Plain Fatigue Research Articles

Plain–fretting fatigue competition and prediction in spline shaft-hub connection

The dynamically loaded spline shaft-hub connection that without macro relative movement between shaft and hub are exposed to the danger of fretting fatigue in the contact zone of teeth flank and plain fatigue at teeth fillet at the same time. The competition of fretting fatigue and plain fatigue determines that which one dominates the failure of it and therefore the fatigue performance of it. In order to deal with this plain–fretting fatigue coexisted situation, a plain–fretting fatigue unified prediction model is introduced in this paper and implemented in the representative spline teeth pair. Predicted by this model, the failure of involute spline shaft-hub connection teeth DIN 5480 45×2×21 is plain fatigue at teeth fillet dominated. Corresponding to the theoretical modeling efforts, a representative teeth pair fatigue test apparatus was developed. With this test apparatus, the initiation and propagation of fatigue cracks can be detected on line by monitoring the change of resonant frequency. The test results also showed that the crack occurs at teeth fillet at first.

A comparative analysis between multiaxial stress and ΔK-based short crack arrest models in fretting fatigue

This paper presents a comparative analysis between a multiaxial stress and a stress intensity factor based fatigue model within the context of short crack arrest in fretting fatigue. The stress-based model involves the calculation of a multiaxial parameter at a critical distance from the contact. The critical distance is identified by means of plain fatigue limits and the threshold stress intensity factor range for long crack propagation. The ΔK-based model compares the mode I stress intensity factor range at a critical distance from the contact with the threshold stress intensity for crack propagation. In this case, the critical distance is defined as the crack transition length between the short and long crack regimes, which is obtained from the Kitagawa–Takahashi diagram. In order to carry out the comparative analysis, new fretting fatigue tests were performed with a pair of cylindrical pads pressed against a flat dog-bone specimen, both made of 7050-T7451 Al alloy. Three series of tests were conducted in the partial slip regime. Within each series the experimental conditions were identical, except the mean bulk load, which varied from a tensile to a compressive value until a run out condition was achieved. The results showed that the predictive methodologies provide different short crack arrest domains for the same contact configuration. The stress-based model yielded slightly better estimates of fatigue endurance than the stress intensity factor based model.

Effect of cold expansion and bolt clamping on fretting fatigue behavior of Al 2024-T3 in double shear lap joints

In this paper the fatigue behavior of double shear lap joints treated by cold expansion and bolt clamping has been investigated. Fatigue tests and numerical simulations were conducted to study the combined effect of cold expansion and bolt clamping on the fatigue life and failure mode. The results showed significant changes on the fatigue behavior of the double shear lap joints at different load ranges. Depending on the degree of cold expansion and clamping torque, both plain fatigue and fretting fatigue failures were observed. The optimum degree of cold expansion in conjunction with the clamping force differs from those reported for joints that were cold expanded only.

Fatigue and SCC Behavior of Sensitized SUS304 Stainless Steel in Pressurized Hot Water at 7.3MPa and 288°C

Plain fatigue and fretting fatigue tests of sensitized SUS304 stainless steel under pressurized hot water at 7.3MPa and 288°C have been carried out. Fatigue strengths for both fatigue tests almost coincided. Fretting contact could nucleate small SCC cracks near the contact edge in the direction perpendicular to cyclic loading. High R–ratio reduced fatigue strength due to longer exposure time to corrosive environment at high mean stress. From the constant load SCC tests of the specimen with small SCC pre–crack induced by fretting contact, it was found that the threshold stress intensity factor for growth of small SCC precrack was 4.1MPa·m1/2, which was significantly lower than that for long crack (10MPa·m1/2).

Fracture toughness and growth of short and long fatigue cracks in ductile cast iron EN‐GJS‐400‐18‐LT

ABSTRACTHeavy components of ductile cast iron frequently exhibit metallurgical defects that behave like cracks under cyclic loading. Thus, in order to decide whether a given defect is permissible, it is important to establish the fatigue crack growth properties of the material. In this paper, results from a comprehensive study of ductile cast iron EN‐GJS‐400‐18‐LT have been reported. Growth rates of fatigue cracks ranging from a few tenths of a millimetre (‘short’ cracks) to several millimetres (‘long’ cracks) have been measured for load ratios R=−1, R= 0 and R= 0.5 using a highly sensitive potential‐drop technique. Short cracks were observed to grow faster than long cracks. The threshold stress intensity range, ΔKth, as a function of the load ratio was fitted to a simple crack closure model. Fatigue crack growth data were compared with data from other laboratories. Single plain fatigue tests at R=−1 and R= 0 were also carried out. Fracture toughness was measured at temperatures ranging from −40 °C to room temperature.

RETRACTED: A simplified approach for predicting plain and notch fatigue resistance of shot peened Al-7075-T651

RETRACTED: A simplified approach for predicting plain and notch fatigue resistance of shot peened Al-7075-T651

Fatigue Failure of Notched Specimen—A Strain-Life Approach

Failure cycles of notched round specimens under strain controlled cyclic loading are predicted using strain—life relations obtained from experiment for plain fatigue round specimens. For notched specimens, maximum strain occurs at notch root and is different from applied controlled strain. The maximum strain is computed by appropriate Finite element analysis using the FE software ABAQUS. FE model and material parameters are validated by comparing the FE results and experimental results of LCF tests of round specimens. This value of maximum strain is used for prediction of failure cycles. Prediction is compared with the experimental results. The results show good matching.

Fretting fatigue behaviour of hard anodizing coated 2014-T6 aluminium alloy with dissimilar mating materials under plane bending loading

The effect of hard anodizing coated 2014-T6 aluminium alloy test samples with dissimilar mating materials on fretting fatigue was investigated. Fretting fatigue configuration involved bridge-type pads on the flat specimen. Bridge-type pads were made of AISI 4140 steel. All the fretting fatigue tests were conducted under plane bending loading with a stress ratio of R = —1. Coated and uncoated specimens were compared for microhardness, surface roughness, tangential force. The specimens were tested under both plain fatigue and fretting fatigue loading at ambient temperature. Micrographs obtained from scanning electron microscope showed that hard anodizing coating had tiny cracks through the thickness of the anodized layer. The hardness of hard anodized coating was higher than that of uncoated specimens and they also exhibited lower tangential force. However, the fretted region of the hard anodizing coated specimens was rougher than that of uncoated samples and despite lower tangential forces, fatigue lives of hard anodizing coated samples were inferior to those of uncoated samples. As the hard anodizing coating had pre-existing tiny cracks and tension residual stress, cracks propagated from the hard anodizing coating through the interface into the substrate. We conclude that these may be the main reasons for inferior fretting fatigue lives compared with uncoated samples.

A STUDY ON FRETTING FATIGUE LIFE IN ELEVATED TEMPERATURE FOR INCOLOY 800

Incoloy 800, which is used within steam generator tubes, is a heat resistant material since it is an iron-nickel-chromium alloy. However, construction of a systematic database is needed to receive integrity data defecting insurance of specific data about room and elevated temperature fretting fatigue behavior for Incoloy 800. Accordingly, this study investigates the specific change in fatigue limitations under the condition of the fretting fatigue as compared to that under the condition of the plain fatigue by performing plain and fretting fatigue tests on Incoloy 800 at 320°C, real operating temperature and at room-temperature, respectively. The change in the frictional force is measured during the fretting fatigue testing against the repeated cycle, and the mechanism of fretting fatigue is investigated through the observation of the fatigue-fracture surface.

Effect of Plasma Nitriding Environment and Time on Plain Fatigue and Fretting Fatigue Behavior of Ti–6Al–4V

Plasma nitriding was performed on Ti–6Al–4V fatigue test samples at 520°C in two environments (nitrogen and nitrogen–hydrogen mixture in a ratio of 3:1) for two time periods (4 and 18 h). Plain fatigue and fretting fatigue tests were conducted on unnitrided and plasma nitrided samples. Plasma nitriding degraded lives under both plain fatigue and fretting fatigue loadings. The samples nitrided in nitrogen exhibited superior lives compared with the samples nitrided in the nitrogen–hydrogen mixture, possibly due to the relatively higher hardness (and presumably lower toughness) of the nitrided layer of the samples nitrided in the nitrogen–hydrogen mixture environment. For those samples nitrided in the nitrogen–hydrogen mixture, those nitrided for 18 h exhibited superior lives compared with those nitrided for 4 h. This trend was observed for samples nitrided in nitrogen gas at lower stress levels only; the converse was true at higher stress levels of 550 MPa and 700 MPa under plain fatigue loading. However, under fretting fatigue loading, the plasma nitriding time did not influence the lives significantly.

The Theory of Critical Distances as an alternative experimental strategy for the determination of KIc and ΔKth

Abstract The present technical note is concerned with the use of the Theory of Critical Distances, applied in the form of the Point Method, to estimate the range of the threshold value of the stress intensity factor, Δ K th , as well as the plane strain fracture toughness, K Ic , of conventional engineering materials. In more detail, it is shown that Δ K th can efficiently be evaluated by measuring two fatigue limits: the plain fatigue limit and a second fatigue limit generated by testing samples containing a stress concentration feature such as a notch. The K Ic , on the other hand, can be accurately estimated by using experimental results obtained by testing samples containing notches of two different sharpnesses. The accuracy and reliability of the proposed experimental methodology was checked by using a large amount of experimental results taken from the literature. Such a systematic validation exercise allowed us to fully confirm that the Theory of Critical Distances is not only an accurate static and fatigue assessment technique, but it can also be considered as an efficient experimental strategy suitable for estimating the classical Linear Elastic Fracture Mechanics material properties.

Plain fatigue resistance of shot peened high strength aluminium alloys: Effect of loading ratio

The effect of different shot-peening treatments on the reverse and pulsating bending fatigue behaviour of Al 7075 T651 was studied. The fatigue improvements with respect to the unpeened condition and the influence of the peening intensity on fatigue were discussed accounting for the effects of surface modifications and residual stresses. In particular, the extent of the residual stress redistribution during loading was investigated by means of X-ray diffraction (XRD) measurements. No significant residual stress relaxation was observed in samples tested to a load level corresponding to the fatigue endurance at 5⋅106 cycles. Residual stress relaxation was observed only when the material plastic flow stress was achieved during the compressive part of the fatigue load cycle. Accordingly, shot peened samples with deep sub-superficial compressive residual stress peak showed a reversed fatigue endurance level corresponding to the condition of incipient plastic flow. This phenomenon was also accompanied by subsuperficial fatigue crack initiation. On the contrary, samples tested at shorter fatigue lives or under pulsating loading conditions showed crack initiation close to the surface. The initial and the stabilised residual stress profiles were considered for discussing the improvement in the fatigue behaviour due to peening. For this purpose, a multiaxial fatigue criterion was adopted to account for the biaxial residual stress field. The fatigue life was quite accurately predicted as long as fatigue initiation occurs on the surface.

High temperature fretting fatigue behavior of IN100

Fretting fatigue behavior of a nickel-base superalloy, IN100, was investigated at 600 °C. Fretting fatigue tests were conducted at various stress levels using cylinder-on-flat contact configuration. Effects of microstructure were also investigated by varying the gamma grain size (3 μm versus 7 μm). Additionally, effects of contact load were studied. Furthermore, plain fatigue tests of IN100 with two microstructures were also conducted. Fretting reduced the strength/life in comparison to those of the plain fatigue almost equally in both microstructures. Increase of contact load reduced the fretting fatigue strength/life. An increase of the gamma grain size decreased the fretting fatigue strength/life of IN100. Fracture surfaces of the 3 μm grain microstructure showed intergranular and tortuous crack path while the 7 μm grain microstructure had transgranular and relatively smoother crack path. Fractographic analysis indicated that the 3 μm grain microstructure had a higher resistance to the fretting fatigue crack nucleation and initiation as well as to the crack growth in comparison to the 7 μm grain microstructure, which was in agreement with the observed plain and fretting fatigue behaviors. Furthermore, plain and fretting fatigue performances improved at 600 °C in comparison to room temperature with both microstructures.

Effects of microstructure on fretting fatigue behavior of IN100

Fretting fatigue behavior of a nickel-base superalloy, IN100, was investigated at room temperature. Two microstructures of IN100 were tested which varied primarily by the gamma grain size (3 μm versus 7 μm). Fretting fatigue tests were conducted at various stress levels using cylinder-on-flat contact configuration. An increase in the grain size was associated with decrease in the fretting fatigue strength/life of IN100. Microscopic analysis showed that the 3 μm grain microstructure provided a higher microstructural barrier to the fretting fatigue crack nucleation and initiation. On the other hand, the 7 μm grain microstructure had a higher intrinsic crack growth resistance due to the tortuous crack path requiring more energy. These features were in agreement with the plain fatigue where fine microstructures generally provide higher resistance to crack initiation but reduce crack propagation resistance while coarse microstructures have the opposite behavior.

On the Use of the Theory of Critical Distances to Estimate K<sub>Ic</sub> and ∆K<sub>th</sub> from Experimental Results Generated by Testing Standard Notches

The present paper is concerned with the use of the Theory of Critical Distances (TCD), applied in the form of the Point Method (PM), to estimate the range of the threshold value of the stress intensity factor, Kth, as well as the plane strain fracture toughness, KIc. In more detail, by reanalysing a large amount of experimental data taken from the literature, it is proved that Kth can successfully be evaluated through the plain fatigue limit and another fatigue limit generated by testing samples containing a known geometrical feature, whereas KIc is suggested here as being estimated by using experimental results generated by testing samples weakened by notches of different sharpness. The validation exercise summarised in the present paper fully confirms that the TCD is not only a reliable method suitable for performing the static and fatigue assessment of real components, but also an efficient experimental strategy capable of accurately estimating the classical Linear Elastic Fracture Mechanics (LEFM) material properties.

Plain fatigue and fretting fatigue behavior of hot-rolled steel sheet after cold spinning

Fretting fatigue may occur on the surface of a wheel disc in the contact area of the mounting face of the wheel to the flange. Plain fatigue and fretting fatigue tests of specimens sectioned from actual fabricated wheels after cold spinning were carried out to understand the influence of surface condition after plastic forming on fretting fatigue behavior. Cold spinning increased surface hardness with low level of compressive residual stress, which is a factor for enhancing fatigue strength. However, cold spinning also increased surface roughness and induced surface defects, which significantly degraded plain fatigue strength. In fretting fatigue, the stress concentration at the fretting contact edge was a more significant factor in controlling fretting fatigue behavior than the surface defects. Therefore, fretting fatigue strengths for grinding, milling and cold spinning surfaces of fretting fatigue specimens almost coincided regardless of surface condition.

真空中におけるアルミニウム合金(Al2024-T4)のフレッティング疲労特性(<小特集>締結・接合・接着部の評価技術)

Plain fatigue, fatigue crack growth and fretting fatigue tests of Al alloy (Al2024-T4) in air and in vacuum were carried out using a fatigue testing machine with SEM for in-situ observation. Fretting fatigue strength in vacuum was higher than that in air, while it was lower than plain fatigue strength in vacuum. High tangential force in vacuum would result in earlier fretting fatigue crack nucleation. However, high fatigue crack growth resistance would take dominant role for higher fretting fatigue strength in vacuum.

Relative performance of alumina coatings prepared by micro arc oxidation and detonation gun spray on AA 6063 under plain fatigue and fretting fatigue loading

The present study compares the performance of alumina coatings prepared by two different methods (micro arc oxidation (MAO) and detonation gun (D-gun) spray) on AA 6063 (Al alloy) fatigue test samples under plain fatigue and fretting fatigue loading. While MAO coating had comparable proportions of γ-Al2O3 and α-Al2O3, D-gun sprayed coating contained γ-Al2O3 with minimal quantities of α-Al2O3. MAO coating was relatively harder than D-gun sprayed coating. As both types of coated samples were ground, they exhibited almost the same surface roughness. D-gun sprayed alumina coated samples exhibited slightly higher magnitude of surface residual compressive stress compared with MAO coated specimens. Both types of coated samples experienced almost the same friction force. D-gun spray coated samples exhibited superior plain fatigue and fretting fatigue lives compared with MAO coated specimens. This may be attributed to layered structure of the D-gun sprayed coating.

A STUDY ON THE FRETTING FATIGUE LIFE OF ZIRCALOY ALLOYS

Studies on the strength and fatigue life of machines and structures have been conducted in accordance with the development of modern industries. In particular, fine and repetitive cyclic damage occurring in contact regions has been known to have an impact on fretting fatigue fractures. The main component of zircaloy alloy is Zr , and it possesses good mechanical characteristics at high temperatures. This alloy is used in the fuel rod material of nuclear power plants because of its excellent resistance. In this paper, the effect of the fretting damage on the fatigue behavior of the zircaloy alloy is studied. Further, various types of mechanical tests such as tension and plain fatigue tests are performed. Fretting fatigue tests are performed with a flat-flat contact configuration using a bridge-type contact pad and plate-type specimen. Through these experiments, it is found that the fretting fatigue strength decreases by about 80% as compared to the plain fatigue strength. Oblique cracks are observed in the initial stage of the fretting fatigue, in which damaged areas are found. These results can be used as the basic data for the structural integrity evaluation of corrosion-resisting alloys considering the fretting damages.

Effect of grinding on plain fatigue and fretting fatigue behaviour of detonation gun sprayed Cu–Ni–In coating on Al–Mg–Si alloy

Uniaxial plain fatigue and fretting fatigue tests were carried out on detonation gun sprayed Cu–Ni–In coating on Al–Mg–Si alloy samples. The samples in three conditions were considered: uncoated, as-coated and ground after coating. Ground coated specimens exhibited superior plain fatigue and fretting fatigue lives compared with uncoated and as-coated specimens. The life enhancement has been discussed in terms of surface finish and residual compressive stresses at the surface.