process through effective work-hardening. 13 refs.
Effect of geometric changes on fatigue strength of w e l d e d joints. Kiuchi,
A., Ohtani, O. and Takeuchi, H. Kobe Res. Dev. July 1988 38, (3), 22-25 (in Japanese)
The effect of geometric changes on fatigue strength of welded joints has been investigsted analytically and experimentally. The fatigue strength was found to depend on attachment size (L) and main plate thickness (B). The analytical investigation led to the formulation of equations predicting the fatigue strength for given values of B and L. The predicted fatigue strength agreed well with experimental results. 5 refs.
influence of specimen size on fatigue crack initiation of welded HY100
High-temperature properties of ferritic spheroidal graphite cast iron. Lui, T. S. and Chao, C. G. J. Mater. ScL July 1989 24, (7), 2503-2507
The behaviour of fracture mode and intermediate temperature embrittlement of ferritic spheroidal graphite cast iron is influenced by many factors. From the experimental results, intermediate temperature embrittlement can be considered to be dominated by dynamic strain ageing and the triaxial stress field developed in the ferrite matrix amongst the graphite particles. To understand the effect of dynamic strain ageing on high-temperature properties, tensile properties, push-pull lowcycle fatigue properties, rotary bending fatigue properties and creep-rupture properties were investigated from room temperature to 500 °C, It was found that all the properties investigated were influenced by dynamic strain ageing. The intermediate temperature embrittlement of ferritic spheroidal graphite cast iron found in different load conditions is reported. Graphs, photomicrographs. 14 refs. Cyclic deformation pehsviour o f s Cu-1.5 mess% Fe alloy w i t h precipitate iron particles. Kato, M., Nishimura, A., Matsuyama, 7". and Horie, H. Mater. ScL Eng. A M a y 1989 111, 17-25 Three different specimens of Cu-1.5 mass% Fe alloy polycrystals were cyclically deformed: solution-treated specimens (specimens S), aged specimens with coherent "y-Feprecipitate particles (specimens G) and aged, deformed and annealed specimens with incoherent ~-Fe particles (specimens A). In both total-strain-controlled and stress-controlled tests, specimen G had the longest fatigue life. Transmission electron microscopic observation revealed that the formation of dipolar walls or fatigue cells was considerably delayed in specimen G compared with specimens S and A. The deformation-induced ~-~ transformation in the Fe particles in specimen G occurred in the very early stage of cyclic deformation, and the transformation induced the formation of tangled dislocations around the particles. It is concluded that the coexistence of the transformed ~-Fe particles and the tangled dislocations is very effective in preventing the rearrangement of dislocations during cyclic deformation. Graphs, photomicrographs. 29 refs, The phase t r a n s f o r m a t i o n and fatigue characteristics by thermal cycles at / i - N I - u u snspe m e m o r y alloys. Lee, O. Y., Chun, B. S., Nam, K. J.
and Cho, K. H. J. Korean Inst. Met. 1989 27, (2), 103-112 (in Korean)
Martensitic transformation and effects of thermal fatigue cycles on the transformation temperature and shape recovery of Ti-Ni-Cu alloys were investigated by means of electrical resistance measurement, thermal fatigue tests end transmission electron microscopy. Thermo-mechanical treatment at 600 °C for 1 h after cold rolling showed the best shape recovery effect irrespective of Cu concentration. Substitution of a small amount of Cu for Ni in the equistomic composition of Ti-Ni showed the following results: Ms temperature of the Ti-N~-Cu alloy increased slightly with the increase of Cu content: the range of transformation temperature for TisoNJ4oCufa alloy (ie TMf_Af)was reduced to 7 °C. After stress relief treatment at 750 °C for 1 h, the TisoNi4sCus alloy showed a good two-way memory effect. Change of the Ms temperature was observed to a certain number of thermal cycles, and it became nearly constant after a critical number of thermal fatigue cycles. Graphs, photomicrographs. 18 refs.
Joining A study of the fatigue strength of incomplete penetration butt welds.
Li, R. and Zhang, X. Hanjie Xuebao (Trans. China Weld. /nst.) June 1988 9, (2), 119-124 (in
Chinese)
One-side-welded butt welds are widely used in welded structures. The results of tests conducted on Iow-C steel bug welds containing incomplete penetration defects under fluctuating tensile stress are given. As the incomplete penetration defects generally occur at the surface of weld in the case of one-side-welded butt welds, the loss of fatigue strength is more severe compared with that of double-sidewelded butt welds of the same defect ratio. Inclusions existing in the tip of incomplete penetration may intensify the stress concentration in the stress concentration zone. This further lowers the fatigue strength. 4 refs.
Int J Fatigue January 1990
steel. Technical memo. Kreuzer, W, Defence Research Establishment Atlantic Report No AD-A 196 219/O/XAB Jan. 1988
The assumption of a statistical distribution of the flaws in a component leads to a prediction of a correlation between crack initiation life and the size of a fatigue loaded part. The influence of the specimen size on the fatigue crack initiation behaviour was analysed for two series of welded HY100 steel plates of different widths. The weldments were prepared with E12018M2 electrodes, The prediction of the number of cycles to crack initiation and of the allowable stresses for samples of a different size agreed well with the experimental results.
Fracture toughness of steel weldments containing lack of penetration
defects, (Dissertation). Byaruhanga, J. K. Diss. Abstr. Int. M a y 1988 48, (11)
The fracture resistance of weldments containing flaws in the as-welded state was studied. The major considerations which prompted this investigation were: (a) the suspicion that the use of standard notches to generate fracture toughness data for assessing real flaws in weldments might be unduly pessimistic; and (b) the fact that workmanship codes and specifications seldom distinguish between welding processes and procedures when nominating allowable defects in weldrnents. Therefore, the major aims were the investigation of the possibility of fracture toughness testing using real defects such as )ack of penetration as opposed to machined and fatigue cracked notches, the effects of welding process and procedure on fracture toughness, and the effects of factors such as notch geometry and angular distortion on the fracture toughness of weldments. The results of these investigations revealed the following: (i) lack of penetration defects and fatigue cracks gave similar fracture resistance values over a range of temperatures; (ii) specimens with shallow notches gave better fracture resistance values than those with standard notches; (iii) different welding processes and procedures gave different fracture resistance data; and I)v) specimens made with a restraining weld had better resistance to fracture than those allowed to distort during welding. The maior implications include: since lack of penetration defects and fatigue cracks gave similar fracture resistance values, the simpler lack of penetration defect could be used to generate fracture toughness data for the assessment of a range of welded structures using fracture mechanics. The fracture resistance of weldments is dependent on notch geometry since the results showed that the critical crack tip opening displacement for shallow notches was much greater than that for deep notches. The fracture resistance of weldments is dependent on the welding process and procedure, a factor not covered in workmanship codes. The reduction of angular distortion in weldments leads to significantly improved fracture resistance.
Mechanical properties Fatigue/creep interaction fracture map at various temperstums. Zhang, H., ~u, Z. and Chen, G. Acta Metal/. Sin, (China) Dec. 1988 24, ('6), A439-A442 lin Chinese) The relative ratio of fatigue resistance to creep resistance of materials varies with test temperature. As the temperature decreases, the creep resistance, since it is a thermal activation process, becomes relatively larger than the fatigue resistance. The fatigue damage therefore becomes predominant, and results in expansion of the fatigue fracture region (F region) and shrinkage, or even complete elimination of the creep fracture region (C region). This phenomenon could be understood on the basis of an integrated model of competitive and cumulative models of fatigue/ creep interaction. A material parameter, Q, can be used to estimate the temperature at which the creep fracture region is completely depressed. 5 refs. cTI~.ormsl fatigue and fracture mechanics analysis o f grey cast iron. Guo,
and Zhou, W. Acta Metal/. Sin. (China) Dec. 1988 24, (6), A419-A425 (in Chinese) The in-phase and out-of-phase thermal fatigue and the C-P type and P-C type isothermal fatigue of grey cast iron were experimentally studied. The fatigue life was evaluated analytically by using the elastic-plastic fracture mechanics method (mainly J integral). The results of experiments and calculations showed that the life times of in-phase and C-P type fatigue are longer than those of out-of-phase end P-C type fatigue respectively within the same strain range. This is in contrast to
73