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Fatigue and corrosion fatigue of beryllium-copper spring materials
Fatigue Abstracts applied potentials. A significant potential dependence of the transient current was found, however, in the stage of stable current (saturation), which is correlated with different electrochemical reactions in the slip bands. Corrosion fatigue lives were measured and analysed in relation to the current behaviour. Photomicrographs, graphs, 25 ref. Cyclic ~ interacflm in m o w - and pelycrymdliae AISI 316L m d a l ~ steel in H2SO4 mintim, m . Potential d e p a d m c e of the mechanical behavior dm'ing corredmn fatigue. Li, Y.-F., Farrington, G.C. and Laird, C. Acta Metall. Mater. (Mar. 1993) 41 (3), 723-737 Measurements of mechanical parameters and surface examinations have been carried out on mono- and polycrystalline specimens of an AISI 316L stainless steel, which were cycled in a 1N H2S04 solution. Analysis was made in relation to both the number of cycles and the applied potentials. The environment was found to have no influence on such bulk properties as the softening rate and flow stress, because the oxide film on the stainless steel is very thin. The magnitude of the strain localization was enhanced by preferential dissolution of atoms in the slip bands, a tendency which decreased with increase in potential. Crack nucleation within the sfip bands was caused either by the high dissolution rate imposed by the applied potential (in the corrosion and the transition regions) or by the galvanic effect (in the passive I region). General corrosion was found to have major effects on the crack propagation process in both the corrosion region, where blunting inhibited propagation, and the transition region, where corrosion-stimulated 'sharpening' promoted propagation. In the passive II region, environment-assisted strain localization and the galvanic effect were prevented by the stable passive film and the rapid passivation reaction. Photomicrographs, graphs, 31 ref. Famine and corrm4oa fatigue of beryllium-copper spring materials. Bagheri, R. and Miller, G.A. ASTM J. Test. Eval. (Mar. 1993) 21 (2), 101-106 Fine gauge, 0.006 in (0.15 mm) thick, B e - C u spring materials with tensile strength in the range of 70-145 ksi (482-999 MPa) were subjected to cyclic loading in air and salt water environments. Plain and notched (centre hole) 'hourglass' specimens were subjected to sinusoidal loading with R (minimum stress/maximum stress) = 0.1 at cyclic fre,'~uencies of 50 Hz in air and 1 Hz in salt water. Fatigue life was typically from 104 to 106 cycles with crack initiation as the dominant fatigue process. The excellent fatigue performance of Be-Cu alloys in salt water is well known; however, current findings demonstrate 10-37% reduction in fatigue strength of unnotched specimens in this environment for a life of 3 x 105 cycles. This strength degradation is attributed to the use of a lower cyclic frequency for present than for previous tests, i.e. 1 vs approx 20 Hz. There was no effect of salt water on crack initiation in notched specimens. The ratios of the fatigue strengths (coldroiled/annealed and aged/annealed) for plain and notched specimens tested in air decreased from 2 to approximately 1.4 as fatigue fife increased from 104 to 106 cycles. This effect is attributed to cyclic hardening of the annealed material. The fatigue stress concentration factor, Kr = (plain fatigue strength/ notched fatigue strength) increased by approximately 30% as fatigue cycles increased from 104 to 106. The ranking of Kf values of the various material conditions from highest to lowest was: cold-rolled, aged, and annealed. Photomicrographs, graphs, 18 ref. Quantitative analysis of cam follower wear in rebtiun to various material properties. Kano, M. and Kimura, Y. Wear (13 Apr. 1993) 162-164, (B), 897-905 Results of wear simulation motoring experiments are presented for various wear-resistant materials; i.e. Si3N4 alloy cast iron, C r - M o steels, low-alloy steels, and high-speed tool steels used to make automotive engine cam followers. A multiple regression analysis is conducted to find the relation between follower wear and typical material properties. A linear regression formula is derived that provides a high multiple correlation coefficient for a series of ferro-bascd powder metals that adhere to the regression formula. Close observation of worn cam follower surfaces reveals that a common wear mechanism is at work: fatigue cracks propagate in the matrix around carbides to detach wear particles. This mechanism coincides with the implications of the formula. Graphs, photomicrographs, 10 ref. Elevated temperatm'¢ fatigue of PM lilum|nlum alloy 8009. Reynolds, A.P. Scr. MetaU. Mater. (15 Jan. 1993) 28 (2), 201-206 A study of the effect of loading frequency and waveform on the fatigue crack growth behaviour of the powder metallurgy aluminium alloy 8009 was carried out at temperatures of 121 and 288 °C in air. Results show that growth rates and effect of loading frequency are enhanced at intermediate temperatures. Time*dependent crack growth appears to be associated with positive crack tip loading rates. These results indicate that environmental interaction is not primarily responsible for crack growth behaviour in 8009 alloy. The exact mechanism is not clear. Graphs, 23 ref. A eampm.ative study on the effects of interference lit and cold exl~n~oa on the f~rltm Me of eradxed boks. Lam, Y.C. Scr. MetaU. Mater. (15 Jan. 1993) 28 (2), 191-195 The fatigue life of cracked holes with cold expansion or interference fit is studied under different loading conditions and crack lengths. Both treatments increased fatigue life. Cold expansion was more effective for low R-ratios and short cracks. Cold expansion was not effective for long cracks or high R-ratios. Interference fit was not as effective as cold expansion at low Rratios but was not sensitive to R-ratio or crack length. Test material: 2024-T3. Graphs, 9 ref.
Effect of external loading on wear maps of alnmlaima alleys. Zhou, Z.R. and Vincent, L. Wear (13 Apr. 1993) 162-164, (A), 619-623 Fretting fatigue tests differ from fretting wear tests in that an axial (or body) load is added to the contact load. In most fretting devices, the contact amplitude, which has been shown to be a governing parameter in crack initiation, depends on the elongation of the test specimen, which itself varies with the axial load. This difficulty can lead to erroneous conclusions when transported to industrial components. In this paper, we present a new device and a new methodology, which give the test conditions leading to crack initiation. In this system, the 'body' and 'contact' loads and amplitude are controlled separately. The test is called 'fretting-static fatigue', owing to the constant body stress (R = ~,,inOm,x = 1). Two fretting wear maps are discussed: in running condition fretting maps, zones of stick, partial slip and gross sliding are identified; in material response fretting maps, which plot equivalent stress vs amplitude, the three zones of no degradation, cracking, and particle detachment are identified. The skin tension ~ is used to plot material response fretting maps. o~, appears to be a good criterion, as it can be compared with the fatigue limit of the material and can take into account the original residual stresses in the crack domain. In addition, ~,= can be used by designers to predict the fife of industrial components. This methodology is applied to the fretting fatigue characterization of three industrial aluminium alloys (2024, 2091 and 775) widely used in aeronautics. Their fretting behaviour is discussed with respect to material properties such as fatigue limit and crack propagation resistance. Photomicrographs, graphs, 17 ref.
Relinhfi~ assessellalt o f ~ ~ n[M}nprobabliisti¢ [ractllre nt~ehmdCS. lshikawa, H., Tsurui, A., Tanaka, H. and lshikawa, H. Prob. Eng. Mech. (1993) g (1), 43-56 The stochastic fatigue crack growth model (termed the Tsurui-Ishikawa model) based upon the Markov approximation method introducing the notion of death point has been proposed, and a great deal of its practical usefulness in the reliability assessment of structures has been demonstrated for those cases where the fatigue crack propagation process plays a crucial role in their failure. By performing the reliability analysis, based upon the model, in consideration of uncertainties of both initial crack length and their number, the effect of such uncertainties has been clarified on the refiability degradation of a structural component. This result is of much interest from a practical viewpoint because it gives a guideline to determine the safe life (design life or inspection interval) to assure the prescribed level of reliability for random loadings with a variety of correlation times. Further, studies have been made on which parameter is the most significant according to the problem through parameter sensitivity studies. With the aid of the proposed model, reliability assurance or reliability-based design can be performed properly against fatigue failure of structures subjected to random loading. Graphs, 62 ref.
Effect of stress ratio on crack propagation life distribulkm under random loading, lshikawa, H., Tsurui, A., Utsumi, A., Tanaka, H. and lshikawa, H. Prob. Eng. Mech. (1993) 8 (1), 35-41 A stochastic crack growth model under stationary random loading has been constructed based upon Walker's growth law, which accounts for the effect of the stress ratio. By use of this model, the crack length distribution and the crack propagation life distribution have been successfully derived, both in a closed form, with the aid of the Marker approximation method and renewal process theory. The validity and applicability of the derived distributions as well as the effect of the stress ratio on the life distribution have been discussed on the basis of the results obtained by Monte Carlo simulation techniques. From these results, first, the crack propagation based upon Walker's law is revealed to be of the Birnbaum-Saunders type, similar to that based upon the Paris-Erdogan law. Secondly, the mean and the variance of the life distribution in consideration of the stress ratio both prove to be smaller than those of the life distribution without consideration of the stress ratio. Finally, the coefficient of variation of the life distribution is, however, almost identical between both cases with and without consideration of the stress ratio. Though the coefficient of variation at the early stage of propagation becomes large, it gradually decreases to a certain value as the crack length increases. Graphs, spectra, 10 ref. Experimental estimation of the probability d i s t r i b ~ lives, ltagaki, H., Ishizuka, T. and Yon, H.P. Prob. Eng. Mech. (1993) g (1), 25-34
o f fatigue crack growth
A method to estimate numerically the reliability of fatigue-sensitive structures with respect to fatigue crack growth is presented. A method is proposed to determine experimentally the probability distribution functions of material parameters of the Paris law, da/dN = C (AK/Ko) m, using stress intensity factor controlled tests. The auto-correlation function of the resistance to fatigue crack growth, 1/C, is also estimated from the experimental data. The results of a high tensile strength steel (4360 Gr.50D) show that the distribution of the parameter m is approximately normal and that of IlC is a threeparameter Weibuil. The merit of the proposed method is that only a small number of tests are required to determine these functions. The probability distribution of the fatigue crack length after a given number of load cycles or the number of load cycles for a crack to reach a given length can be estimated by simulations of non-Gaussian random processes having these functions. Spectra, graphs, numeric data, 19 ref.
Fatigue, 1994, Vol 16, April 233
Effect of external loading on wear maps of alnmlaima alleys. Zhou, Z.R. and Vincent, L. Wear (13 Apr. 1993) 162-164, (A), 619-623 Fretting fatigue tests differ from fretting wear tests in that an axial (or body) load is added to the contact load. In most fretting devices, the contact amplitude, which has been shown to be a governing parameter in crack initiation, depends on the elongation of the test specimen, which itself varies with the axial load. This difficulty can lead to erroneous conclusions when transported to industrial components. In this paper, we present a new device and a new methodology, which give the test conditions leading to crack initiation. In this system, the 'body' and 'contact' loads and amplitude are controlled separately. The test is called 'fretting-static fatigue', owing to the constant body stress (R = ~,,inOm,x = 1). Two fretting wear maps are discussed: in running condition fretting maps, zones of stick, partial slip and gross sliding are identified; in material response fretting maps, which plot equivalent stress vs amplitude, the three zones of no degradation, cracking, and particle detachment are identified. The skin tension ~ is used to plot material response fretting maps. o~, appears to be a good criterion, as it can be compared with the fatigue limit of the material and can take into account the original residual stresses in the crack domain. In addition, ~,= can be used by designers to predict the fife of industrial components. This methodology is applied to the fretting fatigue characterization of three industrial aluminium alloys (2024, 2091 and 775) widely used in aeronautics. Their fretting behaviour is discussed with respect to material properties such as fatigue limit and crack propagation resistance. Photomicrographs, graphs, 17 ref.
Relinhfi~ assessellalt o f ~ ~ n[M}nprobabliisti¢ [ractllre nt~ehmdCS. lshikawa, H., Tsurui, A., Tanaka, H. and lshikawa, H. Prob. Eng. Mech. (1993) g (1), 43-56 The stochastic fatigue crack growth model (termed the Tsurui-Ishikawa model) based upon the Markov approximation method introducing the notion of death point has been proposed, and a great deal of its practical usefulness in the reliability assessment of structures has been demonstrated for those cases where the fatigue crack propagation process plays a crucial role in their failure. By performing the reliability analysis, based upon the model, in consideration of uncertainties of both initial crack length and their number, the effect of such uncertainties has been clarified on the refiability degradation of a structural component. This result is of much interest from a practical viewpoint because it gives a guideline to determine the safe life (design life or inspection interval) to assure the prescribed level of reliability for random loadings with a variety of correlation times. Further, studies have been made on which parameter is the most significant according to the problem through parameter sensitivity studies. With the aid of the proposed model, reliability assurance or reliability-based design can be performed properly against fatigue failure of structures subjected to random loading. Graphs, 62 ref.
Effect of stress ratio on crack propagation life distribulkm under random loading, lshikawa, H., Tsurui, A., Utsumi, A., Tanaka, H. and lshikawa, H. Prob. Eng. Mech. (1993) 8 (1), 35-41 A stochastic crack growth model under stationary random loading has been constructed based upon Walker's growth law, which accounts for the effect of the stress ratio. By use of this model, the crack length distribution and the crack propagation life distribution have been successfully derived, both in a closed form, with the aid of the Marker approximation method and renewal process theory. The validity and applicability of the derived distributions as well as the effect of the stress ratio on the life distribution have been discussed on the basis of the results obtained by Monte Carlo simulation techniques. From these results, first, the crack propagation based upon Walker's law is revealed to be of the Birnbaum-Saunders type, similar to that based upon the Paris-Erdogan law. Secondly, the mean and the variance of the life distribution in consideration of the stress ratio both prove to be smaller than those of the life distribution without consideration of the stress ratio. Finally, the coefficient of variation of the life distribution is, however, almost identical between both cases with and without consideration of the stress ratio. Though the coefficient of variation at the early stage of propagation becomes large, it gradually decreases to a certain value as the crack length increases. Graphs, spectra, 10 ref. Experimental estimation of the probability d i s t r i b ~ lives, ltagaki, H., Ishizuka, T. and Yon, H.P. Prob. Eng. Mech. (1993) g (1), 25-34
o f fatigue crack growth
A method to estimate numerically the reliability of fatigue-sensitive structures with respect to fatigue crack growth is presented. A method is proposed to determine experimentally the probability distribution functions of material parameters of the Paris law, da/dN = C (AK/Ko) m, using stress intensity factor controlled tests. The auto-correlation function of the resistance to fatigue crack growth, 1/C, is also estimated from the experimental data. The results of a high tensile strength steel (4360 Gr.50D) show that the distribution of the parameter m is approximately normal and that of IlC is a threeparameter Weibuil. The merit of the proposed method is that only a small number of tests are required to determine these functions. The probability distribution of the fatigue crack length after a given number of load cycles or the number of load cycles for a crack to reach a given length can be estimated by simulations of non-Gaussian random processes having these functions. Spectra, graphs, numeric data, 19 ref.
Fatigue, 1994, Vol 16, April 233