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Production and evaluation of construction alloy steel as chain material
Creep-fatigue tests were conducted with 21/4Cr-1Mo steel at 550°C in air and in vacuums of 0.1 and 100 pPa to separate the environmental effect from the pure creep-fatigue beheviour. In 0.1 pPa vacuum where no environmental effect was detected creep-fatigue life reduction was observed when the time for tension going stroke exceeded that for compression going stroke. Furthermore, it was observed that a positive mean stress reduced the creep-fatigue life in high vacuum. A good correlation existed between a creep--fatigue life and the fracture mode. No life reduction occurred when the fracture mode was predominantly transgranular. On the contrary, a significant life reduction was observed when it was predominantly intergranular. An environmental effect was also examined qualitatively. The effect of the air environment depended strongly upon the waveform. The above observations were compared to those obtained with 304 steel in a previous study by one of the authors. 5 refs.
Study on the d u c t i l e f r a c t u r e o f a s u r f a c e c r a c k . G r o w t h o f a s u r f a c e crack and f i n i t e e l e m e n t a n a l y s i s . Kikuchi, M., Nishio, T., Yano, K., Mechida, K. and Miyamoto, H. JSME Int. J. I J u l y 1988 31, (3), 5 8 0 - 5 8 7 Ductile fractures of surface cracks were studied experimentally and numerically using two kinds of materials, A508C and WT60. At first, a fatigue pre-crack was introduced, and the aspect ratios of the growing fatigue crack were measured. Then the ductile fracture test was carried out and the distributiOnS of SZW and &a were measured along the crack front for different load levels, It was noticed that &a is the largest where ~. the angle from the surface, is nearly 30" which is considered to be a transition region from plane stress to plane strain conditions. The J-integral distribution was evaluated by the finite element method, and it is shown that the J value is also the largest where ~ is nearly 30", 19 refs,
S t a t i s t i c a l s i z e e f f e c t u n d e r a l t e r n a t i n g l o a d . Scholz, F. and Kuhn, G. Mater. wise. Werkst. tech. Sept. 1988 19, (9), 306-311 (in German) The results of 41 series of tests with smooth cylindrical and notched specimens, subjected to uni- and multiaxial alternating loads (tension-compression, torsion, rotating bending and combined torsion and bending), are compared with theoretically predicted data. The predictions are based on the 'weakest-link-concept', Multiaxial stresses are included either by means of suitable strength criteria, or by a fracture-mechanical consideration of a crack in a multi-dimensional stress field, For the evaluation of the experimental data the twoparametric Weibull's equation was used, The experimental and theoretical results may deviate by less than 20%, when the ratio beWveen the strength at cyclic torsion and cyclic bending is taken into account in the function of survival probability. 17 refs.
Cyclic hardening, y i e l d s u r f a c e and dislocation arrangement in lowcycle f a t i g u e . Schuber~ R. and Rie, K.-T. Mater. wies. Werkst. tech. Nov. 1988 19, (11 ), 3 7 6 - 3 8 3 (in German) In many technical and structural components stress raisers exist which undergo cyclic plastic deformation. Models have been developed to calculate the stress distribution and the resulting life, They are based on the assumptions that Masing-behaviour, isotropic and kinematic hardening are valid with cyclic plasticity. These assumptions have been examined experimentally. An interpretive connection is made between mechanical yield surface and microscopical arrangement of dislocations in the sense of cyclic hardening behaviour. 16 refs.
The failure of hard materials in cyclic compression: m e n t s a n d a p p l i c a t i o n s . Suresh, S. Mater. Sci. Eng. A Dec. 1988 A106--A108, 3 2 3 - 3 2 9
theory, experi-
Fatigue crack propagation t h r e s h o l d . Mami, G., Castro, D.E. and Bechmann, V ASTM J. Test. Eval. Jan. 1989 17, (1), 2 8 - 3 9 Service-type fatigue loading conditions are critically analysed with respect to their relevance for a fatigue crack growth threshold. It was found that a threshold should be experimentally determined as a function of the monotonic-plastic zone size lie as a function of Kml=). For each Kmax the cyclic-plastic zone size depends on the applied &Kand threshold testing should cover the range &K approx. AKth and .~.K(R = 0) for tension fatigue. For a given plastic zone, Kmax and AK fixed, the threshold AKth could occur anywhere between Kmax Kmin, Experimental procedures are presented and results for Inconel 617 and a T ~ A I ~ V alloy furnished which allow one to analyse the influence of the three parameters cited above. It demonstrates the following; the threshold decreases 'lineedy' with increasing monotonic-plastic zone size: this confirms existing data, The cyclic-plastic zone has minimal influence on the fatigue threshold with TI-6AI-4V, while this influence is substantial in the case of Inconel 617, A shift of threshold between Kmax and Kmin does not alter the magnitude of the threshold. 23 refs. E f f e c t s o f s m a l l s u r f a c e c r a c k s o n d u c t i l i t y l o s s in l o w c y c l e f a t i g u e o f 7 0 / 3 0 b r a s s . Murakam~ Y., Makabe, C. and Nisitant~ H. ASTMJ. Test. Eval. Jan. 1989 17, (1), 2 0 - 2 7 The loss of fracture ductility after strain cycling in low cycle fatigue tests is not due to so-called weakening or losing of the strength quality caused by irreversible slips in crystals but rather is attributable to the existence of small surface cracks, The degree of loss of fracture ductility depends on the crack length I, If / is larger than the critical length /c, the fatigue crack causes macroscopic shear fracture in the tensile test after strain cycling, On the other hand, if / < /c the fracture surface becomes the so-called cup-and-cone type. For 70/30 brass,/c = 400 pm 10 refs.
Stochastic models of fatigue crack g r o w t h . Langley, R.S. Eng. Fract. Mech. 1989 32, (1), 1 3 7 - 1 4 5 A number of stochastic models of fatigue crack growth (in AI. steels) under constant amplitude cyclic loading are assessed in the light of experimental data. Particular attention is paid to the predictive performance of the models under a change in the initial crack length, and generally, it is found that the models provide a poor estimate of the standard deviation of the number of cycles to failure. A new model is then introduced which shows improved agreement with the experimental data. 17 refs
Evaluation of stress intensity factors for corner cracked turbine discs under arbitrary loading using finite element methods. Bell, Ft., Pagotto, I.A. and Kirkhope, J. Eng. Frect. Mech. 1989 32, (1), 6 5 - 7 9 Stress intensity factors. K=. obtained using three-dimensional finite elements for a range of depths and shape of corner crack around the bore in a rotating disc are presented, One, wvo, three and four equispeced radial cracks were considered, and the cracks had aspect ratios of b/a = I . 2 and 4. The results are presented in the form of non-dimensiona~ magnification factors which can be superimposed to simulate any loading condition. This stress intensity information is valuable in the prediction of service lives of turbine discs. 22 refs.
On t h e e x p r e s s i o n of fatigue crack initiation life considering the f a c t o r o f o v e r l o a d i n g a f f e c t . Zheng, X. and Lin, C. Eng. Fract. Mech. 1988 31, (6), 9 5 9 - 9 6 6
A summary is presented of recent developments in the understanding of mode I crack growth at room temperature in hard materials subject to uniaxiai cyclic compressive stresses. Experimental observations of fatigue crack growth in cemented carbides, single-phase ceramics, transforming ceramics, ceramic composites and concrete are briefly reviewed. A detailed discussion of the 'driving force' for the growth of a stable crack in a direction macroscopically normal to the far-field compression axis is presented. The 'universal features' of cyclic compression fracture in a wide range of brittle and ductile solids are described. Some important applications of the compression fatigue phenomenon to the fracture toughness testing of brittle materials are highlighted, The overall framework for a general theory of fatigue failure under far-field cyclic compression is developed. 15 refs.
An expression was derived for the fatigue crack initiation life of notched elements with the consideration of overloeding effects. This expression may be used to predict the fatigue crack initiation life of notched element under variable amplitude loading. Experimental work on LY12CZ alloy shows that the test results of fatigue crack initiation life after tension overloading can be well fitted by the formula developed before for fatigue crack initiation life. Tension overloading increases the fatigue crack initiation threshold but has no effect on the coefficient of resistance to fatigue crack initiation. The overloading ratio has no marked effect on crack initiation life. The increase of the crack initiation threshold results in the increase of crack initiaton life, in particular, in long life range. The same results are also obtained by reanalysing some existing test results of overloading effect on crack initiation life given in literature. Consequently, the expression of the fatigue crack initiation life can be obtained by the method given. However. the overloading stress should be determined from the theoretical stress concentration factor of notched element and the maximum nominal stress in the load spectrum of elements. 34 refs.
Fatigue and cavitation wear of the multi-pad journal bearing of highspeed s h a f t . Olszewski, 0. Rev. Roum. ScL Tech.-Mec. App/. M a y - J u n e 1988 33, (3), 2 8 7 - 2 9 3
The crack
Causes of low durability of multi-pad slide bearings are analysed in detail on an example of real industrial objectives, A bearing with hydrodynamic step has been suggested to improve high-speed shaft running stability. Results of theoretical and experimental research on the bearing are presented, 6 refs.
i n i t i a t i o n and growth under high temperature c r e e p , fatigue and creep-fatigue multiplication. Yokobori Jr, A. T. and Yokobori, T.
Eng. Fract. Mech. 1988 31, (6), 9 3 1 - 9 4 5
The relationships among elasticity, plasticity and the development of cracks, measurement of stress along the crack surface and its relationship to the surface morphology of the crack, and the design of aeroplane and other products based on fatigue strength of AI alloys are reviewed. 9 refs.
Recent studies on the crack initiation, early stage crack growth and its subsequent crack growth under high temperature creep, fatigue and creep-fatigue multiplication are discussed, The criteria for these and some new ideas are proposed, For instance, the relative notch opening displacement (RNOD) criterion for the crack initiation and the Q* parameter for the crack growth are critically reviewed, Early stage crack growth and its subsequent crack growth as affected by notch tip acuity were studied. The beheviour of the tail part in the log da/dN vs log C" curve has been attempted, to explain in terms of the curve of the creep beheviour and of the crack length against time. Furthermore, it was proposed that early stage crack growth, say. the so-called first stage crack growth in terms of log da/dN vs tog K curve, may be characterized by the parameter different from those for the so-called second stage crack growth, Materials discussed are SUS304SS and a CrMoV steel, 22 refs.
M i c r o s t r u c t u r e , s t a g e II f a t i g u e crack growth rates and dynamic fracture t o u g h m m s - - a c o r r e l a t i o n , B h a m ~ , SK., S/ngh, V a n d Rajanna,/C Eng. Frect. Mech. 1988 31, (5), 7 8 3 - 7 9 2
Production and evaluation of construction a l l o y s t e a l as chain m a t e r i a l . Wolak, Z and Paczula, B. Neue HutteSept. 1988 33, (9), 3 3 8 - 3 4 2 (in German)
A variety of microstructures were introduced in a 13Cr-Mo-V steel and a 2.SNi-Cr-Mo-V steel by controlled heat treatments. An attempt was made to find correlation between yield strength, fracture toughness and stage II fatigue crack growth rates in each microstructural condition, but no clear trend emerged. Dynamic fracture toughness, determined using an instrumented Charpy impact tester and pracracked Charpy specimens, however, ieflected the occurrence of static mode of fracture during fatigue crack growth in stage I1. 29 refs.
To find out to what degree the amount of the coefficient determining the fatigue limit: tensile strength ration (k = z/Rm) is affected by both the manufacturing process and the chemical composition. 23GHNMA steel was examined. From the results obtained the following conclusions may be drawn. The process of steelmaking may essentially affect fatigue strength. Alterations in fatigue strength caused by heat treatment are directly proportional to alterations in tensile strength. Oxygen and carbon contents exercise a significant influence on fatigue strength, The application of a multiple correlation to determine k
Fatigue s t r e n g t h o f a l u m i n i u m a l l o y s . X V I I I . Takeuchi, K. Kei Kinzoku Yosetsu (J. Light Met. Weld. Constr.) 1988 26, (10), 2 1 - 2 6 (in Japanese)
Int J Fatigue July 1989
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results in a more precise valuation scheme of the fatigue limit, compared to the tensile strength values ascertained under static load. 24 refs.
Fatigue bohaviour of steels with multiple n o t c h , . I. The effect of intorgmtton between notoheo on the rotary bending fatigue propertie=. Wakahara, M., KawJgo~hi, N. and Suenaga, K. Res. Rap. Fac. Eng., Kagoshima Univ. Nov. 1988 (30), 197-206 (in Japanese) When many concentrated stress points exist close together, a different fatigue behaviour pattern is revealed due to their interaction than that shown by a single part. The effect of interaction of notches on fatigue strength was investigated regarding the effect of the number of notches by the round bar specimen of $35C. with multiple 60" V notches subjected to rotary bending. The results obtained are summarized as follows. The stress concentration factor decreased by increasing the number of notches, and it approached a constant value. In relation to this tendency, both the fatigue limit for crack initiation Ow, and the fatigue limit for fatigue (~w=increased gradually with the number of notches. and both also approached constant values, respectively. The Owl showed fluctuation depending on whether or not the number of notches were odd or even. and whether the notch root radius at tbe 'branch point' differed from the odd or even number of notches. These results suggested that some stress factors other than the maximum stress at the root of the notch governed the crack initiation and propagation. The length of the nonpropagation crack became shorter with an increase in the number of notches. 16 refs
Fatigue bohaviour of steele with m u l t i p l e n o t c h e s . II. T h e e f f e c t of interaction between notches on the characteristics of plane bending fatigue. Wakahara, M., Kawagotshi, IV. and Suenaga, K. Res. Rap, Fac. Eng., Kagoshima Univ. Nov. 1988 (30), 207-214 (in Japanese) Fatigue crack initiation and propagation in flat bar specimens, with multiple notches, of carbon steels for machine structural uses, $35C, were examined in plane bending. The results obtained are summarized as follows. The effects of the interaction of closely spaced notches were found on crack initiation and propagation, and the effect of an even number of notches was found to be larger than that of odd ones. The ratio of crack propagation period to fatigue life increased with the number of notches. In general, the number of cycles at crack initiation depended on the stress intensity factor. The crack length at the inflection point in the fatigue crack growth rate curve became shorter with the number of notches. 9 refs.
Fatigue hahaviour of steels with multiple notches. Ill. The effect of interaction between notches on the fatigue crack propagation. Wakahua, M., Suenaga, K. and Kiku, S. Res. Rap. Fac. Eng., Kagoshima Univ. Nov. 1988 (30), 2 1 5 - 2 2 2 (in Japanese) The beheviour of fatigue crack propagation of round bar specimens of $35C with one to three sharp notches was investigated, and the results obtained are summarized as follows. Crack length at notches that did not fracture increased with the overstress ratio and saturated at some ratio. The ratio of the crack propagation period in the total fatigue life was estimated to be approx 98%. regardless of the number of notches and applied stress. The behaviour of crack propagation on specimens with two and three notches was found to be explained well with stress intensity factors accounting for interaction between notches by the principle of superposition, 13 refs.
Surface hardening improveo fatigue strength. Golze. N. Ind.-Anz. Sept. 1 9 8 8 1 1 0 , (74), 2 2 - 2 4 , 26 16 (in German) A surface hardening effect for forged steel (eg Ck35V. Ck45V, Ck45VS, Ck45BY, 49MnVS 3BY, 37Cr4V) parts is initiated by mechanical, thermal or thermo-chemical surface treatments. All three methods produce an internal stress and reduce the surface ductility. The mechanical treatment is most advantageous for steel grades Ck45V and 49MnVS 3BY. A surface hardening increase of 50-100% is achieved through the nitrocarbonization process. The induction method is useful for deep surface treatments in the range of 3-5 mm. The reduction of the surface roughness by grinding results in lower fatigue strength gains than for polishing material. 3 refs.
end fatigue properties of • thermomochanicelly treated 7475 elumlnlum a l l o y . Jahn, M.T. and Luo, J. J. Mater. SciNov. 1988 23, (11), 4 1 1 5 - 4 1 2 0
are reduced to a uniaxial stress by means of a suitable failure criterion or are compared with the specific material strength determined under operation-like testing conditions. The principles are illustrated for static loading of notched and cracked components and for dimensioning in case of creep and fatigue. 19 refs,
Improving the mechanical properties of structural carbon steel by d u e l - p h m h e a t t r e a t m e n t . Aksoy, M. and Esin, A. J. Mater. Eng, Dec. 1988 10, (4), 2 8 1 - 2 8 7 The dual-phese steels represent a newer grade of steels developed to cater to the needs of the automotive industry. The existing work on these steels is, therefore, on sheet steel specimens with a carbon content <0,1% and with thicknesses up to 1.0 mm The dualphase heat treatment was applied successfully to cylindrical specimens (St37. A36) which had diameters up to 7.2 mm and with a nominal C content of 0.20%, The experimental results have indicated that the mechanical strength of the structurel steel, including fatigue strength, can be substantially improved by the dual-phase heat treatment. Barring ductility and impact strength, the mechanical properties of the dual-phase specimens compared extremely well with those of the medium quality heat treatable steels. 18 refs
Low cycle fatigue crack propagation and fractogrephy of • S U S 304 s t a i n l e s s s t e e l a t e l e v a t e d temperature. Kotenuwa, R. and Nosho, T J. So(:. Mater. Sci. Jpn. Sept. 1 9 8 8 37, (420), 1090-1096 (in Japanese) High temperature low-cycle fatigue crack propagation behaviour of SUS 304 stainless steel under four typical kinds of reversed loading patterns (P-P, P-C. C-P and C-C type) was investigated, and the results are discussed in the light of fracture mechanics and electron fractography The stress intensity factor range AK failed to describe the crack propagation behaviour adequately. In the case of loading with tension hold (ie C-P and C-C type), the crack propagation rate was successfully correlated with the modified Jintegral J and agreed with the static deep crack propagation rate. The crack propagation rate for all of the four types of loading was successfully correlated in terms of the cyclic J-integral range ,~.J. and it was not necessary to separate &J into AJr and AJc. The crack propagation rate for the types of loading without tension hold or with short tension hold time (ie P-P and P-C type. and C-P and C-C type with comparatively short tension hold time) was successfully correlated with &Jr, and long tension hold time (ie C-P and C-C type with comparatively long tension hold time) was successfully correlated with AJc. The fracture surfaces where the crack propagation rate was correlated with &Jt were predominantly of the transgranular fatigue type. that is the fracture morphology and the correlating fracture mechanics parameter (&Jr) were of the same fatigue type. On the other hand, those fracture surfaces where crack propagation rate was correlated with AJ c were of the transgranular fatigue type or intergranular creep type or mixed type depending on the condition, that is, the fracture morphology and the correlating fracture mechanics parameter (AJc) were of different types in some cases. There was no significant effect of creep-fatigue interaction on the crack propagation under the combined creep and fatigue conditions, and crack propagation may be assessed by a simple summation of fatigue component and creep components. 12 refs.
E f f e c t s o f b i a x i a l s t r e s s condition and its change on fatigue crack growth p r o p e r t i e s . Yuuki, Ft., A/ira, K, and Kishi, N. J. Soc. Mater. Sci., Jpn. Sept. 1988 37, (420), 1 0 8 4 - 1 0 8 9 (in Japanese) Fatigue tests have been conducted on cruciform flat specimens of a stainless steel with a centre crack by using a high-cycle biaxial fatigue test facility, in order to investigate the effect of biaxial stress on the fatigue crack growth properties &Ki-da/dN. From the comprehensive experiments, no effect of biaxial stress was found in the AKi-da/dN relation if the crack was large and the stress level was low. However. a significant effect of biaxial stress appeared when the crack was small and the stress level was high. The critical region where the effect of biaxial stress appears was clarified quantitatively, based on the crack length measured and the stress level used in the biaxial fatigue tests. Moreover, the effect of changing biaxial stress condition on the fatigue crack growth properties &Krda/d Nwas investigated. Significant acceleration of the crack propagation was observed just aher the uniaxial or equibiaxial stress condition was changed into the shear stress condition, This acceleration cannot be explained by the crack closure and one of the reasons for this acceleration seems to be the change of plastic zone shape at the crack tip 6 refs.
Tensile
High- purity AI-Zn-Mo alloy was thermomachanically treated. The process included solution treatment, pre-ageing, cold.working by rolling and final ageing. Pre-ageing was carried out at 100"C (TAHA1) and room temperature (TAHA2). Experimental results indicated that the TAHA1 process improved the tensile strength significantly, while the TAHA2 process improved the fatigue life more substantially, Fatigue crack initiation sites were examined carefully by scanning electron microscopy. A correlation between fatigue crack initiation, fatigue striation, tearing ridge, dimple distribution and fatigue life was observed. The experimental results are discussed in terms of substructure and are also compared with the tensile and fatigue properties of a thermomechanically treated 7075 AI-Zn-Mg alloy which were previously reported, 12 refs.
The effects of specimen geometry on the static and dynamic loadability of roelsWnce spot-welded joints in plates of deep-drawing eluminlum materlsls of 1-2 mm t h i c k n e s s . Eichhom, F., Harem, K. and Schmit¢ G. Schweissen SchneidenOct. 1988 (10), 4 9 4 - 5 0 0 (in German) The effects of specimen width, length of ovedap and spot pitch on the static and dynamic strength of resistance spot-welded single- and multi-spot weld specimens of the deepdrawing AI materials AIMg5 and AI Mg0,4Si1.2 were determined. The dynamic tests confirm that the fatigue strength of the AI alloys is reached at a number of cycles of 2 x 10v Standardized hollow sections, when subjected to dynamic torsional or bending stress. only reach a fatigue strength of 8-10% of the static strength. (In English p. Et56-E159). 15 refs. M a t e r i e l r e s l s t e r m e p a r a m e t e r = r e l e v a n t for mlmurament. a n d Lobe, D. Metal/. Dec. 1987 41, (12), 1224-1231 (in Gmrnan)
Near threshold fatigue crack growth and closure of a low C steel (0.18% C) with the duplex microstructure of ferrite-martensite were investigated. The highest value of 12 M Pa m ~/= in " the fatigue " threshold stress intensity range, &Kth. was obtained on a sample whose microstructure contained globular martensite in a ferrite matrix with 47 vol.% martensite. among all the samples tested in the study. The threshold value, however, was less than those reported elsewhere on AIS11008 and Fe-2Si-0.1C steels. No significant increase in AKth was observed in the microstructure where a continuous martensite phase encapsulated islands of ferrite. It was concluded that there were excellent fatigue crack growth resistance, &Ke,,th and crack opening level, Kop. 10 refs.
model for propagation of sn~lll fatigue c r a n l u l . Ihara, C. J. Soc. Mater. Sci., Jpn. Sept. 1988 37, (420), 1 0 7 1 - 1 0 7 6 (in Japanese)
A
The growth beheviour of small fatigue cracks is clearly different from that of long fatigue cracks A growth law of small fatigue cracks is proposed based on the stochastic damage accumulation model for long fatigue crack growth, it contains the following three parts. (1) The growth rate of a small crack growing in a grain is proportional to some power of the process region which is limited by the grain boundary. (2) A transgranular small crack propagates into the next grain over the grain boundary, when the stress is beyond the fatigue limit. (3) A small crack growing through the non-continuum propagation begins the continuum one. when the ptastic zone size of crack tip becomes larger then the average grain size. Many experimental facts about small fatigue cracks (eg in C steels) are explained on the basis of this growth law. 22 refs.
Lange, G.
The dimensioning of technical parts is based on the comperision between load and correspondingresistance of the material (egAIMgSiO,5, AIZnMgCul.5. NiCrMo14.5. X4OCrMoV5 1. X46CrVMo8 1. 50CrV4, 40ChN2MG, 32NiCrMo14 5. 40NiCrMo6). Complex stresses
284
F a t i g u e throohold and closure in duplex low carbon s t e e l . Ogura, K., Miyoshi, Y. and Nichikawa, I. J. Soc. Mater. Sci., Jpn. Sept. 1988 37, (420), 1 0 7 7 - 1 0 8 3 (in Japanese)
R e l i a b i l i t y e n g i n e e r i n g approach to fatigue crack growth rate using D C e l e c t r i c a l potontiiml method ( d e v e l o p m e n t o f D C e l e c t r i o e l potential ~ - a t e m a n d p r e l i m i n a r y e x p e r i m e n t s ) . Ichihawa, M., Akita, S. and Takamatsu, T
J. Soc. Mater. Sci., Jpn. Sept. 1988 37, (420), 1 0 1 0 - 1 0 1 7 (in Japanese)
Int J Fatigue July 1989
Study on the d u c t i l e f r a c t u r e o f a s u r f a c e c r a c k . G r o w t h o f a s u r f a c e crack and f i n i t e e l e m e n t a n a l y s i s . Kikuchi, M., Nishio, T., Yano, K., Mechida, K. and Miyamoto, H. JSME Int. J. I J u l y 1988 31, (3), 5 8 0 - 5 8 7 Ductile fractures of surface cracks were studied experimentally and numerically using two kinds of materials, A508C and WT60. At first, a fatigue pre-crack was introduced, and the aspect ratios of the growing fatigue crack were measured. Then the ductile fracture test was carried out and the distributiOnS of SZW and &a were measured along the crack front for different load levels, It was noticed that &a is the largest where ~. the angle from the surface, is nearly 30" which is considered to be a transition region from plane stress to plane strain conditions. The J-integral distribution was evaluated by the finite element method, and it is shown that the J value is also the largest where ~ is nearly 30", 19 refs,
S t a t i s t i c a l s i z e e f f e c t u n d e r a l t e r n a t i n g l o a d . Scholz, F. and Kuhn, G. Mater. wise. Werkst. tech. Sept. 1988 19, (9), 306-311 (in German) The results of 41 series of tests with smooth cylindrical and notched specimens, subjected to uni- and multiaxial alternating loads (tension-compression, torsion, rotating bending and combined torsion and bending), are compared with theoretically predicted data. The predictions are based on the 'weakest-link-concept', Multiaxial stresses are included either by means of suitable strength criteria, or by a fracture-mechanical consideration of a crack in a multi-dimensional stress field, For the evaluation of the experimental data the twoparametric Weibull's equation was used, The experimental and theoretical results may deviate by less than 20%, when the ratio beWveen the strength at cyclic torsion and cyclic bending is taken into account in the function of survival probability. 17 refs.
Cyclic hardening, y i e l d s u r f a c e and dislocation arrangement in lowcycle f a t i g u e . Schuber~ R. and Rie, K.-T. Mater. wies. Werkst. tech. Nov. 1988 19, (11 ), 3 7 6 - 3 8 3 (in German) In many technical and structural components stress raisers exist which undergo cyclic plastic deformation. Models have been developed to calculate the stress distribution and the resulting life, They are based on the assumptions that Masing-behaviour, isotropic and kinematic hardening are valid with cyclic plasticity. These assumptions have been examined experimentally. An interpretive connection is made between mechanical yield surface and microscopical arrangement of dislocations in the sense of cyclic hardening behaviour. 16 refs.
The failure of hard materials in cyclic compression: m e n t s a n d a p p l i c a t i o n s . Suresh, S. Mater. Sci. Eng. A Dec. 1988 A106--A108, 3 2 3 - 3 2 9
theory, experi-
Fatigue crack propagation t h r e s h o l d . Mami, G., Castro, D.E. and Bechmann, V ASTM J. Test. Eval. Jan. 1989 17, (1), 2 8 - 3 9 Service-type fatigue loading conditions are critically analysed with respect to their relevance for a fatigue crack growth threshold. It was found that a threshold should be experimentally determined as a function of the monotonic-plastic zone size lie as a function of Kml=). For each Kmax the cyclic-plastic zone size depends on the applied &Kand threshold testing should cover the range &K approx. AKth and .~.K(R = 0) for tension fatigue. For a given plastic zone, Kmax and AK fixed, the threshold AKth could occur anywhere between Kmax Kmin, Experimental procedures are presented and results for Inconel 617 and a T ~ A I ~ V alloy furnished which allow one to analyse the influence of the three parameters cited above. It demonstrates the following; the threshold decreases 'lineedy' with increasing monotonic-plastic zone size: this confirms existing data, The cyclic-plastic zone has minimal influence on the fatigue threshold with TI-6AI-4V, while this influence is substantial in the case of Inconel 617, A shift of threshold between Kmax and Kmin does not alter the magnitude of the threshold. 23 refs. E f f e c t s o f s m a l l s u r f a c e c r a c k s o n d u c t i l i t y l o s s in l o w c y c l e f a t i g u e o f 7 0 / 3 0 b r a s s . Murakam~ Y., Makabe, C. and Nisitant~ H. ASTMJ. Test. Eval. Jan. 1989 17, (1), 2 0 - 2 7 The loss of fracture ductility after strain cycling in low cycle fatigue tests is not due to so-called weakening or losing of the strength quality caused by irreversible slips in crystals but rather is attributable to the existence of small surface cracks, The degree of loss of fracture ductility depends on the crack length I, If / is larger than the critical length /c, the fatigue crack causes macroscopic shear fracture in the tensile test after strain cycling, On the other hand, if / < /c the fracture surface becomes the so-called cup-and-cone type. For 70/30 brass,/c = 400 pm 10 refs.
Stochastic models of fatigue crack g r o w t h . Langley, R.S. Eng. Fract. Mech. 1989 32, (1), 1 3 7 - 1 4 5 A number of stochastic models of fatigue crack growth (in AI. steels) under constant amplitude cyclic loading are assessed in the light of experimental data. Particular attention is paid to the predictive performance of the models under a change in the initial crack length, and generally, it is found that the models provide a poor estimate of the standard deviation of the number of cycles to failure. A new model is then introduced which shows improved agreement with the experimental data. 17 refs
Evaluation of stress intensity factors for corner cracked turbine discs under arbitrary loading using finite element methods. Bell, Ft., Pagotto, I.A. and Kirkhope, J. Eng. Frect. Mech. 1989 32, (1), 6 5 - 7 9 Stress intensity factors. K=. obtained using three-dimensional finite elements for a range of depths and shape of corner crack around the bore in a rotating disc are presented, One, wvo, three and four equispeced radial cracks were considered, and the cracks had aspect ratios of b/a = I . 2 and 4. The results are presented in the form of non-dimensiona~ magnification factors which can be superimposed to simulate any loading condition. This stress intensity information is valuable in the prediction of service lives of turbine discs. 22 refs.
On t h e e x p r e s s i o n of fatigue crack initiation life considering the f a c t o r o f o v e r l o a d i n g a f f e c t . Zheng, X. and Lin, C. Eng. Fract. Mech. 1988 31, (6), 9 5 9 - 9 6 6
A summary is presented of recent developments in the understanding of mode I crack growth at room temperature in hard materials subject to uniaxiai cyclic compressive stresses. Experimental observations of fatigue crack growth in cemented carbides, single-phase ceramics, transforming ceramics, ceramic composites and concrete are briefly reviewed. A detailed discussion of the 'driving force' for the growth of a stable crack in a direction macroscopically normal to the far-field compression axis is presented. The 'universal features' of cyclic compression fracture in a wide range of brittle and ductile solids are described. Some important applications of the compression fatigue phenomenon to the fracture toughness testing of brittle materials are highlighted, The overall framework for a general theory of fatigue failure under far-field cyclic compression is developed. 15 refs.
An expression was derived for the fatigue crack initiation life of notched elements with the consideration of overloeding effects. This expression may be used to predict the fatigue crack initiation life of notched element under variable amplitude loading. Experimental work on LY12CZ alloy shows that the test results of fatigue crack initiation life after tension overloading can be well fitted by the formula developed before for fatigue crack initiation life. Tension overloading increases the fatigue crack initiation threshold but has no effect on the coefficient of resistance to fatigue crack initiation. The overloading ratio has no marked effect on crack initiation life. The increase of the crack initiation threshold results in the increase of crack initiaton life, in particular, in long life range. The same results are also obtained by reanalysing some existing test results of overloading effect on crack initiation life given in literature. Consequently, the expression of the fatigue crack initiation life can be obtained by the method given. However. the overloading stress should be determined from the theoretical stress concentration factor of notched element and the maximum nominal stress in the load spectrum of elements. 34 refs.
Fatigue and cavitation wear of the multi-pad journal bearing of highspeed s h a f t . Olszewski, 0. Rev. Roum. ScL Tech.-Mec. App/. M a y - J u n e 1988 33, (3), 2 8 7 - 2 9 3
The crack
Causes of low durability of multi-pad slide bearings are analysed in detail on an example of real industrial objectives, A bearing with hydrodynamic step has been suggested to improve high-speed shaft running stability. Results of theoretical and experimental research on the bearing are presented, 6 refs.
i n i t i a t i o n and growth under high temperature c r e e p , fatigue and creep-fatigue multiplication. Yokobori Jr, A. T. and Yokobori, T.
Eng. Fract. Mech. 1988 31, (6), 9 3 1 - 9 4 5
The relationships among elasticity, plasticity and the development of cracks, measurement of stress along the crack surface and its relationship to the surface morphology of the crack, and the design of aeroplane and other products based on fatigue strength of AI alloys are reviewed. 9 refs.
Recent studies on the crack initiation, early stage crack growth and its subsequent crack growth under high temperature creep, fatigue and creep-fatigue multiplication are discussed, The criteria for these and some new ideas are proposed, For instance, the relative notch opening displacement (RNOD) criterion for the crack initiation and the Q* parameter for the crack growth are critically reviewed, Early stage crack growth and its subsequent crack growth as affected by notch tip acuity were studied. The beheviour of the tail part in the log da/dN vs log C" curve has been attempted, to explain in terms of the curve of the creep beheviour and of the crack length against time. Furthermore, it was proposed that early stage crack growth, say. the so-called first stage crack growth in terms of log da/dN vs tog K curve, may be characterized by the parameter different from those for the so-called second stage crack growth, Materials discussed are SUS304SS and a CrMoV steel, 22 refs.
M i c r o s t r u c t u r e , s t a g e II f a t i g u e crack growth rates and dynamic fracture t o u g h m m s - - a c o r r e l a t i o n , B h a m ~ , SK., S/ngh, V a n d Rajanna,/C Eng. Frect. Mech. 1988 31, (5), 7 8 3 - 7 9 2
Production and evaluation of construction a l l o y s t e a l as chain m a t e r i a l . Wolak, Z and Paczula, B. Neue HutteSept. 1988 33, (9), 3 3 8 - 3 4 2 (in German)
A variety of microstructures were introduced in a 13Cr-Mo-V steel and a 2.SNi-Cr-Mo-V steel by controlled heat treatments. An attempt was made to find correlation between yield strength, fracture toughness and stage II fatigue crack growth rates in each microstructural condition, but no clear trend emerged. Dynamic fracture toughness, determined using an instrumented Charpy impact tester and pracracked Charpy specimens, however, ieflected the occurrence of static mode of fracture during fatigue crack growth in stage I1. 29 refs.
To find out to what degree the amount of the coefficient determining the fatigue limit: tensile strength ration (k = z/Rm) is affected by both the manufacturing process and the chemical composition. 23GHNMA steel was examined. From the results obtained the following conclusions may be drawn. The process of steelmaking may essentially affect fatigue strength. Alterations in fatigue strength caused by heat treatment are directly proportional to alterations in tensile strength. Oxygen and carbon contents exercise a significant influence on fatigue strength, The application of a multiple correlation to determine k
Fatigue s t r e n g t h o f a l u m i n i u m a l l o y s . X V I I I . Takeuchi, K. Kei Kinzoku Yosetsu (J. Light Met. Weld. Constr.) 1988 26, (10), 2 1 - 2 6 (in Japanese)
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results in a more precise valuation scheme of the fatigue limit, compared to the tensile strength values ascertained under static load. 24 refs.
Fatigue bohaviour of steels with multiple n o t c h , . I. The effect of intorgmtton between notoheo on the rotary bending fatigue propertie=. Wakahara, M., KawJgo~hi, N. and Suenaga, K. Res. Rap. Fac. Eng., Kagoshima Univ. Nov. 1988 (30), 197-206 (in Japanese) When many concentrated stress points exist close together, a different fatigue behaviour pattern is revealed due to their interaction than that shown by a single part. The effect of interaction of notches on fatigue strength was investigated regarding the effect of the number of notches by the round bar specimen of $35C. with multiple 60" V notches subjected to rotary bending. The results obtained are summarized as follows. The stress concentration factor decreased by increasing the number of notches, and it approached a constant value. In relation to this tendency, both the fatigue limit for crack initiation Ow, and the fatigue limit for fatigue (~w=increased gradually with the number of notches. and both also approached constant values, respectively. The Owl showed fluctuation depending on whether or not the number of notches were odd or even. and whether the notch root radius at tbe 'branch point' differed from the odd or even number of notches. These results suggested that some stress factors other than the maximum stress at the root of the notch governed the crack initiation and propagation. The length of the nonpropagation crack became shorter with an increase in the number of notches. 16 refs
Fatigue bohaviour of steele with m u l t i p l e n o t c h e s . II. T h e e f f e c t of interaction between notches on the characteristics of plane bending fatigue. Wakahara, M., Kawagotshi, IV. and Suenaga, K. Res. Rap, Fac. Eng., Kagoshima Univ. Nov. 1988 (30), 207-214 (in Japanese) Fatigue crack initiation and propagation in flat bar specimens, with multiple notches, of carbon steels for machine structural uses, $35C, were examined in plane bending. The results obtained are summarized as follows. The effects of the interaction of closely spaced notches were found on crack initiation and propagation, and the effect of an even number of notches was found to be larger than that of odd ones. The ratio of crack propagation period to fatigue life increased with the number of notches. In general, the number of cycles at crack initiation depended on the stress intensity factor. The crack length at the inflection point in the fatigue crack growth rate curve became shorter with the number of notches. 9 refs.
Fatigue hahaviour of steels with multiple notches. Ill. The effect of interaction between notches on the fatigue crack propagation. Wakahua, M., Suenaga, K. and Kiku, S. Res. Rap. Fac. Eng., Kagoshima Univ. Nov. 1988 (30), 2 1 5 - 2 2 2 (in Japanese) The beheviour of fatigue crack propagation of round bar specimens of $35C with one to three sharp notches was investigated, and the results obtained are summarized as follows. Crack length at notches that did not fracture increased with the overstress ratio and saturated at some ratio. The ratio of the crack propagation period in the total fatigue life was estimated to be approx 98%. regardless of the number of notches and applied stress. The behaviour of crack propagation on specimens with two and three notches was found to be explained well with stress intensity factors accounting for interaction between notches by the principle of superposition, 13 refs.
Surface hardening improveo fatigue strength. Golze. N. Ind.-Anz. Sept. 1 9 8 8 1 1 0 , (74), 2 2 - 2 4 , 26 16 (in German) A surface hardening effect for forged steel (eg Ck35V. Ck45V, Ck45VS, Ck45BY, 49MnVS 3BY, 37Cr4V) parts is initiated by mechanical, thermal or thermo-chemical surface treatments. All three methods produce an internal stress and reduce the surface ductility. The mechanical treatment is most advantageous for steel grades Ck45V and 49MnVS 3BY. A surface hardening increase of 50-100% is achieved through the nitrocarbonization process. The induction method is useful for deep surface treatments in the range of 3-5 mm. The reduction of the surface roughness by grinding results in lower fatigue strength gains than for polishing material. 3 refs.
end fatigue properties of • thermomochanicelly treated 7475 elumlnlum a l l o y . Jahn, M.T. and Luo, J. J. Mater. SciNov. 1988 23, (11), 4 1 1 5 - 4 1 2 0
are reduced to a uniaxial stress by means of a suitable failure criterion or are compared with the specific material strength determined under operation-like testing conditions. The principles are illustrated for static loading of notched and cracked components and for dimensioning in case of creep and fatigue. 19 refs,
Improving the mechanical properties of structural carbon steel by d u e l - p h m h e a t t r e a t m e n t . Aksoy, M. and Esin, A. J. Mater. Eng, Dec. 1988 10, (4), 2 8 1 - 2 8 7 The dual-phese steels represent a newer grade of steels developed to cater to the needs of the automotive industry. The existing work on these steels is, therefore, on sheet steel specimens with a carbon content <0,1% and with thicknesses up to 1.0 mm The dualphase heat treatment was applied successfully to cylindrical specimens (St37. A36) which had diameters up to 7.2 mm and with a nominal C content of 0.20%, The experimental results have indicated that the mechanical strength of the structurel steel, including fatigue strength, can be substantially improved by the dual-phase heat treatment. Barring ductility and impact strength, the mechanical properties of the dual-phase specimens compared extremely well with those of the medium quality heat treatable steels. 18 refs
Low cycle fatigue crack propagation and fractogrephy of • S U S 304 s t a i n l e s s s t e e l a t e l e v a t e d temperature. Kotenuwa, R. and Nosho, T J. So(:. Mater. Sci. Jpn. Sept. 1 9 8 8 37, (420), 1090-1096 (in Japanese) High temperature low-cycle fatigue crack propagation behaviour of SUS 304 stainless steel under four typical kinds of reversed loading patterns (P-P, P-C. C-P and C-C type) was investigated, and the results are discussed in the light of fracture mechanics and electron fractography The stress intensity factor range AK failed to describe the crack propagation behaviour adequately. In the case of loading with tension hold (ie C-P and C-C type), the crack propagation rate was successfully correlated with the modified Jintegral J and agreed with the static deep crack propagation rate. The crack propagation rate for all of the four types of loading was successfully correlated in terms of the cyclic J-integral range ,~.J. and it was not necessary to separate &J into AJr and AJc. The crack propagation rate for the types of loading without tension hold or with short tension hold time (ie P-P and P-C type. and C-P and C-C type with comparatively short tension hold time) was successfully correlated with &Jr, and long tension hold time (ie C-P and C-C type with comparatively long tension hold time) was successfully correlated with AJc. The fracture surfaces where the crack propagation rate was correlated with &Jt were predominantly of the transgranular fatigue type. that is the fracture morphology and the correlating fracture mechanics parameter (&Jr) were of the same fatigue type. On the other hand, those fracture surfaces where crack propagation rate was correlated with AJ c were of the transgranular fatigue type or intergranular creep type or mixed type depending on the condition, that is, the fracture morphology and the correlating fracture mechanics parameter (AJc) were of different types in some cases. There was no significant effect of creep-fatigue interaction on the crack propagation under the combined creep and fatigue conditions, and crack propagation may be assessed by a simple summation of fatigue component and creep components. 12 refs.
E f f e c t s o f b i a x i a l s t r e s s condition and its change on fatigue crack growth p r o p e r t i e s . Yuuki, Ft., A/ira, K, and Kishi, N. J. Soc. Mater. Sci., Jpn. Sept. 1988 37, (420), 1 0 8 4 - 1 0 8 9 (in Japanese) Fatigue tests have been conducted on cruciform flat specimens of a stainless steel with a centre crack by using a high-cycle biaxial fatigue test facility, in order to investigate the effect of biaxial stress on the fatigue crack growth properties &Ki-da/dN. From the comprehensive experiments, no effect of biaxial stress was found in the AKi-da/dN relation if the crack was large and the stress level was low. However. a significant effect of biaxial stress appeared when the crack was small and the stress level was high. The critical region where the effect of biaxial stress appears was clarified quantitatively, based on the crack length measured and the stress level used in the biaxial fatigue tests. Moreover, the effect of changing biaxial stress condition on the fatigue crack growth properties &Krda/d Nwas investigated. Significant acceleration of the crack propagation was observed just aher the uniaxial or equibiaxial stress condition was changed into the shear stress condition, This acceleration cannot be explained by the crack closure and one of the reasons for this acceleration seems to be the change of plastic zone shape at the crack tip 6 refs.
Tensile
High- purity AI-Zn-Mo alloy was thermomachanically treated. The process included solution treatment, pre-ageing, cold.working by rolling and final ageing. Pre-ageing was carried out at 100"C (TAHA1) and room temperature (TAHA2). Experimental results indicated that the TAHA1 process improved the tensile strength significantly, while the TAHA2 process improved the fatigue life more substantially, Fatigue crack initiation sites were examined carefully by scanning electron microscopy. A correlation between fatigue crack initiation, fatigue striation, tearing ridge, dimple distribution and fatigue life was observed. The experimental results are discussed in terms of substructure and are also compared with the tensile and fatigue properties of a thermomechanically treated 7075 AI-Zn-Mg alloy which were previously reported, 12 refs.
The effects of specimen geometry on the static and dynamic loadability of roelsWnce spot-welded joints in plates of deep-drawing eluminlum materlsls of 1-2 mm t h i c k n e s s . Eichhom, F., Harem, K. and Schmit¢ G. Schweissen SchneidenOct. 1988 (10), 4 9 4 - 5 0 0 (in German) The effects of specimen width, length of ovedap and spot pitch on the static and dynamic strength of resistance spot-welded single- and multi-spot weld specimens of the deepdrawing AI materials AIMg5 and AI Mg0,4Si1.2 were determined. The dynamic tests confirm that the fatigue strength of the AI alloys is reached at a number of cycles of 2 x 10v Standardized hollow sections, when subjected to dynamic torsional or bending stress. only reach a fatigue strength of 8-10% of the static strength. (In English p. Et56-E159). 15 refs. M a t e r i e l r e s l s t e r m e p a r a m e t e r = r e l e v a n t for mlmurament. a n d Lobe, D. Metal/. Dec. 1987 41, (12), 1224-1231 (in Gmrnan)
Near threshold fatigue crack growth and closure of a low C steel (0.18% C) with the duplex microstructure of ferrite-martensite were investigated. The highest value of 12 M Pa m ~/= in " the fatigue " threshold stress intensity range, &Kth. was obtained on a sample whose microstructure contained globular martensite in a ferrite matrix with 47 vol.% martensite. among all the samples tested in the study. The threshold value, however, was less than those reported elsewhere on AIS11008 and Fe-2Si-0.1C steels. No significant increase in AKth was observed in the microstructure where a continuous martensite phase encapsulated islands of ferrite. It was concluded that there were excellent fatigue crack growth resistance, &Ke,,th and crack opening level, Kop. 10 refs.
model for propagation of sn~lll fatigue c r a n l u l . Ihara, C. J. Soc. Mater. Sci., Jpn. Sept. 1988 37, (420), 1 0 7 1 - 1 0 7 6 (in Japanese)
A
The growth beheviour of small fatigue cracks is clearly different from that of long fatigue cracks A growth law of small fatigue cracks is proposed based on the stochastic damage accumulation model for long fatigue crack growth, it contains the following three parts. (1) The growth rate of a small crack growing in a grain is proportional to some power of the process region which is limited by the grain boundary. (2) A transgranular small crack propagates into the next grain over the grain boundary, when the stress is beyond the fatigue limit. (3) A small crack growing through the non-continuum propagation begins the continuum one. when the ptastic zone size of crack tip becomes larger then the average grain size. Many experimental facts about small fatigue cracks (eg in C steels) are explained on the basis of this growth law. 22 refs.
Lange, G.
The dimensioning of technical parts is based on the comperision between load and correspondingresistance of the material (egAIMgSiO,5, AIZnMgCul.5. NiCrMo14.5. X4OCrMoV5 1. X46CrVMo8 1. 50CrV4, 40ChN2MG, 32NiCrMo14 5. 40NiCrMo6). Complex stresses
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F a t i g u e throohold and closure in duplex low carbon s t e e l . Ogura, K., Miyoshi, Y. and Nichikawa, I. J. Soc. Mater. Sci., Jpn. Sept. 1988 37, (420), 1 0 7 7 - 1 0 8 3 (in Japanese)
R e l i a b i l i t y e n g i n e e r i n g approach to fatigue crack growth rate using D C e l e c t r i c a l potontiiml method ( d e v e l o p m e n t o f D C e l e c t r i o e l potential ~ - a t e m a n d p r e l i m i n a r y e x p e r i m e n t s ) . Ichihawa, M., Akita, S. and Takamatsu, T
J. Soc. Mater. Sci., Jpn. Sept. 1988 37, (420), 1 0 1 0 - 1 0 1 7 (in Japanese)
Int J Fatigue July 1989