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Tensile and fatigue properties of Fe-Mn-Al-C alloys
zone was confirmed. The alloy exhibited cyclic strain hardening near the crack tip dudng fatigue. The work hardening of the alloy was attributed to the local cyclic etrein-induesd FCC to HCP msrtensitic transformation taking place in the plastic zone. A low stacking fault energy of the alloy was also considered to be one of the main factors affecting the strein-hardenlng beheviour. 28 refs.
The l o w
,Wcle f a t i g u e d e f o r m a t i o n respones o f = single-orystal superslloy
at 65rC. Gabb, T.P., Welsch, G., Miner, R.V. and Gayda, J. Meter. Sci. Eng. Feb. 1989 A A10e, (1-2), 189-202 The purpose was to characterize the cyclic etress-strain response, the corresponding deformation structure and their relationships in the single crystal Ni-beee superalloy PWA 1480. The isothermal low cycle fatigue response and deformation structures of specimens oriented near the (001), (2520), (3610), (011), (234) and (111) crystallographic orientations were characterized at an intermediate temperature (650"C). The initial yield strength of all these specimens was controlled by the shearing of the ~t' precipietea by dislocation pairs. The low cycle fatigue tests exhibited cyclic hardening, which was associated with dislocation interactions in the ~t matrix. In specimens deforming by slip on a single slip system, dislocations of the primary slip system accumulated in the ~f matrix and formed sessile entanglements. In specimens deforming by slip on several slip systems, the dislocations of the different operative slip systems intersected in the -y matrix and formed sessile arrangements. 16 refs.
Creep and f a t i g u e crack g r o w t h be.ha v i o u r of s o m e cast nickel-baxe alloys. Shahinian, P. and Sadananoa, K. Mater. Sci. Eng. Feb. 1989 A A108, (1-2), 131-140
Creak g r o w t h c h a r a c t e d s t ~ o f m e r a g l n g steel. Diwakar, V., Arumugam,
S., Lakshmanan, T.S. and Sarkar, B.K. J. Mater. Sci. Mar. 1989 24, (3), 881-884 Compact tension (CT) and surface crack tension (SCT) specimens of 18 Ni 1800 MPa grade maraging steel M250 (parent metal and welded) were studied for the cyclic crack growth rate applying in sinusoidal (SL) and block loading (BL) conditions. The BL cycle was designed to simulate the stress intensity levels experienced during proof pressure and static test of a fabricated rocket motor. The threshold stress intensity for stage II crack growth for weldment is found to be approx 0.6 that for the parent metal. For s given stress intensity, the crack growth rate for weldment and parent metal are in the same range under SL or BL. Though-thickness cracks (laboratory condition) in CT specimens and part-through thickness cracks (service condition) in SCT specimens show good correlation for cyclic crack growth rate. The results are of great significance for considering the reuse of the mareging steel rocket motor case. 10 refs.
Testing and control SN curve e s t i m a t i o n of f a t i g u e test using e x p e r i m e n t a l regression analysis. Shin, S. and Yano, H. ". Bull Natl. Ras. Lab. Metrology 1989 38, (1), 7 - 1 8 Several kinds of regression functions of SN curve for fatigue test have been
Crack growth in Ni-beee alloys IN-738, tN-792 and Rene-80 at 927°C under cyclic and static loads was investigated using fracture-mechanics-type specimens. The influence of environment (specifically sir, vacuum and impure helium) on crack growth was examined as well. Crack growth was markedly slower on a time basis in alloys under static load (creep) than under cyclic load (fatigue) and in creep required a higher stress intensity to be initiated. Generally, the resistance to crack growth in creep was higher in air than in vacuum, whereas, in fatigue, the converse was true. The creep crack growth rates in He containing minute amounts of H2, carbon monoxide and CH4 were not significantly different from rates in vacuum, the effect of impure helium being small st most. For a given stress intensity, the fatigue crack growth rates among the alloys in air and in vacuum differed by only a small amount. Also, the creep crack growth rates of the three alloys in vacuum did not vary greatly. The beheviour of the alloys was generally similar to that of other Ni-base superalloys observed previously. 18 refs.
suggested and the leeet-squares method is used to determine parameters in each equation. In the case of a non-lineer function, however, the application of the leastsquares method cannot always adequately explain properties of objective lots. It has been shown that the application of experimental regression analysis is able to correct such defects and to estimate parameters in the functions and regression error. In the experiment, the lots of samples consist of specimens which have been manufactured taking materials, conditions of heat treatment, hardness of specimens, etc into consideration. The fatigue strength (or SN curve) of each lot and overall estimated error are obtained using the method of experimental regression analysis. The estimated error of the regression functions in this experiment has a standard deviation ranging from 21.6-31.4 MPa. Regarding the application method of this new system in the future, it is indicated that the new obtained data of the fatigue test, in addition to the body of accumulated data, are analysed and that SN curves are able to be estimated consistently with each other, even when the number of new data is small. Examples of SCM435 and SUJ2 steel are given. 14 refs.
The arystalloQraphy o f f a t i g u e crack initiation in coarse grained Astroloy st 20°C. Dawdson, D.L. and Chan, K.S. Acta MetalL Apr. 1989 37, (4) 1089-1097
Acoustic emission and v i b r a t i o n in t h e process o f roiling contact fatigue.
The effects of crystallographic orientation on fatigue crack initiation has been examined for coarse-grained Astroloy at 20°C. Specimens were cycled by threepoint bending at stress ranges between 5-95% of the proportional limit until fatigue cracks were detected. The crystallographic orientation of individual grains within which fatigue cracks initiated was determined by use of selected area electron channelling. Grains forming cracks were found to have surface normals near the (100), (011) and (113) directions. Conversely, grains which did not initiate cracks were not similarly grouped in orientation. Calculations of the Taylor factor using the Bishop-Hill approach revealed that fatigue crack initiation in Astroloy occurred at grains with low values of the Taylor factor. 17 refs. Tensile and f a t i g u e properties o f F e - M n - A I - C alloys. Chang, S.C., Hsiau,
Y.H, and Jahn, M.T. J. Mater. ScL Mar. 1989 24, (3), 1117-1120 The tensile properties and fatigue behaviour of three sollution-treated Fe-29 Mn-9 AI-C (wt,%) alloys having various carbon contents leading to different volume fractions of austenite and ferrite phases were investigated. The C contents were 1.06, 0.60, and 0.26%, respectively, and the corresponding volume fractions of austenite were 100, 90 and 45%, respectively. The alloy having 1.06% C possessed the best tensile properties but its fatigue behaviour was only comparable to the other two alloys with lower C contents. The alloy having 0.60% C possessed the lowest yield strength, but its fatigue life was slightly better than the other two alloys. The alloy having 0.26°/=C possessed lowest elongation and medium strength, and its fatigue life was comparable to the other two alloys. Their tensile properties and fatigue behaviour were explained in terms of crack initiation, crack propagation, grain size, constituent arrangement and constituent fraction. 12 refs.
374
I. Yoshioka, T. and Fujiwara, T. Toraibojisto (J, Jpn. Soc. Tribol.) 1989 34, (1), 36-42 (in Japanese) One of the methods of detecting the rolling contact fatigue is by using acoustic emission (AE). The relationship between the shape of acoustic emission and the fatigue is studied. It is concluded that there are three types of AE which are related to the slight metallic contact, heavy contact and formation of cracks. The AE increases dramatically right before the fatigue and the increase in negative peak of the vibration fluctuation has a good correspondence with the flaking. Examples of bearing steel and tool steel are given. 12 refs.
Results o f in-phaes a x i a l - t o r s i o n a l f a t i g u e e x p e r i m e n t s on 304 r a i n l e s s steel. (Report). Bonacuse, P.J. and Kalluri, S. NASA Tech. Memo TM--I01464 1989, 19 pp A series of axial-torsional, in-phase, strein-controlled low-cycle fatigue tests were performed at room temperature on tubular specimens of 304 stainless steel. The experimental equipment and procedures used are described. The tubular specimens were polished on the outer surface to aid in the use of a cellulose film surface replication technique for crack detection. However, cracking initisted predominantly on the internal surface for all specimens. Honing of the bore of the tubular specimens lessened but did not entirely eliminate this problem. The observed fatigue lives are compared with lives calculated from three multiaxial life models. Constants for the life prediction models were obtained from uniaxial and torsional tests performed on the same heat of material. The observed fatigue lives agree with calculated lives to within a factor of two for all but one of the life prediction models. 13 refs.
Int J Fatigue September 1989
The l o w
,Wcle f a t i g u e d e f o r m a t i o n respones o f = single-orystal superslloy
at 65rC. Gabb, T.P., Welsch, G., Miner, R.V. and Gayda, J. Meter. Sci. Eng. Feb. 1989 A A10e, (1-2), 189-202 The purpose was to characterize the cyclic etress-strain response, the corresponding deformation structure and their relationships in the single crystal Ni-beee superalloy PWA 1480. The isothermal low cycle fatigue response and deformation structures of specimens oriented near the (001), (2520), (3610), (011), (234) and (111) crystallographic orientations were characterized at an intermediate temperature (650"C). The initial yield strength of all these specimens was controlled by the shearing of the ~t' precipietea by dislocation pairs. The low cycle fatigue tests exhibited cyclic hardening, which was associated with dislocation interactions in the ~t matrix. In specimens deforming by slip on a single slip system, dislocations of the primary slip system accumulated in the ~f matrix and formed sessile entanglements. In specimens deforming by slip on several slip systems, the dislocations of the different operative slip systems intersected in the -y matrix and formed sessile arrangements. 16 refs.
Creep and f a t i g u e crack g r o w t h be.ha v i o u r of s o m e cast nickel-baxe alloys. Shahinian, P. and Sadananoa, K. Mater. Sci. Eng. Feb. 1989 A A108, (1-2), 131-140
Creak g r o w t h c h a r a c t e d s t ~ o f m e r a g l n g steel. Diwakar, V., Arumugam,
S., Lakshmanan, T.S. and Sarkar, B.K. J. Mater. Sci. Mar. 1989 24, (3), 881-884 Compact tension (CT) and surface crack tension (SCT) specimens of 18 Ni 1800 MPa grade maraging steel M250 (parent metal and welded) were studied for the cyclic crack growth rate applying in sinusoidal (SL) and block loading (BL) conditions. The BL cycle was designed to simulate the stress intensity levels experienced during proof pressure and static test of a fabricated rocket motor. The threshold stress intensity for stage II crack growth for weldment is found to be approx 0.6 that for the parent metal. For s given stress intensity, the crack growth rate for weldment and parent metal are in the same range under SL or BL. Though-thickness cracks (laboratory condition) in CT specimens and part-through thickness cracks (service condition) in SCT specimens show good correlation for cyclic crack growth rate. The results are of great significance for considering the reuse of the mareging steel rocket motor case. 10 refs.
Testing and control SN curve e s t i m a t i o n of f a t i g u e test using e x p e r i m e n t a l regression analysis. Shin, S. and Yano, H. ". Bull Natl. Ras. Lab. Metrology 1989 38, (1), 7 - 1 8 Several kinds of regression functions of SN curve for fatigue test have been
Crack growth in Ni-beee alloys IN-738, tN-792 and Rene-80 at 927°C under cyclic and static loads was investigated using fracture-mechanics-type specimens. The influence of environment (specifically sir, vacuum and impure helium) on crack growth was examined as well. Crack growth was markedly slower on a time basis in alloys under static load (creep) than under cyclic load (fatigue) and in creep required a higher stress intensity to be initiated. Generally, the resistance to crack growth in creep was higher in air than in vacuum, whereas, in fatigue, the converse was true. The creep crack growth rates in He containing minute amounts of H2, carbon monoxide and CH4 were not significantly different from rates in vacuum, the effect of impure helium being small st most. For a given stress intensity, the fatigue crack growth rates among the alloys in air and in vacuum differed by only a small amount. Also, the creep crack growth rates of the three alloys in vacuum did not vary greatly. The beheviour of the alloys was generally similar to that of other Ni-base superalloys observed previously. 18 refs.
suggested and the leeet-squares method is used to determine parameters in each equation. In the case of a non-lineer function, however, the application of the leastsquares method cannot always adequately explain properties of objective lots. It has been shown that the application of experimental regression analysis is able to correct such defects and to estimate parameters in the functions and regression error. In the experiment, the lots of samples consist of specimens which have been manufactured taking materials, conditions of heat treatment, hardness of specimens, etc into consideration. The fatigue strength (or SN curve) of each lot and overall estimated error are obtained using the method of experimental regression analysis. The estimated error of the regression functions in this experiment has a standard deviation ranging from 21.6-31.4 MPa. Regarding the application method of this new system in the future, it is indicated that the new obtained data of the fatigue test, in addition to the body of accumulated data, are analysed and that SN curves are able to be estimated consistently with each other, even when the number of new data is small. Examples of SCM435 and SUJ2 steel are given. 14 refs.
The arystalloQraphy o f f a t i g u e crack initiation in coarse grained Astroloy st 20°C. Dawdson, D.L. and Chan, K.S. Acta MetalL Apr. 1989 37, (4) 1089-1097
Acoustic emission and v i b r a t i o n in t h e process o f roiling contact fatigue.
The effects of crystallographic orientation on fatigue crack initiation has been examined for coarse-grained Astroloy at 20°C. Specimens were cycled by threepoint bending at stress ranges between 5-95% of the proportional limit until fatigue cracks were detected. The crystallographic orientation of individual grains within which fatigue cracks initiated was determined by use of selected area electron channelling. Grains forming cracks were found to have surface normals near the (100), (011) and (113) directions. Conversely, grains which did not initiate cracks were not similarly grouped in orientation. Calculations of the Taylor factor using the Bishop-Hill approach revealed that fatigue crack initiation in Astroloy occurred at grains with low values of the Taylor factor. 17 refs. Tensile and f a t i g u e properties o f F e - M n - A I - C alloys. Chang, S.C., Hsiau,
Y.H, and Jahn, M.T. J. Mater. ScL Mar. 1989 24, (3), 1117-1120 The tensile properties and fatigue behaviour of three sollution-treated Fe-29 Mn-9 AI-C (wt,%) alloys having various carbon contents leading to different volume fractions of austenite and ferrite phases were investigated. The C contents were 1.06, 0.60, and 0.26%, respectively, and the corresponding volume fractions of austenite were 100, 90 and 45%, respectively. The alloy having 1.06% C possessed the best tensile properties but its fatigue behaviour was only comparable to the other two alloys with lower C contents. The alloy having 0.60% C possessed the lowest yield strength, but its fatigue life was slightly better than the other two alloys. The alloy having 0.26°/=C possessed lowest elongation and medium strength, and its fatigue life was comparable to the other two alloys. Their tensile properties and fatigue behaviour were explained in terms of crack initiation, crack propagation, grain size, constituent arrangement and constituent fraction. 12 refs.
374
I. Yoshioka, T. and Fujiwara, T. Toraibojisto (J, Jpn. Soc. Tribol.) 1989 34, (1), 36-42 (in Japanese) One of the methods of detecting the rolling contact fatigue is by using acoustic emission (AE). The relationship between the shape of acoustic emission and the fatigue is studied. It is concluded that there are three types of AE which are related to the slight metallic contact, heavy contact and formation of cracks. The AE increases dramatically right before the fatigue and the increase in negative peak of the vibration fluctuation has a good correspondence with the flaking. Examples of bearing steel and tool steel are given. 12 refs.
Results o f in-phaes a x i a l - t o r s i o n a l f a t i g u e e x p e r i m e n t s on 304 r a i n l e s s steel. (Report). Bonacuse, P.J. and Kalluri, S. NASA Tech. Memo TM--I01464 1989, 19 pp A series of axial-torsional, in-phase, strein-controlled low-cycle fatigue tests were performed at room temperature on tubular specimens of 304 stainless steel. The experimental equipment and procedures used are described. The tubular specimens were polished on the outer surface to aid in the use of a cellulose film surface replication technique for crack detection. However, cracking initisted predominantly on the internal surface for all specimens. Honing of the bore of the tubular specimens lessened but did not entirely eliminate this problem. The observed fatigue lives are compared with lives calculated from three multiaxial life models. Constants for the life prediction models were obtained from uniaxial and torsional tests performed on the same heat of material. The observed fatigue lives agree with calculated lives to within a factor of two for all but one of the life prediction models. 13 refs.
Int J Fatigue September 1989