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The modification in fatigue life of pure polycrystalline nickel by carbon ion implantation
Metresur: the very high level peening t r e a t m e n t . Surfaces Feb. 1989 27, (203), 47-48, 51 (in French) Sabac, a Belgian aerospace company, has developed a procedure to form thin (2-6 mm) AI sheets to precise shapes by shot peening. This manual peen forming can achieve highly accurate profiles and is being used to form body panels for the Ariane rockets. The equipment (a Vacu-Blast PBA06-2) permits the operator to control the forming very precisely. The procedure also improves the fatigue resistance of the product by creating compressive stresses rather than the usually found tensile stresses, which could lead to premature failure.
The threshold value of fatigue crack and the propagation of short cracks in 16Mn steel. Qian, J.-c. and Yao, X.-x. Heat Treat. Met. (China) Oct. 1988 (10), 37-40 (in Chinese) The fatigue behaviour of 16Mn steel in the hot roiled condition was studied. The result shows that with the same driving force (~K), the propagation rate of short cracks is higher by up to two orders of magnitude than that of long cracks. The threshold value of the stress intensity factor of short cracks is lower, down to approx 50%, than that of long cracks. Tables. 9 refs. The m o d i f i c a t i o n in f a t i g u e life o f pure polycrystslline nickel
ion implantation. Xu, M.H., Patu, S. and Wang, Z.G. Vacuum 1989 39, (2-4), 297-299
by carbon
Plates of Ni with and without C ion implantation have been tested in tension-zero fatigue. A 22% increase in endurance limit was found with implantation. The fatigued surfaces have been examined by SEM. Surface deformation favourable to crack initiation is greatly decreased by C ion implantation. Grain boundary cracking is one crack nucleation mode of modified materials besides slip band cracking which is the only crack initiation mode of unmodified specimens. 8 refs.
Improvement of the f a t i g u e lifetime o f steel implanted with nitrogen after heat t r e a t m e n t . Luo, G., Zhang, G., Kou, S. and Wang, S. Vacuum 1989 39, (2-4), 279-280. The fatigue lifetime of steel (No 20) after two different heat treatments (quenching and normalizing) can be further improved by N ion implantation. The implanted samples have been investigated by TEM and X-ray analysis. The effect of ion implantation on the quenched steel is more obvious than on the steel in its normal state. The nitride layer impedes dislocation movement. The quenching treatment stops propagation of cracks. 4 refs.
Joining conveyor bend pulley. Woolhouse, K.W. and Ford, P.R. Mater. Forum First Quarter 1989 13, (1), 64-68
Failure o f s
A metallurgical investigation of the cause of failure of a conveyor bend pulley (made of Fe-0.23C-0.61Mn-0.16Si steel) was carried out in conjunction with a stress analysis and fracture mechanics assessment. The critical crack length was required for future non-destructive testing of other similar pulleys. The bend pulley was found to have failed by fatigue from an unfused-weld root land and associated cracking in the weld heet-affected zone. Of the four methods used to determine the critical crack length for fatigue crack initiation, only the method based upon typical minimum crack growth rates gave a safe estimate of critical crack length, 1 ref. Laser w e l d i n g A I - L i sheet joints. Lin, C.S. Aerosp. Eng. Dec. 1988 8, (12), 23-25 The fracture behaviour of laser-welded joints of 2091-T8X AI-Li alloy sheet, where welding efficiency is nearly 100%, is discussed. The average fracture toughness values of the welding zone with post-weld heat treatment confirmed good recovery of strength and fracture toughness which were only 8-12% lower than those of the base metal Scanning electron microscopy indicated fatigue crack propagation to be primarily trans-crystalline. Residual stress measurements in the welding zone showed a tensile stress of 2.99 psi, compared to 27.3 ksi in tungsten inert gas (TIG) welding, implying higher strength and less residual stress in laser welding. Internal stresses and strains. Braathen, C.M. Sveiseteknikk Nov. 1988 43, (5), 73-84 Offshore steel construction technology requires attention to the causes, magnitudes and measurement of weld stresses, the effects of internal stresses, reduction of welding stresses by thermal and mechanical methods, strain calculation and stress and strain reduction design measures, and the significance of the practical workmanship. The internal stressing, brittle fracture, stress corrosion, fatigue, Hinduced cracking and strain characteristics of C-Mn-Nb steel are discussed and illustrated in this connection.
Designing against fatigue. James, N. S. Afr. Mech. Eng. Nov.-Dec. 1988 38, (11-12), 651-652, 654, 656-658 The nature of the fatigue process is reviewed, covering the effects of surface finish and welding on fatigue strength of high strength steels and illustrating the importance of component detailing and the effect of different types of weld. Common techniques of improvement of fatigue behaviour are briefly reviewed, 12 refs.
A study on repair welding under pulsating stress in service conditions. I1: Development of electrode for welding under pulsating stress. Nakanishi, Y., Nakamura, Y. and Sakai, K. Ishikawajima-Harima Eng, Rev. J u l y 1987 27, (4), 207-211 (in Japanese) Solidification cracks and/or hot cracks occurred in welding crack tests under pulsating stress due to external strain caused by a pulsating stress. Electrodes containing various combinations of alloying elements and impurities were prepared and the effect of chemical composition in deposited metal on crack sensitivity was investigated. The possibility of application of the developed electrodes was examined in welding crack tests under pulsating stress and in joint performance tests, it was
450
confirmed that crack sensitivity under pulsating stress was further improved when compared with conventional electrodes, and that the joint performance satisfied the specifications for mild steel and 490 MPa and 590 MPa class high tensile strength steels. As a result, it has been clarified that the applicable field of welding under pulsating stress in service conditions will be extended by these developed electrodes. The steel welded using these electrodes was grade SM58Q C-Mn steel. 7 refs. Initial fatigue crack growth behaviour in a notched component. V: A s s e s s m e n t of initial defect t o f a t i g u e life in a notched component.
Cho, S.-M. and Horikawa, K. Q. J. Jpn, Weld. Soc. Feb. 1989 7, (1), 111-117 (in Japanese) Elasto-plastic fracture mechanics (EPFM) was applied to an assessment of initial defect in fatigue design. Considering fatigue design methods of welded steel structures, assessment methods of initial defect in notched components were classified into three cases. In Case 1, fatigue design is based on joint classification, where allowable size of initial defect is specified according to joints shape. Fatigue life safety factor varied with shape of components. In Case 2A, fatigue design is based on joint classification, where allowable size of initial defect is, in this case, assessed by ~J and experimental methods. The size depends upon stress level and materials (SS41 or HT80). In Case 2B, fatigue design is based on a priori specified initial defect size and EPFM. By this design method, to increase sectional area is better than to decrease tensile residual stress when fatigue strength is critical in low cycle region, and vice versa. 19 refs.
Crack growth rates during creep, fati~lue and c r e e p - f a t i g u e in an austenitic f e a t u r e w e l d specimen. Gladwm, D.N., Miller, DA. and Priest, R.H. Fatigue Fract. Eng. Mater. Struct. 1989 12, (3), 187-200 Static creep crack growth tests and displacement controlled fatigue and creep-fatigue crack growth tests have been performed on austenitic feature weld specimens (321 welded with 347) at 650 °C. The creep-fatigue tests incorporated hold times of up to 96 h. During these tests, crack growth appeared to comprise cyclic and dwell components. Cyclic crack growth components were characterized by the fracture mechanics parameter K while creep crack growth contributions were correlated with C*. In order to determine K and C* for the non-standard feature weld specimen, elastic and elastic-plastic creep finite element analyses were conducted. Good correspondence is shown between the feature weld data and comparable data from compact tension specimen tests on similar materials. Equations obtained from the compact tension specimen results, which describe total crack growth rates as the sum of the cyclic and dwell contributions, are shown to adequately describe the features test results also. Furthermore, it is demonstrated that a reference stress approach can be used to extimate C~ for the features specimens, Graphs, Photomicrographs, 6 refs. On t h e effect of welding condition on joint performance and f a t i g u e strength characteristics o f similar a u s t e n i t e stainless steel friction
welding joint--study on fatigue strength of fdction welding joint. Yamamoto, Y., Sakai, N., Ogawa, K. and Kaga, S. Setsudai Gakujutsu (ScL Rev. Setsunan Univ.) A Feb. 1989 (8), 17-37 (in Japanese) Austenite stainless steel is widely used in shafts of water pumps, outboard motors, etc, like carbon steel. There are many reports of friction welding of stainless steel; however, there are only a few reports on the general effect of welding factors on weld and fatigue strength characteristics. In future, because of advantages of saving welding energy, simplicity of welding process and high reproductivity of weld quality, it is expected that the utilization of the friction welded joint will increase, so the efficiency improvement of friction welding machine, quality improvement of joint and information on relation welding conditions and joint performance should be studied. The welding condition to obtain s suitable joint performance which has a joint efficiency >100% is investigated, and fatigue strength characteristics made under some welding conditions are made clear. SUS 304 is the material investigated. Graphs. Photomicrographs. 11 refs.
Mechanical properties Fine structures and mechanical properties of t h e r m a l l y cycled SUJ 2 steel. Sakai, H., Ochiai, S. and Ueno, M. Tetsu-to-Hagane (J. Iron Steel Inst. Jpn.) Apr. 1989 75, (4), 657-664 (in Japanese) Results are presented on the mechanical properties of SUJ 2 bearing steel improved by a cyclic heat treatment. The structure of thermally cycled steel consists of finegrained ferrite particles of a size < approx 2 i~m containing fine cementite particles of a size of approx 0.2 i~m. Thermally cycled steel was found to be superplastic at 710°C, just below A1 temperature, at an initial strain rate of 1.67 x 10 4s~, ie elongation to failure was approx 500% and the strain rate sensitivity, mvalue, was approx 0.4. The activation energy of approx 180 kJ/tool, which is nearly equal to that of grain boundary diffusion of Fe atoms in ~-Fe, was obtained for this plastic deformation. Furthermore, the rolling contact fatigue life test was performed at room temperature under constant load. The fatigue life of SUJ 2 steel thermally cycled was found to be prolonged (approx 2.5 times) as compared with that of the conventional one. 22 refs. S i m u l a t i o n investigations of t h e position of f a t i g u e fracture plane in materials w i t h biaxiel loads. (I). Macha, E. Mater. wiss. Werkst. tech. 1989 (4), 132-136 Three months of determination of the expected fatigue fracture plane position under random triaxial stress state have been presented. They are: the weight function method, the variance method and the damage cumulation method. The weight function method for biaxiat cyclic Ioadlngs has been analysed with digital simulation. The fatigue fracture plane position has been determined with mean values of the direction cosines of principal stress axes. Averaging has been done at angle values with the use of weights. Eleven various weights have been presented and their usability has been analysed on the basis of experimental results found in the
Int J Fatigue November 1989
The threshold value of fatigue crack and the propagation of short cracks in 16Mn steel. Qian, J.-c. and Yao, X.-x. Heat Treat. Met. (China) Oct. 1988 (10), 37-40 (in Chinese) The fatigue behaviour of 16Mn steel in the hot roiled condition was studied. The result shows that with the same driving force (~K), the propagation rate of short cracks is higher by up to two orders of magnitude than that of long cracks. The threshold value of the stress intensity factor of short cracks is lower, down to approx 50%, than that of long cracks. Tables. 9 refs. The m o d i f i c a t i o n in f a t i g u e life o f pure polycrystslline nickel
ion implantation. Xu, M.H., Patu, S. and Wang, Z.G. Vacuum 1989 39, (2-4), 297-299
by carbon
Plates of Ni with and without C ion implantation have been tested in tension-zero fatigue. A 22% increase in endurance limit was found with implantation. The fatigued surfaces have been examined by SEM. Surface deformation favourable to crack initiation is greatly decreased by C ion implantation. Grain boundary cracking is one crack nucleation mode of modified materials besides slip band cracking which is the only crack initiation mode of unmodified specimens. 8 refs.
Improvement of the f a t i g u e lifetime o f steel implanted with nitrogen after heat t r e a t m e n t . Luo, G., Zhang, G., Kou, S. and Wang, S. Vacuum 1989 39, (2-4), 279-280. The fatigue lifetime of steel (No 20) after two different heat treatments (quenching and normalizing) can be further improved by N ion implantation. The implanted samples have been investigated by TEM and X-ray analysis. The effect of ion implantation on the quenched steel is more obvious than on the steel in its normal state. The nitride layer impedes dislocation movement. The quenching treatment stops propagation of cracks. 4 refs.
Joining conveyor bend pulley. Woolhouse, K.W. and Ford, P.R. Mater. Forum First Quarter 1989 13, (1), 64-68
Failure o f s
A metallurgical investigation of the cause of failure of a conveyor bend pulley (made of Fe-0.23C-0.61Mn-0.16Si steel) was carried out in conjunction with a stress analysis and fracture mechanics assessment. The critical crack length was required for future non-destructive testing of other similar pulleys. The bend pulley was found to have failed by fatigue from an unfused-weld root land and associated cracking in the weld heet-affected zone. Of the four methods used to determine the critical crack length for fatigue crack initiation, only the method based upon typical minimum crack growth rates gave a safe estimate of critical crack length, 1 ref. Laser w e l d i n g A I - L i sheet joints. Lin, C.S. Aerosp. Eng. Dec. 1988 8, (12), 23-25 The fracture behaviour of laser-welded joints of 2091-T8X AI-Li alloy sheet, where welding efficiency is nearly 100%, is discussed. The average fracture toughness values of the welding zone with post-weld heat treatment confirmed good recovery of strength and fracture toughness which were only 8-12% lower than those of the base metal Scanning electron microscopy indicated fatigue crack propagation to be primarily trans-crystalline. Residual stress measurements in the welding zone showed a tensile stress of 2.99 psi, compared to 27.3 ksi in tungsten inert gas (TIG) welding, implying higher strength and less residual stress in laser welding. Internal stresses and strains. Braathen, C.M. Sveiseteknikk Nov. 1988 43, (5), 73-84 Offshore steel construction technology requires attention to the causes, magnitudes and measurement of weld stresses, the effects of internal stresses, reduction of welding stresses by thermal and mechanical methods, strain calculation and stress and strain reduction design measures, and the significance of the practical workmanship. The internal stressing, brittle fracture, stress corrosion, fatigue, Hinduced cracking and strain characteristics of C-Mn-Nb steel are discussed and illustrated in this connection.
Designing against fatigue. James, N. S. Afr. Mech. Eng. Nov.-Dec. 1988 38, (11-12), 651-652, 654, 656-658 The nature of the fatigue process is reviewed, covering the effects of surface finish and welding on fatigue strength of high strength steels and illustrating the importance of component detailing and the effect of different types of weld. Common techniques of improvement of fatigue behaviour are briefly reviewed, 12 refs.
A study on repair welding under pulsating stress in service conditions. I1: Development of electrode for welding under pulsating stress. Nakanishi, Y., Nakamura, Y. and Sakai, K. Ishikawajima-Harima Eng, Rev. J u l y 1987 27, (4), 207-211 (in Japanese) Solidification cracks and/or hot cracks occurred in welding crack tests under pulsating stress due to external strain caused by a pulsating stress. Electrodes containing various combinations of alloying elements and impurities were prepared and the effect of chemical composition in deposited metal on crack sensitivity was investigated. The possibility of application of the developed electrodes was examined in welding crack tests under pulsating stress and in joint performance tests, it was
450
confirmed that crack sensitivity under pulsating stress was further improved when compared with conventional electrodes, and that the joint performance satisfied the specifications for mild steel and 490 MPa and 590 MPa class high tensile strength steels. As a result, it has been clarified that the applicable field of welding under pulsating stress in service conditions will be extended by these developed electrodes. The steel welded using these electrodes was grade SM58Q C-Mn steel. 7 refs. Initial fatigue crack growth behaviour in a notched component. V: A s s e s s m e n t of initial defect t o f a t i g u e life in a notched component.
Cho, S.-M. and Horikawa, K. Q. J. Jpn, Weld. Soc. Feb. 1989 7, (1), 111-117 (in Japanese) Elasto-plastic fracture mechanics (EPFM) was applied to an assessment of initial defect in fatigue design. Considering fatigue design methods of welded steel structures, assessment methods of initial defect in notched components were classified into three cases. In Case 1, fatigue design is based on joint classification, where allowable size of initial defect is specified according to joints shape. Fatigue life safety factor varied with shape of components. In Case 2A, fatigue design is based on joint classification, where allowable size of initial defect is, in this case, assessed by ~J and experimental methods. The size depends upon stress level and materials (SS41 or HT80). In Case 2B, fatigue design is based on a priori specified initial defect size and EPFM. By this design method, to increase sectional area is better than to decrease tensile residual stress when fatigue strength is critical in low cycle region, and vice versa. 19 refs.
Crack growth rates during creep, fati~lue and c r e e p - f a t i g u e in an austenitic f e a t u r e w e l d specimen. Gladwm, D.N., Miller, DA. and Priest, R.H. Fatigue Fract. Eng. Mater. Struct. 1989 12, (3), 187-200 Static creep crack growth tests and displacement controlled fatigue and creep-fatigue crack growth tests have been performed on austenitic feature weld specimens (321 welded with 347) at 650 °C. The creep-fatigue tests incorporated hold times of up to 96 h. During these tests, crack growth appeared to comprise cyclic and dwell components. Cyclic crack growth components were characterized by the fracture mechanics parameter K while creep crack growth contributions were correlated with C*. In order to determine K and C* for the non-standard feature weld specimen, elastic and elastic-plastic creep finite element analyses were conducted. Good correspondence is shown between the feature weld data and comparable data from compact tension specimen tests on similar materials. Equations obtained from the compact tension specimen results, which describe total crack growth rates as the sum of the cyclic and dwell contributions, are shown to adequately describe the features test results also. Furthermore, it is demonstrated that a reference stress approach can be used to extimate C~ for the features specimens, Graphs, Photomicrographs, 6 refs. On t h e effect of welding condition on joint performance and f a t i g u e strength characteristics o f similar a u s t e n i t e stainless steel friction
welding joint--study on fatigue strength of fdction welding joint. Yamamoto, Y., Sakai, N., Ogawa, K. and Kaga, S. Setsudai Gakujutsu (ScL Rev. Setsunan Univ.) A Feb. 1989 (8), 17-37 (in Japanese) Austenite stainless steel is widely used in shafts of water pumps, outboard motors, etc, like carbon steel. There are many reports of friction welding of stainless steel; however, there are only a few reports on the general effect of welding factors on weld and fatigue strength characteristics. In future, because of advantages of saving welding energy, simplicity of welding process and high reproductivity of weld quality, it is expected that the utilization of the friction welded joint will increase, so the efficiency improvement of friction welding machine, quality improvement of joint and information on relation welding conditions and joint performance should be studied. The welding condition to obtain s suitable joint performance which has a joint efficiency >100% is investigated, and fatigue strength characteristics made under some welding conditions are made clear. SUS 304 is the material investigated. Graphs. Photomicrographs. 11 refs.
Mechanical properties Fine structures and mechanical properties of t h e r m a l l y cycled SUJ 2 steel. Sakai, H., Ochiai, S. and Ueno, M. Tetsu-to-Hagane (J. Iron Steel Inst. Jpn.) Apr. 1989 75, (4), 657-664 (in Japanese) Results are presented on the mechanical properties of SUJ 2 bearing steel improved by a cyclic heat treatment. The structure of thermally cycled steel consists of finegrained ferrite particles of a size < approx 2 i~m containing fine cementite particles of a size of approx 0.2 i~m. Thermally cycled steel was found to be superplastic at 710°C, just below A1 temperature, at an initial strain rate of 1.67 x 10 4s~, ie elongation to failure was approx 500% and the strain rate sensitivity, mvalue, was approx 0.4. The activation energy of approx 180 kJ/tool, which is nearly equal to that of grain boundary diffusion of Fe atoms in ~-Fe, was obtained for this plastic deformation. Furthermore, the rolling contact fatigue life test was performed at room temperature under constant load. The fatigue life of SUJ 2 steel thermally cycled was found to be prolonged (approx 2.5 times) as compared with that of the conventional one. 22 refs. S i m u l a t i o n investigations of t h e position of f a t i g u e fracture plane in materials w i t h biaxiel loads. (I). Macha, E. Mater. wiss. Werkst. tech. 1989 (4), 132-136 Three months of determination of the expected fatigue fracture plane position under random triaxial stress state have been presented. They are: the weight function method, the variance method and the damage cumulation method. The weight function method for biaxiat cyclic Ioadlngs has been analysed with digital simulation. The fatigue fracture plane position has been determined with mean values of the direction cosines of principal stress axes. Averaging has been done at angle values with the use of weights. Eleven various weights have been presented and their usability has been analysed on the basis of experimental results found in the
Int J Fatigue November 1989