Role In Fatigue Life Research Articles

Effect of scanning strategy and laser peening on microstructure and fatigue properties of laser-directed energy deposition-built 15-5 PH stainless steel

PurposeThe aim of this paper is to study the effect of laser shock peening (LSP) on mechanical behaviour of the laser-directed energy deposition (LDED)-based printed 15-5 PH stainless steel with U and V notches. The study specifically concentrates on the evaluation of effect of scan strategy, machining and LSP processing on microstructural, texture evolution and fatigue behaviour of LDED-printed 15-5 PH steel.Design/methodology/approachFor LSP treatment, 15-5 PH steel was printed using LDED process with bidirectional scanning strategy (XX [θ = 0°) and XY [θ = 90°]) at optimised laser power of 600 W with a scanning speed of 300 mm/min and a powder feed rate of 3 g/min. Furthermore, LSP treatment was conducted on the V- and U-notched fatigue specimens extracted from LDED-built samples at laser energy of 3.5 J with a pulse width of 10 ns using laser spot diameter of 3 mm. Post to the LSP treatment, the surface roughness, fatigue life assessment and microstructural evolution analysis is performed. For this, different advanced characterisation techniques are used, such as scanning electron microscopy attached with electron backscatter diffraction for microstructure and texture, X-ray diffraction for residual stress (RS) and structure information, Vicker’s hardness tester for microhardness and universal testing machine for low-cycle fatigue.FindingsIt is observed that both scanning strategies during the LDED printing of 15-5 PH steel and laser peening have played significant role in fatigue life. Specimens with the XY printing strategy shows higher fatigue life as compared to XX with both U- and V-notched conditions. Furthermore, machining and LSP treatment led to a significant improvement of fatigue life for both scanning strategies with U and V notches. The extent of increase in fatigue life for both XX and XY scanning strategy with V notch is found to be higher than U notch after LSP treatment, though without LSP samples with U notch have a higher fatigue life. As fabricated sample is found to have the lowest fatigue life as compared to machines and laser peened with both scan strategies.Originality/valueThis study presents an innovative method to improve the fatigue life of 15-5 PH stainless steel by changing the microstructure, texture and RS with the adoption of a suitable scanning strategy, machining and LSP treatment as post-processing. The combination of preferred microstructure and compressive RS in LDED-printed 15-5 PH stainless steel achieved with a synergy between microstructure and RS, which is responsible to improve the fatigue life. This can be adopted for the futuristic application of LDED-printed 15-5 PH stainless steel for different applications in aerospace and other industries.Graphical abstract

Fatigue crack growth and life assessment of full penetration U-rib welded joints considering residual stresses

The combination of cyclic stresses and welding residual stresses (WRS) can significantly contribute to fatigue cracking in steel bridge decks. This study aims to investigate the effect of WRS on the fatigue life and crack propagation of single-sided and full penetration double-sided U-rib welded joints through experimental and numerical methods. Fatigue tests were conducted to study fatigue crack initiation and propagation behavior. Utilizing the ABAQUS software, a thermoelastic-plastic finite element method was employed to determine the residual stress distribution. Subsequently, based on linear elastic fracture mechanics (LEFM), fatigue crack propagation and life assessment were performed using ABAQUS and FRANC3D software under the coupling of residual stresses and external cyclic stresses. Findings reveal that WRS play a crucial role in fatigue life by altering the effective stress ratio during fatigue crack growth. The effective stress ratio ranges from 0.15 to 0.57, while the changing trends differ between single-sided and double-sided U-rib welded joints. The fatigue crack growth rate of double-sided U-rib welded joints is lower compared to single-sided U-rib welded joints with the same deck thickness. Furthermore, the introduction of WRS induces a mixed mode I, II, and III fracture at the outer weld toe of the U rib, with mode I fracture predominating, which leads to a deviation in the crack propagation path. The fatigue life prediction results agree well with experimental findings when considering WRS. Importantly, these predictions tend to be conservative, thereby ensuring safety and reliability in engineering applications.

Predicting asphalt mixture fatigue life via four-point bending tests based on viscoelastic continuum damage mechanics

A more technically accurate approach to predict fatigue life of asphalt mixtures can enhance the precision of performance evaluation for asphalt pavements. This study applied the viscoelastic continuum damage mechanics (VECD) to investigate the fatigue behavior of asphalt mixtures. The fatigue life of typical asphalt mixtures was evaluated through four-point bending tests under various conditions. The strain-modulus empirical equation was firstly employed to fit the experimental data. However, it was noted that this equation was not entirely suitable for all conditions, as factors like temperature and loading frequency can influence fatigue life not only through the dynamic modulus but also via the damage properties of asphalt mixtures. To address this limitation and achieve a comprehensive fatigue life prediction equation, the Time-Strain Superstition Principle (TSSP) and Frequency-Strain Superstition Principle (FSSP) were introduced to characterize the impact of temperature and loading frequency on fatigue life, which can reduce fitting errors. Additionally, a mechanical prediction equation was also derived by the VECD approach, and its applicability under different conditions was explored. The results revealed that the damage characteristic curve (C-S curve) remained unaffected by loading frequency and strain level but was highly dependent on temperature. Significant fitting errors were observed in different temperatures when employing the VECD method for fatigue life prediction, as the VECD method did not account for the influence of temperature on the viscoelastic properties of asphalt mixtures, which in fact plays a critical role in fatigue life. In response, temperature adjustment coefficients were introduced into the derived equation. The predicted results demonstrated that the newly modified method significantly improved prediction precision, yielding an error of less than 20%.

Experimental study of a CoCrMo alloy treated by SMAT under rotating bending fatigue

The main objective of this work is to understand the fundamental damage mechanisms involved in a SMAT treated CoCrMo alloy subjected to fatigue under rotating bending loads. For this purpose, different load amplitudes in rotating bending are imposed on cylindrical specimens, in as-machined and SMAT states. Different material characterizations are performed in order to determine which features play an important role in fatigue life of the studied alloy. Such characterizations are done via digital microscopy, electron backscatter diffraction (EBSD), roughness measurements and microhardness tests. The fatigue results presented in the form of S-N diagram show that SMAT with a moderate intensity (SMAT-2) can enhance the fatigue performance of the CoCrMo alloy, whereas SMAT with a higher intensity (SMAT-3) seems to deteriorate it. This fatigue life decrease is probably due to surface micro-cracks generated by an over-peening phenomenon.

Ti-6Al-4V lattices obtained by SLM: characterisation of the heterogeneous high cycle fatigue behaviour of thin walls.

Architectured materials are attracting increasing interest since a few years, achieving numerous excellent specific properties compared to fully dense materials. The transport industry sector see periodic assemblies of elementary cells, called lattices, as a solution to lighten structures. This is made possible by the development of Additive Manufacturing technologies (AM). Among the numerous advantages of AM, these processes allow to create a wide range of porous cell topologies, and to tailor their complex geometry with the desired properties. However, understanding their fatigue properties is essential to validate their long-term use in load-bearing parts.The FA process plays an important role in fatigue life, as it generates residual stresses, heterogeneous microstructure, as well as surface and volume defects (roughness, gaz porosities, lack of fusion porosities), which are preferred sites for fatigue crack initiation. The fatigue life of these structures also depends strongly on their geometry, which, due to their complexity, induces scale and stress gradient effects.Recent studies have recognize thin-walls TPMS (Triply Periodic Minimal Surfaces) structures as the most promising structures for fatigue resistance, especially the gyroid geometry, compared to conventional strut-lattices.The first aim of this work is to characterise the major parameters influencing fatigue life at the lattice scale. Roughness, microstructure will be discribed on a lattice specimen, and topology effect on stress distribution will be numerically quantified. In order to understand the influence of these parameters, and identify the critical region for fatigue life, this work focuses on the local thin-wall scale. Here, the aim is to characterise the high cycle (HCF) fatigue heterogeneous response of Ti-6Al-4V thin-walls manufactured, characterising localy the HCF behaviour of a TPMS lattice structure (R=0.1; uniaxial tension loading, N=1.106, f=40Hz).

Microstructure and fatigue damage mechanism of 6082-T6 aluminium alloy welded joint

In this paper, 6mm thick 6082-T6 high-strength aluminium alloy is taken as the research object, and CLOOS ROMAT-3500 industrial robot MIG welder is used for welding. High-cycle fatigue test is carried out on welded joint and 6082-T6 base metal. Microstructure, microhardness, tensile properties and fatigue properties are studied, and fatigue fracture is observed and analyzed. The test results show that: equiaxed crystals exist in the center of the weld. Broken equiaxed crystals are found in the weld due to stirring in the molten pool, a large number of pore and columnar crystal layers are found at the junction of the two beads. A small amount of pore and cellular dendrite are found in the fusion zone. A softening zone with a minimum hardness of 65.5HV exists in the heat affected zone(HAZ). The conditional fatigue limits for base metal and weld specimens are 77.26MPa and 48.69MPa at the set target cycle of 107 respectively. In fatigue fracture, there are a lot of cleavage fracture characteristics and ductile fracture characteristics. The crack initiation is quasi-cleavage fracture characteristic. In the past studies, I have studied the fatigue life of joints, but as the research progresses, I believe that the fatigue behavior and fatigue damage mechanism plays an important role in fatigue life. In this paper, Fatigue fracture process is analyzed by correlation calculation of stress intensity factor. Two crack initiation modes are proposed based on the welding process. The first is fatigue crack initiation caused by stress concentration at the grain boundary where hydrogen elements converged, the second is fatigue crack initiation caused by the gap between equiaxed and columnar crystals inside and outside the central pore of the weld.

Effect of finishing on rolling fatigue life and failure mode

Effect of finishing on rolling fatigue life and failure mode

Rolling fatigue life of PM steel with different porosity and surface finish

Gears made of PM steel are of interest for the automotive industry because they can be produced to near net shape with only a few processing steps.Automotive gears experience a complex contact situation with rolling as well as combined rolling and sliding. They also have to be able to withstand high loads and fairly high temperature variations.Earlier work show that the main limiting parameter of the contact fatigue life of PM steel is the porosity. A higher porosity/lower density will decrease the fatigue life of the PM component.In the present study, the pure rolling contact fatigue life of PM steel with different density and surface finish has been investigated. A rolling contact fatigue test rig, where rods of the tested material are mounted between two rolling wheels, was used. Two densities of PM steel, 6.8 and 7.15 g/cm3 and a full density reference steel with two different surface finishes, centerless grinded and superfinished, were tested. The tests were run for a given number of load cycles or until failure (fatigue life). SEM was used to study the surfaces and cross-sections to reveal the mechanisms of crack initiation and propagation.The higher density PM steel (7.15 g/cm3) outperformed the lower density steel (6.18 g/cm3) by a factor of around 4 in fatigue life at the same surface pressure, regardless of surface finish. Cracks are initiated at a depth of around 100 µm. These cracks propagate and eventually they reach the surface, causing surface damage and failure. For the low density PM steel, both sub surface crack initiation and failure occurred earlier (at a lower number of load cycles) than for the higher density PM steel.Severe surface damage or wear were not found until failure occurred. Still, some initial alteration of the surfaces was seen already after 0.5 million load cycles, in the form of removal of the highest asperity peaks on the centerless grinded surfaces, and opening of the surface pores on the superfinished surface. No effect of surface finish was found on the fatigue life. The difference in surface roughness could induce a difference in local stress concentrations at the surface, but in this test the cracks causing fatigue failure are initiated at a depth where the stress distribution is not affected by local surface stress concentrations. This means that for fairly smooth surfaces roughness, the surface of PM steel is not important when it comes to pure rolling fatigue life.

Rolling fatigue life improvement effect of zinc thin film formed with shot peening

Rolling fatigue life improvement effect of zinc thin film formed with shot peening

Flaking of PEEK under one-point rolling contact fatigue using Al2O3 ball

The growth of flaking as tribological fatigue failure in PEEK was investigated through the one-point type rolling contact fatigue test between a machined PEEK polymer shaft and an alumina bearing's ball. Due to Hertzian contact of cyclic compressive stress, the subsurface fatigue cracks in the PEEK shaft propagated in rolling and axial directions. When the rolling fatigue life of the PEEK shaft reached 106 fatigue cycles, many narrow angled cracks occurred in the near-surface of the rolling track without flaking. On the other hand, when the flaking ocuurred on the PEEK shaft before 106 fatigue cycles, semicircular surface and subsurface crack propagations were observed. From these observations, it was found that micro-flaking occurred due to the linkages between subsurface and surface cracks. Flakingdeveloped due to the accumulation of these micro-flakings.

Effect of ultrasonic peening technology on the thermal fatigue of rolling mill rolls

In this study, the use of ultrasonic peening technology (UPT) on the rolling mill roll graphite steel GSH48 was surveyed in order to improve some surface mechanical and thermal properties. UPT is one of the newest technologies of severe plastic deformation in which vibratory tool strikes the workpiece surface with continual reciprocating motions, resulting in severe plastic deformation on the surface. This method enhances mechanical and thermal properties like fatigue life and thermal fatigue. Thermal fatigue in the rolling mill rolls causes the growth of crack on the surface and growing that in depth leads to the break of the roll. The influence of the UPT on the improvement of thermal fatigue life of the hot-rolling rolls was investigated by conducting thermal fatigue test in which parameters were adjusted in accordance with the process of hot-rolling. By the simulation and manufacturing of peening vibratory tool, preparation of the process was accomplished including setting up the ultrasonic vibratory tool on lathe machine. According to the standard of related devices, samples were prepared form the surface of roll and the examinations of fatigue, thermal fatigue, and surface topology by atomic force microscopy (AFM) were performed on workpieces in different states before and after the UPT process with one, two, and three passes. The process of ultrasonic peening caused severe plastic deformation on surface layers and prevented from crack growth. The results of this research indicated the rise of the fatigue and thermal fatigue life of the pieces after UPT process.

Composition Design and Fatigue Curves of Hardfacing Materials for Cold Roll

In order to improve the fatigue life of cold rolls, a series of hardfacing alloys were designed by orthogonal experiments considering the interaction between carbon, chromium, and niobium. Hardfacing layers were produced by Tungsten Inert Gas (TIG) arc welding. The effects of alloy content on microstructure and carbides and fatigue behavior at different load frequency and different temperature were analyzed. The results show that suitable combination of 0.5% C, 4.0% Cr, and 2.0% Nb can obtain a high hardness of 54.7 HRC for the formation of fine lath martensite and carbides with dispersed distribution. The new designed hardfacing materials have similarΔε-Ncurves with parent material in low load frequency and below 400°C.

306 レーザピーニングした浸炭硬化鋼の転動疲労寿命(機素潤滑設計I)

306 レーザピーニングした浸炭硬化鋼の転動疲労寿命(機素潤滑設計I)

Analysis of Fatigue Stresses on Connecting Rod Subjected to Concentrated Loads At The Big End

The Connecting rod transmits the piston load to the crank causing the latter to turn, thus converting the reciprocating motion of the piston into a rotary motion of the crankshaft. Connecting rods are subjected to forces generated by mass and fuel combustion. Connecting rod is modeled using CATIA software and FE analysis is carried out using ANSYS Software. Load distribution plays important role in fatigue life of the structure. Bush failure changes the loading direction and distribution. Present study is concentrated around the fatigue life due to concentrated load and cosine type load distribution on the bigger end

The influence of rolling speed on the fatigue life of rolls with grooves

In the hot rolling process, rolls with grooves are used for the production of various simple and complex profiles. Main factors influencing the fatigue life of these rolls result from the technological process of the rolling. Rolling speed is an important parameter of technological process which has great influence on overall production. In order to increase rolling production, an analysis of the rolling speed influence on the fatigue life of the rolls has been carried out. The fatigue life estimation is carried out according to the fatigue life stress concept based on the local stress. Stress spectra in critical areas are determined for three different roll speeds. The analysis shows that although increasing the rolling speed causes decrease of the fatigue life of the roll, the stresses caused by the rolling at the highest speed should not lead to roll fracture.

Prediction of Contact Fatigue Life of Alloy Cast Steel Rolls Using Back-Propagation Neural Network

In this study, an artificial neural network (ANN) was employed to predict the contact fatigue life of alloy cast steel rolls (ACSRs) as a function of alloy composition, heat treatment parameters, and contact stress by utilizing the back-propagation algorithm. The ANN was trained and tested using experimental data and a very good performance of the neural network was achieved. The well-trained neural network was then adopted to predict the contact fatigue life of chromium alloyed cast steel rolls with different alloy compositions and heat treatment processes. The prediction results showed that the maximum value of contact fatigue life was obtained with quenching at 960 °C, tempering at 520 °C, and under the contact stress of 2355 MPa. The optimal alloy composition was C-0.54, Si-0.66, Mn-0.67, Cr-4.74, Mo-0.46, V-0.13, Ni-0.34, and Fe-balance (wt.%). Some explanations of the predicted results from the metallurgical viewpoints are given. A convenient and powerful method of optimizing alloy composition and heat treatment parameters of ACSRs has been developed.

小径転動体を有する転がり軸受の転動疲労寿命に及ぼす転動体サイズと潤滑状態の影響(第2報) : 流体潤滑状態での転動疲労寿命

小径転動体を有する転がり軸受の転動疲労寿命に及ぼす転動体サイズと潤滑状態の影響(第2報) : 流体潤滑状態での転動疲労寿命

Compression fatigue behavior of Ti–6Al–4V mesh arrays fabricated by electron beam melting

This paper focuses on the compression fatigue behavior of Ti–6Al–4V mesh arrays with high porosities of ∼60–85%, which were fabricated by an additive manufacturing technique using electron beam melting. The results show that their fatigue lives are mainly determined by uniform deformation through the entire specimens, while their failures are characterized by rapid strain accumulation and a severe crush band at an angle of 45° to the cyclic loading direction. The relation between the relative fatigue strength and relative density can be evaluated by the well-known Gibson–Ashby model with the exponential factor n being 2.7, which is higher than the reported data for aluminum and nickel foams, and almost double the idealized value (n=1.5) of a stochastic open cellular foam. The underlying mechanism of fatigue failure appears to be interaction between cyclic ratcheting and fatigue crack initiation and propagation, while the former plays a dominant role in fatigue life. TEM observations found that dislocations are generated along the interface of the α′ phase and their generation becomes more evident with an increase in the relative density. This would contribute to the retardation of cyclic ratcheting and an improvement in the fatigue strength.

Relation between Corrosion Energy and Rolling Fatigue Life with a Four Ball Test

The authors evaluated the fatigue life using a rolling four ball test with mineral oil samples in which an alkaline metal, a phosphorus system or a sulfur system compound were added. As a result, it was likely that a decrease of the hardness in the vicinity of the ball surface shortened the fatigue life. Moreover, it was found that the larger the corrosion energy in extract water of the oil sample, the shorter the fatigue life. There is a linear relationship between the corrosion energy and the fatigue life. In addition, the technology to extend the fatigue life and the investigation on additive effect are reported.

S112013 エッジロード発生時のころ軸受寿命予測への多点LP法の適用 : カットクラウニングころの場合([S11201]機械要素の設計・製造・応用技術(1))

The crowning profile design method proposed by Sugiura et al. is valuable even though it's an age-old technology. The defect of their method is it cannot be applied to the case when the stress concentration is generated at any place other than roller end, for example raceway edges where undercuts exist. Therefore it is said the above method is not sufficient as design tool. Improved method, "Multi-Point LP Method", has been proposed for rolling fatigue life prediction, and its validity has been reported in the full-crowning roller cases. In this article, the follow-on assessment of Multi-Point LP Method will be reported by taking up the issue of the cut-crowning roller fatigue life prediction.