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Variation in fatigue properties and remaining life prediction
Fatigue Abstracts published results on Ni-based alloys at temperatures up to 700°C and against further published results on Ni-based alloys at temperatures up to 700°C. It appears that for the former series oxidation is the dominant damaging mode, whereas a linear creep damaging mechanism is manifest in the Ni-based alloys. Moreover, levels of cyclic damage in terms of D~ are higher in the latter, ranging between 1[1 3 and 5 x 10 ' a compared with 10 4 to 5 x 10 2 for the steels. A brief comparison is made with damage factors arising from the high strain fatigue deformation mode at elevated temperatures, and other models for the prediction of frequency effects are discussed. Graphs, 35 refs. Some formulae for the effective stress range ratio used in crack growth of 6063-T6 aluminium alloy. Kumar, R. and Singh, K. tnt. J. Pressure Vessels Piping (19941 57 (3), 311-319 The influence of stress ratio R and stress intensity range (AK) on fatigue crack growth experiments were determined for 6063-T6 AI alloy, and crack growth data were analysed with different formulae for the effective stress intensity range ratio U. The data covered R values from 0 to 0.3. A good correlation was obtained from da/dN and AK~fr using the equation for U as a function of R. Graphs, 20 rcf. Prediction method qff probabilistic fatigue strength on the structure of construction. Wang, S.H. and Sun, X.F. Jixie Gongcheng Xuebao (Chin. J. Mech. Eng.) (Feb. 19941 30 (1), 62 68 (in Chinese) An analysis of thc fatigue stochastic damage process was introduced. Then the method predicting probabilistic fatigue strength has been established on the basis of series failure model of surface elements. Many verifications of fatigue testing results indicate that the method has better precision than that of usual fatiguc calculation. A3, 16Mn, 35. 45, 40Cr, 6l)Si2Mn stccls are discussed. Graphs, 8 rcf. Experimental research on stress intensity factor for surface crack at external thread root of threaded connection. Wei, J.Q. Zhong, B.M. and Xu, K.M. .lixie Gongeheng Xuebao (Chin. J. Mech. Eng.) (Feb. 1994) 30 ( l ) , 37-43 (in Chinese) Experimental research on the stress intensity factor in tension for surface cracks at the external thrcad root of a threaded connection is carried out by using James-Anderson's method. On the basis of SIF normalized coefficient values gained from a vast amount of fatigue crack propagation experiments, approximate expressions for stress intensity factor at the deepest point and surtace point of surfacc cracks are obtained by means of stepwise regression analysis. By comparing the results obtained with stress intensity factors for surface cracks in a tcnsion round bar and tension round bar with threads, it is shown that the regularity is good among them. 20CrMo is discusscd. Graphs, 8 ref.
307
micro-hardness as a parameter for the detection of the material's fatigue damage and also for the prediction of the components' remaining life. Graphs, 8 ref.
Improved fatigue life of an autofrettaged thick-walled pressure vessel with an external groove. Koh, S.K. and Stephens, R.I. Int. J. Pressure Vessels Piping (19941 58 (2), 131-145 An autofrettaged thick-walled pressure vessel with an external groove suffers a decreased fatigue life due to cracking at the exterior. To improve the fatigue life of an autofrettaged thick-walled pressure vessel containing an external groove subjected to pulsating internal pressure, a shape change and a shot peening were done at the external groove. The groove shape was changed by using an optimization technique to minimize the stress concentration at the groove root. Stress concentration calculation during the optimization stage was carried out by the finite clement method. Autofrettage residual stresses were simulated by the thermal stresses from the thermal loading analogy. Shot pcening was performed on the changcd groovc region to induce surface compressivc residual stresses. Fatigue tcsts that simulate an autofrettaged thick-walled pressure vessel under pulsating internal pressure loading conditions were performed using C-shaped A723 G r . l C14 steel specimens taken from the autofrettaged thick-walled pressure vessel. Fatigue life improvement of the pressure vessel was achieved by design change of the groove shape to relieve the high stress concentration, and also by surface enhancement at the groove root using shot peening. Simulation fatigue tests resulted in improved fatigue life for the changed and shot peened groove by a factor of 3.5-13. compared with the conventional groove. Graphs, 17 ref.
Effect of preloading on the crack initiation and propagation in notched specimen of a 7075 aluminium alloy. Nakasa, K. J. Jpn Inst. L(fht Met. (May 19941 44 (5), 292-297 (in Japanese) Fatigue tests werc carried out on prcloaded notch specimens of 7075-T6 aluminium alloy under a stress ratio of 11.1 and frequency of 1 IlL and the fatigue crack initiation and propagation behaviours were investigated. The tensile preloading, which corresponds to 80% of fracture load. increases the crack initiation life, while the compressive preloading decreases lhc life. The effect of preloading is larger when the overload ratio, or the ratio of prcload to maximum repeating load. is larger. Through a micro-area X-ray analysis near the notch root, thc compressivc rcsidual stress is discovered to be generated by the tensile prcloading and the maximum repeating stress at notch root is found to be decreased, which will be the main reason for the increase in fatiguc crack initiation life. The crack propagation velocity after crack initiation from the notch root is decreased or increased within the prcload-affccted zonc by the tensile or compressive preloading, respective b Graphs, 18 ref.
The effect of plasma-sprayed coatings on the fatigue of titanium alloy implants. Smith, T. JOM (Feb. 1994) 46 (2), 54-56 The application of Ti plasma-spray coatings to T i - 6 A I - 4 V orthopaedic implants results in a dramatic decrease in high-cycle fatigue performance. The better bonding of the plasma-spraycd and heat-treated implants results in a lower high-cycle fatigue strength. Therefore, the use of plasmaspray textured coatings on implants must be considered with caution. Photomicrographs, 14 rcf. Fatigue behavior of spotwelded galvanized sheets with and without corrosion influence (Schwingfestigkeitsverhalten punktgeschweisster verzinkter Feinbleche ohne und mit Korrosionseinfluss). Dieterich, K. Materialwissenschuft und Werkstofftechnik (Junc 19941 25 (6), 252-263 (in German) The fatigue behaviour of spotwelded sheets from the steels R St 14, St 14 ZE 25/25, St 14 ZE 75/75, St 06 Z 140 and St 06 ZF 140 was investigated. Tests with these connections under constant- and variable-amplitude loading were carried out in air, in a 5% NaCI solution and under condenser water. The results are presented as endurable stresses and cycles to crack initiation. Further, from the comparison of constant- and variable-amplitude testing, damage sums arc derived. Graphs, 17 rcf. High temperature behaviour of materials for gas turbine blades manufactured in new technology (Hochtemperaturverhalten von Werkstoffen aus neuartig gefertigten Gasturbinenschaufeln.) Kloos, K.H., Granacher, J. and Windecker, Th. Materialwisseas'chaft und Werkstofftechnik (June 1994) 25 (6), 235-243 (in German). On gas turbine blades for the middle and last stages of stationary gas turbines, the service-relevant material properties were examined. The specimens were taken from forged blades of alloys Nimonic 101 and Udimet 720 and from two fine-grain versions of cast blades of alloy 1N-792. In the range of servicerelevant temperatures, long-term creep rupture tests, annealing tests, relaxation tests as well as low- and high-cycle fatigue tests were carried out. Graphs, 12 rcf. Variation in fatigue properties and remaining life prediction. Ping, A.. Wang. D.J., Ye, D.Y. and Yang, H.W, J. Northeast Univ., Mater. Sci. (China) (June 19941 15 (3), 263-266 (in Chinese) The variation in mechanical properties of plain carbon steel with carbon content of 0.45% (45) is studied. It was proved that it is feasible to take the
Characterization and quantification of fretting particulates generated in ceramic/metal and metal/metal modular head/taper systems. Bhambri. S.K. and Gilbertson, L.N. Proe. Conf. Biomaterials' Mechanical Properties, Pittsburgh, PA, USA, 5-0 May 1992, pp. 111-126 An cxperimcnal set-up is described for conducting fretting/corrosion fatiguc testing of modular head/taper assemblies used for hip replacement in simulated body environments. The test set-up consisted of a special cell designed to contain simulated body environment and to retain all particles :~ ll.20 ~m, generated due to fretting fatigue. For this purpose, in-line filters were used and the environmental chamber was made of acrylic material to avoid any contamination, The test environment was aerated Ringer's solution circulated in a closed loop at 37°C. The fatigue load was applied on the head in 15° mediolateral anatomic orientation. The functional capabilitics of this set-up were demonstrated by testing alumina ceramic and C o - C r - M o femoral heads fitted on Ti alloy ( T i - 6 A I - 4 V ) tapers, at a fatigue load of 5.34 kN and a stress ratio of 0.1. The results arc summarized in terms of characterization and quantification of any particulates generated, and surface topographical changes on both hcad and taper contact surfaces. Photomicrographs, spectra, 14 ref.
Detection of the onset of fatigue crack growth in rail steels using acoustic emission: Bassim, M.N. Lawrence, S.S.T. and Liu, C.D. Eng. Fract. Mech. (Jan. 19941 47 (2). 207-214 Acoustic emission has held promise for quantitative evaluation of the extent of crack growth in metallic materials during fracture and fatigue. A correlation between acoustic emission and the stress intensity factor was derived, which allows prediction of the stress intensity factor (K or AK) from acoustic emission measurements. At very low values of AK, corresponding to the onset of fatigue crack growth, it was expected that acoustic emission would detect this event. The experimental procedure to verify this assumption involved high-cycle fatigue of four-point bending specimens of a number of rail steels. The fatigue testing was stopped whenever the first indication of acoustic emission activity, manifested by a measureable AK. occurred. This was followed by optical and scanning electron microscopy to detect the sources of cracking in the steels. The results show that, in the rail steels, cracks grow near inclusions. Crack lengths as small as 0.l)09 mm were detected, and the success rate in the detection of the onset of crack growth was IIXI%. Graphs, photomicrographs, 22 ref.
307
micro-hardness as a parameter for the detection of the material's fatigue damage and also for the prediction of the components' remaining life. Graphs, 8 ref.
Improved fatigue life of an autofrettaged thick-walled pressure vessel with an external groove. Koh, S.K. and Stephens, R.I. Int. J. Pressure Vessels Piping (19941 58 (2), 131-145 An autofrettaged thick-walled pressure vessel with an external groove suffers a decreased fatigue life due to cracking at the exterior. To improve the fatigue life of an autofrettaged thick-walled pressure vessel containing an external groove subjected to pulsating internal pressure, a shape change and a shot peening were done at the external groove. The groove shape was changed by using an optimization technique to minimize the stress concentration at the groove root. Stress concentration calculation during the optimization stage was carried out by the finite clement method. Autofrettage residual stresses were simulated by the thermal stresses from the thermal loading analogy. Shot pcening was performed on the changcd groovc region to induce surface compressivc residual stresses. Fatigue tcsts that simulate an autofrettaged thick-walled pressure vessel under pulsating internal pressure loading conditions were performed using C-shaped A723 G r . l C14 steel specimens taken from the autofrettaged thick-walled pressure vessel. Fatigue life improvement of the pressure vessel was achieved by design change of the groove shape to relieve the high stress concentration, and also by surface enhancement at the groove root using shot peening. Simulation fatigue tests resulted in improved fatigue life for the changed and shot peened groove by a factor of 3.5-13. compared with the conventional groove. Graphs, 17 ref.
Effect of preloading on the crack initiation and propagation in notched specimen of a 7075 aluminium alloy. Nakasa, K. J. Jpn Inst. L(fht Met. (May 19941 44 (5), 292-297 (in Japanese) Fatigue tests werc carried out on prcloaded notch specimens of 7075-T6 aluminium alloy under a stress ratio of 11.1 and frequency of 1 IlL and the fatigue crack initiation and propagation behaviours were investigated. The tensile preloading, which corresponds to 80% of fracture load. increases the crack initiation life, while the compressive preloading decreases lhc life. The effect of preloading is larger when the overload ratio, or the ratio of prcload to maximum repeating load. is larger. Through a micro-area X-ray analysis near the notch root, thc compressivc rcsidual stress is discovered to be generated by the tensile prcloading and the maximum repeating stress at notch root is found to be decreased, which will be the main reason for the increase in fatiguc crack initiation life. The crack propagation velocity after crack initiation from the notch root is decreased or increased within the prcload-affccted zonc by the tensile or compressive preloading, respective b Graphs, 18 ref.
The effect of plasma-sprayed coatings on the fatigue of titanium alloy implants. Smith, T. JOM (Feb. 1994) 46 (2), 54-56 The application of Ti plasma-spray coatings to T i - 6 A I - 4 V orthopaedic implants results in a dramatic decrease in high-cycle fatigue performance. The better bonding of the plasma-spraycd and heat-treated implants results in a lower high-cycle fatigue strength. Therefore, the use of plasmaspray textured coatings on implants must be considered with caution. Photomicrographs, 14 rcf. Fatigue behavior of spotwelded galvanized sheets with and without corrosion influence (Schwingfestigkeitsverhalten punktgeschweisster verzinkter Feinbleche ohne und mit Korrosionseinfluss). Dieterich, K. Materialwissenschuft und Werkstofftechnik (Junc 19941 25 (6), 252-263 (in German) The fatigue behaviour of spotwelded sheets from the steels R St 14, St 14 ZE 25/25, St 14 ZE 75/75, St 06 Z 140 and St 06 ZF 140 was investigated. Tests with these connections under constant- and variable-amplitude loading were carried out in air, in a 5% NaCI solution and under condenser water. The results are presented as endurable stresses and cycles to crack initiation. Further, from the comparison of constant- and variable-amplitude testing, damage sums arc derived. Graphs, 17 rcf. High temperature behaviour of materials for gas turbine blades manufactured in new technology (Hochtemperaturverhalten von Werkstoffen aus neuartig gefertigten Gasturbinenschaufeln.) Kloos, K.H., Granacher, J. and Windecker, Th. Materialwisseas'chaft und Werkstofftechnik (June 1994) 25 (6), 235-243 (in German). On gas turbine blades for the middle and last stages of stationary gas turbines, the service-relevant material properties were examined. The specimens were taken from forged blades of alloys Nimonic 101 and Udimet 720 and from two fine-grain versions of cast blades of alloy 1N-792. In the range of servicerelevant temperatures, long-term creep rupture tests, annealing tests, relaxation tests as well as low- and high-cycle fatigue tests were carried out. Graphs, 12 rcf. Variation in fatigue properties and remaining life prediction. Ping, A.. Wang. D.J., Ye, D.Y. and Yang, H.W, J. Northeast Univ., Mater. Sci. (China) (June 19941 15 (3), 263-266 (in Chinese) The variation in mechanical properties of plain carbon steel with carbon content of 0.45% (45) is studied. It was proved that it is feasible to take the
Characterization and quantification of fretting particulates generated in ceramic/metal and metal/metal modular head/taper systems. Bhambri. S.K. and Gilbertson, L.N. Proe. Conf. Biomaterials' Mechanical Properties, Pittsburgh, PA, USA, 5-0 May 1992, pp. 111-126 An cxperimcnal set-up is described for conducting fretting/corrosion fatiguc testing of modular head/taper assemblies used for hip replacement in simulated body environments. The test set-up consisted of a special cell designed to contain simulated body environment and to retain all particles :~ ll.20 ~m, generated due to fretting fatigue. For this purpose, in-line filters were used and the environmental chamber was made of acrylic material to avoid any contamination, The test environment was aerated Ringer's solution circulated in a closed loop at 37°C. The fatigue load was applied on the head in 15° mediolateral anatomic orientation. The functional capabilitics of this set-up were demonstrated by testing alumina ceramic and C o - C r - M o femoral heads fitted on Ti alloy ( T i - 6 A I - 4 V ) tapers, at a fatigue load of 5.34 kN and a stress ratio of 0.1. The results arc summarized in terms of characterization and quantification of any particulates generated, and surface topographical changes on both hcad and taper contact surfaces. Photomicrographs, spectra, 14 ref.
Detection of the onset of fatigue crack growth in rail steels using acoustic emission: Bassim, M.N. Lawrence, S.S.T. and Liu, C.D. Eng. Fract. Mech. (Jan. 19941 47 (2). 207-214 Acoustic emission has held promise for quantitative evaluation of the extent of crack growth in metallic materials during fracture and fatigue. A correlation between acoustic emission and the stress intensity factor was derived, which allows prediction of the stress intensity factor (K or AK) from acoustic emission measurements. At very low values of AK, corresponding to the onset of fatigue crack growth, it was expected that acoustic emission would detect this event. The experimental procedure to verify this assumption involved high-cycle fatigue of four-point bending specimens of a number of rail steels. The fatigue testing was stopped whenever the first indication of acoustic emission activity, manifested by a measureable AK. occurred. This was followed by optical and scanning electron microscopy to detect the sources of cracking in the steels. The results show that, in the rail steels, cracks grow near inclusions. Crack lengths as small as 0.l)09 mm were detected, and the success rate in the detection of the onset of crack growth was IIXI%. Graphs, photomicrographs, 22 ref.