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Effect of sensitizing heat treatment on fatigue crack growth properties at liquid helium temperatures
420
Fatigue Abstracts
Computational strategies for fatigue crack growth in three dimensions with application to aircraft components O'Donoghue, P.E., Atluri, S.N. and Pipkins, D.S. Eng. Fract. Mech. (1995) 52 (l), 51-64
Experimental research of toroid-shaped bellows behaviour Li, T., Luo, X. and Long, X. Int. J. Pressure Vessels Piping (1995) 63 (2), 141-146
The finite element alternating method, which has proved to be an extremely efficient scheme for the accurate calculation of stress intensity factors, is augmented here by an algorithm to calculate the fatigue life, under cyclic loading of three-dimensional structural components. The alternating method involves the combination of an analytical infinite body solution with a numerical solution for the uncracked physical structure. The advantage here is that mesh generation and computational time are considerably reduced, since this finite element approach only entails an analysis of the uncracked body. These simplifications make it possible to implement a three-dimensional fatigue crack growth algorithm into the alternating method. This approach has been applied here to various fatigue problems in complex 2024 aircraft components. Solutions were initially developed for constant-amplitude loading and then extended to the more difficult case of variable-amplitude loading. Graphs, 12 ref.
Cumulative damage assessment of pressurized piping branch junctions under in-plane run pipe simulated seismic bending Taguaiyu, K., Moffat, D.G. and Moreton, D.N. Int. J. Pressure Vessels Piping (1995) 63 (2), 119-128
Crack growth resistance in bimetallic weldment Homma, H., Kanto, Y., Kubo, T. and Tanaka, Y. Int. J. Pressure Vessels Piping (1995) 63 (3), 225-236 Two types of welded specimen were used in an experiment relating to crack growth behaviour near to and in a welding bead. One was cut from a weldment of two A533B steel plates (A533B welded specimen) and the other from a weldment of A533B steel with high-strength steel HT80 plate (A533B-HT80 welded specimen). In the experiments, the crack growth resistance curves were measured using compact tension specimens. In all the welded specimens an initial fatigue crack was introduced perpendicularly to the welding bead. In the A533B welded specimen the crack growth resistance curves were measured for the five cases where an initial crack tip was at a position 1.5 mm distant from the fusion line; in a heat-affected zone (HAZ); at the fusion line; in the weld resistance evaluated by J-integral varied in respect to the base metal, the weld metal, the HAZ, and the fusion line. The resistance values for these crack tip locations, however, spread only over a narrow range. This can be explained by the fact that the mechanical properties of the base metal, the weld metal and the HAZ are only slightly different from each other. On the other hand, in the A533B-HT80 specimens, the crack growth resistance was strongly affected by the relative positions of the steels in the specimen and the width ratio of each steel to the specimen. The experimental results are discussed in terms of the stress analysis results obtained by finite element method (FEM).
X-ray diffraction investigations on individual grains in the polycrystalline nickel-base superalloy IN939 during cyclic loading. I. X-ray rocking curve broadening Dupke, R. and Reimers, W. Z. Metallkd. (1995) 86 (5), 371-377 X-ray diffraction investigations were carried out to prove that X-ray methods can be applied for the assessment of fatigue-induced changes in the microstructure of Ni-base superalloys. Since the investigations were performed on single grains of a coarse-grained alloy (IN 939), analysis of X-ray rocking curves can be applied. It was shown that the width of a rocking curve is sensitive to even small plastic deformations, and that for the given experimental conditions the broadening can be taken as a measure of the accumulated plastic strain resulting from cyclic loading. The observed anisotropic behaviour of rocking curve broadening could be explained by the concept involving activation of selected slip systems.
Artificial neural network technology as a method to evaluate the fatigue life of weldments with welding defects Han, Y.-L. Int. J. Pressure Vessels Piping (1995) 63 (2), 205-209 The neural network method is introduced to evaluate the fatigue [ile of weldments with welding defects. In particular, as an example it was used to evaluate the fatigue life of a specimen with welding defects. This example shows the feasibility that the neural network can be used to predict the fatigue life of a welding specimen with welding defects.
Life prediction of pressure vessel nozzles Giglio, M. and Vergani, L. Int. J. Pressure Vessels Piping (1995) 63 (2), 199-204 When a material yields, local stress and strain behaviour changes, especially if there is a notch: determination of the local strain value can be difficult. Therefore it is not easy to predict the life of mechanical components in the low-cycle region. In the present work pressure vessels are considered and fatigue tests carried out. The most stressed zones, which are at the connections between the nozzles and the vessel, are subjected to cyclic loads with subsequent repeated plastic strains, which cause nucleation and propagation of fatigue cracks. The life of such a mechanical component under low cycle fatigue can be predicted by utilizing the life strain curves e Nf or the energy approach (plastic strain and total strain energy density), in the present work, life prediction is performed by considering several different approaches. The results are compared with the experimental results obtained by fatigue testing pressure vessel nozzles. The material considered is Fe510 B UNI 7070-72 steel.
The paper expounds experimental results of toroidal bellows behaviour. The analysis shows that, compared with U-shaped bellows, toroidal bellows have smaller internal pressure-induced stress, longer fatigue life, stronger ability to resist internal pressure instability, and are more suited for higher internal pressure situations.
The ASME Code, Section lII, Subsection NB cumulative damage assessment method has been used to assess the results from tests performed on 23 pressurized piping branch junctions, subjected to simulated seismic loadings that induced resonant, in-plane run pipe bending. Other methods of componenl life evaluation are also briefly reviewed and their relative merits discussed. The significance of the relevant parameters used in the assessment is described and the results are contrasted with others, obtained using the same method, from tests on similar components performed elsewhere. Usage factors greater than I, which are indicative of a conservative prediction of fatigue failure using the Code standard procedure, are reported. The level of conservation of the Code method is discussed. SEM observations on cyclic deformation process of titanium monocrystal stressed along [0001] Tan, X.L. and Gu, H.C. Chin. J. Mater. Res. (1995) 9 (2), 103-106 (in Chinese) Monocrystals were grown from zone-melting refined titanium. A specimen with the loading axis parallel to the [0001] direction was cyclically deformed within the chamber of a scanning electron microscope. The results indicated that the cyclic strain was accommodated almost entirely by twin bands consisting of ~1012(, {1122(, and {1124( twins. Fatigue cracks were found to initiate along the midrib of twin hands. Photomicrographs, 10 ref.
In situ SEM measurements of crack closure for small fatigue cracks in aluminium 2024-T351 Halliday, M.D., Poole, P. and Bowen, P. Fatigue Fract. Eng. Mater. Struet. (1995) 18 (6), 717 729 Crack closure has been measured for a range of small, selt~-initiated fatigue cracks using in situ SEM loading. Cracks were grown at positive R ratios in the aluminium alloy 2024-T351 and at nominal AK levels that extend substan. tially below the corresponding long crack threshold. The crack closure stress of the small cracks decreased and the K~ level increased with increasing crack size until the long crack value near threshold was reached. For cracks of depth larger than about one grain size, a good correlation was obtained between small and long crack growth rate data in terms of AK~,. Photomicrographs, graphs, 36 ref. Effect of sensitizing heat treatment on fatigue crack growth properties at liquid helium temperatures Konosu, S., Kishiro, T., Ivano, 0., Nunoya, E, Nakajima, H. and T~uji. H. Fatigue Fraet. Eng. Mater. Struct. (June 1995) 18 (6), 671 678 Many cases exist where materials supporting superconducting magnets at liquid helium temperature (4.2 K) are subjected to repeated applications of thermal and electromagnetic stresses. Additionally, since welding cannot be avoided, it is highly desirable that the materials used for supporting superconducting magnets possess excellent strength and toughness in addition to superior mechanical properties after heat treatment. In the current research, an austenitic stainless steel was subjected to a sensitizing heat treatment whose effects, at 4.2 K, on the tensile and the fatigue crack growth properties were clarified. Tensile ductility of the sensitized material was markedly reduced to about one half that of the solution-treated material because of an intergranular form of fracturing in such material. Fatigue crack growth rate of the sensitized material was faster than that of the solution-treated material because of the tendency [or cracks to develop intergranularly. Photomicrographs, graphs, 12 ref.
Passivation effects on crack closure in the fatigue crack propagation of a peak-aged A L - L i - Z r alloy in NaCI a n d Na2SO 4 solutions Chun, Y.-G. and Pvun, S.-I. Fatigue Fraet. Eng. Mater. Struct. (1995) 18 (6), 661~670 Fatigue cracking of a peak-aged A L - L i - Z r alloy was investigated by measuring crack closure as a function of applied anodic potential in 0.6 M NaCI and 0.5 M Na2SO4 solutions with an unloading elastic compliance technique, and by comparison with crack closure in dry air. The present work involves complementary anodic behaviour of the AI-Li-Zr alloy in both solutions by potentiodynamic polarization and potentiostatic current transient experiments. From the repassivation rates in the passivation potential range in both solutions, it is indicated that a more stable passive film is formed at lower applied anodic potential than at higher applied anodic potential. The intrinsic fatigue crack propagation (FCP) rates under unstable passivation potential in both solutions were significantly larger than those obtained in dry air. Under stable passivation potential in both solutions, however, the intrinsic FCP rates in the low AK~. range were slightly lower than those obtained in dry air. The crack closure in the low AK~, range increased under stable passivation potential, in dry air and under unstable passivation potential. The high crack closures appearing in the low AK~.t~ range were characterized by a tortuous fracture
Fatigue Abstracts
Computational strategies for fatigue crack growth in three dimensions with application to aircraft components O'Donoghue, P.E., Atluri, S.N. and Pipkins, D.S. Eng. Fract. Mech. (1995) 52 (l), 51-64
Experimental research of toroid-shaped bellows behaviour Li, T., Luo, X. and Long, X. Int. J. Pressure Vessels Piping (1995) 63 (2), 141-146
The finite element alternating method, which has proved to be an extremely efficient scheme for the accurate calculation of stress intensity factors, is augmented here by an algorithm to calculate the fatigue life, under cyclic loading of three-dimensional structural components. The alternating method involves the combination of an analytical infinite body solution with a numerical solution for the uncracked physical structure. The advantage here is that mesh generation and computational time are considerably reduced, since this finite element approach only entails an analysis of the uncracked body. These simplifications make it possible to implement a three-dimensional fatigue crack growth algorithm into the alternating method. This approach has been applied here to various fatigue problems in complex 2024 aircraft components. Solutions were initially developed for constant-amplitude loading and then extended to the more difficult case of variable-amplitude loading. Graphs, 12 ref.
Cumulative damage assessment of pressurized piping branch junctions under in-plane run pipe simulated seismic bending Taguaiyu, K., Moffat, D.G. and Moreton, D.N. Int. J. Pressure Vessels Piping (1995) 63 (2), 119-128
Crack growth resistance in bimetallic weldment Homma, H., Kanto, Y., Kubo, T. and Tanaka, Y. Int. J. Pressure Vessels Piping (1995) 63 (3), 225-236 Two types of welded specimen were used in an experiment relating to crack growth behaviour near to and in a welding bead. One was cut from a weldment of two A533B steel plates (A533B welded specimen) and the other from a weldment of A533B steel with high-strength steel HT80 plate (A533B-HT80 welded specimen). In the experiments, the crack growth resistance curves were measured using compact tension specimens. In all the welded specimens an initial fatigue crack was introduced perpendicularly to the welding bead. In the A533B welded specimen the crack growth resistance curves were measured for the five cases where an initial crack tip was at a position 1.5 mm distant from the fusion line; in a heat-affected zone (HAZ); at the fusion line; in the weld resistance evaluated by J-integral varied in respect to the base metal, the weld metal, the HAZ, and the fusion line. The resistance values for these crack tip locations, however, spread only over a narrow range. This can be explained by the fact that the mechanical properties of the base metal, the weld metal and the HAZ are only slightly different from each other. On the other hand, in the A533B-HT80 specimens, the crack growth resistance was strongly affected by the relative positions of the steels in the specimen and the width ratio of each steel to the specimen. The experimental results are discussed in terms of the stress analysis results obtained by finite element method (FEM).
X-ray diffraction investigations on individual grains in the polycrystalline nickel-base superalloy IN939 during cyclic loading. I. X-ray rocking curve broadening Dupke, R. and Reimers, W. Z. Metallkd. (1995) 86 (5), 371-377 X-ray diffraction investigations were carried out to prove that X-ray methods can be applied for the assessment of fatigue-induced changes in the microstructure of Ni-base superalloys. Since the investigations were performed on single grains of a coarse-grained alloy (IN 939), analysis of X-ray rocking curves can be applied. It was shown that the width of a rocking curve is sensitive to even small plastic deformations, and that for the given experimental conditions the broadening can be taken as a measure of the accumulated plastic strain resulting from cyclic loading. The observed anisotropic behaviour of rocking curve broadening could be explained by the concept involving activation of selected slip systems.
Artificial neural network technology as a method to evaluate the fatigue life of weldments with welding defects Han, Y.-L. Int. J. Pressure Vessels Piping (1995) 63 (2), 205-209 The neural network method is introduced to evaluate the fatigue [ile of weldments with welding defects. In particular, as an example it was used to evaluate the fatigue life of a specimen with welding defects. This example shows the feasibility that the neural network can be used to predict the fatigue life of a welding specimen with welding defects.
Life prediction of pressure vessel nozzles Giglio, M. and Vergani, L. Int. J. Pressure Vessels Piping (1995) 63 (2), 199-204 When a material yields, local stress and strain behaviour changes, especially if there is a notch: determination of the local strain value can be difficult. Therefore it is not easy to predict the life of mechanical components in the low-cycle region. In the present work pressure vessels are considered and fatigue tests carried out. The most stressed zones, which are at the connections between the nozzles and the vessel, are subjected to cyclic loads with subsequent repeated plastic strains, which cause nucleation and propagation of fatigue cracks. The life of such a mechanical component under low cycle fatigue can be predicted by utilizing the life strain curves e Nf or the energy approach (plastic strain and total strain energy density), in the present work, life prediction is performed by considering several different approaches. The results are compared with the experimental results obtained by fatigue testing pressure vessel nozzles. The material considered is Fe510 B UNI 7070-72 steel.
The paper expounds experimental results of toroidal bellows behaviour. The analysis shows that, compared with U-shaped bellows, toroidal bellows have smaller internal pressure-induced stress, longer fatigue life, stronger ability to resist internal pressure instability, and are more suited for higher internal pressure situations.
The ASME Code, Section lII, Subsection NB cumulative damage assessment method has been used to assess the results from tests performed on 23 pressurized piping branch junctions, subjected to simulated seismic loadings that induced resonant, in-plane run pipe bending. Other methods of componenl life evaluation are also briefly reviewed and their relative merits discussed. The significance of the relevant parameters used in the assessment is described and the results are contrasted with others, obtained using the same method, from tests on similar components performed elsewhere. Usage factors greater than I, which are indicative of a conservative prediction of fatigue failure using the Code standard procedure, are reported. The level of conservation of the Code method is discussed. SEM observations on cyclic deformation process of titanium monocrystal stressed along [0001] Tan, X.L. and Gu, H.C. Chin. J. Mater. Res. (1995) 9 (2), 103-106 (in Chinese) Monocrystals were grown from zone-melting refined titanium. A specimen with the loading axis parallel to the [0001] direction was cyclically deformed within the chamber of a scanning electron microscope. The results indicated that the cyclic strain was accommodated almost entirely by twin bands consisting of ~1012(, {1122(, and {1124( twins. Fatigue cracks were found to initiate along the midrib of twin hands. Photomicrographs, 10 ref.
In situ SEM measurements of crack closure for small fatigue cracks in aluminium 2024-T351 Halliday, M.D., Poole, P. and Bowen, P. Fatigue Fract. Eng. Mater. Struet. (1995) 18 (6), 717 729 Crack closure has been measured for a range of small, selt~-initiated fatigue cracks using in situ SEM loading. Cracks were grown at positive R ratios in the aluminium alloy 2024-T351 and at nominal AK levels that extend substan. tially below the corresponding long crack threshold. The crack closure stress of the small cracks decreased and the K~ level increased with increasing crack size until the long crack value near threshold was reached. For cracks of depth larger than about one grain size, a good correlation was obtained between small and long crack growth rate data in terms of AK~,. Photomicrographs, graphs, 36 ref. Effect of sensitizing heat treatment on fatigue crack growth properties at liquid helium temperatures Konosu, S., Kishiro, T., Ivano, 0., Nunoya, E, Nakajima, H. and T~uji. H. Fatigue Fraet. Eng. Mater. Struct. (June 1995) 18 (6), 671 678 Many cases exist where materials supporting superconducting magnets at liquid helium temperature (4.2 K) are subjected to repeated applications of thermal and electromagnetic stresses. Additionally, since welding cannot be avoided, it is highly desirable that the materials used for supporting superconducting magnets possess excellent strength and toughness in addition to superior mechanical properties after heat treatment. In the current research, an austenitic stainless steel was subjected to a sensitizing heat treatment whose effects, at 4.2 K, on the tensile and the fatigue crack growth properties were clarified. Tensile ductility of the sensitized material was markedly reduced to about one half that of the solution-treated material because of an intergranular form of fracturing in such material. Fatigue crack growth rate of the sensitized material was faster than that of the solution-treated material because of the tendency [or cracks to develop intergranularly. Photomicrographs, graphs, 12 ref.
Passivation effects on crack closure in the fatigue crack propagation of a peak-aged A L - L i - Z r alloy in NaCI a n d Na2SO 4 solutions Chun, Y.-G. and Pvun, S.-I. Fatigue Fraet. Eng. Mater. Struct. (1995) 18 (6), 661~670 Fatigue cracking of a peak-aged A L - L i - Z r alloy was investigated by measuring crack closure as a function of applied anodic potential in 0.6 M NaCI and 0.5 M Na2SO4 solutions with an unloading elastic compliance technique, and by comparison with crack closure in dry air. The present work involves complementary anodic behaviour of the AI-Li-Zr alloy in both solutions by potentiodynamic polarization and potentiostatic current transient experiments. From the repassivation rates in the passivation potential range in both solutions, it is indicated that a more stable passive film is formed at lower applied anodic potential than at higher applied anodic potential. The intrinsic fatigue crack propagation (FCP) rates under unstable passivation potential in both solutions were significantly larger than those obtained in dry air. Under stable passivation potential in both solutions, however, the intrinsic FCP rates in the low AK~. range were slightly lower than those obtained in dry air. The crack closure in the low AK~, range increased under stable passivation potential, in dry air and under unstable passivation potential. The high crack closures appearing in the low AK~.t~ range were characterized by a tortuous fracture