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Fatigue strength of two-ply bellows at elevated temperature
crack propagation, particularly in non-equiexed microstructures. Cracks with depths approximating to the grain size were seen to vary significantly in shape, it is suggested that s better correlating parameter for short crack growth is crack ares rather than surface crack length which is commonly used at present.
Surface f a t i g u e crack p r o p a g a t i o n b e h e v i o u r in a residual stress field (fatigue crack g.,mwth, l a w and evaluation o f f a t i g u e crack p r o p a g e t i o n
rate). Torii, 7"., Hones, K. and Sugiyama, M. JSME Int. J. I J u l y 1989 32, (3), 4,~0-457
The fatigue life of plain carbon steel with residual stress was studied with special reference to the in/tietJon and the propagation of surface fatigue cracks. Tensile residual stresses had no significant influence on crack initiation lives, but increased the fatigue crack propagation rate for surface fatigue cracks. The propagation rate of a surface fatigue crack was controlled by the parameter {(&K)°.s (K~n=x)°.s} in which AK and Km=~were, respectively, the stress intensity factor range and stress intensity factor calculated from the maximum stress distribution containing residual stresses measured st the stress cycles of the initiation of surface cracks. This parameter also served to help understand surface fatigue crack shape in a residual stress f'mld. Finally, the equation of (&KIP (Kmu)q = Km,x - pKmi, was derived under the condition of both p + q = 1 and the minimum stress intensity factor Kmin < Km=x. Ths effects of Kmin (< 0) on fatigue crack propagation sre obtained from the mechanical behaviour of the plsstically deformed layer left in the wake of the advancing crack. 25 refs.
Effect o f oil viscosity on t h e f a t i g u e l i m i t of drilled specimens and t h e small crack g r o w t h law. Gate, M., Nisitani, H., Miyegawa, H. and
Yanagawa, Y. JSME Int. J. I July 1989 32, (3), 4 4 4 - 4 4 9
Rotating bending fatigue tests of an annealed 0.34% carbon steel smooth specimen with s small blind hole were carried out using four types of base oils in order to evaluate the effect of oil viscosity on the fatigue limit and small crack growth law. The results showed that there was a limited affect from the oils on the fatigue limit, but that the small-crack growth law, dlldN = C1 o~al,was affected by the oils and the value of n tended to increase with an increase in the viscosity of oil; n approx. = 8 in sir, n approx. = 10 in the lower oils end n approx. = 11 in the higher viscosity oils. These phenomena were accounted for by the penetration of the oils into the cracks. 13 refa.
Fracture modes and f a t i g u e life evaluation o f 8 U 8 3 0 4 stainless steel
under n _ o n . ~ ,
nnl biexiel luedlng ¢ e M i t i e ~ at SSO =C. Nitre, A., ugsta, I. and Kuwabaro, K. J. Sac. Mater. Sci., Jpn. Apr. 1989 38, (427), 4 1 6 - 4 2 2 (in Japanese) The authors have conducted in-phase and 90° out-of-phase push-pull and torsion fatigue tests on SUS304 stainless steel st 550 "C, and investigated its fracture mechanism and fatigue failure criterion. This paper assesses the results of the push-pull and torsion fatigue tests, which have the shear strain to normal strain ratio of 1.5 with 30~, 45°, 60~ phase difference st 550 oC, and discusses the transition condition of the fracture mode and the low cycle fatigue failure criterion for the bisxial fatigue data obtained in this study, as well as for those in the previous study. From the strain analysis and the fracture surface observation in the in-phase and out-of-phase tests, the fracture mode transition condition which depends on both the values of ~UErnlx/~k~maxand ~u~n/A~lmaxwes determined, and the bisxial fatigue fracture mode map for s SUS304 stainless steel at 550 °C was drawn on the basis of these values. Equivalent strain energy, AE, was defined by leo-fatigue life evaluation from s plane with tensile strain energy, AEI on the y axis and shear strain energy, AEII on the x axis. Fatigue failure life under out-of-phase straining conditions could be correlated well with equivalent strain energy. 7 refs.
S t u d y o n m e c h a n i s m o f f a t i g u e crack propagation b y v a d e b l e loading A K decreasing test m e t h o d . Masuda, H. andMatsuoka, S. J. Sac. Mater. Sci., Jpn. Apr. 1989 38, (427), 4 1 0 - 4 1 5 (in Japanese) In order to predict the most reliable fatigue life under variable loading conditions such as service environments, s new fatigue test method was developed, and by using it the fatigue crack propagation properties were studied for HTS0, SMSOB and SUS 304 steels. The test results show that, although no crack closure occurred in both the variable and constant loading tests, the crack propagation rate under the variable loading test condition was much faster than that under the constant loading test condition for all tested alloys, especially at low &K levels. The maximum acceleration of the crack propagation was dependent on the variable loading amplitude. When the variable load was frequently applied, the crack propagation rate became proportional to second power of ~K. From these results, it can be said that the new fatigue test method is one of the best methods to predict the most reliable fatigue life under variable loading conditions. 3 refs.
Crack g r o w t h characteristics o f a h i g h strength steel under application aT over- and understresses (effect o f t h e m e a n stress w a v e form). A n e x a m i n a t i o n o f t h e notch effect in f a t i g u e o f carbon steels based on linear n o t c h mechanics. Nisitani, H., Noguchi, H., Uchihori, H. and Nakae,
H. JSME Int. J. I July 1989 32, (3), 4 3 9 - 4 4 3
Fatigue tests of 0.31% C steel specimehs with a circumferential notch were made under a wide range of configuration parameters. The results confirmed that linear notch mechanics (LNM) can be successfully applied to the evaluation of notch effects in fatigue. Master curves useful for the evaluation of notch effects in the fatigue of C steels were obtained by arranging previously published data, based on LNM. The fatigue limit of a specimen with a drilled hole was discussed using these master curves. 15 refs.
Fatigue strength o f t w o - p l y b e l l o w s at elevated temperature. Abe, H.,
Shimoyashiki, S. and Maeda, O. J. Sac. Mater. Sci., Jpn. Apr. 1989 38, (427), 4 3 0 - 4 3 6 (in Japanese)
In order to investigate the fatigue strength of bellows at elevated temperature, fatigue tests at room temperature and 500 °C and stress analyses have been conducted on manufactured bellows. The manufactured bellows are a two-ply type, in which strain can be decreased by axial extension and compression without loss of stiffness against pressure. It was found that the strain distribution changed with tbe bellows' thickness and usually the maximum strain appeared st the outer surface of the root in the outer bellows. In order to estimate the fatigue lifetime of bellows, the octahedrel shearing strain derived from both the axial and circumferential strains was found to be more effective than the estimation with only the axial strain, which is commonly used. Fatigue cracks were produced in the maximum strain area, and the cracks propagated from the outer surface to the inner surface of the bellows. It seems that the strain intensity factor obtained from the measured strain is effective for estimation of fatigue crack propagation rates. 11 refs.
Thermal f a t i g u e crack p r o p e g a t i o n and failure life evaluation on C r - M o - V and SUS304 steels. Nitta, A., agate, 7". and Kuwabara, K. J. Sac. Mater. Sci., Jpn. Apr. 1989 38, (427), 4 2 3 - 4 2 9 (in Japanese) In order to investigate the fracture mechanics law of macroscopic crack propagation in thermal fatigue, strein-controlled thermal fatigue tests on Cr-Mo-V rotor steel and SUS304 stainless steel were carried out by using a notched specimen. A smooth specimen was also employed for thermal fatigue tests under the same conditions as the crack propagation tests, to discuss the applicability of the fatigue life law (is, the strein-energy parameter approach) derived from the macroscopic crack propagation law to thermal fatigue life evaluation. The results obtained are summarized as follows. (1) The characteristics of thermal fatigue crack propagation could be classified into two types (is, cycle-dependent and time-dependent) by applying the transition criterion between the types. (2) The fracture modes in the cycle- and time-dependent thermal fatigue were of transgrenular and intergranular types, respectively. (3) The fatigue J-integral range, Ajr, was e fracture mechanics parameter controlling the crack propagation rate, d//dN, in the cycle-dependent thermal fatigue, with the creep J-integral range, ~Jc, in the time-dependent thermal fatigue, in this case, rapid straining could be successfully applied to the partition of the inelastic strain into plastic and creep components for evaluating the ~,J¢ value. The crack propagation law (is, the dl/dN-AJf and dl/dN-&Jc relations) in thermal fatigue was identical with that obtained in isothermal fatigue. (4) The thermal fatigue failure life of the smooth specimen was correlated with the strain-energy parameter, and the correlation agreed with that in isothermal fatigue. Also, it could be predicted from the crack propagation characteristics obtained by using the notched specimen. 24 refs.
146
Kamata, T. and Nishida, S. ,,I, Sac. Mater. Sci,, Jpn. Apr. 1989 38, (427), 4 0 4 - 4 0 9 (in Japanese)
Push-pull fatigue tests were conducted on 80 kgf/mm 2 steel under the combination of regularly applied understresses and intermittently applied overstresses. The mean stress superimposed on understresses changed periodically to form an overstress range pair at the time of the mean stress change. The effects were investigated of understress application, mean stress superposition on understresses and the mean stress wave form, on the crack growth rats. Crack initiation and propagation lives, in the tests conducted under the combination of over- and under-stresses, were much shorter than expected when only the overstress cycles were counted, neglecting the damage of understresses. The stress amplitude, even approx 50% of the endurance limit of the steel, was judged effective to make both crack initiation and growth lives shorter. Crack initiation and growth lives, in the tests with the sporadic down-spike stress change and with the rectangular stress change, seemed almost equal to each other, and much shorter than those for the constant amplitude test. In two-step P-N interval tests, the crack growth rate was higher than that for the two-step N-P interval test, and even the crack growth rate for the N-P test was higher than that for the completely reversed constant amplitude test at relatively smaller values of /~K. 12 refs.
Fatigue crack g r o w t h properties of nickel-base alloys in h i g h pressure /~/.drogen at r o o m t e m p e r a t u r e . Fukuyama, S., Yolkogawa, K. and Araki,
J. Sac. Mater. Sci., Jpn. M a y 1989 38, (428), 5 3 9 - 5 4 5 (in Japanese) The fatigue crack growth properties of the Inconel 718 and Udimet 720 Ni-base alloys used for liquid H fueled rocket engine materials were investigated as functions of ~,K and frequency, in high pressure H, at 19.7 MPa, at room temperature. The results obtained are as follows. (1) The fatigue crack growth rate in H was larger than that in Ar for both Inconel 718 and Udimet 720. The effect of H on fatigue crack growth rate increased with decreasing frequency of cyclic loading. The effect of H on fatigue crack growth of Udimet 720 was higher than that of Inconel 718. (2) Above the ~K at which striations were observed on the fracture surface in Ar, H showed a marked effect on the fatigue crack growth, is, the fracture along the interfaces between the 5 phase end ~/ matrix for Inconel 718 and that along the interfaces between the -/ phase and ~ matrix for Udimst 720 were observed on the fracture surface in H, respectively. 15 refs.
Influence o f segregation o n f a t i g u e strength o f rails. Urashima, C. and
Nishida, S. J. Sac. Mater. Sci., Jpn. M a y 1989 38, (426), 5 3 3 - 5 3 8 (in Japanese) Segregation is recognized to be very harmful for reliability in structural steels. Some fatigue tests were performed to investigate this. The main results obtained are as follows. (1) Carbon, Mn and phosphorus were segregated positively in the segregation band, where the proof stress, tensile strength and hardness became higher but the elongation and reduction of area became lower than the other positions. (2) The rotating bending fatigue strength varied little, irrespective of the presence or absence of segregation, the degree of segregation or the orientation of test specimens in the rail. (3) The fatigue crack initiated in the position where there is no segregation, and its place of origin showed a flat surface, which seamed to be a parallel face along s pearlite 1smeller. (4) The axial pulsating fatigue strength of bolt-holed specimens varied little with the presence or absence of segregation and degree of segregation. (5) It is considered that the segregation has no influence on the fatigue strength due to the high resistance for slip in the segregation band. 8 rsfs.
Int J Fatigue March 1990
Surface f a t i g u e crack p r o p a g a t i o n b e h e v i o u r in a residual stress field (fatigue crack g.,mwth, l a w and evaluation o f f a t i g u e crack p r o p a g e t i o n
rate). Torii, 7"., Hones, K. and Sugiyama, M. JSME Int. J. I J u l y 1989 32, (3), 4,~0-457
The fatigue life of plain carbon steel with residual stress was studied with special reference to the in/tietJon and the propagation of surface fatigue cracks. Tensile residual stresses had no significant influence on crack initiation lives, but increased the fatigue crack propagation rate for surface fatigue cracks. The propagation rate of a surface fatigue crack was controlled by the parameter {(&K)°.s (K~n=x)°.s} in which AK and Km=~were, respectively, the stress intensity factor range and stress intensity factor calculated from the maximum stress distribution containing residual stresses measured st the stress cycles of the initiation of surface cracks. This parameter also served to help understand surface fatigue crack shape in a residual stress f'mld. Finally, the equation of (&KIP (Kmu)q = Km,x - pKmi, was derived under the condition of both p + q = 1 and the minimum stress intensity factor Kmin < Km=x. Ths effects of Kmin (< 0) on fatigue crack propagation sre obtained from the mechanical behaviour of the plsstically deformed layer left in the wake of the advancing crack. 25 refs.
Effect o f oil viscosity on t h e f a t i g u e l i m i t of drilled specimens and t h e small crack g r o w t h law. Gate, M., Nisitani, H., Miyegawa, H. and
Yanagawa, Y. JSME Int. J. I July 1989 32, (3), 4 4 4 - 4 4 9
Rotating bending fatigue tests of an annealed 0.34% carbon steel smooth specimen with s small blind hole were carried out using four types of base oils in order to evaluate the effect of oil viscosity on the fatigue limit and small crack growth law. The results showed that there was a limited affect from the oils on the fatigue limit, but that the small-crack growth law, dlldN = C1 o~al,was affected by the oils and the value of n tended to increase with an increase in the viscosity of oil; n approx. = 8 in sir, n approx. = 10 in the lower oils end n approx. = 11 in the higher viscosity oils. These phenomena were accounted for by the penetration of the oils into the cracks. 13 refa.
Fracture modes and f a t i g u e life evaluation o f 8 U 8 3 0 4 stainless steel
under n _ o n . ~ ,
nnl biexiel luedlng ¢ e M i t i e ~ at SSO =C. Nitre, A., ugsta, I. and Kuwabaro, K. J. Sac. Mater. Sci., Jpn. Apr. 1989 38, (427), 4 1 6 - 4 2 2 (in Japanese) The authors have conducted in-phase and 90° out-of-phase push-pull and torsion fatigue tests on SUS304 stainless steel st 550 "C, and investigated its fracture mechanism and fatigue failure criterion. This paper assesses the results of the push-pull and torsion fatigue tests, which have the shear strain to normal strain ratio of 1.5 with 30~, 45°, 60~ phase difference st 550 oC, and discusses the transition condition of the fracture mode and the low cycle fatigue failure criterion for the bisxial fatigue data obtained in this study, as well as for those in the previous study. From the strain analysis and the fracture surface observation in the in-phase and out-of-phase tests, the fracture mode transition condition which depends on both the values of ~UErnlx/~k~maxand ~u~n/A~lmaxwes determined, and the bisxial fatigue fracture mode map for s SUS304 stainless steel at 550 °C was drawn on the basis of these values. Equivalent strain energy, AE, was defined by leo-fatigue life evaluation from s plane with tensile strain energy, AEI on the y axis and shear strain energy, AEII on the x axis. Fatigue failure life under out-of-phase straining conditions could be correlated well with equivalent strain energy. 7 refs.
S t u d y o n m e c h a n i s m o f f a t i g u e crack propagation b y v a d e b l e loading A K decreasing test m e t h o d . Masuda, H. andMatsuoka, S. J. Sac. Mater. Sci., Jpn. Apr. 1989 38, (427), 4 1 0 - 4 1 5 (in Japanese) In order to predict the most reliable fatigue life under variable loading conditions such as service environments, s new fatigue test method was developed, and by using it the fatigue crack propagation properties were studied for HTS0, SMSOB and SUS 304 steels. The test results show that, although no crack closure occurred in both the variable and constant loading tests, the crack propagation rate under the variable loading test condition was much faster than that under the constant loading test condition for all tested alloys, especially at low &K levels. The maximum acceleration of the crack propagation was dependent on the variable loading amplitude. When the variable load was frequently applied, the crack propagation rate became proportional to second power of ~K. From these results, it can be said that the new fatigue test method is one of the best methods to predict the most reliable fatigue life under variable loading conditions. 3 refs.
Crack g r o w t h characteristics o f a h i g h strength steel under application aT over- and understresses (effect o f t h e m e a n stress w a v e form). A n e x a m i n a t i o n o f t h e notch effect in f a t i g u e o f carbon steels based on linear n o t c h mechanics. Nisitani, H., Noguchi, H., Uchihori, H. and Nakae,
H. JSME Int. J. I July 1989 32, (3), 4 3 9 - 4 4 3
Fatigue tests of 0.31% C steel specimehs with a circumferential notch were made under a wide range of configuration parameters. The results confirmed that linear notch mechanics (LNM) can be successfully applied to the evaluation of notch effects in fatigue. Master curves useful for the evaluation of notch effects in the fatigue of C steels were obtained by arranging previously published data, based on LNM. The fatigue limit of a specimen with a drilled hole was discussed using these master curves. 15 refs.
Fatigue strength o f t w o - p l y b e l l o w s at elevated temperature. Abe, H.,
Shimoyashiki, S. and Maeda, O. J. Sac. Mater. Sci., Jpn. Apr. 1989 38, (427), 4 3 0 - 4 3 6 (in Japanese)
In order to investigate the fatigue strength of bellows at elevated temperature, fatigue tests at room temperature and 500 °C and stress analyses have been conducted on manufactured bellows. The manufactured bellows are a two-ply type, in which strain can be decreased by axial extension and compression without loss of stiffness against pressure. It was found that the strain distribution changed with tbe bellows' thickness and usually the maximum strain appeared st the outer surface of the root in the outer bellows. In order to estimate the fatigue lifetime of bellows, the octahedrel shearing strain derived from both the axial and circumferential strains was found to be more effective than the estimation with only the axial strain, which is commonly used. Fatigue cracks were produced in the maximum strain area, and the cracks propagated from the outer surface to the inner surface of the bellows. It seems that the strain intensity factor obtained from the measured strain is effective for estimation of fatigue crack propagation rates. 11 refs.
Thermal f a t i g u e crack p r o p e g a t i o n and failure life evaluation on C r - M o - V and SUS304 steels. Nitta, A., agate, 7". and Kuwabara, K. J. Sac. Mater. Sci., Jpn. Apr. 1989 38, (427), 4 2 3 - 4 2 9 (in Japanese) In order to investigate the fracture mechanics law of macroscopic crack propagation in thermal fatigue, strein-controlled thermal fatigue tests on Cr-Mo-V rotor steel and SUS304 stainless steel were carried out by using a notched specimen. A smooth specimen was also employed for thermal fatigue tests under the same conditions as the crack propagation tests, to discuss the applicability of the fatigue life law (is, the strein-energy parameter approach) derived from the macroscopic crack propagation law to thermal fatigue life evaluation. The results obtained are summarized as follows. (1) The characteristics of thermal fatigue crack propagation could be classified into two types (is, cycle-dependent and time-dependent) by applying the transition criterion between the types. (2) The fracture modes in the cycle- and time-dependent thermal fatigue were of transgrenular and intergranular types, respectively. (3) The fatigue J-integral range, Ajr, was e fracture mechanics parameter controlling the crack propagation rate, d//dN, in the cycle-dependent thermal fatigue, with the creep J-integral range, ~Jc, in the time-dependent thermal fatigue, in this case, rapid straining could be successfully applied to the partition of the inelastic strain into plastic and creep components for evaluating the ~,J¢ value. The crack propagation law (is, the dl/dN-AJf and dl/dN-&Jc relations) in thermal fatigue was identical with that obtained in isothermal fatigue. (4) The thermal fatigue failure life of the smooth specimen was correlated with the strain-energy parameter, and the correlation agreed with that in isothermal fatigue. Also, it could be predicted from the crack propagation characteristics obtained by using the notched specimen. 24 refs.
146
Kamata, T. and Nishida, S. ,,I, Sac. Mater. Sci,, Jpn. Apr. 1989 38, (427), 4 0 4 - 4 0 9 (in Japanese)
Push-pull fatigue tests were conducted on 80 kgf/mm 2 steel under the combination of regularly applied understresses and intermittently applied overstresses. The mean stress superimposed on understresses changed periodically to form an overstress range pair at the time of the mean stress change. The effects were investigated of understress application, mean stress superposition on understresses and the mean stress wave form, on the crack growth rats. Crack initiation and propagation lives, in the tests conducted under the combination of over- and under-stresses, were much shorter than expected when only the overstress cycles were counted, neglecting the damage of understresses. The stress amplitude, even approx 50% of the endurance limit of the steel, was judged effective to make both crack initiation and growth lives shorter. Crack initiation and growth lives, in the tests with the sporadic down-spike stress change and with the rectangular stress change, seemed almost equal to each other, and much shorter than those for the constant amplitude test. In two-step P-N interval tests, the crack growth rate was higher than that for the two-step N-P interval test, and even the crack growth rate for the N-P test was higher than that for the completely reversed constant amplitude test at relatively smaller values of /~K. 12 refs.
Fatigue crack g r o w t h properties of nickel-base alloys in h i g h pressure /~/.drogen at r o o m t e m p e r a t u r e . Fukuyama, S., Yolkogawa, K. and Araki,
J. Sac. Mater. Sci., Jpn. M a y 1989 38, (428), 5 3 9 - 5 4 5 (in Japanese) The fatigue crack growth properties of the Inconel 718 and Udimet 720 Ni-base alloys used for liquid H fueled rocket engine materials were investigated as functions of ~,K and frequency, in high pressure H, at 19.7 MPa, at room temperature. The results obtained are as follows. (1) The fatigue crack growth rate in H was larger than that in Ar for both Inconel 718 and Udimet 720. The effect of H on fatigue crack growth rate increased with decreasing frequency of cyclic loading. The effect of H on fatigue crack growth of Udimet 720 was higher than that of Inconel 718. (2) Above the ~K at which striations were observed on the fracture surface in Ar, H showed a marked effect on the fatigue crack growth, is, the fracture along the interfaces between the 5 phase end ~/ matrix for Inconel 718 and that along the interfaces between the -/ phase and ~ matrix for Udimst 720 were observed on the fracture surface in H, respectively. 15 refs.
Influence o f segregation o n f a t i g u e strength o f rails. Urashima, C. and
Nishida, S. J. Sac. Mater. Sci., Jpn. M a y 1989 38, (426), 5 3 3 - 5 3 8 (in Japanese) Segregation is recognized to be very harmful for reliability in structural steels. Some fatigue tests were performed to investigate this. The main results obtained are as follows. (1) Carbon, Mn and phosphorus were segregated positively in the segregation band, where the proof stress, tensile strength and hardness became higher but the elongation and reduction of area became lower than the other positions. (2) The rotating bending fatigue strength varied little, irrespective of the presence or absence of segregation, the degree of segregation or the orientation of test specimens in the rail. (3) The fatigue crack initiated in the position where there is no segregation, and its place of origin showed a flat surface, which seamed to be a parallel face along s pearlite 1smeller. (4) The axial pulsating fatigue strength of bolt-holed specimens varied little with the presence or absence of segregation and degree of segregation. (5) It is considered that the segregation has no influence on the fatigue strength due to the high resistance for slip in the segregation band. 8 rsfs.
Int J Fatigue March 1990