Fatigue Failure Mechanism Research Articles

Fatigue Life Prediction of 2024-T3 Al Alloy by Integrating Particle Swarm Optimization—Extreme Gradient Boosting and Physical Model

The multi-parameter characteristics of the physical model pose a challenge to the fatigue life prediction of 2024-T3 aluminum (Al) alloy. In response to this issue, a parameter-solving method that integrates particle swarm optimization (PSO) with extreme gradient boosting (XGBoost) is proposed in this study. The fatigue performance and failure mechanism of the 2024-T3 Al alloy are analyzed. Furthermore, the fatigue life prediction physical model of the 2024-T3 Al alloy is established by using the energy method of fracture mechanics. The physical model incorporates critical physical parameters. Meanwhile, the PSO algorithm optimizes the hyperparameters of the XGBoost model based on fatigue data of the 2024-T3 Al alloy. Eventually, the optimized XGBoost model is used to solve the parameters of the physical model. Furthermore, the analytical equation of the fatigue life prediction model is obtained. This paper provides a new method for solving the parameters of the fatigue life prediction model, which reduces the error and cost of obtaining the model parameters in the experiment and shortens the time required.

Rolling Contact Fatigue Behaviors of 20CrNi2Mo Steel by a New Carbon and Nitrogen Composite Infiltration Process

ABSTRACTIn this paper, a new type of composite infiltration process was adopted for 20CrNi2Mo steel. Rolling contact fatigue (RCF) tests were carried out on the specimens treated with carburizing (C) and composite infiltration with carburizing and nitriding (C‐N). The results showed that after C and C‐N treatments were performed, the surface microhardness was increased by 78% and 114%, respectively, and the maximum CRS were −220 and −530 MPa. Moreover, the residual austenite volume fraction was controlled to approximately 10% for each treated sample. The fatigue limit of the C‐N sample was 11.3% higher than that of the C sample. The fatigue failure mechanisms are caused by the maximum shear stress distribution and surface roughness. The surface layer of the C‐N sample with higher hardness and more compressive residual stress inhibited the initiation of fatigue cracks, and the appropriate residual austenite in the carbon‐nitrogen infiltrated layer inhibited the propagation of fatigue cracks.

Thermo-mechanical coupling characteristics of the shearer’s guiding shoe during the friction

The reliability and longevity of the guiding shoe are crucial for the proper functioning of coal mining machines. The heavy wear of the sliding surface under thermal stress coupling is the primary factor influencing the service life of the guiding shoe. To reveal the heat flow distribution patterns and the thermo-stress coupling mechanisms of the guiding surface, a thermo-mechanical coupling model of the guiding shoe and the pin row is established. The transient thermodynamic behavior of the guiding shoe under different load and speed conditions is studied using the coupled temp-displacement analysis method in Abaqus. The results indicate that the overall temperature of the guiding shoe friction surface experiences a rapid increase during the initial running-in phase, followed by a progressively slower temperature increase over time. Temperature and stress concentration regions on the friction surface primarily localize at the corners of the shoe groove, and the distribution of temperature and stress shows a strong coupling. Furthermore, elevated traction speed and mechanical load exacerbate the thermo-elastic instability of the guiding shoe, consequently augmenting thermal stress on the friction surface. The increase in support load results in significant thermal shock on the lower area of the left side of the guiding shoe. The research provides a reference for exploring the fatigue failure and wear mechanisms of the guiding shoe while considering thermal effects.

Fatigue reliability analysis methodology based on fatigue life and failure mechanism for carburized gear

Gears are one of the important components in mechanical products, and their fatigue reliability determines the safety performance of mechanical products. In this paper, the fatigue characteristics of carburized gears under different torque and constant rotational speed conditions are investigated by using a gear contact fatigue testing machine, and combined with the dynamic maximum contact stress distribution on the subsurface of the meshing gears, the very-high cycle fatigue P-S-N curves of carburized gears under a stress ratio of −1 is established. Local stress concentration in the surface or subsurface of carburized gears causes grain dislocation movement under the combined influence of maximum contact and residual stresses, and then causes dislocation pileup and transcrystalline rupture after being hindered by grain boundaries, ultimately leading to pitting and fatigue failure of gears. Based on the dislocation energy method and combined with the fatigue failure mechanism of gears, a life prediction model of gears with good prediction results is established by considering the interaction of factors such as dynamic load, grain size, initial crack length, residual stress, slip band length and width. A fatigue reliability analysis method of gears is established based on the life state equation of gears considering the life prediction model. Further analyses of the influence of rotational speed, grain size, residual stress, slip band width, slip band length and initial crack size on the fatigue life reliability index of the gears resulted in the conclusion that the fatigue reliability of the gears not only decreases with the increase of the above-mentioned parameters, but also shows decreasing trend with the increase of time. This is of significance for evaluating the fatigue reliability of gears under very-high cycle fatigue conditions.

Vibration fatigue behavior and failure mechanism of Ni-based single-crystal film cooling hole structure under high temperature

Film cooling hole structures significantly influence vibration fatigue performance of Ni-based single crystal turbine blades. This study investigates the vibration fatigue behavior and failure mechanism of film cooling hole structure of Ni-based single crystal superalloy at high temperature by using the plate specimens with film cooling holes. The vibration fatigue cracks are all initiated at the edge of the film cooling hole on specimen surface, and the macroscopic crack path is a straight line path. At the microscopic scale, the crack path at 850 °C is a Zigzag path, but the crack path at 980 °C still shows a straight line path. The crack initiation of the specimen shows the oxidation crack nucleation in the stress concentration area under the coupling effect of high temperature and alternating stress. The macroscopic crack propagation direction at high temperature depends on the stress gradient direction of the resolved shear stress. At the microscopic scale, the crack propagation at 850 °C is the dislocation slip-climb mechanism, and the crack propagation at 980 °C more inclined to produce only the dislocation climb mechanism. The vibration fatigue cracks have the temperature dependence. The high temperature environment promotes the activation of slip system and the enhancement of dislocation mobility, the microscopic raft structure promotes the crack propagation along the γ phase with a large number of dislocations, the oxidation crack promotes the oxygen to enter the alloy matrix, which accelerates the Mode-I crack propagation.

Study on vibration fatigue of lifeguard in a metro bogie and methodology for damage estimation based on the measured acceleration

The lifeguard is more like a cantilever beam installed on the end of bogie frame, used to remove foreign body on the rail. Due to severe vibration condition, the lifeguard has been reported to be subjected to fatigue failure by railway operators. This paper thus studied on fatigue failure mechanisms of lifeguard through both the field test and numerical simulation. In the field test, the vibration acceleration and dynamic stress developed on the lifeguard were measured to identify main contributors to the fatigue failure. The test results showed that the structural resonance arising from the rail corrugation-induced high frequency impact serves as the main causal factor. To better understanding the failure mechanism, a numerical model considering the flexibility of lifeguard was established to determine the stress field of lifeguard based on the modal method, which was further used to estimate the residual fatigue lifetime for given loading conditions. The results showed that the obtained dynamic stress for given position on lifeguard is quite comparable with those obtained through the field test. Based on the obtained dynamic stress, the fatigue damage was further estimated and concluded that the fatigue lifetime of lifeguard is much less than the designed lifetime under the considered loading condition. The rail grinding and the structural improvement are thus suggested to mitigate the vibration fatigue of lifeguard.

The High-Cycle Tensile-Shear Fatigue Properties and Failure Mechanism of Resistance Spot-Welded Advanced High-Strength Steel with a Zn Coating.

Advanced high-strength steels (AHSSs) with Zn coatings are commonly joined by the resistance spot welding (RSW) technique. However, Zn coatings could possibly cause the formation of liquid metal embrittlement (LME) cracks during the RSW process. The role of a Zn coating in the tensile-shear fatigue properties of a welding joint has not been systematically explored. In this study, the fatigue properties of tensile-shear RSW joints for bare and Zn-coated advanced high-strength steel (AHSS) specimens were comparatively studied. In particular, more severe LME cracks were triggered by employing a tilted welding electrode because much more stress was caused in the joint. LME cracks had clearly occurred in the Zn-coated steel RSW joints, as observed via optical microscopy. On the contrary, no LME cracks could be found in the RSW joints prepared with the bare steel sheets. The fatigue test results showed that the tensile-shear fatigue properties remained nearly unchanged, regardless of whether bare or Zn-coated steel was used for the RSW joints. Furthermore, Zn mapping adjacent to the crack initiation source was obtained by an electron probe micro-analyzer (EPMA), and it showed no segregation of the Zn element. Thus, the failure of the RSW joints with the Zn coating had not initiated from the LME cracks. It was concluded that the fatigue cracks were initiated by the stress concentration in the notch position between the two bonded steel sheets.

Low cycle fatigue behavior and failure mechanism of 34CrNiMo6 steel used as connecting rod for diesel engine

Abstract In this paper, for the 34CrNiMo6 steel material used in diesel engine connecting rods, the low-cycle fatigue properties and failure mechanism were studied. The metallographic structure of 34CrNiMo6 has been investigated by using optical microscopes, scanning electron microscopes, and transmission electron microscopes. Tensile tests and low-cycle fatigue experiments were performed at different levels of strain amplitudes, and the microstructural changes were monitored. The examination indicates that the structure of 34CrNiMo6 steel consisted primarily of a ferrite base and small spherical and rod-shaped carbides, with a mean particle size measuring 2 μm. It had exceptional mechanical characteristics of high strength and moderate plasticity. The total strain amplitude (TSA) of 34CrNiMo6 steel affected the cycling behavior, which was stable at low TSA (0.2% ~ 0.3%). At high TSA (0.4% ~ 0.7%), a large number of dislocations were annihilated through the dynamic recovery process, showing a typical cyclic softening phenomenon. The low-cycle fatigue failure behavior was mainly a combined mode of quasi-cleavage fracture and cross-grain fracture.

Effects of electrochemical machining on high-cycle fatigue of Inconel 718 blades

Blades made from Inconel718 (IN718) are generally machined using electrochemical machining (ECM), and the high-cycle fatigue (HCF) of such blades significantly impacts the service life of aeroengines. In this study, modal analysis was performed to obtain the blade modal shape and stress distribution at first-order frequency, after which blades were machined at different current densities (9.5A/cm2, 18.2A/cm2, 34A/cm2, 46.7A/cm2, 61.2A/cm2, 70.1A/cm2) and then subjected to detailed surface-integrity analysis and fatigue tests. No surface defects (e.g., intergranular corrosion, recast layers) were observed, the microhardness was unchanged, and new residual stress was not found to be introduced to the machined surfaces. The machined surfaces were uneven and contained micro-pits, and high current density contributed to better surface quality. At a constant load of 520 MPa, the blade machined at 70.1A/cm2 had the best fatigue life of 1.4×106. The blades fractured because of micro-pits, and as the surface quality of the blades improved, so did their fatigue performance. Therefore, the fatigue failure mechanism characterized in this work provides a reference for the HCF behavior of blades machined by ECM.

Long-term performance of concrete pipes under fatigue traffic loads

In recent years, there has been a concerning increase in road collapses triggered by failures in urban drainage systems. Concrete pipes, commonly uesd in urban drainage pipelines, endure prolonged cyclic loading from traffic above. However, the mechanisms governing the long-term performance and fatigue damage remain unclear. Through conducting fatigue model box tests on concrete pipes, the effects of different fatigue loading cycles on the circumferential strain of concrete pipes were investigated. A fatigue life prediction equation for concrete pipes was proposed, and the crack propagation under various fatigue loading cycles was observed. Additionally, corresponding 3D FE models of concrete pipe-soil interaction with bell-and-spigot joints and gaskets were constructed. These models were used to explore the vertical displacements, circumferential bending moments, and circumferential stresses of the concrete pipes under different fatigue loading cycles, the damage and failure mechanisms of the concrete pipes under fatigue loading were revealed. The results indicate that the potential failure location of concrete pipes is within the inner crown of the bell under the fatigue traffic loads. The circumferential strains and crack propagation exhibiting a three-stage evolution pattern under fatigue loads. The proposed fatigue life prediction equation accurately predicts the remaining life of concrete pipes. Upon reaching 21.89 million loading cycles, the strain at the inner crown of the bell reaches 575.0 με, resulting in complete failure. Cracks on the inner crown of the bell extend inward and to the right from the middle of the joint, forming a channel for crack propagation. The vertical displacements at the crown and the circumferential bending moments of the bell and spigot exhibit rapid increases, stabilization, and subsequent declines with the increasing loading cycles. When concrete pipes undergo fatigue fracture, the maximum vertical displacement and circumferential bending moment at the bell are measured as 2.26 mm and 17.82 kN·m/m, respectively. Stress concentration at the bell and spigot during fatigue loading leads to crack propagation and convergence, causing redistribution of stress fields characterized by an initial increase followed by a decrease in the inner crown and invert of the bell.

Fatigue failure mechanism of high-speed train bearing steel after long-term service

The remaining useful life prediction of the bearings after long-term service is a crucial issue. Exploring the fatigue failure mechanism of bearing is helpful to grasp the dynamic evolution law during its whole period. In this paper, the tensile and fatigue property degradation law of bearings for high-speed train under different service mileages were explored. The results display that there is a downward trend for the tensile/fatigue strength and elongation of the bearing as prolonging its service mileage. The area proportion of dimples declines while that of cleavage plane increases in bearing steel after long-term service. The variations of secondary crack length and equivalent diameters of cleavage plane indicate that more cracks initiated in damaged bearing under cyclic loading. Based on the energy principle, the fatigue failure mechanism of bearings after long-term service was elaborated with the plastic deformation, crack initiation and growth resistance. The results would provide theoretical reference for the fatigue property degradation law of high-speed train bearings.

Research on ship-ice collision model and ship-bow fatigue failure Mechanism based on elastic-plastic ice constitutive relation

Collisions between sea ice and ships can damage the hull structure and pose a threat to crew safety in severe cases. The modelling of ice materials is crucial, but it is difficult to study ice-ship interactions. In this study, an ice constitutive model including the temperature factor was verified through experiments and numerical simulations of uniaxial and triaxial compression. Furthermore, the effects of salinity and porosity on the compressive strength of ice were studied using experiments and numerical simulations. The mechanical behaviour of sea ice was then simulated using the constitutive model mentioned above. A numerical model of collisions between polar ships and sea ice was established to investigate the ice-breaking processes of ships under different working conditions. The collision force and the level of structural damage were obtained. The influences of the initial pore size, hull speed, bow angle, and bow shape on the collision force and structural damage in the ship-ice collision process were analysed. Finally, fatigue damage to the bow structure at different ice thicknesses and speeds was calculated. The present results provide a reference for the structural design and optimisation of polar ships to a certain extent and improve the theory of ship-ice collisions.

Investigation on high temperature fatigue-oxidation behavior of Ni-based single crystal with film cooling holes considering arrangement effect

The fatigue-oxidation behavior of Ni-based single crystal with film cooling holes (FCHs) fabricated by femtosecond laser was investigated considering arrangement effect. Low cycle fatigue tests were conducted under 900 °C/713 MPa and 1000 °C/500 MPa. The experimental results show that fatigue lifetime reduced as the temperature increased at equal proportional stress. And, the specimens with square penetration pattern have an average fatigue life that is higher than the specimens with triangle penetration pattern at the same condition. Then, the crack propagation modes are characterized on the fracture path, and the fatigue failure mechanism is revealed by analyzing the fracture morphology. The microstructure evolution around the FCHs shows that the fatigue crack nucleation is caused by the coupling effect of fatigue and oxidation. According to the damage mechanism, a new fatigue-oxidation coupling damage model is proposed based on crystal plastic theory. The calculation results using crystal plasticity finite element method (CPFEM) considering coupling damage show that the maximum resolved shear stress (RSS) of the FCHs triangular arrangement is higher than that of quadrilateral arrangement at the same condition. Finally, fatigue life is predicted based on coupling damage accumulation, and the results show that the accuracy of life prediction is within 2 times data dispersion band.

Modeling thermo-mechanical fatigue for rolling die under continuous casting process

In the continuous casting process, the rolling die is exposed to non-steady stress conditions that can initiate thermo-mechanical fatigue damage. Understanding the rolling die failure mechanism is essential in metal-forming industries. Thermo-mechanical fatigue damage mechanism (crack growth) is governed by highly localized stresses in the crack tip region. This paper presents analytical models to determine thermo-mechanical fatigue failure mechanism based on the elastoplastic fracture mechanics and continuum damage mechanics. The model includes new proposed analytical equations for low-cyclic fatigue crack propagation. To verify the analytical models, experimental data and finite element simulation are considered. Results show good agreement with experimental data and finite element simulation.

Heterogeneity induced fracture characterization of concrete under fatigue loading using digital image correlation and acoustic emission techniques

Understanding the fatigue failure mechanisms in concrete is complex and remains an area of ongoing investigation. Material heterogeneity, along with the size effect, plays a significant role in specifying the crack propagation behaviour and fatigue life in case of repetitive loading conditions. In this study, the influence of material heterogeneity on the fatigue behaviour of concrete has been examined. Three different-size beam specimens with varying heterogeneity (aggregate sizes) have been considered to investigate various fracture characteristics under repetitive load conditions. Acoustic emission and digital image correlation techniques have been employed to analyse crack growth behaviour. The results revealed that stiffness degradation and crack propagation rates are faster for the specimens with smaller aggregate sizes compared to the larger aggregate size specimens of the same depth. Moreover, the fatigue life and effective crack length at failure are also higher in the case of larger aggregate sizes compared to smaller ones. Therefore, a heterogeneity-adjusted, analytical model of fatigue crack growth has been proposed. Further, the AE parameters have been utilized to characterize the tensile and shear crack dominance in different stages of fatigue crack propagation. The outcome of this study can be utilized to anticipate the crack propagation behaviour and residual fatigue life for any combination of specimen size and aggregate size.

Effect of TiN monolithic and Ti/TiN multilayer coating on the fatigue behavior of titanium alloy under tension-tension

This paper investigates the fatigue failure mechanism of mono- and multilayer coatings on the fatigue performance of TC11 titanium alloy under tension-tension. The morphology, phase composition, mechanical properties were measured by scanning electron microscope, X-ray diffractometer and nanoindentation. Electron back scatter diffraction was employed to investigated the failure mechanism. Fatigue limits obtained of uncoated TC11, TC11 with TiN coating, TiN/Ti multilayer (ML-6, ML-3, ML-1) and after 1 × 107 cycles are 855 MPa, 550 MPa, 525 MPa, 500 MPa and 400 MPa. Under fatigue loading, the hard-coating/TC11 substrate experiences fatigue failure through coating cracking hastens the substrate's fatigue failure. EBSD analysis results indicate that the main slip system of TC11 titanium alloy under tension-tension fatigue load is α phase (10-10)[-12-10]. After 1 × 107 cycles at fatigue limits, the average dislocation density on the surface of the TC11 with TiN coating is lower than that of TC11. Due to the surface defect induced by coating preparation and high crack propagation velocity, the hard coating significantly deteriorates fatigue property of TC11 by reducing fatigue crack initiation period. Therefore, instead of approaching from the perspective of coating structure design to increase the fatigue crack propagation cycles, it is more effective to reduce the surface roughness of the coating and enhance the fatigue crack initiation cycles.

Analysing the mechanism of fracture in drive pins used in magnetically controlled growth rods

The MAGnetic Expansion Control (MAGEC) spinal implant has transformed the treatment of early-onset scoliosis (i.e. abnormal curvature of the spine in children). Despite the innovative solution, the MAGEC device has encountered various performance issues. One component that has been frequently reported amongst the failure issues is the drive pin and the cause of these reoccurring fractures may be associated with multiple factors including over-loading, fatigue, and corrosion. This study aimed to examine the failure of eight broken drive pins from explanted MAGEC rods through fractography analysis, to better understand the factors leading to their fracture. The fracture surface of the drive pins was examined using Scanning Electron Microscopy (SEM). The clinical data were compared against observed failure modes. The fracture surfaces of four drive pins showed low cycle (high stress) or high cycle (low stress) fatigue failure mechanisms. The other four drive pins displayed environment assisted stress corrosion cracking. Almost all samples had evidence of corrosion after fracture with the amount of corrosion implying fracture occurred a relatively long time before explantation. Since multiple failure mechanisms of low cycle fatigue, high cycle fatigue or simultaneous effect of tension and corrosive environment have been observed, the fracture mechanisms illustrate the complexity of loading in these spinal growing rods. Evidence of corrosion after the failure recognises that the pins have snapped long before the device was explanted.

Fracture mechanism of Ti60 alloy at high temperature in very high cycle fatigue regime and fatigue life prediction

AbstractThis study aimed to investigate the failure mechanism of Ti60 titanium alloy in the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) at 500°C. Ti60 specimens were characterized before and after the 500°C VHCF test, and the fracture surfaces were observed. The results show that there are three different fatigue failure mechanisms at 500°C: (i) equiaxed primary α phase (αp) cleavage, forming small unsmooth facets and rough fracture area (RA), and fusion of non‐adjacent facets to grow into the main crack. (ii) αp grains gather into large grain with triple junction, and large grain slip to form large fusion facet. (iii) Oxide shedding and then cracks form. A dynamic recurrent neural network model is used to predict the fatigue life of Ti60 alloy, 91% of the overall predictions were within the scatter band of 3.0, and 100% were within the scatter band of 5.0.

Fatigue behavior and damage mechanism of steel plate-UHPC composite bridge deck subjected to negative bending moment

In order to investigate the fatigue behavior and failure mechanism of steel plate-UHPC composite bridge deck under hogging moment, a total of four full-scale specimens with two class of reinforcement ratio (Three specimens with reinforcement ratio of 1.58 %, 1.69 %, 1.86 %, respectively, which called longitudinal specimen. One specimen with reinforcement ratio of 0.89 %, which called transverse specimen.) were designed and tested under fatigue loading. Test results reveal that when the fatigue loading ratio was 0.25 with maximum load of 0.8 times of the static cracking load, taking the crack width of 0.10 mm as the fatigue failure criterion, the fatigue life of longitudinal specimen over 16 million cycles. However, the fatigue life of transverse specimen was only 9.08 million cycles. The longitudinal reinforcement restricts the propagation of fatigue cracks along the depth of the UHPC slab, and tensile fracture of the steel fibers occurred in the region between the top layer of longitudinal reinforcement and the UHPC surface. The fatigue damage mechanism resulting from fatigue degradation of the UHPC layer in the tension zone is identified. In addition, The fatigue design of the steel plate-UHPC composite bridge deck should be controlled by the durability rather than the strength. The established tensile S-N curve with 0.05 mm critical UHPC crack width could be used evaluate the fatigue cracking resistance of composite bridge deck.

Investigation on fatigue crack propagation failure mechanism of hydraulic lifting pipe in deep‐ocean natural gas hydrate exploitation

AbstractIn deep‐ocean natural gas hydrate exploitation operation, the fatigue failure mechanism has attracted more and more attention from scholars, but it has not been effectively disclosed. Therefore, in this work, a multifield coupling and multiple‐nonlinear vibration model of lifting pipe is established, which can accurately determine the alternating stress of deep‐ocean lifting pipe. Second, according to Forman theory, the calculation method of crack propagation length and depth on the surface of a deep‐water riser is established, which is verified by the comparison between the experimental and theoretical model calculation results. The results demonstrate that, first, the effect of residual stress in the welded joint of deep‐ocean lifting pipe should be considered in the later parameter influence analysis. Second, the fatigue growth life of deep‐water pipe with small outflow velocity is mainly determined by tensile stress, and that is determined by both tensile stress and bending stress with large outflow velocity. Third, more attention should be paid to the vibration of the lower pipe on‐site to reduce its vibration frequency and vibration stress amplitude, which can effectively reduce the surface crack propagation state of the deep‐ocean pipe and improve the service life of the pipe. Fourth, properly adjusting the tension coefficient of the tensioner during field operation can effectively improve the safety of the pipe, and the optimal tension coefficient is related to the configuration of the deep‐ocean pipe system, which can be analyzed and determined by the model.