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Fatigue crack initiation in 403 stainless steel in simulated steam cycle environments: hydroxide and silicate. solutions
Fatigue Abstracts H was found to reduce the fatigue properties of Monel K-500, but did not affect the performance of Marinel alloy. No evidence of obvious microstructural change induced by H was apparent, but the use of H diffusivity data was made in calculations relating to the diffusivity and trapping of H in the two materials. It was demonstrated that the solubility of H, the degree of dislocation-H interaction, and the ease of H trap formation (as a precursor to crack initiation) were lower in Marinel alloy than in Monel K-500, thus contributing to an explanation of the resistance of Marinel alloy to the debilitating effects of H. Graphs, diffraction patterns, 20 ref. Fatigue crack initiation in 403 stainless steel in simulated steam cycle environments: hydroxide and silicate.solutions. Shalaby, H.M., Begley, J.A. and Macdonald, D.D. Br. Corros. J. (1994) 29 (1), 43-52 The fatigue crack initiation behaviour of a 12% chromium turbine blade alloy (403 stainless steel) was studied at a single alternating stress level of 448 MN/m -2 in deaerated solutions of NaOH at pH 10, 12 and 14 and in 1M Na4SiO4 solution (pH 10) at 100 °C. Fatigue life in the hydroxide solution increased with increasing pH and was also good in the silicate solution. Long cracks of similar appearance were found to be initiated on the surface of the steel in all the solutions except NaOH at pH 14, in which short incipient microcracks of a transgranular nature initiated on the specimen surface, regardless of the selective attack that occurred at grain and phase boundaries. It was found that increasing the pH of the hydroxide solution and the presence of the silicate anion both cause the initiated cracks to propagate into the bulk of the material in a transgranular mode, thereby resulting in a longer fatigue life. Graphs, photomicrographs, 19 ref. Fatigue strength of nickel electrodeposits prepared in ultrasonically agitated bath. Prasad, P.B.S.N.V.. Ahila, S., Vasudevan, R. and Seshadri, S.K. J. Mater. Sci. Lett. (1 Jan. 1994) 13 (1), 15-16 The beneficial effect of a nickel coating on the fatigue properties of steels is reported. The aim was to elucidate the problem of catastrophic failure due to hydrogen embrittlement in Ni-plated high-strength steels. Mild steel was coated with a 20 o,m layer of Ni using static bath and ultrasonically agitated bath techniques. Fatigue testing was carried out in air at room temperature (25 °C). The number of cycles to failure was found to be significantly greater for the ultrasonically prepared specimens. This was ascribed to a reduction in the tensile component of residual stresses due to a smoother surface finish (fewer surface irregularities at which fatigue failure was initiated). Ultrasonically prepared Ni deposits contain little H, whereas in statically coated deposits some H enters the deposit, causing embrittlement, while the rest rises along the cathode surface, causing streaky deposits. Graphs, 8 ref. The influence of the waveform on the behavior of the early stage of fatigue for aluminium. Fei, G. T. Scr. Metall. Mater. (15 Nov. 1994) 31 (10), 1405-1408 The change of ultrasonic attenuation under the action of two kinds of fatigue strain waveform for 99.999 AI is investigated. Results show that the variation of ultrasonic attenuation with strain amplitude initially follows either a butterfly or a sinusoidal function. In each case it takes 3000 cycles to reach equilibrium. At a strain amplitude of 400×10 6 the variation of ultrasonic attenuation is greater and not found to stabilize after 2500 cycles. Therefore, at low strain amplitude, the waveform has some influence on the fatigue behaviour. At high strain amplitudes the strain waveform has less influence on the fatigue behaviour. Graphs, 7 ref. Fatigue crack growth characteristics of laser-hardened 4130 steel. Wei, M.Y. and Chen, C. Scr. Metall. Mater. (15 Nov. 1994) 31 (10), 1393-1398 Characteristics of fatigue crack growth rate (da/dN) in laser-hardened AISI 4130 steels have been investigated using residual stress measurements. It has been reported that laser hardening of Cr-Mo-Si steel could i'etard da/dN in the near-AK region. Retardation is mainly due to microstructural changes in the hardened zones of specimens. In addition to microstructure the residual stress also has a significant influence on da/dN. Lower scan rates result in a deeper hardened zone and a higher H/T ratio. In the laser-hardening process a hard layer of martensite with compressive residual stresses is generated on the laser-impinged area. The compressive stress decreases the mean stress and enhances the crack closure. As a result the overall decrease in da/dN of laser-treated 4130 specimens was observed as the crack propagates along the hardened bands. Maximum retardation is observed at a particular H/T ratio coinciding with the highest compression residual stress in the hardened zones of the specimen. Graphs, photomicrographs, 14 ref.
585
The influence of low-cycle fatigue properties of metals on scuff resistance. Kim, K. Dissertation, University of Michigan Many studies have been devoted to the solution of the scuffing problem, and there have been three goals in this research: (1) prediction of scuffing; (2) prevention of scuffing; and (3) development of a descriptive scuffing mechanism: Correct identifcation of scuffing mechanisms appears to be the most valuable of these pursuits in the long run, since knowledge of mechanisms would enable prediction and prevention of scuffing. Several models or possible mechanisms in the initiation of scuffing have been proposed to date. However, none of these scuffing models or mechanisms gives a complete description of the scuffing processes, and none of these models considers cyclic stress properties of the materials involved. It is hypothesized that lowcycle fatigue (LCF) is the one of the factors responsible for the initiation of scuffing, and the purpose of this thesis is to investigate the relation between LCF and scuffing to confirm or refute that hypothesis. Since work-hardening ability can be used as a simple representation of LCF resistance, the influence of LCF resistance on scuffing was investigated by observing the change of surface work-hardening in conventional step-loading tests. Then relations between true fracture ductility, LCF properties and scuff resistance were developed from proportional loading tests. This correlation is useful for the selection of scuff-resistant materials in steels. The work-hardening behaviour of a sliding surface is shown by microhardness indentations on wear tracks. Relations between true fracture ductility, LCF properties and scuff resistance are investigated using correlation analysis after measuring true fracture ductility and estimating LCF properties from measured tensile properties for specimens with a wide range of hardness. From this study, a strong correlation was found between the sliding endurance in scuffing tests under the condition of proportional loading and the true fracture ductility in tensile tests, which in turn correlates with LCF resistance of materials. This implies that the sliding endurance relates with the fatigue life of sliding materials. A phenomenological correlation between LCF and scuffing, along with similarities between them, confirms that LCF is one of the factors responsible for scuffing initiation of steels. Treatment of random fatigue loads of criteria for load spectrum preparation. Wang, D., Ping, A. and Xu, H. J. Northeast. Univ. Nat. Sci. (China) (1994) 15 (4), 327-331 (in Chnese) The choice criteria for small random fatigue loads and the interactions and sequence effects of loads on the fatigue failure are studied. A preparation method with relevant criteria is thus developed for fatigue load spectrum by which the equivalent failure due to random history can be found. Graphs, 5 ref. The crack growth toward the grain boundary of a fatigued aluminium bicrystal. Li, S., Chen, M., Zhang, T., Sun, L. and Wang, Z. Scr. Metall. Mater. (1 Oct. 1994) 31 (7), 897-902 Super-pure (99.999%) AI bicrystals were subjected to push-pull fatigue testing at room temperature in dry air at 0.4 Hz frequency. After 2000 cycles, the well-developed slip bands were examined by SEM and TEM. The crack initiation and growth occur preferentially along slip bands in fatigued A1 bicrystals due to cumulative fatigue damage. For the mono-slip component, a growing crack approaching the grain boundary is deflected away from its original path and may stop growing. For the multi-slip component, a growing crack approaching the grain boundary is also deflected away from its original path but could grow in a nominal mode I manner. The internal stress resulting from dislocations distributed in between the crack tip and grain boundary plays a major role in crack deflection. Photomicrographs, 6 ref. The effects of load ratio and cyclic frequency on the fatigue crack growth rate of 63/37 brass in liquid gallium. Fernandes, P.T.L. and Jones, D.R.H. Scr. Metall. Mater. (1 Oct. 1994) 31 (7), 809-813 Experimental study of fatigue crack growth (FCG) of 63/37 brass (CZ108) in liquid Ga was conducted to investigate the effects of load ratio (R) and cyclic frequency. The tests were carried out in accordance with the ASTM E647 test at 35-+2 °C using a sinusoidal load. At AK>AKth, FCG rates (i.e. crack growth per cycle) in air are independent of load ratio and cyclic frequency, and can be described by the Paris law. FCG rates in liquid Ga are approximately an order of magnitude greater. AKtnvalues in air and liquid Ga increase with decreasing load ratio as a result of roughness-induced crack closure phenomena. In liquid Ga, metal dissolves, which blunts the crack tip, leading to higher values of Akth than those observed in air. In the previously studied aluminium in mercury system, crack tip oxidation caused dewetting of the liquid metal. This led AK,h to increase with time. Graphs, 22 ref.
The effect of infiltration-induced crack closure on crack growth retardation. Sheu, B.C., Song, P.S. and Shin, C.S. Scr. Metall. Mater. (15 Nov. 1994) 31 (10), 1301-1306
The fatigue strength of steel wire ropes. I. Jimenez Atienxa, F.J. Wire Ind. (Oct. 1994) 10, 678-683
The effect of infiltration-induced crack closure on crack growth retardation in AISI 304 stainless steel is examined. Fatigue tests were performed and the crack closure behaviour was monitored after infiltration by different types of epoxy resin. Fatigue life was increased, and the crack growth rate was found to improve on infiltration for all types of epoxy resin. This improvement is more than predictions based on Paris' law. Infiltration-induced artificial crack closure can be useful in prolonging fatigue life. Graphs, photomicrographs, 13 ref.
One of the factors that has the greatest influence on the life of a rope, on its effective life, is the fatigue strength that it must support. This effective life is determined by the succession of alternating stresses. These stresses are defined not only by intensity, by amplitude of the oscillations that such stresses involve, but also by frequency. For calculation of the alternating tensions, it is of primary importance to have exact knowledge of the geometry of the rope, and of the geometric variations imposed by the working conditions during service. Graphs, 5 ref.
585
The influence of low-cycle fatigue properties of metals on scuff resistance. Kim, K. Dissertation, University of Michigan Many studies have been devoted to the solution of the scuffing problem, and there have been three goals in this research: (1) prediction of scuffing; (2) prevention of scuffing; and (3) development of a descriptive scuffing mechanism: Correct identifcation of scuffing mechanisms appears to be the most valuable of these pursuits in the long run, since knowledge of mechanisms would enable prediction and prevention of scuffing. Several models or possible mechanisms in the initiation of scuffing have been proposed to date. However, none of these scuffing models or mechanisms gives a complete description of the scuffing processes, and none of these models considers cyclic stress properties of the materials involved. It is hypothesized that lowcycle fatigue (LCF) is the one of the factors responsible for the initiation of scuffing, and the purpose of this thesis is to investigate the relation between LCF and scuffing to confirm or refute that hypothesis. Since work-hardening ability can be used as a simple representation of LCF resistance, the influence of LCF resistance on scuffing was investigated by observing the change of surface work-hardening in conventional step-loading tests. Then relations between true fracture ductility, LCF properties and scuff resistance were developed from proportional loading tests. This correlation is useful for the selection of scuff-resistant materials in steels. The work-hardening behaviour of a sliding surface is shown by microhardness indentations on wear tracks. Relations between true fracture ductility, LCF properties and scuff resistance are investigated using correlation analysis after measuring true fracture ductility and estimating LCF properties from measured tensile properties for specimens with a wide range of hardness. From this study, a strong correlation was found between the sliding endurance in scuffing tests under the condition of proportional loading and the true fracture ductility in tensile tests, which in turn correlates with LCF resistance of materials. This implies that the sliding endurance relates with the fatigue life of sliding materials. A phenomenological correlation between LCF and scuffing, along with similarities between them, confirms that LCF is one of the factors responsible for scuffing initiation of steels. Treatment of random fatigue loads of criteria for load spectrum preparation. Wang, D., Ping, A. and Xu, H. J. Northeast. Univ. Nat. Sci. (China) (1994) 15 (4), 327-331 (in Chnese) The choice criteria for small random fatigue loads and the interactions and sequence effects of loads on the fatigue failure are studied. A preparation method with relevant criteria is thus developed for fatigue load spectrum by which the equivalent failure due to random history can be found. Graphs, 5 ref. The crack growth toward the grain boundary of a fatigued aluminium bicrystal. Li, S., Chen, M., Zhang, T., Sun, L. and Wang, Z. Scr. Metall. Mater. (1 Oct. 1994) 31 (7), 897-902 Super-pure (99.999%) AI bicrystals were subjected to push-pull fatigue testing at room temperature in dry air at 0.4 Hz frequency. After 2000 cycles, the well-developed slip bands were examined by SEM and TEM. The crack initiation and growth occur preferentially along slip bands in fatigued A1 bicrystals due to cumulative fatigue damage. For the mono-slip component, a growing crack approaching the grain boundary is deflected away from its original path and may stop growing. For the multi-slip component, a growing crack approaching the grain boundary is also deflected away from its original path but could grow in a nominal mode I manner. The internal stress resulting from dislocations distributed in between the crack tip and grain boundary plays a major role in crack deflection. Photomicrographs, 6 ref. The effects of load ratio and cyclic frequency on the fatigue crack growth rate of 63/37 brass in liquid gallium. Fernandes, P.T.L. and Jones, D.R.H. Scr. Metall. Mater. (1 Oct. 1994) 31 (7), 809-813 Experimental study of fatigue crack growth (FCG) of 63/37 brass (CZ108) in liquid Ga was conducted to investigate the effects of load ratio (R) and cyclic frequency. The tests were carried out in accordance with the ASTM E647 test at 35-+2 °C using a sinusoidal load. At AK>AKth, FCG rates (i.e. crack growth per cycle) in air are independent of load ratio and cyclic frequency, and can be described by the Paris law. FCG rates in liquid Ga are approximately an order of magnitude greater. AKtnvalues in air and liquid Ga increase with decreasing load ratio as a result of roughness-induced crack closure phenomena. In liquid Ga, metal dissolves, which blunts the crack tip, leading to higher values of Akth than those observed in air. In the previously studied aluminium in mercury system, crack tip oxidation caused dewetting of the liquid metal. This led AK,h to increase with time. Graphs, 22 ref.
The effect of infiltration-induced crack closure on crack growth retardation. Sheu, B.C., Song, P.S. and Shin, C.S. Scr. Metall. Mater. (15 Nov. 1994) 31 (10), 1301-1306
The fatigue strength of steel wire ropes. I. Jimenez Atienxa, F.J. Wire Ind. (Oct. 1994) 10, 678-683
The effect of infiltration-induced crack closure on crack growth retardation in AISI 304 stainless steel is examined. Fatigue tests were performed and the crack closure behaviour was monitored after infiltration by different types of epoxy resin. Fatigue life was increased, and the crack growth rate was found to improve on infiltration for all types of epoxy resin. This improvement is more than predictions based on Paris' law. Infiltration-induced artificial crack closure can be useful in prolonging fatigue life. Graphs, photomicrographs, 13 ref.
One of the factors that has the greatest influence on the life of a rope, on its effective life, is the fatigue strength that it must support. This effective life is determined by the succession of alternating stresses. These stresses are defined not only by intensity, by amplitude of the oscillations that such stresses involve, but also by frequency. For calculation of the alternating tensions, it is of primary importance to have exact knowledge of the geometry of the rope, and of the geometric variations imposed by the working conditions during service. Graphs, 5 ref.