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Fatigue performance of holes with different finishing processes
584
Fatigue Abstracts
steel wire and were heated by electric contact and quenched continuously by passing through oil; thereafter they were tempered on the same production line. The structures of the nitriding layer and the fatigue properties were observed and analysed. The results proved that the fatigue life of the springs was increased. A shearing fatigue model of the surface strengthening spring is suggested. Graphs, diffraction patterns, photomicrographs, 6 ref. Kinetics and application of rare-earth elements catalysed nitrocarburizing for ductile iron. Feng, A.H., Xiao, Z.H. and Tian, G.X. Heat Treat. Met. (China) (Sept. 1994) 205 (9), 4-8, 37 (in Chinese)
The kinetics and catalysis mechanism of rare-earth elements on nitrocarburizing for ductile iron (QT700-2) by adding various amount of rare-earth elements into conventional nitrocarburizing media are discussed. When rare-earthcatalysed nitrocarburizing for the ductile iron crankshaft of a diesel engine, the nitrocarburizing rate can be increased by 55% and the productivity can be increased by 33% compared with conventional nitrocarburization, and the properties (microhardness, toughness, wear resistance, fatigue resistance) of the layer can be increased remarkably; the quality of products can be stabilized. Graphs, photomicrographs, spectra, 5 ref. The fatigue behaviour of adhesive joints. Kinloch, A.J., Jethwa J.K.K. and Osiyemi, S.O. Proc. Conf. EUR ADH 94 Adhesion, Mulhouse, France (12-15 Sept. 1994) 284-288
The fatigue performance of structural adhesives suitable for bonding carbonfibre-reinforced epoxy and PEEK composites, and aluminium alloys, was studied by relating the maximum applied strain energy release rate to the rate of crack growth through the adhesive layer. The influence of parameters such as the specimen displacement ratio, frequency of loading and environment was studied. Also, a model has been proposed that uses the material constants obtained from the experimental fatigue clata to predict theoretically the service life of other types of bonded joint. Results from the proposed model were in good agreement with experimental results. Graphs, 6 ref. Durability of bonded metal joints in motor vehicle construction. Lachmann, E. Proc. Conf. EUR ADH 94 Adhesion Mulhouse, France (12-15 Sept. 1994) 277-283 To estimate the long-term behaviour of bonded joints, investigations on shear strength and fatigue strength were conducted on lap shear specimens of sheet metal (steel and aluminium alloys) in the as-received condition and after weathering (weathering cycle according to the modified VDA-climate test and IN-test respectively). Additional fatigue tests on typical structural specimens were included in the tests. Mierostructural investigations on tested specimens gave evidence of the damage process and damage character. Appropriate selection of adhesives and sheet metal types (state of the metal surface) give satisfactory resistance for the application of adhesive bonded metal joints to primary structural parts. Fatigue life data and stresses sustained, respectively, of undamaged and pre-corroded specimens are well above those of comparable assemblies made by point jointing techniques like spot-welding and clinching. Graphs, 4 ref. Frequency effect on fatigue crack growth rate in joints bonded with either filled or filled and toughened adhesive. Xu, X.X., Crocombe, A.D. and Smith, P.A. Proc. Conf. EUR ADH 94 Adhesion, Mulhouse, France (12-15 Sept. 1994) 232-236
Mode I fatigue crack growth tests were conducted on steel joints bonded with a filled adhesive (A) at frequencies of 20 Hz and 2 Hz and on joints bonded with a filled and toughened adhesive (B) at frequencies of 20, 2, 0.2 and 0.02 Hz. Incorporating the loading rate dependence of the adhesive modulus, the cyclic strain energy release rate range, AG, was calculated by finite element anaysis and correlated with fatigue crack growth rate (FCGR). The FCGR in the joints bonded with adhesive A was relatively independent of frequency, while it increased with decreasing frequency at given AG for the joints bonded with adhesive B. The fatigue processes in both adhesives were found to involve the cracking of the filler particle and subsequent linkage of the resultant microcracks. The process zone ahead of the crack tip in adhesive B is larger than that in adhesive A, and it increases in size with decreasing frequency, resulting in the increasing FCGR with decreasing frequency and the higher FCGR as compared with adhesive A. Graphs, photomicrographs, 4 ref. Growth of multiple cracks and their linkup in a fuselage lap joint. Singh, R., Park, J.H. and Atluri, S.N. AIAA J. (Nov. 1994) 32 (11), 2260-2268 An issue of concern in ageing aircraft is the growth of multiple cracks emanating from a row of fastener holes, typically in a pressurized aircraft fuselage lap splice. This multi-site damage (MSD), or widespread fatigue damage, if allowed to progress, can suddenly become catastrophic. The understanding of the failure behaviour dictates the level of compromise between safety and economy. The complexity of the structure due to various stiffening elements makes it unamenable to a simple direct analysis. A twostep elastic finite element fatigue analysis combining a conventional finite element method and the Schwartz-Neumann alternating method with analytical solutions is developed to understand fatigue growth of multiple cracks and to obtain a first estimate of the residual life of a stiffened fuselage shell
with MSD in the riveted lap joint. The analysis procedure is validated by simulating a laboratory fatigue test on a 2024-T3 lap joint in a flat coupon. Both the coupon and'the shell panel are found to have fatigue lives only up to the first link-up of the neighbouring crack tips. Graphs, 10 ref. structure
An aid for defining the fillet weld geometry in symmetrically welded assemblies subject to fatigue loads. Janosch, J.J. and Debiez, S. Weld. World (1994) 33 (5), 370-381
The principle and procedure of using a numerical tool for optimizing the fatigue behaviour of assemblies with fillet welds subjected to transverse loads are described as a function of weld geometries. Based on a concomitant analysis of the geometrical parameters, formulations are developed to calculate the local stress amplitude in three susceptible zones of the fillet weld. The quality of the weld is characterized by the value of the weld toe radius. A working algorithm is developed as an aid for defining the geometry of the fillet weld assembly, with examples of its application. Graphs, numerical data, 6 ref. Fatigue performance of holes with different finishing processes. Lai, M.O. and Koh, S.F. J. Mater. Process. Technol. (1 July 1994) 44 (1-2), 118-128
The fatigue performance of a hole in a component is related to its surface roughness and surface integrity as well as to the presence of residual stress, these factors being very much governed by the manufacturing processes employed in machining or finishing the holes. The present study examines the effect of five such processes on the fatigue lives of pre-machined holes in plates of Assab 760 steel, the processes investigated being electro-discharge machining, drilling, reaming, baUizing and polishing. Fatigue tests on the hole surfaces were carried out using an applied tensile cyclic stress with mean and dynamic loads that were set and maintained constant for all specimens so that the fatigue lives of the test specimens could be compared. For all of the hole-finishing processes applied, the results showed the expected trend of the fatigue life decreasing as the surface roughness increased. Holes that had been ballized generally showed the longest fatigue lives, while those manufactured with electro-discharge machining showed the shortest; polishing, reaming and drilling, in the order of decreasing fatigue life, were observed to be sandwiched between those for ballizing and electro-discharge machining. Ballizing appeared to be the best hole-finishing process, not only because it enhances the fatigue performance of the holes through compressive residual stress, but also because it can produce good surface finish economically and quickly. Conversely, the effect of tensile residual stress produced as a result of the re-cast layer rendered a poor fatigue performance in specimens that had been machined using electro-discharge machining. Effect of surface rolling on fatigue strength as influenced by the strain hardening rate. Rebinsky, D.A. and Vitovec, F.H. Scr. Metall. Mater. (15 Feb. 1994) 35 (4), 417-422
Comparative tests on two steels of different strain-hardening rates showed that yield strength is the main factor determining fatigue strength after surface rolling rather than the rate of strain hardening and depth of cold work produced by the rolling. Thermomechanically mill-treated high-strength lowalloy steel (Fe-0.1C-1.55Mn-0.27Si-0.1MNb-0.035V-0.34AI- 0.014P-0.006S) was machined and polished, providing high-yield-strength samples with low strain-hardening rate. Some of this steel was further normalized, machined, annealed, and quenched to obtain low-yield strength with high rate of strain hardening. Comparative mechanical properties, surface residual stress from X-ray diffraction and fatigue results are tabled. The Holloman equation ~r = Ken (tr is true stess, e is true strain and n is strain-hardening exponent) quantifies the work hardening. A graph of n vs true plastic strain illustrates the strain-hardening characteristics of the two steels. Microhardness plots give depth of work hardening, and normalized residual stress shows relaxation with fatigue cycles. Graphs, 22 ref. Fractal analysis on the fatigue fracture surface along the crack propagation direction. Hao, Y., Wang, Z. and Kant, Y. Steel Res. (July 1994) 65 (7), 305-308
The fractal dimension along the crack propagation direction on the fatigue fracture surface of a dual-phase steel was investigated by both a vertical section profile method and a secondary electron line scanning method. Results from the vertical section profile method showed that during the crack propagation, the fractal dimension of the fracture surface increased with increasing stres intensity factor; however, the secondary electron line scanning method presented somewhat different results for the fractal dimension and was proved not feasible in all kinds of fracture surfaces, so this method is not suggested in calculating the fractal dimension of the fracture surface. Graphs, photomicrographs, 5 ref. Hydrogen embHttlement resistance of ultrahigh strength cupronickel alloy: effects of exposure to gaseous hydrogen environment on fatigue resistance. Tuck, C.D.S., Zeng, X. and Talbot, D.E.J. Br.Corros. J. (1994) 29 (1), 70-74
The ultra-high-strength cupro-nickel alloy Marinel and the nickel alloy Monel K-500 were saturated with gaseous H at 4506 °C and their fatigue behaviour was measured and compared with that of H-free material. The presence of
Fatigue Abstracts
steel wire and were heated by electric contact and quenched continuously by passing through oil; thereafter they were tempered on the same production line. The structures of the nitriding layer and the fatigue properties were observed and analysed. The results proved that the fatigue life of the springs was increased. A shearing fatigue model of the surface strengthening spring is suggested. Graphs, diffraction patterns, photomicrographs, 6 ref. Kinetics and application of rare-earth elements catalysed nitrocarburizing for ductile iron. Feng, A.H., Xiao, Z.H. and Tian, G.X. Heat Treat. Met. (China) (Sept. 1994) 205 (9), 4-8, 37 (in Chinese)
The kinetics and catalysis mechanism of rare-earth elements on nitrocarburizing for ductile iron (QT700-2) by adding various amount of rare-earth elements into conventional nitrocarburizing media are discussed. When rare-earthcatalysed nitrocarburizing for the ductile iron crankshaft of a diesel engine, the nitrocarburizing rate can be increased by 55% and the productivity can be increased by 33% compared with conventional nitrocarburization, and the properties (microhardness, toughness, wear resistance, fatigue resistance) of the layer can be increased remarkably; the quality of products can be stabilized. Graphs, photomicrographs, spectra, 5 ref. The fatigue behaviour of adhesive joints. Kinloch, A.J., Jethwa J.K.K. and Osiyemi, S.O. Proc. Conf. EUR ADH 94 Adhesion, Mulhouse, France (12-15 Sept. 1994) 284-288
The fatigue performance of structural adhesives suitable for bonding carbonfibre-reinforced epoxy and PEEK composites, and aluminium alloys, was studied by relating the maximum applied strain energy release rate to the rate of crack growth through the adhesive layer. The influence of parameters such as the specimen displacement ratio, frequency of loading and environment was studied. Also, a model has been proposed that uses the material constants obtained from the experimental fatigue clata to predict theoretically the service life of other types of bonded joint. Results from the proposed model were in good agreement with experimental results. Graphs, 6 ref. Durability of bonded metal joints in motor vehicle construction. Lachmann, E. Proc. Conf. EUR ADH 94 Adhesion Mulhouse, France (12-15 Sept. 1994) 277-283 To estimate the long-term behaviour of bonded joints, investigations on shear strength and fatigue strength were conducted on lap shear specimens of sheet metal (steel and aluminium alloys) in the as-received condition and after weathering (weathering cycle according to the modified VDA-climate test and IN-test respectively). Additional fatigue tests on typical structural specimens were included in the tests. Mierostructural investigations on tested specimens gave evidence of the damage process and damage character. Appropriate selection of adhesives and sheet metal types (state of the metal surface) give satisfactory resistance for the application of adhesive bonded metal joints to primary structural parts. Fatigue life data and stresses sustained, respectively, of undamaged and pre-corroded specimens are well above those of comparable assemblies made by point jointing techniques like spot-welding and clinching. Graphs, 4 ref. Frequency effect on fatigue crack growth rate in joints bonded with either filled or filled and toughened adhesive. Xu, X.X., Crocombe, A.D. and Smith, P.A. Proc. Conf. EUR ADH 94 Adhesion, Mulhouse, France (12-15 Sept. 1994) 232-236
Mode I fatigue crack growth tests were conducted on steel joints bonded with a filled adhesive (A) at frequencies of 20 Hz and 2 Hz and on joints bonded with a filled and toughened adhesive (B) at frequencies of 20, 2, 0.2 and 0.02 Hz. Incorporating the loading rate dependence of the adhesive modulus, the cyclic strain energy release rate range, AG, was calculated by finite element anaysis and correlated with fatigue crack growth rate (FCGR). The FCGR in the joints bonded with adhesive A was relatively independent of frequency, while it increased with decreasing frequency at given AG for the joints bonded with adhesive B. The fatigue processes in both adhesives were found to involve the cracking of the filler particle and subsequent linkage of the resultant microcracks. The process zone ahead of the crack tip in adhesive B is larger than that in adhesive A, and it increases in size with decreasing frequency, resulting in the increasing FCGR with decreasing frequency and the higher FCGR as compared with adhesive A. Graphs, photomicrographs, 4 ref. Growth of multiple cracks and their linkup in a fuselage lap joint. Singh, R., Park, J.H. and Atluri, S.N. AIAA J. (Nov. 1994) 32 (11), 2260-2268 An issue of concern in ageing aircraft is the growth of multiple cracks emanating from a row of fastener holes, typically in a pressurized aircraft fuselage lap splice. This multi-site damage (MSD), or widespread fatigue damage, if allowed to progress, can suddenly become catastrophic. The understanding of the failure behaviour dictates the level of compromise between safety and economy. The complexity of the structure due to various stiffening elements makes it unamenable to a simple direct analysis. A twostep elastic finite element fatigue analysis combining a conventional finite element method and the Schwartz-Neumann alternating method with analytical solutions is developed to understand fatigue growth of multiple cracks and to obtain a first estimate of the residual life of a stiffened fuselage shell
with MSD in the riveted lap joint. The analysis procedure is validated by simulating a laboratory fatigue test on a 2024-T3 lap joint in a flat coupon. Both the coupon and'the shell panel are found to have fatigue lives only up to the first link-up of the neighbouring crack tips. Graphs, 10 ref. structure
An aid for defining the fillet weld geometry in symmetrically welded assemblies subject to fatigue loads. Janosch, J.J. and Debiez, S. Weld. World (1994) 33 (5), 370-381
The principle and procedure of using a numerical tool for optimizing the fatigue behaviour of assemblies with fillet welds subjected to transverse loads are described as a function of weld geometries. Based on a concomitant analysis of the geometrical parameters, formulations are developed to calculate the local stress amplitude in three susceptible zones of the fillet weld. The quality of the weld is characterized by the value of the weld toe radius. A working algorithm is developed as an aid for defining the geometry of the fillet weld assembly, with examples of its application. Graphs, numerical data, 6 ref. Fatigue performance of holes with different finishing processes. Lai, M.O. and Koh, S.F. J. Mater. Process. Technol. (1 July 1994) 44 (1-2), 118-128
The fatigue performance of a hole in a component is related to its surface roughness and surface integrity as well as to the presence of residual stress, these factors being very much governed by the manufacturing processes employed in machining or finishing the holes. The present study examines the effect of five such processes on the fatigue lives of pre-machined holes in plates of Assab 760 steel, the processes investigated being electro-discharge machining, drilling, reaming, baUizing and polishing. Fatigue tests on the hole surfaces were carried out using an applied tensile cyclic stress with mean and dynamic loads that were set and maintained constant for all specimens so that the fatigue lives of the test specimens could be compared. For all of the hole-finishing processes applied, the results showed the expected trend of the fatigue life decreasing as the surface roughness increased. Holes that had been ballized generally showed the longest fatigue lives, while those manufactured with electro-discharge machining showed the shortest; polishing, reaming and drilling, in the order of decreasing fatigue life, were observed to be sandwiched between those for ballizing and electro-discharge machining. Ballizing appeared to be the best hole-finishing process, not only because it enhances the fatigue performance of the holes through compressive residual stress, but also because it can produce good surface finish economically and quickly. Conversely, the effect of tensile residual stress produced as a result of the re-cast layer rendered a poor fatigue performance in specimens that had been machined using electro-discharge machining. Effect of surface rolling on fatigue strength as influenced by the strain hardening rate. Rebinsky, D.A. and Vitovec, F.H. Scr. Metall. Mater. (15 Feb. 1994) 35 (4), 417-422
Comparative tests on two steels of different strain-hardening rates showed that yield strength is the main factor determining fatigue strength after surface rolling rather than the rate of strain hardening and depth of cold work produced by the rolling. Thermomechanically mill-treated high-strength lowalloy steel (Fe-0.1C-1.55Mn-0.27Si-0.1MNb-0.035V-0.34AI- 0.014P-0.006S) was machined and polished, providing high-yield-strength samples with low strain-hardening rate. Some of this steel was further normalized, machined, annealed, and quenched to obtain low-yield strength with high rate of strain hardening. Comparative mechanical properties, surface residual stress from X-ray diffraction and fatigue results are tabled. The Holloman equation ~r = Ken (tr is true stess, e is true strain and n is strain-hardening exponent) quantifies the work hardening. A graph of n vs true plastic strain illustrates the strain-hardening characteristics of the two steels. Microhardness plots give depth of work hardening, and normalized residual stress shows relaxation with fatigue cycles. Graphs, 22 ref. Fractal analysis on the fatigue fracture surface along the crack propagation direction. Hao, Y., Wang, Z. and Kant, Y. Steel Res. (July 1994) 65 (7), 305-308
The fractal dimension along the crack propagation direction on the fatigue fracture surface of a dual-phase steel was investigated by both a vertical section profile method and a secondary electron line scanning method. Results from the vertical section profile method showed that during the crack propagation, the fractal dimension of the fracture surface increased with increasing stres intensity factor; however, the secondary electron line scanning method presented somewhat different results for the fractal dimension and was proved not feasible in all kinds of fracture surfaces, so this method is not suggested in calculating the fractal dimension of the fracture surface. Graphs, photomicrographs, 5 ref. Hydrogen embHttlement resistance of ultrahigh strength cupronickel alloy: effects of exposure to gaseous hydrogen environment on fatigue resistance. Tuck, C.D.S., Zeng, X. and Talbot, D.E.J. Br.Corros. J. (1994) 29 (1), 70-74
The ultra-high-strength cupro-nickel alloy Marinel and the nickel alloy Monel K-500 were saturated with gaseous H at 4506 °C and their fatigue behaviour was measured and compared with that of H-free material. The presence of