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Steel structures, such as bridges, must be continuously maintained. Due to increasing traffic loads, design and execution shortcomings, many steel bridges are subject to various types of damage, such as cracks. The bridges must be maintained by crack removal and re-welding the cracks. During this work, the bridge is closed for traffic in order to suppress the crack flank movement during welding. As a result, traffic loads on other routes are higher, which increases further damage on detour routes and subsequently additional welding work and costs on these structures. Therefore, the aim is to provide a method that allows welding work on steel structures under running traffic, respectively under cyclic loads. First, measurements at a representative steel bridge were conducted to derive gap opening parameters of amplitude and frequency for welding tests under cyclic loads. In a test setup for reproducible and comparable welding tests, specimen were welded under cyclic loads. Deep grinding of the root layer allowed defect-free welding within the range of 0.1 mm amplitude at a frequency of 2 Hz loadings. For such welds, the weld quality and the fatigue strength was comparable to the standard requirements. • Structural health monitoring was used to measure the gap opening of a typical crack. • Welding under service conditions is under certain aspects possible. • Optically defect-free welds were welded up to a limit of 0.1 mm amplitude. • Unavoidable smaller hot cracks have to remove by deep grinding of the root layer. • Weld seams can be realized with regard to weld quality and fatigue strength. [ABSTRACT FROM AUTHOR]

• Pioneering research in the domain of rock mechanics, offering a multidimensional examination of artificial rock fatigue behavior under diverse cyclic loading conditions. • A comprehensive investigation, encompassing three groups of cylindrical concrete specimens, to uncover the influence of material strength on fatigue response. • Introduction of the Stress-life (S-N) model as a novel approach to describe rock fatigue behavior, culminating in a robust equation that enhances our grasp of this complex phenomenon. • Distinctive insights into the evolution of fracture and geometries under cyclic loading, showcasing how fractures are distributed extensively throughout the specimen volume. • Recognition of the porosity variable as a valuable descriptor for characterizing the rock damage process provides a novel perspective on fatigue-induced damage in rocks. In numerous engineering projects, such as tunnel construction, underground gas storage in caverns, and the impact of earthquakes, rock materials experience cyclic loading. However, the response of rock materials to cyclic loading, which may vary in terms of waveform, frequency, and amplitude, is not uniform. Consequently, comprehending the mechanical attributes and fatigue behavior of rocks holds significant importance in engineering designs. This study focuses on subjecting a collection of cylindrical concrete specimens, categorized into three groups with distinct mechanical properties, to both monotonic and cyclic loading within a laboratory environment. Three groups of cylindrical concrete samples with different mixing designs are prepared to evaluate the effect of the mechanical strength of the samples on the fatigue response of the rock. In such a way that: The first group (G1) with Uniaxial Compressive Strength (UCS): 19 MPa, the second group (G2) with (UCS): 49 MPa, and the third group (G3) with (UCS): 71 MPa. In addition, the discrete element method is utilized to simulate uniaxial cyclic compression tests under various loading conditions, such as monotonic and cyclic loading. The resulting fracture propagation patterns and geometries are then analyzed. Numerical and experimental results show that the cyclic uniaxial compressive strength, due to the presence of damage and fatigue phenomena, has decreased relative to the monotonic tests. Also the cyclic elastic modulus values (E c) have decreased by 53 %, 25 %, and 11 % relative to the monotonic elastic modulus (E m) for the three groups of G1, G2, and G3, respectively. The Stress-life (S-N) model is used to express the fatigue behavior of rock, and the final equation for the S-N model is expressed. [ABSTRACT FROM AUTHOR]

• Completed graded upper stress limit interval fatigue (GUIF) tests and graded lower stress limit interval fatigue (GLIF) tests, comparing the effects of different time intervals and stress amplitudes on the fatigue failure characteristics of mudstone. • The fatigue life of mudstone shows an increasing trend with increasing time intervals. • The study found that the residual strain cycles before and after the time intervals exhibited opposite patterns in the GUIF tests compared to the GLIF tests. • In discontinuous graded fatigue tests, the impact of the fatigue stage on the damage to mudstone was smaller than the impact of the interval stage. During the operation of an underground salt cavern gas storage, Fatigue failure occurs in the surrounding rock of gas storage reservoirs under non-continuous gas injection and extraction loading. Due to the special layered salt rock structure in China, the mudstone interlayer is the weak part of the gas storage. It is necessary to study the effect of stress magnitude and interval time on the fatigue mechanical properties of mudstone. Graded upper stress limit interval fatigue (GUIF) test and graded lower stress limit interval fatigue (GLIF) test were carried out on mudstone respectively. And different interval times were set to investigate the effect of interval time on the mechanical properties of mudstone. With the increase in the interval time, the fatigue life and peak strain of the mudstone increased. Under the same interval time, the lower-limit interval test result showed a significantly higher fatigue life than the upper-limit interval test result. The stress–strain curve exhibited three stages: scattered–dense–scattered. During the unloading phase, the modulus of elasticity increased with increasing stress levels, indicating that the internal structure of the mudstone is extremely sensitive to the stress. In the (GUIF) test, the average residual strain increased with the increase in the interval time, and the residual strain during the cycle after the time interval under different grades was lower than the residual strain before the time interval; the results of the (GLIF) test showed the opposite trend. In the (GUIF) test, the average creep strain increased with increasing interval time under the same stress level, and the average creep strain was greater than the average residual strain, and the creep stage had a greater effect on mudstone damage than the fatigue stage. The post-fatigue creep strain was significantly greater than the pre-fatigue creep strain. The research results can be useful in ensuring the stable operation of gas storage in salt caverns. [ABSTRACT FROM AUTHOR]

• The carbon nanotubes (CNTs) reinforced closed-cell Al-Si composite foams (C-ASCFs) with CNTs content of 0.50 wt% have fatigue strength of 0.697 σ s (7.40 MPa), showing a superior improvement of the fatigue properties. • The appropriate incorporation of CNTs can change the fatigue failure mode, reduce the crack growth rate, and delay the fracture, hence raising the fatigue life. • The microstructure optimization of C-ASCFs influenced by CNT and its content was deeply investigated to interpret the influences on the fatigue properties of C-ASCFs. • The load transfer effect of CNTs in composite foams was firstly revealed, the contribution of which exhibits the largest of 2.07 MPa in 0.50 wt% C-ASCFs accounting for 22.5 % of its yield strength. As the requirement of compressive fatigue loading on the mechanical properties of aluminium foams increase rapidly, the limited fatigue performance of them significantly restricts their engineering applications. In this study, the compression-compression fatigue properties of carbon nanotubes (CNTs) reinforced closed-cell Al-Si composite foams (C-ASCFs) were investigated. The fatigue strength of C-ASCFs with 0.50 wt% CNTs increased by 54% than that of Al-Si foams, where the CNTs contributed to decrease the crack expansion rate, transfer the fatigue load and hence change the fatigue failure mode, causing a combination of plastic and brittle deformation in them. Meanwhile, the appropriate incorporation of CNTs decreased pore nucleation threshold, optimized the pore morphology, and promoted the formation and refinement of eutectic Si. Such inhibited the probability of fatigue cracks initiation, resulting in the enhancement of fatigue life. This work provides theoretical and practical basis of design strategy of Al-Si composite foams and broadens their application prospect. [ABSTRACT FROM AUTHOR]

• A rail grinding car prevents rail damage and derailment of the vehicle. • Hardness deficiency of the shaft can be improved through low-temperature tempering. • Rough surface finishing lead to fatigue failure of the rotating shaft. • The non-metallic inclusions can reduce the fatigue strength of the material. Rail grinders belonging to special vehicles have fewer accidents than general railroad vehicles and parts, and the causes are diverse. Therefore, there is a lack of basic data for inspection methods and preventative measures necessary for accident prevention, and the collection and analysis of accident cases are also necessary. In this paper, a failure analysis of the recently derailed rail grinding car's rotating shaft was conducted. Various analyses, including fractography, chemical analysis, metallography and hardness measurement, were performed on the failed shaft. In the fracture surface of the shaft, ratchet marks and fatigue striations indicative of fatigue failure were observed. Consequently, it was confirmed that the failure of the shaft was attributed to fatigue, with the primary cause being identified as the cracks found on the fillet area surface. Chemical analysis of the observed inclusions in the sample revealed manganese (Mn) at 6.16 wt% and sulfur (S) at 1.35 wt%. These are attributed to non-metallic MnS inclusions, which are presumed to have adversely affected the fatigue strength of the material. Additionally, hardness deficiency due to heat treatment defects on the shaft surface was identified. The surface hardness measured approximately HV400, suggesting that it is desirable to achieve a surface hardness of HV600 or HRC55 or higher during high-frequency heat treatment. Lastly, the finish state of the fillet area surface was not smooth. Given that the fillet area is a region where stress concentration occurs, the presence of such machining traces raises the possibility of progressing into fatigue cracks. Finite element analysis revealed that the von-Mises stress was less than the yield strength of the material, and a safety factor based on the yield strength was calculated to be 3.5. The results confirmed that fatigue cracks in the fillet area were caused by the hardness deficiency due to the poor heat treatment, the rough surface finish, and the presence of non-metallic inclusions. [ABSTRACT FROM AUTHOR]

Mechanical joining techniques are fundamental in the industrial landscape, with welded joints standing out as a primary method across diverse manufacturing sectors. In this work, we present a novel contribution to fatigue life assessment of welds through 3D-Scanning of weld seam. The methodology is applied on welded specimens tested in alternate bending fatigue, showing that for real case applications, statistical approach to surface irregularities of the joint plays a keyrole. In particular by means of surface scanning, some statistical geometric parameters are obtained to characterize the weld seam. Then by experimental fatigue testing a relation between geometrical measured parameters, experimental cycles to failure and crack nucleation sites is obtained. Then FEM models generated basing on 3d scanning are used for FEM simulations aiming at validating the stress concentration related to surface geometric irregularities and fatigue life. A dedicated software, called 3D-life, was developed to process surface scans and the results of the numerical simulation and life estimations were used to predict the crack nucleation sites. • The weld bead aesthetical parameters have a key role in fatigue life assessment. • It is possible to assess the fatigue limit from a 3D scan of the weld bead. • Predicting the crack initiation location in weld beads can be achieved by analyzing their local curvature metrics. [ABSTRACT FROM AUTHOR]

• Effect of the rock strength on the fatigue performance of rock bolt systems. • Effect of the cyclic load frequency and amplitude on the damage of rock bolt systems. • Acoustic Emission for the damage evolution in rock bolt systems under cyclic loading. • Cumulative AE energy slope method for macro crack initiation assessment. Rock bolt support is one of the key methods to maintain the stability of underground space. The durability of the rock bolt can be weakened by cyclic loading, resulting in premature failure of the underground structures. A comprehensive understanding of the performance of the bolting system under cyclic loading is essential to assess the safety of the bolting system and underground structures. In this context, this study investigated the mechanical performance of rock bolts installed in simulated soft and medium hard rock and subjected to cyclic loading. The Acoustic Emission (AE) technique was used to monitor internal damage to the bolt system under different loading conditions. A cumulative AE energy slope method has been proposed to determine the onset of the macro crack formation stage. The rock bolt demonstrated an extended fatigue life in soft rock, but its condition worsened when implanted in medium hard rock. The cyclic loading resulted in a slight improvement in the load bearing capacity of the soft rock bolt system and a significant deterioration in the medium hard rock bolt counterpart. The main fatigue failure modes of the rock bolt systems were splitting and shear failure of the surrounding rock, and debonding of the interface. Increasing the amplitude of the cyclic loading reduced the macro crack initiation cycle for both rock bolt systems, whereas increasing the frequency had different effects. The damage variable increased with frequency and amplitude for both rock bolt systems. The toughness of the soft rock bolt degraded during cyclic loading, while the high frequency cyclic loading did not modify the toughness of the medium hard rock bolt. [ABSTRACT FROM AUTHOR]

• Axial fatigue and wear properties of GBIH-nitrided Ti-6Al-4V alloy were examined. • Surface asperities led crack initiations and decrease of the fatigue strength. • Compressive residual stress increased the fatigue strength of GBIH-nitrided alloy. • Nitrogen compound layer led crack initiations and decrease of the fatigue strength. • Forming of hard and smooth nitrided layer improved the wear resistance of the alloy. The effects of surface characteristics on the axial fatigue properties and wear resistance of the GBIH-nitrided titanium alloy were investigated to improve the fatigue strength and wear resistance of Ti-6Al-4V alloy rapidly nitrided by induction-heating in a nitrogen atmosphere with blowing nitrogen gas (GBIH-nitriding). The fatigue strength of the GBIH-nitrided Ti-6Al-4V alloy was lower than that of the mirror-polished specimen owing to the formation of a brittle nitrogen compound layer and grain coarsening. Fatigue tests using specimens prepared by combining GBIH-nitriding and particle collision treatments revealed that the formation of nitrogen diffusion layers at the outermost surface and the generation of compressive residual stress without forming surface asperities increased the fatigue strength of the GBIH-nitrided Ti-6Al-4V alloy. Moreover, the formation of a nitrided layer and suppression of surface asperities effectively improved the wear resistance of the Ti-6Al-4V alloy. Therefore, formation of a nitrogen diffusion layer and the introduction of compressive residual stress without grain coarsening, a compound layer, and surface asperities increased the fatigue strength and wear resistance of the GBIH-nitrided alloy. [ABSTRACT FROM AUTHOR]

• The fatigue fracture life of the same batch of flexible shaft is not the same. • By analyzing the fracture flexible shaft, it is found that there is a corrosion pit at the fracture location. • After the specimen is corroded, the fatigue life is shortened by 30%. • The fatigue life of the flexible shaft is prolonged after anti-corrosion treatment. In order to solve the problem of non-expectancy life fracture of the flexible shaft of oil drilling, the force of the flexible shaft is analyzed and calculated, and the static load strength of the flexible shaft and the fatigue strength of torque and bending moment all meet the safety factor requirements, and the fracture flexible shaft is further analyzed for the fracture shaft of metal materials, and it is found that it is fatigue fracture, and there is corrosion at the fracture, in order to determine the effect of corrosion on fatigue fracture, fatigue tests were carried out on corroded specimens and uncorroded specimens, and it is found that the life of the corroded specimens is reduced by 30% compared with the non-corroded specimens. According to the fatigue test conclusion, the deformation zone of the flexible shaft was anti-corrosion treatment, and the service life was found to be improved after on-site trial, which effectively solved the problem of non-expected life fracture of the flexible shaft. [ABSTRACT FROM AUTHOR]

• The corrosion fatigue performances of EA4T axle steel fabricated via ultrasonic surface rolling process was investigated. • The enhancement mechanism of the strengthened specimens of the electrochemical behavior and corrosion fatigue resistance was clarified. • The dominant factor attributed to the superior corrosion fatigue property of the EA4T railway axle subjected to the USRP was revealed. Surface treatment has been validated to improve the fatigue crack resistance of engineering components, while the coupling effect of corrosive atmosphere and external loading is relatively less reported with detailed experimental studies. In this study, gradient structure (GS) axle EA4T alloy steel specimens were prefabricated by using the ultrasonic surface rolling process (USRP), and their corrosion fatigue resistances were investigated. First, the optimal USRP parameters were determined via orthogonal tests. After the USRP treatment, the microstructure, surface topography, surface roughness, residual stress, and electrochemical corrosion behavior were measured to characterize the surface under various conditions. The electrochemical tests results indicated that the compressive residual stress (CRS) is an important factor in improving the corrosion resistance of axle steel. Rotating bending fatigue tests in both air atmosphere and corrosion liquid showed that the fatigue and corrosion fatigue performances could be significantly improved with the strengthened layer obtained via the USRP. Factor separation analyses substantiated that the remarkable enhancement of fatigue and corrosion fatigue strengths can be mainly attributed to the CRS introduced by the surface strengthening treatment. Simultaneously, the GS layer and hardened layer exhibited a synergistic effect. [ABSTRACT FROM AUTHOR]

• Although there are many studies on fretting wear at present, they are limited to phenomena and mechanisms. Their calculation is very complex and not suitable for engineering design. To solve this engineering problem, this article firstly proposes a calculation method for the fretting contact fatigue strength. This method has never been published. There is absolutely no plagiarism in this paper. • The calculation method for the fretting contact fatigue strength has never been published in any international literature. This is the first submission in your journal. • Previously published papers focused on strength failure, but not on micro motion. This time it's about the fretting contact fatigue strength calculation. Fretting wear and gear contact fatigue belong to adhesive wear. They have similar causes, failure mechanisms, and failure appearance. Drawing inspiration from the gear contact fatigue strength theory, this article creatively proposes a calculation method for the fretting contact fatigue strength. The safety factor of fretting fatigue is calculated to be 0.34. Due to the singularity of the contact point at the edge of the oil groove, the mesh size near this point needs to be sufficiently fine to 0.025 mm. The contact pressure at the edge contact point of the oil groove is calculated by finite element method (FEM) to be 1034 MPa, which is 6.8 times the Lame theoretical value of 152 MPa. The stress concentration is very severe. The fretting contact fatigue strength at the edge of the oil groove is severely insufficient. The friction torque of the interference connection is calculated to be 3.1 times the overload torque of the motor. The fundamental cause of fretting wear is excessive interference and unreasonable design. [ABSTRACT FROM AUTHOR]

• Predicting fatigue strength of details with weld imperfections by FEM. • Limit function for failure location at the cruciform joint. • Calculation of stress increase due to external weld imperfections. The paper presents an investigation into the fatigue resistance of load-carrying cruciform joints that exhibit weld imperfections. To accomplish this, a finite-element model of the joint is validated by a comparison to experimental investigations. The model includes both a global and a submodel that integrates the effective notch stress concept into its design. This enables the simulation of various types of weld imperfections, such as lack of penetration, lack of root fusion, undercut, excessive convexity, incorrect weld toe, excessive asymmetry of fillet welds and linear misalignment, to assess their impact on the fatigue strength of the cruciform joint. The analysis reveals that these imperfections lead to an increase in stress at the notches of the cruciform joint, which can be characterized as a function of the joint's geometrical properties. Global geometry influences on the fatigue strength of different cruciform join geometries can be regarded independently from the influence of the weld imperfections that is given by stress concentration factors. The normalised stress concentration factor enables a comparison between imperfection influences and shows, that the notch-softer design with full penetration welding at the cruciform joint is in a relative relation more strongly influenced by imperfections than the design with fillet welds. Also, the undercut represents the imperfection with the strongest effect in a relative relation within the sizes considered. Being able to evaluate the fatigue strength values of steel components with weld imperfections eliminates the need for costly repairs and new fabrications, which would otherwise result in a loss of resources and economic efficiency. [ABSTRACT FROM AUTHOR]

• The 310S stainless steel weld joint was subjected to SGP treatment, forming a strengthened layer at the weld joint. • The treated samples exhibited significant grain refinement and substantial residual stress. • The processed samples also demonstrated excellent high-temperature fatigue resistance. • The in-situ high-temperature fatigue test was carried out, and the fatigue failure mechanism of the material was analyzed. This study employed the strengthened grinding process (SGP) for surface enhancement treatment of 310S stainless steel weld joints. The surface characteristics and high-temperature fatigue performance were investigated. Initially, the effects of different SGP durations on the surface morphology, microhardness, and residual stress of the weld joints were studied. Subsequently, the high-temperature fatigue life of samples processed through SGP was examined, and the potential mechanisms underlying the impact of SGP on the high-temperature fatigue behaviour of 310S stainless steel weld joints were discussed. The maximum hardness of SGP-6M samples was 337 HV, while the average hardness of UP samples was 163 HV, and the maximum hardness of SGP-6M samples increased by 90.18 % compared to UP samples. The surface residual stress changed from a residual tensile stress of 205.24 MPa to a residual compressive stress of −864.76 MPa. At 25 °C, 500 °C, 600 °C, and 700 °C, the fatigue life increased by 36.9 %, 31.7 %, 25.9 %, and 18.6 %, respectively. This research demonstrates that SGP is an effective method for increasing the high-temperature fatigue life of turbine blades. [ABSTRACT FROM AUTHOR]

• The effect of a U-shaped stress relief groove on the fretting fatigue was investigated. • The fretting fatigue crack initiation position can be shifted between the contact and groove zone when the characteristic parameters of SRG are varied. • With optimized design of the SRG, the crack initiation life can be extended by more than 3.5 times compared with that of the non-grooved specimen. • The dimensionless difference of the maximum damage parameter δ ¯ SWT can serve as a convenient index to evaluate the effect of the SRG on the crack initiation life of fretting fatigue. A U-shaped stress relief groove was developed to enhance fretting fatigue strength. The effects of the groove on crack initiation location and life were evaluated using the finite element method and the critical plane method. The results demonstrated that by varying the geometry parameters of the groove, the crack initiation location was altered between the contact zone and the groove. When the damage in both the contact zone and the groove was comparable, the life of fretting crack initiation was increased by up to 3.5 times compared with that of the non-grooved specimen. These findings were expected to propose a potential strategy for enhancing the material's resistance to fretting fatigue by designing a groove near the contact zone and to provide insights into the development of components with improved fatigue resistance. [ABSTRACT FROM AUTHOR]

• A high Si low Mo ductile cast iron was tested for thermal fatigue under oxidation conditions at 600 °C. • The relation between microstructure and the degradation mechanisms was established. • The degenerated graphite nodules with ferrite particles were found to be more susceptible to oxidation. • Pearlite degradation is characterized by cracking of cementite lamellae and favorable oxidation of ferrite phase. • Thermal fatigue resistance can be improved by reducing, prevent degeneration and ensuring uniform distribution of graphite nodules. Thermal fatigue tests were conducted on a high Si low Mo ductile cast iron (DCI) under oxidation conditions at 600 °C. The study aimed to understand the evolution of surface degradation, focusing on complex composed graphite nodules, pearlite islets, and their impact on crack initiation and growth in relation to oxidation processes, etc. Degenerated graphite nodules, that include ferrite particles, and areas of increased graphite nodule density, along with pearlite islets, were examined for their oxidation behavior. At lower thermal cycles numbers cracks primarily initiated of at the graphite-matrix interface and grew faster in the case of successively arranged graphite nodules and their higher local number density. Graphite degradation involved debonding between graphite and matrix, followed by complex oxidation processes. Degenerated nodules exhibited higher oxidation rates due to the presence of ferrite which acts as oxidation pathways. Areas with increased graphite density and larger sizes facilitated accelerated oxidation via crack formation. Additionally, pearlite degradation started with cracked cementite lamellae, followed by oxidation. Strategies to enhance thermal fatigue resistance included reducing graphite nodule diameter, ensuring their uniform distribution, preventing of formation of degenerated nodules and eliminating porosity. These findings improve understanding of thermal fatigue behavior in DCI that has proven to be even more complex than previously thought. The findings will guide the development of advanced materials for demanding applications. [ABSTRACT FROM AUTHOR]

• The fatigue damage and life of a large-span tower-line system is investigated; • The combined distribution effect of wind direction and speed is fully considered; • A multivariate fatigue damage analysis method for members is proposed; • The fatigue damage mechanism of member in structural different parts are revealed. To accurately evaluate the fatigue life of transmission line structures under wind loads, this study proposes a multivariate member fatigue damage analysis method for investigating the wind-induced fatigue performance of a large-span transmission tower-line with full consideration of the combined distribution effects of wind direction and speed in the actual wind field. With the background of in-service transmission line project, a refined finite element model of the large-span transmission tower-line system is established, and the wind load is simulated and generated based on the linear filtering method. According to the meteorological statistics of the project site in the past 50 years, the wind-induced fatigue sensitivity analysis of the tower-line system is performed through considering the combined distribution probability of wind direction and speed. The wind-induced fatigue damage of the tower-line system is calculated based on the rain-fall counting method and Miner's fatigue cumulative damage theory, and its wind-induced fatigue life is further analyzed. The analysis results show that the sensitive members of the tower-line system are mainly distributed in the 2nd, 6th, 8th and 9th segments by combining the effects of wind attack angle and wind speed. The fatigue damage of the sensitive members decreases gradually with the increase of wind attack angle (0° wind attack angle damage is the largest), and the effect of wind speed on the vertical main member is larger than that of the crossarm upper chord member. Moreover, the fatigue damage at the end of the member is significantly larger than that in the center, and even at small wind speeds, the member's end can produce a stress amplitude larger than the fatigue cut-off limit. The fatigue life of crossarm upper chord members is 72.89 years, and that of the vertical main member is 77.60 years. In particular, the vertical main member should be employed as the control member for the structural fatigue life when considering extreme wind loads. [ABSTRACT FROM AUTHOR]

• Compressive fatigue tests were performed on Polyurethane foams of three densities in load control. • The degradation of the materials was characterized by a relatively sudden increase in strain. • Stress–strain curves were recorded at given intervals to estimate the damage onset cycles values. • S-N curves were generated based on the proposed failure criterion. • SEM investigations showed that the damage onset was caused by the occurrence of shear bands. • The shear bands evolved into macroscopically observable crushed regions with cycle progression. This paper investigates the compression-compression fatigue behaviour of polyurethane rigid (PUR) foams of three relative densities (RDs): 0.0854, 0.1239 and 0.2564 respectively. Preliminary tensile and compression tests were performed in order to obtain the stress–strain characteristics of the investigated materials and to determine the yield stresses in compression, required for the establishment of the relative stress levels used in the fatigue tests. It was observed that the failure mechanism during fatigue consisted in the collapse of a region of the specimens, which was characterized by a sudden increase in strain. In consequence, stress–strain cycles were recorded at various cycle intervals in order to narrow the degradation cycle interval. The resulting compression-compression fatigue curves show a similar behaviour between the RDs of 0.0854 and 0.1239 (with the latter exhibiting the best fatigue strength of the three investigated RDs), that can be described by a single trend line for each, while the foam at 0.2564 RD showed the lowest fatigue strength, the curve being characterized by two regions. [ABSTRACT FROM AUTHOR]

• Fracture of the crankshaft belongs to high-cycle bending fatigue failure. • Root of the fatigue fracture was the inadequate thickness of quenching layer at the fillets. • The bending moment could be promoted by the increasing thickness of the hardening layer in a certain range. • Thickness of the medium frequency induction hardening layer was recommended about 3.5 mm based on overall considerations. A failure investigation was performed into the fractured 42CrMo4 crankshaft used for wide-body mining dump truck in this paper. Fracture morphology, chemical composition, microstructure and mechanical properties of the crankshaft material were studied to investigate the premature failure mechanism. All the crankshaft broke at the 4th or 6th necks and a high-cycle bending fatigue type in this case could be identified by the observation of beach marks and fatigue striations in the propagation area according to fractography results. The fatigue source is underneath the hardening layer of R fillet and the root cause could be identified as the designed inadequate thickness of quenching layer at the fillets obtained through medium frequency induction quenching (MFIQ), which could not provide adequate fatigue strength upon cyclic loadings for long term. Fatigue validation test indicated that the bending moment increased with the increasing thickness of the quenching layer, and the appropriate thickness was recommended about 3.5 mm based on overall consideration. [ABSTRACT FROM AUTHOR]

• Correlations established between process, microstructure, properties, and very high cycle fatigue of WAAM'd AWS ER100S-G. • The endurance limit in USF samples of ER100S-G was found to be 390 MPa at 109 cycles. • Fractography showed the characteristic fish eye morphology in the VHCF region. • No statistical differences regardless of the number of cycles to failure in USF and Conventional fatigue tests. This paper presents a comprehensive study on the very high cycle fatigue (VHCF) characterization of a wire arc additive manufactured (WAAM) AWS ER100S-G steel. The demand for high-performance materials with superior fatigue properties has grown exponentially. However, the VHCF behavior of large-format WAAM'd structures remains relatively unexplored. In this study, a series of VHCF tests were conducted under fully reversed cyclic loading conditions to investigate the extended fatigue life (performance) of the WAAM ER100S-G steel. The VHCF properties, relative to conventional fatigue employing a servohydraulic testing system, of the WAAM ER100S-G steel were evaluated by analyzing the stress-life (S-N) curves, fatigue crack initiation, and propagation behavior, in a statistical framework, and the fracture surfaces. The results revealed the controlling mechanisms of VHCF failure of the WAAM ER100S-G steel and the fatigue response of the material beyond the conventional fatigue limit of 107 cycles. The findings provide valuable insights into the influence of WAAM-induced defects/microstructure on the extended fatigue performance of WAAM ER100S-G steel, which can aid in optimizing fatigue and durability design guidelines for additive manufacturing applications in high-cycle and very high-cycle fatigue domains. [ABSTRACT FROM AUTHOR]

• Improvement of nonlinear fatigue cumulative models considering load sequence effect. • Probabilistic model to take into account the uncertainties of load and material character. • Incorporation of load exceedance variation of fatigue load spectrum. • Verification on 2297-T87 aluminum–lithium alloy under spectrum loading. A probabilistic fatigue cumulative damage model that can be applied to the fatigue life prediction of aluminum alloy under spectrum loading is proposed in this paper. The model is constructed by a novel nonlinear cumulative damage model, the P – S – N curve, and the probabilistic load–exceedance curve. It introduces the randomness of the loading process and fatigue resistance of the material to the deterministic model. In this model, it is derived that the cumulative damage under fleet spectrum loading exhibits an approximate lognormal distribution, and a method to calculate the distribution parameters is provided. Finally, the validity of the proposed probabilistic model is verified through fatigue tests on 2297-T87 aluminum–lithium alloy specimens under random loading, demonstrating its capability to capture the probabilistic nature of the fatigue behavior of aluminum alloy effectively. [ABSTRACT FROM AUTHOR]

• Impact of FSW input parameters such as rotational speed, welding speed, shoulder radius, and tool geometry are investigated. • FSW output parameters include welding joint quality, including strength, toughness, hardness, fractography, and fatigue behavior. • Fatigue life in the base material and joints of three pins is obtained by the finite element analysis. • Numerical simulation results with the experimental results of fatigue life for the BM are in acceptable agreement. • Fatigue life of the threaded pin is better represented by FEA than that of two simple and truncated triangular pyramid pins. The friction stir welding (FSW) process is a solid phase type applied in this study to connect AA7075-T651 aluminum alloy plates. This study investigates the impact of welding input quantities such as tool rotational speed, welding speed, shoulder radius, and tool geometry on welding joint quality, including strength, toughness, hardness, fractography, and fatigue behavior. Also, in this study, the fatigue life in the base material (BM) and joints obtained from the simple, threaded, and truncated triangular pyramid pins as an FSW effective input parameter was obtained by the finite element analysis (FEA). The experimental outcomes represented that the mechanical attributes of the threaded pin are higher than that of the simple and truncated triangular pyramid pins with the same input parameters. Also, the outcomes of the numerical simulation with the experimental outcomes of fatigue life for the BM were in acceptable agreement, and the error value of the validation result for σ max = 0.5 σ y for the stress ratio R = - 1 was equal to 0.4%. In addition, the FEA results indicated that the fatigue strength of FSW joints in the stir zone for the threaded, simple, and truncated triangular pyramid pins in the fatigue life of 10 7 cycles was 64%, 63%, and 43% of the BM, respectively. [ABSTRACT FROM AUTHOR]

• Effects of material's nonuniformity on fatigue properties are uniformly described by initial damage. • Relationships between the initial damage dispersion and scatter of sampling tests have been explored. • Reliability of two crankshafts is evaluated based on actual dispersions of initial damage. Premature failure due to fatigue would occasionally happen even in a well-designed crankshaft. The microstructural nonuniformity (including micro-defects) plays an essential role in the premature failure due to fatigue, which can lead to the scatter of strength and fatigue life properties. In this paper, the statistical distribution of initial damage corresponding to microstructural nonuniformity has been introduced to uniformly characterize scattering behaviors of tensile strength, fatigue life and impact energy in sampling tests of crankshafts. The goal of this study is to investigate quantitative relationships between the dispersion of initial damage and scattering behaviors of the above sampling tests, so that dispersion properties of a crankshaft can be determined only by relatively simple experiments. By impact sampling tests and several single-throw crankshaft fatigue tests, probability density functions of initial damage have been determined for two crankshafts provided by different manufacturers. It is found that the fatigue reliability of a crankshaft depends on its actual dispersion properties. For a crankshaft with large dispersion of initial damage, the safety factor in the fatigue strength design should be sufficiently large to prevent its premature failure due to fatigue, rather than the one directly recommended in the design manual. [ABSTRACT FROM AUTHOR]

• Ultrafine-grained (UFGed) microstructure of pure titanium (Ti). • UFGed microstructure was achieved by multi-directional forging (MDFing). • Fatigue behavior was evaluated using thin wires and foils. • MDFed materials exhibited higher fatigue strength than conventional Ti. • Wires exhibited higher fatigue strengths than foils due to the strong texture. Thin wires and foils comprising of ultrafine-grained pure titanium (Ti) were made by combined processes of multi-directional forging (MDFing) and either drawing or rolling processes. The MDFed wires and foils exhibited higher tensile strength than the conventional pure Ti wires and plates due to the ultrafine-grained structure. The axial fatigue tests were conducted to investigate their fatigue behavior. The fatigue strengths of conventional pure Ti wires and plates were nearly the same, while the MDFed Ti wires and foils had higher strengths. When the fatigue strengths of MDFed Ti wires and foils were compared, the wires had higher fatigue strength than the foils. EBSD analyses revealed that strong textures were formed in both wires and foils. The basal planes were parallel to the specimen surfaces in wires, while they were inclined against the surface in foils. The texture with the inclined basal planes resulted in the lower crack initiation resistance, resulting in the lower fatigue strength of foils than wires of the MDFed Ti. [ABSTRACT FROM AUTHOR]

• Thermal-accumulated fatigue resistance in service is closely related to microstructure stability. • Lamellar fracture and cementite spheroidization lead to relatively lower pearlitic wheel resistance. • Bainitic structure stability plays a dominant role in wheel service sustainability. Novel train rails/wheels with low-carbon bainitic microstructure have drawn much attention recently owing to their good match of strength and toughness in mechanical properties from retained austenite and microstructure multi-orientation, as a supplement to the existing pearlitic wheels. However, the heat-affected zone is found on the pearlitic and bainitic wheel tread after 100,000 km of test running, while several severe failure cracks were found in both pearlite and bainite wheel treads, particularly in the pearlitic one. Their service advantage in accumulated damage resistance caused by alternating thermal/force loads in service is controversial and their excellent mechanical properties sometimes correspond not to expected fatigue resistance. Thus, the thermal-accumulated microstructure stability of low-carbon bainitic treated by 560 °C tempering, with similar initial strength and hardness levels compared with pearlitic wheel steel was investigated. The comparison of the two results shows that the bainitic structure composed of bainite ferrite and cementite shows relatively stronger crack resistance and better hardness stability (∼355 HV). Grain boundary strengthening and solid solution strengthening in bainite ferrite still play a dominant role in its stability. While pearlitic structure demonstrates a stronger tendency to fatigue cracking and the hardness decreases from ∼ 355.2 HV to ∼ 336.0 HV due to spheroidizing evolution and lamellar fracture, accompanied by element segregation and two-phase lattice mismatching. These comparisons mean that the thermal-accumulated service performance of wheel steel is not solely determined by original higher mechanical properties, but is close to the contribution of microstructure stability for service sustainability. [ABSTRACT FROM AUTHOR]

• A prediction method of S - N curve without fatigue tests is proposed. • The method is based on the small crack growth model; da dN = C ∗ σ σ w - 1 m ∗ a n ∗ . • The constants are C * = 10–4, m * = 2.0 and n * = 1 regardless of materials. • The predicted S - N curves are in good agreement with the experimental data. A prediction method of S - N curve without fatigue tests is proposed based on the small crack growth model expressed as d a d N = C ∗ σ σ w - 1 m ∗ a n ∗ , where a : crack size in terms of area , σ : applied stress amplitude, σ w : fatigue limit which decreases cycle by cycle with crack growth. The constants C *, m * and n * were identified to be C * = 10–4, m * = 2.0 and n * = 1 for various steels, cast irons and alloys. S - N curves for various materials were predicted by the proposed model and were compared with experimental data. The predicted S - N curves are in good agreement with the experimental results for conservative predictions. [ABSTRACT FROM AUTHOR]

• In this paper, the research status of rail vehicle brake disc is summarized from five aspects: mode, vibration, temperature field, stress field, wear and fatigue crack. It is found that most of the research focuses on internal excitation such as brake disc material, structure and its own braking condition, and the brake disc is jointly affected by internal and external excitation in the braking process. Therefore, the research can be carried out from the aspects of wheel-rail excitation, heat transfer between brake disc and axle. As the core parts of the braking system of rail vehicle, the braking performance of the brake disc will directly affect the safety of vehicle operation, and then lead to vehicle safety accidents. The braking performance of the brake disc can be evaluated from five aspects: modal characteristics, vibration characteristics, heat-mechanical coupling characteristics, wear characteristics and fatigue resistance. In order to better reveal the current research status and the factors affecting brake characteristics of the brake disc, firstly, the influence factors of brake disc modal and vibration were summarized. Based on modal coupling theory, the research status of vibration modal and noise modal was summarized. The influence of brake disc structure and vehicle operating environment on the vibration characteristics of brake disc was described. Secondly, the influence of brake disc material, structure and braking conditions on the coupling characteristics of brake disc was summarized. The effects of ferrous metal materials and new composite materials on the wear characteristics of brake disc were described from the aspects of numerical simulation and experimental study, and the advantages and disadvantages of ferrous metal materials and new composite materials were compared. Finally, based on the current research status of the brake disc, it is expected that the research of the brake disc should be combined with the line tracking test to systematically determine the relationship between the service conditions of the brake disc and the wheel-rail coupling excitation such as wheel polygon and rail wave wear. The relationship between operating conditions and brake disc fatigue damage is quantified to achieve accurate prediction of brake disc fatigue damage under different operating conditions, and the mechanism of brake disc fatigue crack continued to extend to deep crack and finally fracture is revealed, thus prolonging the service life of the brake disc. [ABSTRACT FROM AUTHOR]

• A comprehensive review of fatigue failure of centrifugal compressor impellers. • Studying various industrial case studies as well as academic research. • Investigating the effect of different factors in fatigue failure and service life of centrifugal compressor impellers. • Investigating interaction of multiple failure causes and how they contribute to failure of centrifugal compressor impellers. • Investigating various approaches for studying fatigue behavior in centrifugal compressor impellers. • Proposing design strategies for preventing failures and enhancing service life of centrifugal compressor impellers. Fatigue failure can be considered as the main failure mode of impellers in various kinds of turbomachinery, especially centrifugal compressors. Studying and understanding the fatigue failure mechanism is a milestone in the structural design and optimization of centrifugal compressor impellers. Having a sound knowledge of fatigue failure mechanism, and how it starts, develops and leads to fracture, equips turbomachinery engineers and researchers with new reliable design criteria, enabling them to predict and prevent future potential failures. This paper presents a comprehensive review of fatigue failure of centrifugal compressor impellers considering numerous case studies and research papers. Different factors contributing to fatigue failure of centrifugal compressor impellers are first classified as internal and external factors and then investigated separately by reviewing extensive failure case reports and research papers. High cycle fatigue (HFC) is the most prevalent failure mode in centrifugal impellers which occurs as a result of high-frequency, low-amplitude vibration due to impeller-diffuser interaction or upstream flow distortions. Low cycle fatigue (LCF), having the second rank, happens mainly because of high mechanical stress and/or primary resonant vibration which are due to improper design or successive loading, unbalanced operation, installation error, or variation in the operating condition of the compressor. On the other hand, corrosive medium, high temperature, and microstructural and manufacturing defects degrade material properties and fatigue resistance, facilitating and precipitating fatigue failure. The current study aims to bring up an encyclopedic, yet detailed review of fatigue failure of centrifugal compressor impellers suitable for both academic and industrial research. [ABSTRACT FROM AUTHOR]

• Fatigue failure mechanism was elucidated for multi-stage centrifugal pump shaft. • Specific technical measures to prevent pump shaft failure were proposed. • Fatigue resistance design is performed for pump shaft structure and coupling. • Feasibility of the new pump shaft system has been verified by experiment. In the operation of multistage centrifugal pump, the pump shaft of 304 stainless steel is subjected to a variety of alternating loads. It is one of the parts prone to failure. The fracture microscopic observation, chemical composition analysis and mechanical property measurement of the fractured pump shaft are carried out. Through the fracture analysis, it is found that the pump shaft failure is caused by fatigue mechanism with characteristic of multi-source crack initiation, and there are many cavities and inclusions at the fracture. From the numerical analysis, it is found that there is significant stress concentration at the fracture, which exceeds the fatigue limit of the material and eventually leads to the fatigue fracture. Besides, the appropriate fillet radius and elastic coupling are designed for the pump shaft, which can effectively reduce the stress concentration and improve the service life of the pump shaft. Finally, the fatigue life of the improved pump shaft was experimentally verified. [ABSTRACT FROM AUTHOR]

• This paper presents the failure analysis of a topologically optimised landing gear nose wheel fork of a light aircraft that was produced in Ti6Al4V(ELI) through selective laser melting (SLM). The study was motivated by the intention of the South African producer of the Advanced High-Performance Reconnaissance Light Aircraft (AHRLAC) to consider replacing conventional manufacturing of some structural components with additive manufacturing (AM). However, the defects typically associated with AM, such as inherent surface roughness and porosity, still complicate the certification of AM parts due to their detrimental effects on fatigue performance. An experimentally validated numerical simulation, fractographic analysis, and microscopic investigation were carried out on a scaled-down Ti6Al4V(ELI) component to devise preventative actions to avoid failure of the full-scale fork. The mass saving, strength and fatigue limitations of the actual nose wheel fork of the AHRLAC are discussed. This study also outlines an effective failure analysis and data collection method necessary to qualify SLM of Ti6Al4V(ELI) to produce other airworthy mission-critical structural aircraft components. This paper presents the failure analysis of a topologically optimised landing gear nose wheel fork of a light aircraft that was produced in Ti6Al4V (ELI) through selective laser melting (SLM). The study was motivated by the intention of the South African producer of the Advanced High-Performance Reconnaissance Light Aircraft (AHRLAC) to consider replacing conventional manufacturing of some structural components with additive manufacturing (AM). However, the defects typically associated with AM, such as inherent surface roughness and porosity, still complicate the certification of AM parts due to their detrimental effects on fatigue performance. An experimentally validated numerical simulation, fractographic analysis and microscopic investigation were carried out on a scaled-down Ti6Al4V(ELI) component to devise preventative actions to avoid failure of the full-scale fork. The mass saving, strength and fatigue limitations of the actual nose wheel fork of the AHRLAC are discussed. This study also outlines an effective failure analysis and data collection method necessary to qualify SLM of Ti6Al4V(ELI) to produce other airworthy mission-critical structural aircraft components. [ABSTRACT FROM AUTHOR]

• The UPM and PI iterative methods can accurately reconstruct the residual stress field induced by rolling processing. • The extended finite element method and the weight function method are applied to solve the stress intensity factor. • The necessity of deep rolling treatment for axles is verified. • The influence of interference and initial crack position on the remaining life of axle is explored. • The damage tolerance analysis of the axle was carried out. Deep rolling surface strengthening is an effective way to introduce compressive residual stress (CRS) along the railway axle, which can improve the fatigue resistance of the material. The CRS field was rebuilt adopting the proportional-integral (PI) iteration method and the unit pressure method (UPM) to study the fatigue cracking behavior of deep-rolled EA4T railway axles. The remaining life prediction model and the stress intensity factor (SIF) solution method were then validated using simulations and testing with small-sized specimens. The remaining life of the EA4T railway axle was then calculated by applying a realistic vertical load spectrum. The results showed that CRS prevented crack propagation, enhanced the critical propagation size of railway axle cracks, and prolonged the remaining life of the axle. Additionally, the remaining life of the axle may not support the following maintenance period if a crack with an extendable size emerges at the unloading groove of the railway axle. This work provides a theoretical basis for the optimization of the non-destructive testing (NDT) interval of deep-rolled EA4T railway axles. [ABSTRACT FROM AUTHOR]

• Local stress peaks in shape-complex forging die usually exceed yield point for hundredths of a second. • Calculated stress and temperature distributions in the hot forging die. • Fatigue resistance reduction influenced by numbers of re-profiling of die cavity. • Pragmatic knowledge for forging industry about fatigue dies failure. Re-profiling of hot forging dies is the most common method of die repairing in industry. Due to the surface to core hardness gradient caused by the limited hardenability of the die material, the surface layer after re-profiling possesses lower hardness than the first one, causing decrease of the tool lifetime in means of wear, but also can lead into total failure of the die due to other damaging mechanisms. Performed failure analysis of a hot forging die manufactured from 56NiCrMoV7 which included microstructure analysis, hardness profile, tensile and fatigue tests showed a 31 % decrease of fatigue properties when surface and core material is compared. Based on the experimental results it was calculated, that an optimal preventive action to increase the service life is to perform the re-heat treatment after every 10th re-profiling. The 16th re-profiling is critical; beyond this point, there is a significant risk of total die failure. [ABSTRACT FROM AUTHOR]

• AM metallic components: fatigue strength assessment and lifetime estimation. • To such an aim an analytical procedure is proposed. • The procedure takes into account the presence of intrinsic defects. • The Kitagawa diagram and the criterion of Carpinteri et al. are exploited. • The novel procedure is applied to AM AlSi10Mg specimens. In the present paper, a novel analytical procedure for both fatigue strength assessment and lifetime estimation of Additively Manufactured (AM) metallic components is proposed. More precisely, the procedure is able to take into account the intrinsic defects (generally characterising AM metals), which are responsible for a detrimental effect on fatigue limits. Such a procedure is based on the joint application of: (i) the Kitagawa-Takahashi diagram, for the fatigue limits calculation and (ii) the criterion of Carpinteri et al., for the fatigue strength assessment and lifetime estimation. In particular, such a diagram is formulated by alternatively exploiting the area parameter model and the modified El-Haddad model. The novel procedure is applied to some experimental data available in the literature related to AM AlSi10Mg specimens, subjected to cyclic axial and torsional loading. The theoretical results are compared with the experimental data, highlighting which of the above two formulations provides more accurate results. [ABSTRACT FROM AUTHOR]

• Fatigue of additively manufactured lattices for medical implants is critical. • Accelerating fatigue testing would be time-saving and advantageous. • Increasing fatigue test frequency has a minimal effect on the measured strength. Additively manufactured (AM) porous titanium lattices, with their ability to match the mechanical properties of bone and avoid stress shielding, are a popular candidate material for orthopaedic implants. Such implants are now emerging as treatments for conditions like osteoarthritis and fixation of bone fractures. Fatigue tests are critical due to the cyclic loading environment and must be carried out at an accelerated loading rate to simulate many years of use. Tests are typically performed with servohydraulic instruments, which limits the cyclic compression to relatively low frequencies (15 Hz). Fatigue testing at a higher frequency would accelerate research, however, may introduce phenomena such as heat accumulation and strain rate effects. In this study the fatigue behaviour of a pure titanium stochastic lattice was determined at two test frequencies, 15 Hz and 110 Hz. Testing was conducted using an electromechanical dynamic system. The fatigue strengths at 106 cycles were 5.607 ± 0.106 MPa and 5.764 ± 0.214 MPa at 15 Hz and 110 Hz respectively. A hypothesis t -test at a 95% confidence level stated that there was significant evidence that the population means were not the same, demonstrating evidence of a difference in fatigue strength with testing frequency. However, we can conclude that the 2.8% increase in fatigue strength due to test frequency effects is inconsequential relative to the time saved (16 h per test) and typical batch-to-batch variability in fatigue strength of approximately 12%. The results of this study should help accelerate research into the fatigue properties of AM porous lattices. [ABSTRACT FROM AUTHOR]

The fatigue limits of shafts and shaft-hub connections are subject to a probability distribution. This distribution can be described by the mean value and the scatter of the fatigue limit. The mean fatigue limit can be determined with very few samples, whereas the scatter cannot be determined precisely. In order to develop a reliable design of shafts and shaft-hub connections, it is certainly necessary to know the scatter of the fatigue limit. Parameters that may influence the scatter are investigated on the basis of evaluated test series from literature, for shafts with failure at the free surface and shaft-hub connections. The analysis focuses on the type of load, the highly stressed surface or the shaft-hub connection type. A calculation method for determining the fatigue limit for a given survival probability will be presented. • Weighted scatter method to determine the scatter of fatigue limit for test blocks • Shafts have a lower scatter of fatigue limit than shaft-hub connections. • Type of shaft-hub connection has influence on the scatter of fatigue limit. • Method for calculating fatigue limit values for given survival probabilities [ABSTRACT FROM AUTHOR]

• Welding defects play an important role in crack initiation and evolution. • The fracture surface is characterized by multi-source fatigue initiation. • The high-frequency load response is caused by wheel polygons and rail corrugation. • The low-frequency load response is caused by track plate irregularity. • High frequency and high amplitude vibration promote unexpected fatigue failure. A wire bracket is a cantilever structure connected to the axle box of a high-speed train. Its force is complex and it is prone to vibration fatigue failure. Combined with fracture analysis and on-track tests, the local cracking of the wire bracket is studied and the mechanism and cause of structural failure are revealed. The results show that a fatigue crack in the wire bracket initiates from the incomplete penetration defect of the bolt hole weld of the cantilever side mounting seat and propagates to the upper cover plate and vertical plate. The joint action of wheel polygon and rail corrugation results in higher vibration energy of the wire bracket in 400–800 Hz. The welding defects reduce the fatigue strength of the weld, and the high-frequency and high-amplitude vibration caused by wheel-rail excitation makes the stress concentration near the weld, which brings the possibility of fatigue crack initiation and propagation of the wire bracket during the on-track operation. [ABSTRACT FROM AUTHOR]

• Under low cycle fatigue condition, hydrogen embrittlement enhances the small cracks initiation and growth rate and leads to multiple origins and faceted appearance of the fracture surface in the initiation area. • The fatigue strength ratio of A286 alloy in the over aged condition is less than 0.2. • Segregation of phosphorus at the grain boundaries and over aging condition of A286 alloy increase susceptibility to hydrogen embrittlement and decrease fatigue resistance, therefore more restrictions on P content (<0.001 wt%) and under aged heat treatment condition are recommended for Tie-bolt manufacturing. • Non-uniform grain size and banding of coarse MC carbide particles lead to the evolution of fatigue damage. Failure in a turbo-expander Tie-Bolt (stud) made of superalloy A-286 was investigated. The evaluation of the chemical composition and tensile properties confirmed compliance with the relevant standard. However, the coarsening of γ ′ due to over aging condition, the non-uniform grain size and banded coarse MC carbide particles, the segregation of phosphorus to grain boundaries and the growth of carbide particles at the grain boundaries led to a decrease in fatigue strength of the alloy. Fractography studies showed that fracture occurred due to primary axial and secondary bending loads. Multiple ratchets and tire tracks on the fracture surface were consistent with low-cycle fatigue (LCF) failure mechanism. Fatigue striations spacing and micro hardness profile of the threads were used to calculate the stress amplitude and estimate the fatigue strength of Tie-bolt. Neuber's rule was used to estimate the local stress and strain in the thread root. The calculation results showed that the failure occurred due to the application of cyclic loads at a stress level lower than fatigue strength of the stud. A large amount of sulfur detected at the multiple cracks initiation areas by EDS analysis, indicated the presence of H2S in the environment, which has caused cathodic hydrogen charge and reduced the steel ductility and accelerated fatigue crack nucleation and growth. [ABSTRACT FROM AUTHOR]

• Random crack generation is identified by image processing & numerical modelling. • Dependent crack ratio quantifies the severity of interaction among matrix cracks. • Scatter source of matrix crack evolution among multiple samples is explored. • A strength-based probabilistic model is built to predict random crack evolution. The present work aims at understanding the stochastic matrix crack evolution in CFRP cross-ply laminates under tension–tension fatigue loading. An experimental campaign was carried out on twenty-three specimens at different stress levels, while two optical techniques were used for the in-situ monitoring of the accumulation of transverse matrix cracks. The results showed a significant scatter in crack evolution among specimens. This stochastic behaviour was further investigated using image analysis and numerical modelling. It was found that transverse matrix cracks can be classified into the independent and dependent cracks based on a critical crack spacing. Furthermore, the severity of interaction among cracks was quantified by introducing a dependent crack ratio. Finally, a strength-based probabilistic model was proposed to describe the scattering regime of the crack evolution. The agreement between model and test results indicates that local strength variations of 90 plies are the dominant scattering source governing the initial fatigue resistance to cracking and determining the accumulation of transverse matrix cracks among specimens. These results may provide a new insight into the stochastic nature of matrix cracking in composite laminates and aid in the design of fatigue resistance properties. [ABSTRACT FROM AUTHOR]

• This study investigated the effects of high-density pulsed electric current (HDPEC) on fatigue behaviours of non-prestrained and prestrained aluminium alloys (A6061-T6). • Fatigue life of the specimen to which the HDPEC was applied increased significantly. • Decreased slip bands caused by the fatigue load leads to delay fatigue crack initiation. • Effect of local melting and thermal compressive stress, induced by Joule heating, caused a decrease in the FCG rates leading to delaying fatigue crack propagation. This study quantitatively analysed the effect of an electric current on improving the fatigue life of the aluminium alloy A6061-T6. The effect of a high-density pulsed electric current (HDPEC) was investigated for non-prestrained and prestrained aluminium alloys because they are frequently exposed to plastic deformation. The results showed that the HDPEC contributed to increasing the fatigue life of both materials with and without prestrain, and those without prestrain increased significantly with the HDPEC effect. Local melting sites were observed at the fatigue crack tip on the fracture surface of the non-prestrained and prestrained cases treated with HDPEC. Fatigue crack growth tests confirmed the improved fatigue life of the HDPEC effect. The results pave the way toward enhancing the resistance of fatigue crack growth in welded joints. [ABSTRACT FROM AUTHOR]

The manufacturing industry increasingly demands mechanical components, which must undergo different loads. Each industry has its own requirements and regulations, where the common demand is that the loads are repetitive according with the components functions. It is then well known that it is necessary to employ the fatigue assessment to evaluate if the component would not fail over its expected working life. In recent years, there has been an increasing interest in additive manufacturing due to it can be an alternative to manufacture designs more organics and enhanced shapes. However, the main weakness with this option is that the obtained components can fail under operational condition with repeated loads. Therefore, these components would not be used as a final product, so up to now this manufacturing process is not suitable for a large-scale production. It is also important to mention that any manufacturing process needs the fatigue prediction to estimate durability considering different sources of dispersion of properties such as the material and manufacturing process. The purpose of this investigation is to proposes an S-N life curve for PLA considering different printers and filament colours to include the scatter in the estimation. This S-N line curve can be used to understand the mechanism of fatigue failure, the structure of the failure was analysed. This curve is based on 5 regions of amplitude depending on the load levels. However, it was not possible to perform it as a percentage of ultimate resistance since it is presented a dispersion in quasi-static loads. • To propose an entirely novel S-N curve for PLA 3D-printed elements. • This S-N curve involves the effects from the damage accumulation process. • Fatigue assessment can be performed with PLA 3D-printed elements. • The is not a fatigue limit in PLA 3D-printed elements. • It might be possible to manufacture PLA 3D-printed elements for High Cycle Fatigue. [ABSTRACT FROM AUTHOR]

• Additive manufacture is a potential technology for advanced railway components. • Internal defect is a critical issue to assess the fatigue resistance. • Damage tolerance is urgent for the additively manufacture metal components. Additive manufacturing (AM) is being increasingly applied in aerospace, healthcare, automotive, and energy fields. Despite good design flexibility, short lead times, and high material utilization, the application of AM by the railway industry is still on the way to engineering, particularly when compared with those of the aerospace and automotive industries. In addition, the role of various AM components in maintenance, optimizing design and production is not fully understood. To this purpose, the advantages and challenges in the utilization of AM technologies are well summarized, and the fatigue assessment aspects of AM components have been emphasized. Potential design methods to tackle the challenges including the well-recognized structural integrity, and future prospects are discussed in details. The findings are not only beneficial to the development of AM for railway engineering, but also for enabling the lightweight design of metallic components, and improving the performance evaluation and safety inspection strategies. [ABSTRACT FROM AUTHOR]

• Analyze the effect of stress ratios (R = −1, 0.1, 0.5, and 0.7) on fatigue life of DMR 249A grade steel joints. • The S-N curve was constructed and derived fatigue properties correlated with mechanical properties and microstructural characteristics. • Identified safe unsafe region fabrication of ship hull structure through Goodman and Soderberg diagram. In this investigation, the influence of stress ratio on high cycle fatigue (HCF) behavior of GMAW butt joints made of micro alloyed HSLA steel is studied. The fatigue test was performed for 50–90 % yield strength with different stress ratios (R = 0.1, 0.5, 0.7, and −1). The evaluated fatigue strength of the GMAW joint is relative to 91 %, 89 %, 86 %, and 84 % of the parent metal fatigue strength, and 62.2 %, 57.4 %, 50.7 %, and 47.5 % are equal to the transverse tensile strength of the GMAW joints for the different stress ratio. From the experimentation, if the stress ratio increases from −1 to 0.7 the fatigue strength of the welded get decreased. Because the crack tip experienced deformation accelerated by higher stress ratio, which directly impacted on number of cycles to fracture. Although, the operating unsafe and safe regions are established through goodman – Soderberg diagrams with the effect of stress ratio, which clearly indicates that the R increases the area of safe region get decreased. [ABSTRACT FROM AUTHOR]

• Ti-5Al-7.5V alloy shows attractive tensile and high cycle fatigue strengths. • Crack initiation occurred at facets matching basal planes with high Schmid factor and occasionally occurred in hard grains badly oriented for < a > type slips. • α p grain pair bounded by (0001) or near (0001) twist grain boundary was a kind of high cycle fatigue sensitive microstructure configuration. • Intense slip bands were absence in faceted grain and fatigued α p grains. • The role of the silicide on fatigue crack initiation still needs further detailed studies. Fatigue crack initiation mechanism at high cycle regime in a bimodal Ti-5Al-7.5V alloy are investigated by fracture observations, focused-ion-beam cross-section and electron back-scattered diffraction characterizations. The aged Ti-5Al-7.5V exhibits superior tensile and fatigue properties, alongside a wide range of fatigue life when tested at the stress levels of ∼ 700–800 MPa. Fatigue failure was dominated by surface and subsurface crack initiation at facets matching basal planes. These faceted primary α (α p) grains generally have a medium or high Schmid factor (SF) for basal < a > slip. Moreover, a basal faceting process also occurred in the "hard" grains, in which the c-axis of the HCP-α grains was approximately parallel to the loading axis so that the < a > type slips were thought to be suppressed. The observed internal microcracks were formed along the grain boundaries located in clusters of α p grains, especially along (0001) twist boundaries. Furthermore, transmission electron microscope observations evidenced the absence of intense slip bands within faceted grain and fatigued α p grains, which indicates that the facet growth should not along the pre-existing slip bands resulting from high cycle fatigue loadings. The pre-existing structural defects including dislocation networks and subgrain boundaries within α p grains are relatively stable configurations under fatigue loadings. The observed fine (∼500 nm in diameter) silicides were widely dispersed, whether the silicide can act as the crack nucleation site still needs further more detailed studies and this remains an open question. [ABSTRACT FROM AUTHOR]

• Carburizing improve the fatigue performance of notched specimens significantly. • The macro-plasticity has little effect on the fatigue performance. • Carburizing reduce the notch sensitivity of notched specimens. • The fatigue sources of the notched specimens are on the root surface of the notch. • During fatigue, carburized specimens retain a portion of stable retained austenite. Since stress concentration is easily formed at the notch, improving the fatigue performance of notched parts is critical. The carburizing process is widely used to manufacture notched parts. In this research, the effects of carburizing process and notch stress concentration on fatigue performance were analyzed by bending fatigue tests. In addition, the microstructure and hardness evolution processes of the carburized notched 18CrNiMo7-6 specimens were observed quasi-in situ. The results showed that macro-plasticity has little effect on the bending fatigue performance of notched samples and that the improvement in fatigue performance is primarily attributable to the high hardness and residual compressive stress introduced by carburizing. The fatigue notch sensitivity is therefore reduced after carburizing. Compared to the uncarburized specimens, the fatigue limit of the carburized specimens is increased by up to 128%. With the increase of the effective hardening layer depth, the fatigue limit increases first and then decreases. Moreover, the brittle phase transformation product (twinning martensite) of metastable retained austenite is easy to produce stress concentration. Conversely, the 'film-like' retained austenite with an extremely high stability can effectively avoid the phase transformation products. [ABSTRACT FROM AUTHOR]

• Roughness measurement and high-cycle fatigue test were performed to investigate the effect of turning parameters on the quality and strength of aluminum products. • The difference in the effects of turning parameters on surface roughness and fatigue behavior of different aluminum series (2xxx and 7xxx) was investigated experimentally. • Two-stage artificial neural network model was presented to predict the fatigue life of turned aluminum parts with higher accuracy than the usual ANN model. Various classification of aluminum alloys is one of the most common applied materials in transportation industries due to the specific mechanical and material properties. Body of vehicles, including cars, ships, and airplanes, are constantly exposed to different cyclic loads that lead to surface damage and finally, fatigue failure occurs by crack growth. Therefore, the quality of the machined surface has a direct effect on the fatigue life of the products. In this regard, the most important source of surface roughness is the choice of machining parameters. To understand it, turning operations were performed on 2xxx and 7xxx series aluminum alloys considering different values of process parameters. For any series of aluminums, 189 high-cycle fatigue testing specimens were prepared, and experiments were performed by axial tension–compression fatigue test machine in 7 levels of stress (all tests were repeated three times and the mean failure cycles were reported as the fatigue life). Next, an Artificial Neural Network (ANN) based on the Back Propagation (BP) error algorithm was developed to predict fatigue life of Al alloys which are machined with different conditions. To this end, the parameters considered as input variables to the neural network structure include the Yield Strength (YS) and Ultimate Tensile Strength (UTS) to identify the aluminum series, as well as the process parameters such as cutting depth (d), rotational speed (R), and feed speed (V). In addition, the applied cyclic stress (S) to specimen was considered as input. Furthermore, surface roughness (Z) and number of cycles to failure (N) were considered as ANN output. The comparison of the obtained results from ANN predicting with the experimental values indicates that this approach was tuned finely. Eventually, the presented model can be a suitable alternative to perform fatigue tests with high costs and time-consuming.‌‌ Also, the most effective machining parameter on the surface roughness and fatigue limit was reported. [ABSTRACT FROM AUTHOR]

• AW-6016-T4 aluminum sheets are screw-bonded with cross-laminated birch veneer plates. • The adhesive layer mainly contributes to the static strength and to the fatigue performance of the joints. • The screws and the thickness of the veneer plate mainly determine the energy absorption of the joints. • Debonding of the aluminum sheet from the veneer plate is identified as critical failure mechanism. • Optimizing the bonding conditions can improve the mechanical performance of the joints. Integrating wood-based lightweight components into advanced multi-material car bodies requires capable and reliable technologies for joining or bonding of dissimilar materials. Therefore, the present experimental study investigates hybrid lap joints of 1.5 mm-thick sheets of EN AW-6016-T4 aluminum alloy and 9 mm- or 13 mm-thick plates of cross-laminated 1 mm-thick birch veneers. Two self-cutting screws and single-component polyurethane-based adhesive were used for each joint. The mechanical performance and the fracture behavior were tested under both quasi-static and cyclic shear-tensile loadings. At each load condition fracture of the joint occurred, but neither fracture of the aluminum alloy sheet nor fracture of the veneer plate were observed. Debonding of the aluminum alloy sheet from the birch veneer plate was identified as critical failure mechanism. The adhesive provided the main contribution to both the static strength and the fatigue performance of the joints. However, the energy absorption of the joint was mainly determined by the pull-out resistance of the screws, which was dependent on the thickness of the veneer plate. To optimize the strength-to-weight ratio of the joint and to exploit the load-bearing potential of the materials, the focus should be placed on the improvement of the bonding conditions or on the adaptation of the sheet/plate thicknesses. [ABSTRACT FROM AUTHOR]

• The compositions of and the tensile properties of the three 439 stainless steels are similar. But the fatigue strength at room temperature is quite different. Their crack propagation resistance has negative correlation with fatigue strength. • The fracture surface of high stressed samples with low fatigue life is close to that of tensile fracture. The fatigue strength of materials can be quantitatively predicted by the area of cleavage zone. • The weakening of ferrite grain boundary is an important reason for the decrease of fatigue strength after the further increase of temperature. As one of the important steel, 439 stainless steel has been widely used in automobile, construction and other fields, but the studies of its high cycle fatigue properties are not enough. In this paper, the tensile and high cycle fatigue properties of three 439 stainless steels coming from different suppliers were compared. The tensile and high cycle fatigue at room temperature, 150 °C, 350 °C and 550 °C were evaluated. The results show that the tensile properties of the studied steels are very close to each other, but their fatigue properties are different, and the fatigue strength is inversely related to the crack resistance. With the increase of temperature, carbide precipitation and solute atom diffusion affect the linear trend of fatigue strength decline of ferritic stainless steel. The weakening of ferrite grain boundary is an important reason for the decline of fatigue strength in high temperature. Based on the cleavage surface in the fatigue crack source, the fatigue strength can be predicted quantitatively. [ABSTRACT FROM AUTHOR]

• The tubing components composed of tubular form-fit joints are fabricated by elastomeric swaging. • The platform for rotating-bending fatigue tests is established to simulate the high-frequency vibration of aircraft tubing components. • The failure position of tubular form-fit joint causing the fatigue fracture is explored by numerical simulation. • The failure mechanism of bending-torsion multiaxial fatigue crack initiation and propagation is revealed by SEM observation. Tubular form-fit joints play a key role of connecting and sealing in the pipeline system of aircraft. However, they experience the complex fatigue behavior in operating conditions of compound excitation with internal fluid pulse pressure and external structural high-frequency vibration. To investigate the above fatigue behavior, the tubing component composed of tubular form-fit joints is fabricated by elastomeric swaging firstly; then the rotating-bending experimental platform for the tubing component is built to simulate the operating conditions in the above actual service period, and the rotating-bending fatigue (RBF) tests of tubing components under different deflections are carried out, so that the relationship between the fatigue strength and life is obtained; then, the bending-torsion multiaxial mechanical behavior of tubing component is analyzed when it is filled with constant internal pressure, bent at a deflection and rotated at a high speed in the RBF test. It can be found that the area near the sharp edge of sleeve groove is the most prone to crack initiation. Furthermore, the mechanism causing the fatigue fracture of tubing component is explored at the certain position of the joined tube by means of numerical simulation. Eventually, with the aid of scanning electron microscope, the mechanism of bending-torsion multiaxial fatigue crack initiation and propagation is revealed by fracture morphology observation and analysis. It can be found that the fatigue crack source on the outer wall of the joined tube is various, and the crack propagation direction is from the outer wall to the inner wall along the radial direction. [ABSTRACT FROM AUTHOR]

• Fretting fatigue is a highly relevant fretting phenomenon. • A novel customized non-standard specimen was designed for four-point rotating bending fatigue testing. • The most remarkable feature of the specimen is that it allows for the complete disassembly of the shaft and hub. • Consequently, the mating surfaces after cycling may be carefully analyzed to detect fretting wear and damage. Interference-fitted joints are widely used to join a shaft and a hub. The contact pressure produced by the interference induces stress concentration on the shaft at the hub end. FEA can be helpful in evaluating the related stress concentration factor. However, fretting damage may be generated and may arise from micro-sliding between the mating surfaces. It is currently not feasible to take this occurrence into account and to properly and reliably address this phenomenon by a standard numerical simulation. In order to tackle this question, an ad hoc specimen was designed for four-point rotating bending fatigue testing. The new specimen has three main advantages: the first one is the reduced dimensions with respect to the usually tested shafts, the second is the possibility of controlling the average contact pressure, and the third is the capability of easily dismounting the specimen without damaging the coupled surfaces. The specimen has been then tested. The study focused on C40 normalized steel, whose fretting fatigue limit was experimentally evaluated by the aforementioned device. The mating surfaces could also be carefully analyzed for fretting damage detection after cycling. The fatigue limit retrieved was 254 MPa and fretting damage and induced cracks were detected in the specimens, which proves the effectiveness of the introduced testing rig at reproducing fretting fatigue damage. [ABSTRACT FROM AUTHOR]

• Method to determine the nominal fatigue-strength scatter. • Detection of shaft-inherent fatigue-strength scatter and scatter between shafts. • Consideration of competing failure mechanisms in the HCF and VHCF regimes. • Description of the distribution of non-metallic inclusion size using micro-CT scans. • Predictable S-N curve in the HCF and VHCF regimes to avoid failures of shafts. The fatigue strength of shafts is subject to scatter. Knowledge of this scatter is essential for producing safe shaft designs. Therefore, this paper investigates the possibility of quantifying the fatigue-strength scatter in the high-cycle and very-high-cycle fatigue regimes. For this purpose, experimental tests were carried out on exemplary shafts to determine the fatigue-strength scatter. A probabilistic model was developed that considers the failure mechanisms of quenched and tempered steels from the surface and the interior. Therefore, the scatter-influencing parameters were statistically modelled. The parameters act as input in local-strength approaches for the failure mechanisms. Using Monte Carlo simulations, shafts can be randomly generated. The shafts so generated are submitted to the approaches for the failure mechanisms by means of finite-element analyses. By statistical evaluation of fictitious nominal stress levels with respect to calculated failures and runouts of the shafts, the probability distribution of the fatigue strength can be determined. [ABSTRACT FROM AUTHOR]

• The causes of failure of the threaded hole of the main bearing are analyzed from both test and simulation. • The properties, chemical composition, and microstructure of the material are obtained from the analysis of the test failure site. • The cylinder block fatigue test results show that the main bearing threaded hole bottom internal tread is the weakest position. • Stress amplitude due to simulated gas forces is the main cause of main bearing threaded hole bottom buckle cracking. Under the development trend of high-strength and high-load diesel engines, the reliability problem of its cylinder block is becoming more and more serious. Aiming at the problem that the main bearing threaded hole of the cylinder block often fails, it is necessary to clarify the failure mechanism. The study first carried out the fatigue test of the cylinder block and selected the failed cylinder block to carry out the material mechanical property test, the material metallographic structure, chemical composition analysis, and the analysis of the failure section morphology. Then the numerical analysis model of the virtual test was established and the assembly preload and simulated gas pulse load were considered. Finally, the fatigue strength of the main bearing was evaluated based on the critical plane method, and the effect of fatigue load on the failure in the threaded hole was studied. The results show that the fatigue test of the cylinder block has verified that the position of the main bearing threaded hole is prone to fracture failure and the repeatability is extremely high. The fracture surface shows typical high-cycle fatigue characteristics, and cracks are generated near the bottom internal tread of the threaded hole. The bottom internal tread of the threaded hole obtained by the numerical analysis is the most dangerous position, which is consistent with the actual cracking position. The failure mechanism is high cycle fatigue failure caused by the gas-dominated stress amplitude exceeding the bearing capacity of the material and structure. [ABSTRACT FROM AUTHOR]