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Fatigue strength examinations of weld surfaced parts
r l t i g u e strength assessment o f spot-welded joints on the basis of local stress p a r a m e t s r ¢ Redaj, D. Stahlbau July 1990 50, (7), 201-208 (in German) A finite-element approach, based on three loading modes leading to failure is dmmribed for accurately determining the stress and strain conditions of spot-welded joints. The calculations consider the base loading, the joint force system at the spot edge, the bending effects in shear, notch stresses and stress intensity factors. Potential applications with appropriate tests are indicated. Limitations in the approach are noted. Graphs. 22 refs,
Strength e x a m i n a t i o n s of samples of St 355 Z2 with sheets of St 36 u2 welded on in t h e longitudinal direction. Neumann, K., Lipkow, G. and
Mobius, W. ZIS Report Sept. 1990 1, (9), 3 7 - 4 0 (in German) Experiments on special test pieces determine the effect of the longitudinal fillet weld on the loading capacity of structural components made of the material ST 355 Z,2 (TGL 22 426) when the yield point load R~ arises at a maximum oscillation force in the welded-on St 38u-2 (TGL 7960) sheet. According to TGL 135 000/01, welded steel structures are designed for fatigue on the basis of service strength. The designer has to know the tolerable or permissible stresses for k = 1 with 2 x 10s load reversals, and the test pieces, fabricated to the production specification, must have the same notch stress concentration as the structural component. Graphs. 9 refs. Increasing the fatigue strength o f w e l d joints. Zaczek, Z. ZIS Report Sept. 1990 1, (9), 22-26 (in German) The Gdansk Technical University Department of Machine Materials Technology and Welding Techniques has for five years researched to increase the fatigue strength of butt-welded joints. Normalized or heat-treated low-alloy 12 mm thick constructional steel plates are improved in this way by either mechanical levelling of the weld, TIG arc fusion of their transitions in four operations, or TIG arc fusion of the weld reinforcement in two operations, by 58, 53 and 56%, respectively. Fusion or hardening of the reinforcement or of the HAZ in two operations by electron beam welding does not improve the butt welds. Graphs. Fatigue strength examinations o f w e l d Imrioced parts. Grutke, W. ZlSReport Sept. 1990 1, (9), 18-22 (in German) Comparative tests determine the dynamic bearing capacities of front-axle necks regenerated by MAG-based building-up. The 40Cr4 steel tractor axle necks, regenerated with 30 MnCrTi 5 alloy and optionally high-frequency induction hardened, show that both the induction hardening and the 30 MnCrTi 5 alloy regeneration give batter dynemic strength under bending pulsating loading compared with the original axles, it is concluded that the MTS 50/80 tractor axles can and should be regenerated as described, for economy end performance reasons. Graphs, photomicrographs. 2 refs. Fatigue crack initiation life prediction f o r w e l d e d joints by a low-cycle fatigue approach. Skorupa, M. Fatigue Fract. Eng. Mater. Struct. 1990 13, (6), 597-613 Analytical procedures based on low-cycle fatigue theory are used to estimate the fatigue crack initiation life (Ni) for s cruciform welded joint in mild steel under constant-amplitude tensile cyclic loading, the fatigue crack initiating st the weld toe. Effects arising from welding such as residual stresses, geometrical variability and changes in material properties are handled. It is shown that for high mean stresses the discrepancies observed between the Ni estimates provided by commonly used analytical procedures exceed an order of magnitude. For the base metal (BM) the discrepancies become negligible if cyclic relaxation of notch mean stress is taken into consideration. The differences between the N. estimates for heat-affected zone (HAZ) material (where fatigue cracks at the weld toe usually initiate) and for the BM are quantified. The applicability of the HAZ material properties, estimated from hardness, to the ~ prediction is evaluated. Additional materials mentioned are A36, A514 Gr.F, 1020, and 5083 AI. Graphs. 33 refs.
material and associated crack tip shielding. This produced an enhancement of crack growth rates at all values of AK significantly above the threshold regime. The role of carbide/matrix interface embrittlement constitutes a third mechanism of H embrittlement and tamper embrittlament interaction in fatigue crack growth, additional to those of carbide precipitation and grain boundary .embrittlement previously reported. Photomicrographs, graphs. 14 refs. Effects of ageing condition on the high-tumperature properties of precipitation hardened 15Cr-26NI-1.25Mo iron-bess e i i o y ¢ lijima, K,,
Yamada, N., Fukui, Y., Kirihare, S. and Kaneko, R. Tetsu-to-Hegane (J. Iron Steel Inst. Jpn.) July 1990 76, (7), 1147-1154
(in Japanese) The optimum ageing condition suitable for large components made of low-carbon Iow-Ti 15Cr-26Ni-l.25Mo Fe-bsee alloys was examined. The alloys are beneficial for making rotors for ultraeupercritical steam turbines for generators. After solution treatment, the alloys were aged at 740=C for 1-64 h, or 700-780°C for 16h. The experimental results are summarized as follows. (1) Ageing in s range of 720-780 °C for 16 h yielded spheroidal ~t' particles. However, after ageing at 780°C for 16 h coarsened "y' particles precipitated on the grain boundary. (2) Superior tensile properties resulted after ageing at 740 °C for 16-32 h or 740-760 °C for 16 h. (3) Creep properties st 650 °C were affected by the ageing temperature. The long-term creep strength was little affected by the ageing temperature in the range of 710-760°C for 16 h. Creep ductility was significantly improved by elevating the ageing temperature up to 760 °C, (4) Low-cycle fatigue strength at 650 °C was not affected by the ageing conditions when tested under a constant total strain amplitude. (5) A drum with a weight of 4.5 t was produced and eolutionized and aged at 740 °C for 32 h. The test pieces were cut from four typical locations of the drum, and creep tested at 650 °C. It was confirmed that dispersion of creep strength with respect to the location was negligible. Graphs, photomicrographs, diffraction patterns, 12 refs. Effect o f t i t a n i u m content on mechanical properties of an 'A' segregation region in large A286 iron-bess superelloy forgings. Kohno, M.,Honjo,
T. and Tsuchtyama, T. Tetsu-to-Hagane (J. Iron Steel Inst, Jpn.) July 1990, 76, (7), 1139-1146
(in Japanese) It has been planned to apply A286 Fe-buse superalloy to the rotor material of an uitrasupercritical steam turbine in which the main steam temperature is 649°C, because of its high strength at high temperatures. In this case, s large ESR ingot weighing approx. 40 t is necessary. However, in the large ESR ingot of this material, an 'A'-type segregation is easily formed which may cause the properties of the forgings to be inferior. Therefore, the characteristics of the 'A' segregation and mechanical properties of the segregated region, compared with the normal region, in large A286 alloy forgings made from 1000-1350 mm diameter ESR ingots with different Ti contents have been investigated. The following results are obtained. (1) Lowering Ti content is fevourable for reducing the 'A' segregation. (2) The tensile properties, creep rupture properties, high- and low-cycle fatigue strengths except for the tensile ductilities at less than 200 °C and low-cycle fatigue strength in strain at more than 1.(P/o are not damaged by 'A' segregation in A,?.86 alloy with 1,9% Ti. (3) Lowering the Ti content improves the tensile ductility and the low-cycle fatigue strength in the higher strain range. (4) The influence of the 'A' segregation on mechanical properties can be well explained by the difference in hardness between the normal and the segregated regions after work hardening by each test. Graphs, photomicrographs. 12 refs. Testing of t o t a l hip replacements: endurance tests and stress measuremerits. I. Endurance tests. Humphreys, P.K,, Orr, J.F. and Bahrani, A.S. Prec. Inst. Mech. Eng. H, J. Eng. Mad. 1990 204, (H1), 29-34 Three methods proposed as standards for determining the endurance characteristics of stemmed femoral components (ISO/DP 7206/3 and the 1984 and 1986 drafts of BS DD91) were assessed on the basis of relevant fatigue tests on Howse-II hip prostheses. The provisions of BS DD91:1984 were evidently too severe, early failures incompatible both with known in-service endurances of the prostheses and with results in terms of BS DD91:1986 being recorded. The latter draft and the ISO proposals proved either adequate or lax, in that all the specimens accordingly tested survived 5 x 10e cycles of up to 4.1 kN Ioedings at 1-10 Hz. The effect of the 15° offset angle proposed in BS DD91 is discussed in particular. 6 refs.
Fatigue crack g r o w t h in multi-pass butt-welded joints of mild steel.
Nicoletto, G. Int. J. Pressure Vessels Piping 1990 42, (3), 363-378
Testing o f t o t a l hip replacements: endurance tests and stress measurements. II. Stroes measurements. Humphreys, P.K., Orr, J.F. and Behrani,
Fatigue crack growth rate properties obtained by testing multipess butt-welded joints in the through-the-thickness direction are presented along with a characterization of the mild-steel base material. Edge-notched four-point-bending specimens are used to investigate the R-ratio, specimen geometry and postweld heat treatment effects on the fatigue crack growth rates. The pervasive influence of residual stresses on welded-joint fatigue testing using the fracture mechanics approach is also discussed. For these multipess joints, conservative fatigue crack growth rates are obtained with postweld heat-treated specimens. Graphs, photomicrographs. 25 refs.
A.S. Proc. Inst. Mech. Eng. H, J. Eng. Mad. 1990 204, (H1), 35-41
Mechanical properties rogen e m b r i t t i e m e n t , thermal ageing, and role of carbides in fatigue igh-strongth steel. Hippsley, C.A. end Lane, C.E. ~h Meter. Sci. Technol. Aug. 1990 6, (8), 735-742 The influences of thermal ageing and environment on the Paris-Erdogan regime fatigue crack growth rates and mechanisms in a high-strength Cr-Ni steel (300M) have been investigated. Crack growth rates were measured in inert (vacuum) and aggressive (H) environments, for quenched and tempered meterial before and after thermal ageing at 500 °C. Ageing induced an acceleration of crack growth in vacuum at low values of ~,K, but a retardation at high values of AK. The crack path was trenegranular throughout, and followed the carbide/metrix interfaces. These effects were associated with the embrittlement of carbide/metrix interfaces by phosphorus segregation, which facilitated transgrenular crack growth at low values of AK, but produced crack tip shielding by voids surrounding the crack at high values of ~K. Hydrogen acted synergistically with P to ambrittle the carbide/metrix interfaces, but it also localized slip deformation at crack tips, reducing void formation in surrounding
280
Previous assessments of three proposed standards for fetigue-testing stemmed femoral components (see preceding abstract) were extended to stress determinations by the brittle-lacquer and strain-gauge techniques. The theoretical stress-distribution model developed is illustrated, and the fetigue-stress limit values calculated in terms of the value for the Ti-6AI- 4V alloy are presented. The undue severity of the loading proposals in BS DD91: 1984, which excessively deflected the specimens and produced premature fatigue failure, was corroborated. In contrast, the proposals in the 1986 version might be lax, and the peak load of 2.31 kN might be beneficially increased to 4.1. The loading conditions in ISO/DP 7206/3, which specifies a O° offset angle, are regarded as unrealistic, the stresses in the stem and the likelihood or otherwise of failure of the prosthesis by fatigue are, however, calculable from all the Ioedings specified. 13 refs. Fatigue crack nucleation in metallic materials. Polak, J.
Acta Tech. CSAV 1990 35, (2), 156-174
The behsviour of metallic materials such as Cu subjected to cyclic straining is reviewed and important stages of the cumulative damage are identified. Cyclic strain localization starts after the initial hardening of soft materials, influences the cyclic stress-strain response and is also decisive for crack nucleation. The theory of fatigue crack nucleation is based on the strain localization to persistent slip bands. The surface relief builds up to mass redistribution assisted by point defect migration and dislocation motion. Microcreck initiation results from environment-assisted irreversible slip-unslip from the intrusions. Crack linking and short-crack growth turns into macrocrack initiation. The comparison of experimental observations on model and technical materials supports the model of fatigue initiation. Photomicrographs. 24 refs.
Int J Fatigue May 1991
Strength e x a m i n a t i o n s of samples of St 355 Z2 with sheets of St 36 u2 welded on in t h e longitudinal direction. Neumann, K., Lipkow, G. and
Mobius, W. ZIS Report Sept. 1990 1, (9), 3 7 - 4 0 (in German) Experiments on special test pieces determine the effect of the longitudinal fillet weld on the loading capacity of structural components made of the material ST 355 Z,2 (TGL 22 426) when the yield point load R~ arises at a maximum oscillation force in the welded-on St 38u-2 (TGL 7960) sheet. According to TGL 135 000/01, welded steel structures are designed for fatigue on the basis of service strength. The designer has to know the tolerable or permissible stresses for k = 1 with 2 x 10s load reversals, and the test pieces, fabricated to the production specification, must have the same notch stress concentration as the structural component. Graphs. 9 refs. Increasing the fatigue strength o f w e l d joints. Zaczek, Z. ZIS Report Sept. 1990 1, (9), 22-26 (in German) The Gdansk Technical University Department of Machine Materials Technology and Welding Techniques has for five years researched to increase the fatigue strength of butt-welded joints. Normalized or heat-treated low-alloy 12 mm thick constructional steel plates are improved in this way by either mechanical levelling of the weld, TIG arc fusion of their transitions in four operations, or TIG arc fusion of the weld reinforcement in two operations, by 58, 53 and 56%, respectively. Fusion or hardening of the reinforcement or of the HAZ in two operations by electron beam welding does not improve the butt welds. Graphs. Fatigue strength examinations o f w e l d Imrioced parts. Grutke, W. ZlSReport Sept. 1990 1, (9), 18-22 (in German) Comparative tests determine the dynamic bearing capacities of front-axle necks regenerated by MAG-based building-up. The 40Cr4 steel tractor axle necks, regenerated with 30 MnCrTi 5 alloy and optionally high-frequency induction hardened, show that both the induction hardening and the 30 MnCrTi 5 alloy regeneration give batter dynemic strength under bending pulsating loading compared with the original axles, it is concluded that the MTS 50/80 tractor axles can and should be regenerated as described, for economy end performance reasons. Graphs, photomicrographs. 2 refs. Fatigue crack initiation life prediction f o r w e l d e d joints by a low-cycle fatigue approach. Skorupa, M. Fatigue Fract. Eng. Mater. Struct. 1990 13, (6), 597-613 Analytical procedures based on low-cycle fatigue theory are used to estimate the fatigue crack initiation life (Ni) for s cruciform welded joint in mild steel under constant-amplitude tensile cyclic loading, the fatigue crack initiating st the weld toe. Effects arising from welding such as residual stresses, geometrical variability and changes in material properties are handled. It is shown that for high mean stresses the discrepancies observed between the Ni estimates provided by commonly used analytical procedures exceed an order of magnitude. For the base metal (BM) the discrepancies become negligible if cyclic relaxation of notch mean stress is taken into consideration. The differences between the N. estimates for heat-affected zone (HAZ) material (where fatigue cracks at the weld toe usually initiate) and for the BM are quantified. The applicability of the HAZ material properties, estimated from hardness, to the ~ prediction is evaluated. Additional materials mentioned are A36, A514 Gr.F, 1020, and 5083 AI. Graphs. 33 refs.
material and associated crack tip shielding. This produced an enhancement of crack growth rates at all values of AK significantly above the threshold regime. The role of carbide/matrix interface embrittlement constitutes a third mechanism of H embrittlement and tamper embrittlament interaction in fatigue crack growth, additional to those of carbide precipitation and grain boundary .embrittlement previously reported. Photomicrographs, graphs. 14 refs. Effects of ageing condition on the high-tumperature properties of precipitation hardened 15Cr-26NI-1.25Mo iron-bess e i i o y ¢ lijima, K,,
Yamada, N., Fukui, Y., Kirihare, S. and Kaneko, R. Tetsu-to-Hegane (J. Iron Steel Inst. Jpn.) July 1990 76, (7), 1147-1154
(in Japanese) The optimum ageing condition suitable for large components made of low-carbon Iow-Ti 15Cr-26Ni-l.25Mo Fe-bsee alloys was examined. The alloys are beneficial for making rotors for ultraeupercritical steam turbines for generators. After solution treatment, the alloys were aged at 740=C for 1-64 h, or 700-780°C for 16h. The experimental results are summarized as follows. (1) Ageing in s range of 720-780 °C for 16 h yielded spheroidal ~t' particles. However, after ageing at 780°C for 16 h coarsened "y' particles precipitated on the grain boundary. (2) Superior tensile properties resulted after ageing at 740 °C for 16-32 h or 740-760 °C for 16 h. (3) Creep properties st 650 °C were affected by the ageing temperature. The long-term creep strength was little affected by the ageing temperature in the range of 710-760°C for 16 h. Creep ductility was significantly improved by elevating the ageing temperature up to 760 °C, (4) Low-cycle fatigue strength at 650 °C was not affected by the ageing conditions when tested under a constant total strain amplitude. (5) A drum with a weight of 4.5 t was produced and eolutionized and aged at 740 °C for 32 h. The test pieces were cut from four typical locations of the drum, and creep tested at 650 °C. It was confirmed that dispersion of creep strength with respect to the location was negligible. Graphs, photomicrographs, diffraction patterns, 12 refs. Effect o f t i t a n i u m content on mechanical properties of an 'A' segregation region in large A286 iron-bess superelloy forgings. Kohno, M.,Honjo,
T. and Tsuchtyama, T. Tetsu-to-Hagane (J. Iron Steel Inst, Jpn.) July 1990, 76, (7), 1139-1146
(in Japanese) It has been planned to apply A286 Fe-buse superalloy to the rotor material of an uitrasupercritical steam turbine in which the main steam temperature is 649°C, because of its high strength at high temperatures. In this case, s large ESR ingot weighing approx. 40 t is necessary. However, in the large ESR ingot of this material, an 'A'-type segregation is easily formed which may cause the properties of the forgings to be inferior. Therefore, the characteristics of the 'A' segregation and mechanical properties of the segregated region, compared with the normal region, in large A286 alloy forgings made from 1000-1350 mm diameter ESR ingots with different Ti contents have been investigated. The following results are obtained. (1) Lowering Ti content is fevourable for reducing the 'A' segregation. (2) The tensile properties, creep rupture properties, high- and low-cycle fatigue strengths except for the tensile ductilities at less than 200 °C and low-cycle fatigue strength in strain at more than 1.(P/o are not damaged by 'A' segregation in A,?.86 alloy with 1,9% Ti. (3) Lowering the Ti content improves the tensile ductility and the low-cycle fatigue strength in the higher strain range. (4) The influence of the 'A' segregation on mechanical properties can be well explained by the difference in hardness between the normal and the segregated regions after work hardening by each test. Graphs, photomicrographs. 12 refs. Testing of t o t a l hip replacements: endurance tests and stress measuremerits. I. Endurance tests. Humphreys, P.K,, Orr, J.F. and Bahrani, A.S. Prec. Inst. Mech. Eng. H, J. Eng. Mad. 1990 204, (H1), 29-34 Three methods proposed as standards for determining the endurance characteristics of stemmed femoral components (ISO/DP 7206/3 and the 1984 and 1986 drafts of BS DD91) were assessed on the basis of relevant fatigue tests on Howse-II hip prostheses. The provisions of BS DD91:1984 were evidently too severe, early failures incompatible both with known in-service endurances of the prostheses and with results in terms of BS DD91:1986 being recorded. The latter draft and the ISO proposals proved either adequate or lax, in that all the specimens accordingly tested survived 5 x 10e cycles of up to 4.1 kN Ioedings at 1-10 Hz. The effect of the 15° offset angle proposed in BS DD91 is discussed in particular. 6 refs.
Fatigue crack g r o w t h in multi-pass butt-welded joints of mild steel.
Nicoletto, G. Int. J. Pressure Vessels Piping 1990 42, (3), 363-378
Testing o f t o t a l hip replacements: endurance tests and stress measurements. II. Stroes measurements. Humphreys, P.K., Orr, J.F. and Behrani,
Fatigue crack growth rate properties obtained by testing multipess butt-welded joints in the through-the-thickness direction are presented along with a characterization of the mild-steel base material. Edge-notched four-point-bending specimens are used to investigate the R-ratio, specimen geometry and postweld heat treatment effects on the fatigue crack growth rates. The pervasive influence of residual stresses on welded-joint fatigue testing using the fracture mechanics approach is also discussed. For these multipess joints, conservative fatigue crack growth rates are obtained with postweld heat-treated specimens. Graphs, photomicrographs. 25 refs.
A.S. Proc. Inst. Mech. Eng. H, J. Eng. Mad. 1990 204, (H1), 35-41
Mechanical properties rogen e m b r i t t i e m e n t , thermal ageing, and role of carbides in fatigue igh-strongth steel. Hippsley, C.A. end Lane, C.E. ~h Meter. Sci. Technol. Aug. 1990 6, (8), 735-742 The influences of thermal ageing and environment on the Paris-Erdogan regime fatigue crack growth rates and mechanisms in a high-strength Cr-Ni steel (300M) have been investigated. Crack growth rates were measured in inert (vacuum) and aggressive (H) environments, for quenched and tempered meterial before and after thermal ageing at 500 °C. Ageing induced an acceleration of crack growth in vacuum at low values of ~,K, but a retardation at high values of AK. The crack path was trenegranular throughout, and followed the carbide/metrix interfaces. These effects were associated with the embrittlement of carbide/metrix interfaces by phosphorus segregation, which facilitated transgrenular crack growth at low values of AK, but produced crack tip shielding by voids surrounding the crack at high values of ~K. Hydrogen acted synergistically with P to ambrittle the carbide/metrix interfaces, but it also localized slip deformation at crack tips, reducing void formation in surrounding
280
Previous assessments of three proposed standards for fetigue-testing stemmed femoral components (see preceding abstract) were extended to stress determinations by the brittle-lacquer and strain-gauge techniques. The theoretical stress-distribution model developed is illustrated, and the fetigue-stress limit values calculated in terms of the value for the Ti-6AI- 4V alloy are presented. The undue severity of the loading proposals in BS DD91: 1984, which excessively deflected the specimens and produced premature fatigue failure, was corroborated. In contrast, the proposals in the 1986 version might be lax, and the peak load of 2.31 kN might be beneficially increased to 4.1. The loading conditions in ISO/DP 7206/3, which specifies a O° offset angle, are regarded as unrealistic, the stresses in the stem and the likelihood or otherwise of failure of the prosthesis by fatigue are, however, calculable from all the Ioedings specified. 13 refs. Fatigue crack nucleation in metallic materials. Polak, J.
Acta Tech. CSAV 1990 35, (2), 156-174
The behsviour of metallic materials such as Cu subjected to cyclic straining is reviewed and important stages of the cumulative damage are identified. Cyclic strain localization starts after the initial hardening of soft materials, influences the cyclic stress-strain response and is also decisive for crack nucleation. The theory of fatigue crack nucleation is based on the strain localization to persistent slip bands. The surface relief builds up to mass redistribution assisted by point defect migration and dislocation motion. Microcreck initiation results from environment-assisted irreversible slip-unslip from the intrusions. Crack linking and short-crack growth turns into macrocrack initiation. The comparison of experimental observations on model and technical materials supports the model of fatigue initiation. Photomicrographs. 24 refs.
Int J Fatigue May 1991