Fatigue Limit Of Steel Research Articles

Evaluation of the Methods for Estimating the Fully Reversed Unnotched Fatigue Limits of Steels

Experimental determination of the fatigue limit is expensive considering the time and effort involved. To overcome this drawback, several empirical relations based on monotonic tensile properties and/or hardness have been developed for estimating the fatigue limit. In this study, ten estimation methods are evaluated and compared using the experimental data of 171 steels from literature. The scatter band criterion, standard deviation criterion, and statistical analysis are all used to evaluate and compare the predictability of the considered empirical relations. It is found that the fatigue limit can be well correlated with the Brinell hardness. In the absence of Brinell hardness, the ultimate tensile strength-based direct estimation method may be an alternative to estimate the fatigue limit of steels. It is not recommended to estimate the fatigue limit by using the indirect method on the basis of Basquin’s fatigue properties estimated by the monotonic tensile properties even though the fatigue limit of steel is often determined by the experimental Basquin’s curve at 106 cycles.

ステンレス鋼 SUS304 の微小疲労き裂の進展下限界に及ぼす水素の影響

For the safety use of hydrogen utilization systems, it is necessary to understand properly the effect of hydrogen on the fatigue properties of structural materials. In the present study, fatigue life tests of 304 stainless steel with small artificial defects were carried out under the presence of hydrogen; the tests in hydrogen gas environment and the tests using hydrogen-charged specimens, and the effect of hydrogen on the fatigue limit of the material was investigated by paying attention to the behavior of short fatigue cracks. As a result, the fatigue limit was not degraded in hydrogen gas environment, whereas there was slight degradation of fatigue life in short life regime (i.e. Nf < 105 ). On the other hand, fatigue limit of hydrogen-charged specimens was increased compared with that of non-charged specimens. It is noteworthy that non-propagating cracks existed in the unbroken specimens in all environmental conditions. As is well known, fatigue limit of steels with low or moderate strength is determined by the non-propagation limit of small fatigue cracks. Consequently, it was revealed that the fatigue limit of the specimens was determined by the arresting limit of fatigue cracks, which was not degraded in the tests in hydrogen gas as well as in the tests using hydrogen-charged specimen.

Piezo-Barkhausen Emission as an Indicator of the Fatigue Limit of Steel

The fatigue properties of two variants of AISI 1018 steel samples were measured in a series of 33 experiments using new kinds of magnetic diagnostics. An MTS-810 servohydraulic test machine applied sinusoidal fully reversed (R = −1) loads under strain (Є) control in the range of 0.0008 ≤ (Є)≤ 0.0020. In 28 experiments, the number of cycles to fatigue failure Nf varied between 36,000 &lt; Nf &lt; 3,661,000. By contrast, in five runs extending over 107 cycles, the specimens showed no detectable signs of weakening or damage. The corresponding “S-N” or classical Wöhler plots indicated that the transitions from fatigue failure to nominally infinite life (i.e., the fatigue limit) occurred at strains of about Є = 0.0009 and Є = 0.0010, respectively, for the two types of steel. Every loading cycle of each test was instrumented to record continual values of stress and strain. Flux gate magnetometers measured the variations of the piezomagnetic fields near the specimens. A 1000-turn coil surrounding the test pieces detected the piezo-Barkhausen pulses generated by abrupt rearrangements of their internal ferromagnetic domain structures. Analyses of the magnetic data yielded four independent indices each of which located the fatigue limits in complete agreement with the values derived from the Wöhler curves.

Influence of some key factors on material damping of steel beams

Material damping affects the dynamic behaviors of engineering structures considerably, but up to till now little research is maintained on influence factors of material damping. Based on the damping-stress function of steel, the material damping of steel beams is obtained by calculating the stress distribution of the beams with an analytical method. Some key influence factors of the material damping, such as boundary condition, amplitude and frequency of excitation, load position as well as the cross-sectional dimension of a steel beam are analyzed respectively. The calculated results show that even in elastic scope, material damping does not remain constant but varies with these influence factors. Although boundary condition affects material damping to some extent, such influence can be neglected when the maximum stress amplitude of the beam is less than the fatigue limit of steel. Exciting frequency, load position and cross-section dimension have great effects on the material damping of the beam which maintain the similar changing trend under different boundary conditions respectively.

Effect of orientation of small defects on fatigue limit of steels

In order to clarify the effect of defect orientation on the fatigue limit of three types of steels; JIS-S15C, JIS-S45C and JIS-SNCM439, a small semi-circular slit was introduced into the surface of a round specimen. The slits were tilted at 0 ∘ , 30 ∘ or 60 ∘ with respect to the plane normal to the loading axis, but all of them had the same defect size, = 188 μm, where the area denotes the area of the domain defined by projecting the defect on a plane normal to the loading axis. In all the combinations of the materials and tilting angles, a non-propagating crack was found at the fatigue limit, i . e . the fatigue limit was determined by the non-propagation condition of crack initiated from the defect. In JIS-S15C and JIS-S45C, the fatigue limit was nearly independent of the tilting angle, which was in good agreement with the predicted value by the parameter model. On the other hand, in JIS-SNCM439, the fatigue limit was also in agreement with the prediction at the tilting angle of 0 ∘ , but it increased with an increase in the tilting angle. These results indicated that the parameter model can predict a conservative fatigue limit for the tilted defects. In this paper, the mechanistic reason for the effect of the tilting angle on the fatigue limit will be discussed by paying special attention to the crack path and length of non-propagating crack.

Correlation between the piezo-Barkhausen effect and the fatigue limit of steel

Many types of ferrous metals can sustain an indefinite number of repeated loading cycles (N ⩾ 107 cycles) provided that the maximum imposed stresses do not exceed certain critical values usually referred to as fatigue or endurance limits. In current practice, these limits are primarily inferred from statistical analyses of numerous fatigue experiments that relate the number of cycles to failure, Nf, to the loading programs. Numerous attempts have been made to bypass these time consuming tests by the direct observation of changes in material microstructures utilizing a variety of physical effects ranging from neutron diffraction, x-ray radiography, acoustic emission and even positron radiation patterns; but none of these approaches has yielded any unambiguous indices of damage. Recently, it has been found that the evolution of piezomagnetic hysteresis, due to magnetization changes induced in ferromagnetic steels by tension and compression, is a reliable indicator of the development of fatigue damage and can lead to practical predictions of service life. Further detailed information concerning processes at the microstructural level can be obtained from measurements of flux jumps associated with the piezomagnetic fields. Sequences of flux variations of the order of 10−3 Mx or 10−11 Wb, comparable to those observed in conventional Barkhausen experiments, appear when ferromagnetic steels are subjected to tension or compression. The amplitude distribution of these piezo-Barkhausen pulses increases markedly in the vicinity of the endurance limit and appears to provide a rapid means for distinguishing between stable, i.e. safe, loading regimes and those terminating in fatigue failure.

Fatigue limits of steels and stress gradient*

Based on generalizing the results of numerous experimental investigations, the empirical relationships between the fatigue limit of steels and the stress gradient are proposed and justified, which take into account the fatigue damage behavior of smooth specimens and specimens with stress concentrators. A method for determining the parameters of these relationships with consideration of the mechanical properties of steels is proposed. Good agreement of the proposed relationships with the experimental results is shown.

Influence of machining parameters on fatigue endurance limit of AISI 4140 steel

The general purpose of this research is to study the influence of commercial machining parameters on fatigue limits of steels. Specifically in this work, the influence of cutting speeds, depth of cut, feed rate and residual stresses of turned surfaces of AISI 4140 steel specimens on fatigue strength were analyzed. In some specimens, the residual stress was eliminated by heat treatment. The fatigue experiments were carried out at room temperature, applying a cyclical frequency of 58Hz, with mean stress equal to zero (R=-1), on a rotating-bending fatigue testing machine of the constant bending moment type. It was used the staircase (or up-and-down) method to determine the fatigue limit of the specimens.

Fatigue Limit of Steel with an Arbitrary Crack under a Stress Controlled Constant with a Positive Mean Stress

In this paper, push–pull fatigue tests of notched specimens under R=−1, 0 and 0.5 are carried out on annealed 0.1 % carbon steel and quenched-tempered 0.5 % carbon steel with HrmBsimeq 600. The fatigue limit of a long crack, sigmaw2, is obtained from that of a notched specimen with a sharp and deep notch whose radius is smaller than the branch point rho0. Using the present and past sigmaw2 data, the effect of the positive mean stress on the dKw of the long crack is evaluated using 3.2 HrmB (simeqsigmarmB) and sigmarmS(3.2 HrmB), where dKw is the stress intensity factor range for predicting the fatigue limit of a metal with an arbitrary crack, sigmarmS is the lower yield stress or 0.2% proof stress, sigmarmB is the ultimate tensile strength and HrmB is the Brinell hardness. Although the sigmaw2 decreases with the mean stress, sigmaw2 is cut off by the threshold stress sigmawe of the plastic deformation at the crack tip. For the quantitative prediction of the fatigue limit of a cracked steel with an arbitrary crack length under a positive mean stress, the sigmaw2 and sigmawe values are approximated by simple formulae.

The effect of material hardness and mean stress on the fatigue limit of steels containing small defects

ABSTRACTFatigue tests on material containing small defects were performed under a wide range of mean stress for three grades of steels with different hardness. The ΔKth of small defects had a peculiar dependency on material hardness and mean stress, which was quite different from those of long cracks or plain specimens. The crack closure of short cracks was measured. It was shown that the formation of the crack closure was affected by the material hardness and mean stress. This behaviour of crack closure resulted in characteristic fatigue limit properties of materials containing small defects.

Comment on “Notch Size Effects in the Fatigue Limit of Steel” by M. Makkonen [Int J Fatigue 25 (2003) 17–26

Comment on “Notch Size Effects in the Fatigue Limit of Steel” by M. Makkonen [Int J Fatigue 25 (2003) 17–26

Response to comments by Prof. Taylor on “Notch Size Effects in the Fatigue Limit of Steel” by M. Makkonen [Int J Fatigue 25 (2003) 17–26

Response to comments by Prof. Taylor on “Notch Size Effects in the Fatigue Limit of Steel” by M. Makkonen [Int J Fatigue 25 (2003) 17–26

Notch size effects in the fatigue limit of steel

The fatigue behaviour of grooved test specimens has been investigated in this paper. It is shown that there are two kinds of size effects connected to notches: statistical size effect and geometric size effect. The statistical size effect is calculated based on the distribution of the maximum depth of initiated cracks in specimens with varying stress area. The geometric size effect depends on the stress gradient and can be estimated with the help of the linear elastic fracture mechanics. It is concluded that the notch size effect in blunt notches can be explained with those two factors. When the notch gets sharper, after certain limit the magnitude of the plastic portion of the strain starts to play an important role in the fatigue crack initiation, and the fatigue limit is lower than that predicted by statistical and geometric size effects. Another estimation method shall be used to that kind of notches.

Statistical size effect in the fatigue limit of steel

There is always a large quantity of initiated cracks in a specimen subjected to cyclic loading. This kind of specimen forms a sample of initial cracks: the larger the specimen, the larger the sample. A method for the prediction of the statistical size effect due to the sample size is introduced in this paper. The statistics of extremes can be used to calculate an estimate of the largest expectable crack in specimens with varying surface area. Connection between the initiated crack size and the fatigue limit is obtained with the help of the linear elastic fracture mechanics. The presented method is tested to eight sets of experimental data for cylindrical specimens made of steel 34CrNiMo8. The mean fatigue limit tends to decrease and the scatter increase in proportion to increasing material thickness. If these effects can be accounted for, as done in this paper, the constant amplitude fatigue limit can be very accurately predicted. The error of the calculated estimates is within −3% to +6% compared to experimental results.

Predicting the fatigue limit of steels hardened by chemical-thermal treatment

Predicting the fatigue limit of steels hardened by chemical-thermal treatment

Effect of laser deposition on the fatigue limit and war resistance of steel 45

1. The wear resistance of layers deposited by laser beam with the use of industrial powder materials based on nickel (PN73Kh16S3R3) and iron (PGFBKh-6-2) and their different composites with and without lubricants is 2.5–5 times greater than the wear resistance of steel 45. 2. The fatigue limit of steel 45 with deposited layers of powder materials is practically equal to the fatigue limit of the initial material; in contact strength these layers are practically not inferior to steel 45 in a broad range of loads. 3. The obtained results made it possible to work out a number of technologies for treating machine parts that were introduced in repair establishments.

Size Effect on Rotating Bending Fatigue in Steels

Rotating bending fatigue tests were performed for forged and cast steels of which specimen sizes are in the range from 8 to 40mm in diameter. The cast steel including originally many defects exhibits a decrease of about 27% in the fatigue limit with an increase in the size from 8 to 40mm, while such a decrease is about 13% in the forged steel of comparatively homogeneous substance. The measurement of the strain during tests manifests that a plastic strain of about 80×10-6 is produced at the fatigue limit in the forged steel, independently of specimen size, and on the other hand, the cast steel yields no macroscopic plastic strain at the fatigue limit of this material. From these results, it is suggested that in the former the size dependent plastic strain, which is caused by the difference in the stress gradient produced in the cross section of the specimen, and in the latter the scatter in the fatigue strength induced by the defects, are the dominant factors controlling the size effect on the fatigue limit of steels.

Determining the degree of influence of iron coatings on the endurance of steel 45

1. The application of electrolytic iron coatings leads to a reduction in the finite fatigue limit of steel 45 by 20–30%, and the lower the probability of failure, the greater the reduction. 2. The test base has a significant influence on the coefficient of reduction of the finite fatigue limit and on the statistical characteristics of the spread in fatigue of steel 45 with and without a coating. With an increase in the base from 106 to 107 cycles the coefficient of reduction in the fatigue limit decreases by 10–12%. 3. The endurance of samples of steel 45 with and without a coating is described with the help of the parameters SL of the Johnson distribution. The determinations obtained of the parameters SL for various test bases makes it possible to predict the finite fatigue limits of the steel-coating bimetal and of the steel 45 with any probabilities of failure. 4. The decrease in the finite fatigue limits of steel 45 with a coating and the increase in the characteristics of spread of fatigue are related to peculiarities in the mechanism of deformation and failure of the steel-coating bimetal.

Regularities of the distribution of bounded fatigue limit of specimens of steel 45 with electrolytic iron coating

1. The upper and lower bounds of the bounded fatigue limit of the bimetal steel 45 + coating were determined, and also the other parameters of the empirical distributions, on two test bases: N = 5·105 and l06 cycles. Fatigue curves with probability of failure equal to zero and to unity were plotted. 2. It was established that the scatter of the bounded fatigue limit of the bimetal depends on the test base: With increasing test base it diminishes. The variation coefficient of the bounded fatigue limit of the bimetal depends weakly on the test base, and the hypothesis of its being constant is accepted. 3. Probability diagrams of fatigue were plotted in coordinates P-N, δa-N, and P-δa; this made it possible to examine the regularities of the scatter of the bounded fatigue limit of steel 45 with electrolytic iron and to determine the type of distribution function. By unifying the mentioned diagrams, it is possible to plot the full probability diagram of fatigue δa-N-P of steel 45 with electrolytic iron.

Estimation of Fatigue Limit of Steel Subjected to Bending Loads

A method of estimating the fatigue limit of polished steel specimens subjected to bending loads, in terms of brinell hardness number for values of stress ratios other than (−1) and mean stresses other than zero is proposed in this paper.