Fatigue Life Of Steel Research Articles

The effects of material combination and surface roughness in lubricated silicon nitride/steel rolling contact fatigue

Four kinds of commercially finished 12.7 mm HIPed silicon nitride bearing balls with surface roughness values R a ranging from 0.002 to 0.016 μm were tested using a four-ball rolling configuration. They were rolling against two types of steel testing balls with different surface roughness and hardness, in fully lubricated condition at a maximum compressive stress of 6.58 GPa and at a speed of 10 000 rpm for over 135 million stress cycles. Rolling track surfaces were examined by microscope, SEM, 3-D surface analysis and interference profilometry. Experiment results show that the composite surface roughness are most influential. The shape of the surface topography of silicon nitride are not very sensitive. The slight difference in steel hardness may lead to significant differences in steel fatigue life.

The effect of contact load reduction on the fatigue life of pearlitic rail steel in lubricated rolling–sliding contact

Twin‐disc contact simulation tests were carried out to investigate the influence of contact pressure variation on rail steel fatigue life. Both a colloidal suspension of molybdenum disulphide in an oil carrier fluid (similar to a commercial flange lubrication product) and water were used as lubricants. It was found that the reduction from 1500 to 900 MPa of the maximum Hertzian contact pressure (at which a molybdenum–disulphide‐lubricated and previously worn rail sample was tested) extended the fatigue life of the rail steel by over five times. For water lubrication a similar reduction in contact pressure produced only a marginal increase in fatigue life. The results were found to be in qualitative agreement with the predictions of the newly developed Three Mechanism (TM) model of rolling contact fatigue, which is introduced here. This model combines the mechanisms of ratcheting and the fracture mechanics‐based mechanisms of both shear stress‐ and tensile stress‐driven, fluid‐assisted, crack growth.

The effect of intermittent lubrication on the fatigue life of pearlitic rail steel in rolling-sliding contact

Railway flange lubrication can be unreliable, resulting in intermittent rather than continuous lubrication. Twin-disc contact simulation tests were carried out to investigate the influence of intermittent lubrication on rail steel fatigue life, using both a colloidal suspension of molybdenum disulphide in an oil carrier fluid (similar to a commercial flange lubrication product) and water. A brief interruption of the lubricant supply during molybdenum disulphide lubrication produced rapid surface failure of the rail steel, which was followed by rapid contact fatigue crack growth upon reapplication of the lubricant. During water lubrication the interruption of the lubricant (water) supply did not produce such rapid crack growth. The results were found to be in qualitative agreement with the predictions of the three-mechanism model of rolling contact fatigue, which combines the mechanisms of ratchetting (accumulation of unidirectional plastic strain until the critical failure strain of the material is reached) and the fracture mechanics-based mechanisms of shear stress driven and tensile fluid assisted crack growth. Analysis of the test results using this model revealed crack face friction to be an important factor controlling crack growth, which may be responsible for the difference in behaviour between contacts lubricated with the molybdenum disulphide-based lubricant and those lubricated by water.

Effects of LWR Coolant Environments on Fatigue Lives of Austenitic Stainless Steels

Fatigue tests have been conducted on Types 304 and 316NG stainless steels to evaluate the effects of various material and loading variables, e.g., steel type, strain rate, dissolved oxygen (DO) in water, and strain range, on the fatigue lives of these steels. The results confirm significant decreases in fatigue life in water. Unlike the situation with ferritic steels, environmental effects on Types 304 and 316NG stainless steel are more pronounced in low-DO than in high-DO water. Experimental results have been compared with estimates of fatigue life based on a statistical model. The formation and growth of fatigue cracks in air and water environments are discussed.

Effect of mean stress and ratcheting strain on fatigue life of steel

Detailed results of stress-controlled fatigue tests with tensile mean stress on ASTM A-516 Gr. 70 steel are presented. By using different preloading procedures, the ratcheting effect on the fatigue life of materials was separated from the mean stress effect. A previously proposed energy-based life prediction criterion is extended to include the effects of both mean stress and ratcheting. A comparison between the theoretical prediction with the present test results is found to be quite satisfactory.

Use of Fatigue Fuses for Prediction of Fatigue Life of Steel Bridges

The fatigue fuse is a device for predicting the fatigue life of steel highway bridge members when the bridge is subject to variable loads. The fuse is calibrated so that the cracking of each of its four legs can be related to damage in the structure. In a preliminary laboratory study, fatigue fuses are attached to eight steel girders, selected to represent three types of structural details found in existing highway bridges. The fuses are cemented to the girders and the girders subjected to a constant-amplitude fatigue loading. Cracking of the fatigue fuses is monitored by checking electrical continuity across each fuse leg. Tests are continued until girder failure or until all fuse legs are broken and the mean fatigue life of the girder as predicted by AASHTO is reached. The breaking of the fuse legs is used to predict the fatigue life of each girder, which is then compared with the actual cycles to failure of the girder and the AASHTO mean life. The prediction gives satisfactory agreement with the AASHTO...

The effect of two-frequency low-cycle loading on the fatigue life of steels and welded joints

Some parts of nuclear power equipment (NPE) are subjected mostly to two-frequency loading during their service. Oscillations with a lower stress amplitude are superimposed on the basic slow loading with high stress (or strain) amplitude. The damage cumulation law, which is valid relatively well for random loading, seems to be less suitable for two-frequency loading. According to the design specifications [1] the service life of parts at two-frequency loading may be 10 to 20 times lower than that at single-frequency loading. The decrease in life depends on both the ratio of loading frequencies and amplitudes, and the material characteristics.

An abnormally shortened fatigue life of steels caused by anelasticity: Ishizaki, K. and Mineura, K. J. Mater. Sci. Jan. 1989 24, (1), 239–242

Fretting is associated with small amplitude oscillatory movements between two surfaces in contact. One possible consequence of fretting is the formation and subsequent growth of cracks at the edges of the contact. This paper presents an experimental investigation of the cracking behaviour under fretting loading of two different aluminium alloys: 2024-T351 and 7075-T651. Systematic and controlled experiments with a cylinder-flat contact under partial slip fretting conditions were carried out. A model which combines both crack nucleation and propagation processes is used to predict the crack extension throughout the life of the component. The direction of crack propagation experimentally observed was taken into account by the model. Furthermore, an analytical prediction of crack nucleation based on the process volume approach is made. The predictions of both crack extension and nucleation are compared with the experimental results, and show good agreement.

An abnormally shortened fatigue life of steels caused by anelasticity

Some abnormal fatigue life shortenings dependent upon load frequency for several steels are discussed. A possible relation between anelasticity caused by interstitial atoms and the abnormal fatigue life drop is presented. Normally, interstitial atoms are in a position which minimizes the energy around a dislocation, the Snoek ordering sites. We consider the Snoek effect as a typical example of anelasticity, and the possibility on atoms moving from attractive sites to repulsive ones when repeated stresses are applied and discuss a theory to explain the reduction of the fatigue life using Snoek ordered atoms moving out by fatigue stress at the frequency of Snoek effect. Bending fatigue tests were conducted to obtain the relationship between fatigue life and load frequency at two different temperatures (298 K and 333 K) for an iron nitrided steel. A sharp fatigue life drop was observed at a load frequency corresponding to the resonant frequency of the Snoek effect for nitrogen atoms. The frequency was about 3 Hz and 298 K and shifted to a higher frequency — about 6 Hz — at 333 K. Results reveal that the possible explanation to those abnormal phenomena may be anelasticity.

無電解Ｎｉ‐Ｐめっき材の腐食疲労強度

Corrosion fatigue strength of electroless Ni-P steel was investigated by rotating bending fatigue test at 0.6 and 60Hz in dropping 3% NaCl solution. The changes of microstructure of Ni-P film by cyclic stressing were examined by X-ray technique. 1. Ni-P film keeps amorphous structure and exhibits an excellent corrosion resistance regardless of the presence of applied stress. 2. Since a pre-microcrystalline forms in Ni-P film by cyclic stressing, the corrosion resistance decreases, accopmanied by negative shift of the corrosion potential. 3. The corrosion resistance of the plated layer decreases with increasing the number of cyclic stressings or local crystallization. Then corrosion pits were produced on the surface, stress concentration is induced at the bottom of pit and then the pit grows up to corrosion fatigue crack. 4. The corrosion fatigue life of steel was improved by about 50 percent by Ni-P plating, which is not as much as was expected for the amorphous metal.

Effect of Lubricant Additives on Water-Accelerated Fatigue

A rotating beam fatigue technique has been used to determine the effectiveness of additives for mitigating the deleterious effect of a small quantity of water in a mineral oil on steel fatigue life. The technique exhibits a high sensitivity to the effect of water contamination and provides a means to investigate wide variations in effectivenss of additives. The utility of the measurements as predictors for performance in rolling contact is considered, a rating equation for the additives is proposed, and the mechanisms by which additives may counteract the effect of water are discussed.

Influence of some varieties of abrasive fuels on the fatigue life of steel 45

Influence of some varieties of abrasive fuels on the fatigue life of steel 45

Criteria relating to the fatigue life of steels subjected to alternating loads under conditions of uniaxial and biaxial static strain

1. We have analyzed existing criteria relating to fatigue strength for asymmetrical loading cycles under conditions of uniaxial and biaxial strain. We have shown that at present there are no criteria really suitable for describing the behavior of all materials. 2. We have proposed a fatigue-strength criterion which gives an excellent description of the behavior of ductile steels for asymmetrical loading cycles under conditions of uniaxial and biaxial strain. 3. We have shown that the proposed criterion may be modified to describe the behavior of materials sensitive to biaxial strain.

The effect of ultrahigh vacuum environment on the fatigue life of steel: D W Morecroft, Shell Research Unit, Chester, England

The effect of ultrahigh vacuum environment on the fatigue life of steel: D W Morecroft, Shell Research Unit, Chester, England

Plastic Fatigue Life of Steel Subjected to a Multiple Repeated Stress under Rotary Bending

The fatigue damage most closely related to the practical fatigue life of the material should be the accumulation of a power function of the plastic strain. On the basis of this concept, the authors proposed a fracture criterion based on strain under varying strain amplitude instead of the linear damage law, (Σn/N)f=1, based on stress. The fracture criterion under varying strain amplitude is expressed as below : In the present report, this criterion was extended and applied to the results of the plastic fatigue tests on steels under rotary bending which were carried out over several years in their laboratory. The experimental results were summarized by the above criterion and compared with those calculated by the linear damage law. As a result, this criterion based on strain is found applicable to the estimation of the fatigue life as precisely as under the linear damage law. Although the linear damage law is well established for the low-cycle fatigue, it is expected that the criterion based on strain will be more effective for the ordinary fatigue of comparatively lower stress levels than for the low-cycle fatigue.

Deformation and Low-Cycle Fatigue Life of Steel due to the Multiple Repeated Loads under Rotating Bending

Vehicles in general such as airplanes, automobiles and railroad cars, and structures in general, such as bridges, are subject to random repeated loads. To design machine elements included in those vehicles and structures, ordinary statistical summarization of stress spectra is performed and the“linear damage criterion”, (Σn/N)f=1, is applied to the resulting cumulative cycle ratio. The value of cumulative cycle ratio to fracture obtained from experiments does not always coincide with the value calculated from the linear damage criterion. As the authors consider that the cause of this fact comes from the variation of strain amplitude due to stress interaction, several series of low-cycle fatigue tests of steel are conducted under the condition of rotating bending with the multiple repeated loads and the relation between the deformation (deflection) measured during the tests and the resulting fatigue life is discussed.

The Influence of Non-metallic Inclusions on the Fatigue Strength and the Statistical Nature of Steel

Three series of specimens were specially prepared so that they may contain various degrees of MnS non-metallic inclusions, other parameters being kept constant especially the amount of manganese in solution as much as possible. Fatigue tests were carried out with a rotating bending fatigue machine.The results obtained are as follows:(1) The definite relationship could not be recognized between the inclusion ratings and the statistical nature of fatigue life of steel, which is in accordance with the previous work by one of the present authors, but contrary to the result by Epremian and Mehl.(2) The ferrite grain size is a predominant metallurgical factor in the statistical nature of fatigue fructure of steel.(3) For the same stress amplitude, the scatter of fatigue life increases and the probability of fructure decreases with the decrease of grain size.(4) For the equivalent stress amplitude, the scatter of fatigue life appears not to be affected by inclusion ratings and ferrite grain size.(5) The longitudinal fatigue strength of carbon steel is not so much affected by the content of MnS as inclusions. The effect by ferrite grain size or other statistical parameters may also be large.

Effects of Restraint on Thermal Fatigue Strength of Steels

Investigation was performed on the effects of degree of restraint on thermal fatigue life of steels. Relations between strain amplitude, stress amplitude and cycles to failure were confirmed, using Coffin type thermal fatigue testing apparatus for some cast steels and 18Cr 8Ni stainless steel. Based on these relations then, the effects of restraint on thermal fatigue life and on some other factors were calculated.The results indicate that, although the alleviation of restraint is effective to prolong the thermal fatigue life, the degree of the effects varies remarkably according to the kind of materials and the amount of strain amplitude.

X-Ray Investigation on the Prediction of Fatigue Life : On the Changes in Half-Value Breadth of Age Hardenable Alloy under Constant and Varying Stress Amplitude

As a continuation of previous investigation concern with prediction of fatigue life of steels under constant or varying stress amplitude, the fatigue process in age-hardenable Al-Cu alloy is studied by observing the half-value breadth of intensitity distribution curves taken from X-ray diffraction lines. It is found that the fatigue process of Al-Cu alloy is similar to that of annealed carbon steel from the stand point of the change of half-value breadth, namely, the relation between b/B and log n/N or log Σ n/N, where b and B are the current and the initial value of half-value breadth and n/N and Σ n/N are the cycle ratio or summation of cycle ratio respectively, is represented by a liner relation of magnitude or history of alternate stress amplitude. This relation offers a certain method of the prediction of fatigue life.

高温高速疲労における運転休止の影響

High frequency cantilever beam rotating fatigue test was carried out with 0.44% carbon steel at a temperature of 500°C with a frequency of 10000rpm, and the effect of periodically applied intermittent loading upon the specimen was investigated at two stress levels that were chosen from the basic S-N curve obtained from the ordinary test without rest periods.From the obtained results, it was concluded that the existence of rest periods which were given with definite periods in the loading cycles, rather reduced the fatigue life of steel at elevated temperature, compared with that of the continuous loading test, especially in the case when loading frequency is as high as 10000rpm.Such tendency does not agree with that of the previous investigations by several authors. The cause and the meaning of these different tendencies seem to be caused by many factors, such as testing frequency, method of inserting rest period, kind of stress, but it is not easy to clarify these points at the present stage of study.