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The paper presents an analysis of the low-cycle fatigue (LCF) properties of C45, X20Cr13, and 34CrNiMo6 steels subjected to various heat treatment processes. Strain-controlled LCF tests were carried out with a total cyclic strain amplitude equal to 0.5, 1 and 1.5%. Fatigue life, cyclic stress-strain behavior and hardness were analyzed. Qualitative and quantitative relationships between material LCF properties resulting from the heat treatment processes, were related to the indentation force P*, which was derived experimentally by applying an instrumented indentation procedure with the use of the Vickers indenter. The proposed parameter P* and its changes ΔP* seem to be promising for the identification of the structural stress parameter σ* that is necessary for deriving values of the fatigue strength coefficients σf' corresponding to different tempering temperatures. The common feature of all steels analyzed in this paper is that the elastic parts of the strain-life characteristics remain parallel after being subjected to different tempering temperatures. [ABSTRACT FROM AUTHOR]

The fatigue behavior of a high-strength bearing steel tempered under three different temperatures was investigated with ultrasonic frequency and conventional frequency loading. Three kinds of specimens with various yield strengths exhibited obvious higher fatigue strengths under ultrasonic frequency loading. Then, a 2D crystal plasticity finite element method was adopted to simulate the local stress distribution under different applied loads and loading frequencies. Simulations showed that the maximum residual local stress was much smaller under ultrasonic frequency loading in contrast to that under conventional frequency at the same applied load. It was also revealed that the maximum local stress increases with the applied load under both loading frequencies. The accumulated plastic strain was adopted as a fatigue indicator parameter to characterize the frequency effect, which was several orders smaller than that obtained under conventional loading frequencies when the applied load was fixed. The increment of accumulated plastic strain and the load stress amplitude exhibited a linear relationship in the double logarithmic coordinate system, and an improved fatigue life prediction model was established. [ABSTRACT FROM AUTHOR]

Carbon fiber‐reinforced polymer (CFRP) is increasingly used to improve the fatigue behavior of damaged steel structures due to its advantages, including high strength and convenient processing. However, several issues, such as the effects of the adhesive property and CFRP arrangement, still need to be studied. In this study, a total of 20 single‐cracked steel specimens were tested under fatigue load, including two unstrengthened specimens, six single‐sided strengthened specimens, and 12 double‐sided strengthened specimens. The failure mode, fatigue life, crack propagation pattern, and interface damage development were obtained from experiments. The results show that epoxy resin structural adhesives (adhesives Araldite 420 and J133C) have the best bonding properties with CFRP. For the conventional epoxy adhesives, Araldite 420 and J133C can considerably improve fatigue life, which increased by more than 44.84 times to unstrengthened specimens. CFRP plate strengthening can significantly improve the fatigue life of single‐edge cracked steel plates. For the double‐sided strengthened specimens, the fatigue life can be improved by 6.93–44.84 times that of unstrengthened specimens. For the single‐sided, the fatigue life can be improved by 2.24–2.77 times. Properties of epoxy adhesive have a more significant effect on fatigue life compared to the thickness of the CFRP plate due to debonding. Highlights: Ductile epoxy adhesives are most conducive to improving the fatigue behavior of CFRP strengthened steel plates.The fatigue life of steel plates can be improved by increasing the thickness of CFRP plates and using double‐sided CFRP strengthening.Interface debonding is the main failure mode of CFRP plates strengthening single‐edge cracked steel plates under fatigue. [ABSTRACT FROM AUTHOR]

Load‐bearing capacity tests on large scale test specimens for modular polygon tower sections of wind turbines The verification for stability and fatigue of steel towers for onshore wind‐turbines require large dimensions due to the high static and dynamic loads. Since, the rated power as well as the hub height will further increase for wind turbines in the future, also the dimensions of the tower must be increased. Some kind of turbines will require a tower base diameter of > 4.5 m. Tubular steel sections with this dimensions cannot be transported (economically) by road. Therefore modular construction methods have been developed, whereby the tubular steel sections consist of longitudinally divided segments, which will finally assembled on site. Furthermore, the detail design of the connections between the structural components is also a challenge when planning wind turbines for the next generation. As a technical alternative to the existing tower configurations, a concept for a modular polygon tower made of steel is presented, where single plate segments can be connected along the longitudinal edges using extruded profiles so that no further bolted or welded connections are required for the final assembly on site. This technical proposal allows a longitudinal manufacturing of tower segments with steel plates but without any formwork with rolling and bending machines. As part of a research project, the technical feasibility of a modular polygon tower for a hub height of 200 m and a wind turbine class with 10 MW rated power was analysed to offer technical solutions for the next generation of onshore wind turbines. Load cases were generated for a fictitious reference wind turbine to carry out a pre‐design for the tower sections. A test programme was created on the basis of the calculated tower dimensions and ultimate load bearing tests were carried out on test specimens at a scale of 1 : 10. This paper presents the results of the experimental investigations, comparing the load‐bearing capacity of the various tower configurations and the observed failure mechanisms are explained. [ABSTRACT FROM AUTHOR]

Evaluation of significant parameters influencing the fatigue strength of typical details – experimental investigations The phenomenon of fatigue plays a significant role in many constructions of modern infrastructure. Therefore, the fatigue assessment of steel structures is of great importance. In order to make fatigue design acc. to DIN EN 1993‐1‐9 more efficient, important influencing factors on the fatigue strength of standard fatigue details were analyzed in the research project EVOKERB. This contribution presents the corresponding experimental research results, with a focus on influences related to geometry, manufacturing, and weld quality. In addition, test data from the literature are included through a soon‐to‐be‐publicly‐available fatigue test database. The database comprises the essential background data of DIN EN 1993‐1‐9. In summary, the presented test results identify or exclude important influences on the fatigue strength of typical details. In the future, the scope of investigations will be expanded through numerical simulations, allowing for the derivation of general normative rules. These rules are intended to contribute to a more efficient fatigue assessment – an important step towards greater resource efficiency and sustainability in steel construction. [ABSTRACT FROM AUTHOR]

Materials used in nuclear power plants are exposed to cyclic loading, which is why the understanding of fatigue behaviour is of great importance. Because of high time investments and resulting increased costs, Lifetime Prediction Methods, which significantly reduce the amount of specimen, have already been developed. Within this paper, the Lifetime Prediction Method MiDAcLifeincr is presented, which enables a determination of a trend S‐N curve in the High‐Cycle‐Fatigue‐regime based on only one fatigue test and the combination of conventional fatigue testing with NDT‐related measurement techniques. The process‐orientated monitoring of the cyclic deformation behaviour provides the basis for the time‐ and cost‐effective provision of fatigue data. Compared with previous methods, the consideration of variable loading is an essential aspect of the research application. The test material is a 20MnMoNi5‐5 steel, the results of which are extended to include other steels for validation reasons. Highlights: The new method enables a fatigue life calculation on the basis of only one fatigue test.A correlation between the material reaction and the introduced damage could be found.The applicability of the method is independently of the applied measurement technique. [ABSTRACT FROM AUTHOR]

The advent of non-conventional and renewable energy sources places a tremendous strain on generic sources of power generation, which have been historically conceived and designed for constant-load criteria, as they are compelled to conform to a 'fluctuating' mode of operation so as to comply with modern-day energy requirements. Power plants undergo a starting schedule, followed by sustained operation at intermediate loads when the energy requirement is mediocre. This renders the evaluation of material behaviour under creep-fatigue conditions, a critical component of failure prevention and prediction. ASTM has come up with a standard E-2760 for creep-fatigue crack growth (CFCG) testing, wherein Compact tension, C(T) specimens, are subjected to trapezoidal loading waveforms. In this article, the crack tunnelling phenomenon has been objectively evaluated along with exploring the propagation of crack growth fronts and the crack tip opening angles (CTOA). [ABSTRACT FROM AUTHOR]

The microstructure, mechanical and fatigue properties of two kinds of complex steel (CP800 and CP690) were studied. Bainite was identified by the unique peak in Kikuchi band contrast diagram. Surface quality had little effect on the fatigue lifetime of coarse-grained steel (CP690). A model is proposed to unify the fatigue lifetime of two kinds of complex phase steels with different grain sizes, based on the defect effective projected area model. The model is valid for specimens with wire electrical discharge machining surface quality. The fatigue process is analyzed using the crystal plasticity finite element modeling. The results show that strain localization tends to occur in grains with relatively soft orientation but not in grains with the softest orientation. [ABSTRACT FROM AUTHOR]

S420M steel subjected to strain-controlled low-cycle fatigue does not exhibit a period of cyclic properties stabilization. The maximum stress on a cycle continuously drops until fracture. For this reason, it is difficult to plan experimental research for different types of control in such a way that their results can be considered comparable. The aim of this paper is to present and discuss the results of tests conducted in various conditions of low-cycle fatigue of S420M steel specimens, both undeformed and pre-strained. In both loading conditions, after initial deformation, a significant change in the cyclic properties of steel described by the parameters of the hysteresis loop was observed. Also, the fatigue life of the pre-strained specimens appeared to be different from unstrained specimens and was affected by the test loading conditions. The reduction in life under controlled stress conditions was attributed to the increase in the extent of plastic deformation and stress and the occurrence of creep. [ABSTRACT FROM AUTHOR]

Bridge cable wires suffer from alternating stress and environmental erosion, leading to premature failure prior to its design life. This paper investigates the fatigue and mechanical behaviors of corroded bridge cable wires with a zinc–aluminum (Zn-Al) alloy coating. Based on the salt spray corrosion test and microstructure analysis, the anti-corrosion resistance and corrosion appearance characteristics of the Zn-Al alloy coating and galvanized coating were investigated. The Zn-Al alloy coating was superior in resistance to corrosion fatigue for the improvement in toughness and the generation of anti-corrosion Zn-Al and Fe-Zn-Al phases. Equations of the accelerated corrosion depth of the steel wires had been regressed to roughly estimate the corrosion life of the Zn-Al alloy coating, which can reach 29.1 years with a thickness of 70 μm. The fatigue and mechanical properties of the bare wires after the salt spray test were further studied based on tensile tests and fatigue tests. The fatigue properties of the bridge cable wire would decrease with the corrosion degree due to the deterioration and embrittlement of materials, where ductility characterized by the elongation rate was the most affected. Fracture surfaces of the wires were captured and analyzed based on a method for recognizing graphical contours. Insufficient fatigue life may occur in the steel wires after corrosion and increase with the degree of corrosion. The pit depth logarithmically weakened the fatigue life of steel wires for the weakening of fatigue toughness and the bearing area. The flat fracture was more common with a single fatigue source, while multiple fatigue sources led to step-like fractures for the generation of multiple dispersed crack propagation regions. Corrosion fatigue was more sensitive to the existence of fatigue sources than the reduction. Multiple initiation sources significantly reduced the fatigue life due to the cracking facilitation of the joint effect of multiple pits. The electrochemical reactions of corrosion can lead to material embrittlement and a reducing effect on the fracture toughness of the steel wires. [ABSTRACT FROM AUTHOR]

To investigate the residual stress relaxation behaviors and fatigue strength, EA4T steel specimens are subjected to micro-shot peening (MSP), and part of them are isothermally annealed at 250 °C for 2 hours. Fatigue experiments are conducted on a four-point rotating bending machine under constant and variable loads. Surface compressive residual stress (CRS) and full width at half maximum (FWHM) before the experiment and during fatigue loading are analyzed using the x-ray diffraction method. The results indicate that the CRS of the MSP specimens are relaxed after the isothermal annealing, leading to a decrease in their fatigue strengths. Variable loading slightly increased the fatigue life of the un-peened specimen, but significantly reduced that of the MSP specimens. The effect of CRS relaxation on fatigue strength is analyzed, and the relationship between CRS and FWHM is also discussed. [ABSTRACT FROM AUTHOR]

Evaluating the technical conditions and performance for historic bridges is essential to ensure their structural safety and determine their need for strengthening. This study investigates the first railway steel bridge built in China in 1894, which is listed as a national preservation unit and industrial heritage site. The bridge was not only exposed to years of weather change but also suffered a geological disaster in 1976. In addition, the surroundings have changed, including the construction of new railway lines and scenic areas. Thus, it is imperative to evaluate its technical conditions and performance, particularly its material properties. To this end, evaluation procedures were formulated. First, the material composition, properties, and grades of steel were determined by microstructural analysis: the grade of nonmetallic inclusions in steel was determined by metallographic analysis; the corrosion rate of steel was obtained by electrochemical analysis; and the crystal type, size, element product of the corrosion layer, as well as the fracture type of the steel, were analyzed by phase composition and elemental analysis. Next, the static performance indices of the steel were obtained by mechanical property tests: the hardness value of the steel was obtained from hardness test; the yield and tensile strengths of the steel were obtained from tensile tests; and the fatigue properties of the steel were analyzed through fatigue tests. The S-N curve of the steel was determined by fitting the tested data. This study provides a reference for the evaluation of the technical conditions and performance of historic bridges. [ABSTRACT FROM AUTHOR]

Understanding the recrystallization behavior of cold‐rolled silicon steel during continuous heating is essential for optimizing continuous annealing parameters and accurately controlling material performance. To address the limitations of isothermal annealing studies in interpreting actual continuous annealing processes, this study investigates the recrystallization kinetics of Fe–2.3 wt%Si steel using a continuous heating three‐point bending method. The method effectively determines the characteristic recrystallization temperatures. Interestingly, these recrystallization characteristic temperatures remain unaffected by the initial load but shift toward higher temperatures with increasing heating rates in the range of 5–15 °C min−1. The average activation energy of recrystallization is estimated to be 144.5 kJ mol−1, comparable to the value of 147.0 kJ mol−1 obtained from the isothermal process through microhardness measurement. The recrystallization kinetics, described by an extended version of the Ozawa–Flynn–Wall model, exhibits excellent agreement with experimental evaluations. By combining the present processing technologies with continuous heating recrystallization kinetics, different recrystallization temperatures and times can be determined, offering valuable insights for optimizing annealing processes. [ABSTRACT FROM AUTHOR]

In the last few decades, the advancements made in material characterisation equipment and physics-based multiscale material modeling have generated vast database in the field of Material Science and Engineering. This has inspired material innovators to attempt predicting mechanical properties of synthesised materials using big-data so as to reduce the cost, time and effort for materials innovation. However, the impact of collinerarity has always been a matter of concern in emperical research, specially in such predictions of mechanical properties. In the present work, we revisit NIMS database for steel and study the effect of multicollinearity on regression based models for predicting fatigue strength for the material. We use an iterative scheme to isolate highly correlated parameters contributing in determination of the fatigue strength of the steel. We then construct a regression model using only the non-correlated parameters to make the model more efficient computationally. Our results show that the regression model built after consideration of multicollinearity of the variables provide better performance in comparison with regression model built without consideration of the same. [ABSTRACT FROM AUTHOR]

One of the techniques commonly applied today for deep foundation construction is based on selfdrilling injection micropiles. Micropiles are structural elements intended primarily for reinforcing foundations and buildings, particularly under difficult terrain conditions. The goal of the tests presented herein is to inspect the fatigue resistance, strength and ductility of injection micropiles formed from 28Mn6 steel at loads significantly exceeding the values defined for the fatigue test in the requirements of the relevant European Assessment document (EAD). The test results and the micropile bar strain model εM presented in this paper are primarily of interest to designers for the purposes of determining the fatigue resistance of steel micropiles, which find particular application in land degraded by mining activity that is characterised by frequent terrain vibration and mining-induced tremors. None of the R25N injection micropile bars failed during the fatigue resistance testing at 2·106 cycles at a load Fu = 0.7·FRe0.2 (under the yield strength of the 28Mn6 steel) as well as at Fu = 1.0·FRe0.2 and Fu = 1.2·FRe0.2, where the bars operated at the limit of and significantly above the load FRe0.2 which results in stress at the yield point of the 28Mn6 steel. Furthermore, the bar tests conducted at static and cyclic loading demonstrated the high strength and good ductility of the 28Mn6 steel. [ABSTRACT FROM AUTHOR]

Wind turbine (WT) foundations with an embedded steel ring (ESR) are widely used in onshore WTs due to construction convenience. The research group found that WT foundations with damage were often accompanied by blade issues. To investigate the potential correlation between aerodynamic imbalance and fatigue damage of the WT foundation with an ESR, this study focuses on a 2 MW WT with an ESR. It investigates the influence of an error in pitch angle (PAE) on the WT's foundation load and stress, utilizing one year of SCADA data to analyze the fatigue damage caused by PAE. The main conclusions are as follows: Firstly, the effect of PAE on the amplitude value of load and stress is significantly greater than on the average value of load and stress. Secondly, when the PAE is within the range of −3° to 3°, the foundation fatigue damage incurred over one year is minimal, but once this limit is exceeded, the foundation fatigue damage increases dramatically. Thirdly, the peak value of fatigue damage to the foundation caused by PAE does not necessarily occur in the main wind direction, but in the direction with the highest probability of the occurrence of high wind speeds, and the larger the PAE, the more significant the trend. [ABSTRACT FROM AUTHOR]

Steel–concrete composite decks are commonly employed in narrow-width steel box composite girder bridges to augment their lateral spanning capabilities, while the concurrent omission of longitudinal stiffeners leads to a substantial reduction in the number of components, thereby yielding a structurally optimized bridge configuration. This paper delineates the structural design parameters of a narrow-profile steel box composite girder bridge and assess the mechanical behavior of its incorporated steel–concrete composite deck under static and fatigue loading conditions. To this end, two full-scale segment specimens from the composite bridge decks were subjected to equal amplitude cyclic fatigue tests. The investigation specifically concentrated on the impacts of two types of shear connectors—namely, perforated steel plates combined with shear studs and perfobond rib shear connectors (PBL connectors)—on the static and fatigue performance, including fatigue stiffness, of the steel–concrete composite bridge decks. The results indicate that, under the static bending condition, the composite deck specimen equipped with stud connectors demonstrates superior overall flexural stiffness in comparison to the specimen featuring PBL connectors. Furthermore, the flexural stiffness of the steel–concrete composite specimens experiences a negligible alteration across two million fatigue loading cycles. Upon the completion of two million fatigue loading cycles, the composite deck specimens incorporating the shear connectors composed of perforated steel plates and shear studs exhibit relatively wider crack widths under the static peak load. Both configurations of the steel–concrete composite bridge deck specimens manifest evident interfacial detachment, signifying insufficient tensile pull-out stiffness of the shear connectors. It is recommended to increase the quantity of the shear connectors or select the pertinent types in order to enhance the interface shear resistance. [ABSTRACT FROM AUTHOR]

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In order to examine the mechanical properties and rotational bending fatigue performance of 40CrNi2MoE steel subsequent to tempering at varying temperatures, the steel specimen was subjected to tempering within the range of 400~460 °C. SEM, EBSD, and TEM were used to analyze the microstructure as well as precipitates. The strain hardening law was studied using the modified Crussard–Jaoult method. Investigations were undertaken to reveal the rotational bending fatigue life with respect to the tempering temperature. The findings indicate that the strength and fatigue life of the examined steels exhibit a decline as the tempering temperature increases, with the primary factor affecting this trend being the alteration in dislocation density. No notable impact on the fatigue fracture morphology exerted by tempering temperature was found within the range of the experiment. The C–J model analysis reveals that the work-hardening behavior of the trial steels is influenced by dislocations and the second phase. [ABSTRACT FROM AUTHOR]

Higher carbon 1060 steel can be completely transformed to austenite at 850, a 100 °C lower temperature than that for conventionally used 1045 steel, allowing development of very small austenite grains during induction hardening. Torsion fatigue test specimens were machined from quenched and tempered martensite and as hot-rolled pearlitic bars of 1060 steel. Specimens from both initial conditions were induction hardened to a 3 mm case depth with peak surface temperatures of 1050 and 850 °C followed by tempering at 176 °C. Specimens were fatigue tested in torsion at R = 0.1 and peak stresses of 1222 to 1444 MPa, corresponding to 49 to 58% of the estimated shear ultimate strength and fatigue lives of 104 to 106 cycles. The fractures for all conditions except three of the 1050 °C pearlite specimens were initiated as small longitudinal cracks in shear (Mode III) at the surface and showed a Mode I (tensile) fatigue zone on a 45-degree spiral plane followed by rapid fracture. Microstructures were evaluated by light optical and scanning electron microscopy and by Mossbauer spectroscopy. Surface residual stresses were determined by x-ray measurements and found to be lower for the 850 °C cycle. The pearlitic as-rolled microstructure resulted in a higher case hardness and a more abrupt case to core hardness transition, but lower fatigue life as compared to the quenched and tempered martensitic microstructure. The initial martensitic microstructure and higher peak induction hardening temperature resulted in a higher surface compressive residual stress and the longest low cycle torsional fatigue life. The 850 °C peak induction temperature for the QT 850 condition produced a very small prior austenite grain size (3 µm) that contributed to a long fatigue life, but a lower compressive residual stress that partially offset the benefit of the small austenite grain size. [ABSTRACT FROM AUTHOR]

Two methods of durability prediction of fillet welds were researched in this study. Namely, the structural Hot-Spot method and the structural stress method fe-safe Verity were applied to fatigue life estimation of a double plate lap fillet weld made of high-strength complex phase CP-W800 steel. Durability predictions were compared against available high-cycle fatigue experimental data obtained for the same weld detail and material. Both 2D and 3D finite element meshes were considered in the simulations. It was shown that comparable predictions were obtained using either the Hot-Spot method or the fe-safe Verity module in the case of the 3D FE mesh. On the contrary, a less conservative durability prediction was observed using the Hot-Spot method and a more conservative durability prediction was gained using the fe-safe Verity module in the case of the 2D FE mesh due to a different consideration of stress concentration around the weld. [ABSTRACT FROM AUTHOR]

Improved analyses of remaining fatigue life – performance test of damage equivalent factors λ This contribution is dealing with the concept of damage equivalent factors λ ${\lambda }$ for assessment of the remaining fatigue service life of steel railway bridges, as it is also used in the relevant national guidelines for existing structures. However, what is considered here is not the suitability of country‐specific traffic mixes, but only the effects of the implicit calculation assumptions of this concept on the results of the fatigue damage – and subsequently the remaining fatigue service life of existing bridges. On the one hand, it is analysed whether these λ ${\lambda }$ ‐factors – which are always based on the shape of the influence line for the bending effect of a single‐span beam at midspan – also produce accurate results for other practical shapes of influence lines (e. g. for components of open bridge decks, or members of truss main girders). On the other hand, it is also shown, that the actual fatigue strength Δσc ${\Delta \sigma _{\rm{c}} }$ of the existing structure, which is not included in the λ ${\lambda }$ ‐factors and is usually higher than implicitly assumed, can lead to conservative results and offers potential for an improved alternative assessment of the remaining service life. [ABSTRACT FROM AUTHOR]

Recently, a new dissimilar mechanical joining method, dimple spot welding (DSW), has been developed for joining steel sheets and aluminum alloys. In this study, tensile shear tests and fatigue tests were conducted on four types of dissimilar lap joints, with two types of steel sheets and two types of Al alloys joined by DSW. Both the tensile shear strength and fatigue strength of DSW joints were found equal to or greater than those of a self‐piercing riveting (SPR) joint. In all four types of DSW joints, fatigue cracks were initiated from the Al alloy and were associated with fretting induced by repeated contact and friction. A finite element analysis showed that the tangential stress was mainly governed by the friction coefficient and also affected by the steel sheet strength. Higher‐strength steel led to lower tangential stress, resulting in a longer fatigue life for the DSW joint. Highlights: A dimple spot welding (DSW) is developed for joining steel sheets and aluminum alloys.Tensile shear tests and fatigue tests are conducted on DSW joints and SPR joint.DSW joints shows greater tensile shear strength and longer fatigue lives than SPR joint.Fatigue cracks in DSW joints were initiated associated with fretting. [ABSTRACT FROM AUTHOR]

Very high‐cycle fatigue life (VHCF) prediction of high‐strength steel based on machine learning (ML) was investigated in this paper. First, a total of 173 sets of experimental data on the VHCF of high‐strength steel were collected to train the ML model. The sensitivity coefficient analysis indicated that inclusion size and maximum stress were the strongest correlation parameters with fatigue life and selected as the input features for the final model training. The S–N curve predicted by the obtained ML model closely aligns with the actual S–N curve. Among the three algorithm models, namely, random forest, XG boost, and gradient boosting, the gradient boosting model exhibited superior performance and achieved the highest accuracy in predicting the VHCF life of high‐strength steel. A comparison between the Murakami model and the gradient boosting model was conducted. It is indicated that ML exhibits superior predictive performance with high efficiency and excellent accuracy. Highlights: S–N curve predicted by machine learning model closely aligns with that by experiments.Gradient boosting model exhibited superior performance in predicting the VHCF life.Machine learning model outperforms the Murakami model in the terms of accuracy. [ABSTRACT FROM AUTHOR]

In order to raise the hardness and strength of the surface layer of mechanical components and induce favorable residual compressive stresses, case‐hardening procedures have become established in the heat treatment of steel. In this work, a calculation concept for the fatigue strength of components that have been case‐hardened through carburizing heat treatment is being developed. The residual stress and the load stresses in complex‐shaped, carburized materials are determined using a finite element (FE) model. The fatigue limit of the components is derived using probabilistic methods and taking into account hardness gradients, residual stresses, and non‐metallic inclusions. The model is validated with available axial bending fatigue test data and then used to predict the rotating bending fatigue limit of samples with various geometries and heat‐treatment conditions. This work demonstrates the capability of combining probabilistic and FE‐based modeling to represent complex interactions between variables that affect the fatigue of heat‐treated components, such as steel cleanliness, notch shape, case‐hardening depth, or loading conditions. Highlights: Combined FE‐based and probabilistic methods can predict fatigue strength accurately.Interplay of heat‐treatment output, geometry, load, and material is considered.Crack initiation position gets shifted by increased case‐hardness depth.Fatigue strength reduction due to defects in steel depends on load concentration. [ABSTRACT FROM AUTHOR]

Material informatics has emerged as a valuable research field in material science, providing solutions to previously unsolvable problems or accelerating deliverables. Fatigue failure, as a complex and non‐deterministic phenomenon, requires a probabilistic approach to assess the uncertainty of the fatigue strength prediction. This study compares various probabilistic data‐driven models for credible fatigue strength predictions for three distinct steel groups. The analysis considers data and model uncertainty, evaluating their impacts on predictive quality from engineering and data science perspectives. Results reveal that deep ensembles outperform other probabilistic models regarding negative log‐likelihood (NLL), while random forest exhibits the lowest root mean square error (RMSE). Notably, the prediction accuracy of case‐hardened steels is negatively affected by insufficient material properties definitions, while stainless steels demonstrate the best performance compared to other steel types. Highlights: DeepEnsembles is the best ML model for probabilistic fatigue strength predictions.Random forest is the best ML model for deterministic fatigue strength predictions.The accuracy and credibility of data‐driven fatigue strength predictions depends on material properties.Understanding and considering the dominant fatigue damage influencing factors are crucial for prediction improvements. [ABSTRACT FROM AUTHOR]

In this study, using a C(T) specimen for 12Cr steel used for a steam turbine rotor, crack growth tests under creep-fatigue conditions with and without overloading were conducted and the fundamental behaviours of deformation and crack growth were investigated experimentally. As a result, load line displacement was found to be suppressed under overload condition regardless of temperature and stress holding time. Crack initiation life under high temperature and low stress condition with overloading was delayed as compared with no overload condition. However, under low temperature and high stress condition with short stress holding time, crack initiation was accelerated remarkably. Furthermore, although crack growth life under creep-fatigue conditions with overloading was found to be shortened as compared with no overloading, the effect of overloading on crack growth life was decreased with an increase in stress holding time. [ABSTRACT FROM AUTHOR]

The z-pinning reinforcement technique, which involves inserting thin pins through the body of a laminate, has proven highly effective in enhancing the strength of various composite joint configurations. This investigation aims to explore the enhancements achievable through selective z-pinning at very low pin contents on both the static and fatigue performance of composite joints. Single-step joints between carbon/epoxy adherends were reinforced using steel pins arranged in two, three, or four rows of pins parallel to the edges of the overlap, resulting in pin contents ranging from 0.2% to 0.4%. Joint panels were manufactured through co-curing, and coupons were extracted from the panels for static and fatigue tensile testing. The experimental tests show that z-pinning improves the static strength (by about 15%) and extends the fatigue lives of the joints. The ultimate failure of both unpinned and pinned joints is due to the unstable propagation of a crack at the bond line. The superior performances of pinned joints are mainly due to the bridging tractions imposed between the crack faces by z-pins, which delay the growth of the debonding crack. The enhancements in static and fatigue strength achieved by z-pinning were essentially independent of the number of pin rows, and the pins positioned near the joint edges were found to play a dominant role in controlling the structural performance of pinned joints. [ABSTRACT FROM AUTHOR]

Orthotropic steel bridge decks (OSDs) are very popular all over the world because of the low dead load, high stiffness in the longitudinal direction, high strength ratio to weight, and can be used in various types of bridges. The life of these bridges is affected by fatigue cracks in different portions. One of major areas where the fatigue cracks appear in these bridges is rib-to-deck connection. In this research finite element analysis is carried out by using ABAQUS/CAE 2022 software to determine the ways to increase the fatigue life at rib to deck connection in OSDs. In the first part, smaller models are simulated; stress concentration is analyzed and hot spot stress (HSS) is calculated according to International Institute of Welding (IIW) and Det Norske Veritas (DNV) recommendations. In the second part, a parametric analysis is carried out to analyze the effect of weld penetration, thickness of deck, thickness of rib and rib to deck connection type. In the third part, simulation of models similar to the real field is carried out to determine whether the double welded connections are better than single welded connections. Different models are analyzed for different load cases like single wheel load, double wheel load and also the position of the wheels is changed. The boundary conditions are changed to analyze whether the boundary condition has any significant effect on the result obtained. It is found that thicker decks, thinner ribs, and low penetrated welded connections reduce the stress concentrations at rib to deck connections which ultimately increase fatigue life. Among the parameters examined, deck thickness is the most important parameter. It is found that the percentage of stress increase with percentage decrease in deck thickness follows a power relation. The overall fatigue life of double welded connection is excepted to be lower since the stress concentration is maximum at the weld toe at deck on the outer side of the closed stiffener; however, if the cracks initiate on the inner side of closed stiffener, the cracks at the weld root of single welded connection can propagate much rapidly than the cracks initiating on the inner side of the closed stiffener at the weld toe, thereby reducing the fatigue life of the single-welded specimen significantly. [ABSTRACT FROM AUTHOR]

To investigate the damage evolution behavior of corroded steel wires under the influence of alternating loads, a damage evolution model for steel wires based on the theory of continuous damage mechanics was established. The damage evolution process at corrosion pits was simulated by using the element birth and death technique in ANSYS 2020R2. Then, a certain cable-stayed bridge was chosen as the research subject, the stress–time data of the sling were computed using a traffic–bridge–wind simulation analysis model, and the influence of corrosion pit distribution on the mechanical properties and fatigue life of wires under an alternating load was discussed. The results show that, in comparison to single-pitted steel wires, double-pits distributed circumferentially across the cross-section of the steel wires lead to more severe stress concentration, accelerating the damage evolution process and significantly reducing the fatigue life of the steel wires. Conversely, the stress concentration caused by double pits distributed along the longitudinal direction of steel wire is similar to that caused by single pits, and it will be even weaker than that caused by single pits with the change in the relative distance of the double pits. Based on the calculation results of the damage evolution model of steel wire, it was found that the corrosion pit crack nucleation life of steel wire under alternating load accounts for nearly 80% of the fatigue life of steel wire, and different corrosion pit distribution modes will significantly affect the fatigue life of steel wire. [ABSTRACT FROM AUTHOR]

Steel slag is a solid byproduct of the steelmaking process, widely generated in the metallurgical industry. Due to its alkaline nature and excellent adhesive properties with asphalt, it represents a potential road construction material with outstanding road performance, making it well-suited for utilization in highway construction. This paper conducts a systematic analysis of the physical and chemical properties of steel slag, specifically South Steel Electric Furnace slag, and compares it with natural basalt and limestone aggregates. The aim is to establish a foundation for the application of steel slag in asphalt mixtures. Building upon this foundation, we carry out proportioning design for AC-13C and SMA-13 steel slag asphalt mixtures, followed by a comprehensive study of their high-temperature stability, low-temperature stability, water stability, and fatigue performance. Our research reveals variations in the chemical composition of different steel slags, with CaO, SiO2, and Fe2O3 being the primary components. The content of harmful elements varies depending on the steelmaking raw materials and additives used. Notably, the optimum asphalt-to-aggregate ratios for AC-13C and SMA-13 significantly surpass the specified requirements. The freeze–thaw splitting strength ratio and residual stability of steel slag AC-13C and SMA-13 asphalt mixtures exceed the specified requirements, with AC-13C demonstrating the highest water stability, boasting a freeze–thaw splitting strength ratio of 94.07%, and a residual stability of 93.8%. In terms of fatigue characteristics, SMA-13 exhibits a longer fatigue life than AC-13C, indicating superior fatigue performance for steel slag SMA-13. Steel slag enhances the abrasion resistance and rutting resistance of asphalt pavement surface layers, fully meeting the performance requirements for high-grade road surface layers. [ABSTRACT FROM AUTHOR]

This study introduces a data-driven approach for updating the fatigue failure probability of the orthotropic steel deck (OSD) using Bayesian backward propagation. The OSD in steel bridges is considered as a parallel system composed of two critical fatigue-prone components, namely, the rib-to-diaphragm and rib-to-deck joints. A probabilistic model for fatigue reliability is established based on the equivalent structural stress method and limit state function. The system-level fatigue reliability model is then constructed, taking into account the correlations between limit states of individual components through Bayesian network forward propagation. The key advantage of the Bayesian network-based framework is its ability to perform backward propagation, allowing for the updating of failure probabilities for critical components when the system-level failure of the OSD is observed. Consequently, the proposed approach enables the identification of vulnerable components through data-driven fatigue failure probability updating. Finally, the approach is applied to a real instrumented steel bridge to determine the time-dependent fatigue failure probability at both the system and component levels over its service life. The results show that the component-level fatigue failure probability model will underestimate the fatigue life in comparison to the system-level model. Meanwhile, the proposed method could identify vulnerable components by quantifying the fatigue failure probability of in-service steel bridges. [ABSTRACT FROM AUTHOR]

This work develops the optimization of torsional, wear, and fatigue life behaviors based on the hybrid emperor penguin social ski-driver for reinforced steel wire. Using granite and rutile particles reinforcement, steel wires are strengthened. Normal steel wire rope and reinforced wire rope are prepared with 7 strands and 15 wires. Using hybrid emperor penguin optimization-based social ski driver Optimization (Hybrid EPSSD), the failure tests such as wear analysis, fatigue life, and torsional behavior are optimized. Besides, the performances of the experimented wire rope are predicted by using hybrid Elman recurrent Neural Network-based EPO (Hybrid ERNN-EPO). Using the Matlab 2018a platform, the optimization and prediction processes are performed. In this, reinforced wire ropes deliver enhanced performances for both experimented and optimization behaviors. From the results, the reinforced wire rope has the best performance which possesses less wear rate, more fatigue life, and torsion behavior are obtained. The experimental outcome of wear depth for reinforced wire rope is 0.18 mm and the optimized wear depth outcome from the Hybrid EPSSD approach is 0.16 mm. For reinforced wire rope, the optimized fatigue life is 4.50 × 104 times at 500 KN and the maximum fatigue life experimentally is 4.20 × 104 times. At a particular hoisting time, the optimization value for the location of maximum torsion angle is 243 to 18 mm is obtained and the experimental values are 240 to 15 m. The reinforced wire rope has a better performance compared to the steel wire rope. [ABSTRACT FROM AUTHOR]

Deformation‐induced mechanisms, namely, transformation‐induced plasticity (TRIP) and twinning‐induced plasticity (TWIP), are primarily responsible for improved tensile properties in medium‐Mn steels. Additionally, lower density and processing costs make these steels useful in various industries, particularly the automotive industry, which mandates a good understanding of underlying processing–microstructure–property correlations. Therefore, the present study reviews different thermomechanical processes and corresponding microstructural evolutions, followed by mechanical properties. In addition, an assessment of the fatigue behavior of medium‐Mn steels based on duplex or multiphase microstructure and associated mechanisms has been presented. In high‐cycle fatigue (HCF) loading, strain‐induced martensite formation through TRIP at the crack tip is a barrier to dislocation motion. It deviates the crack propagation path to adjacent phases, which results in higher fatigue life. On the other hand, relatively high martensite boundaries initiate microcracks and accelerate crack propagation, resulting in lower life in low‐cycle fatigue (LCF). However, the TWIP mechanism prevents cyclic softening and promotes cyclic saturation, extending fatigue life. The compositions of medium‐Mn steel for enhanced fatigue resistance have been proposed. To that end, it is hypothesized that the TRIP + TWIP mechanisms lead to exceptional LCF performance. Further, microalloyed medium‐Mn steels are expected to exhibit improved LCF and HCF behavior. [ABSTRACT FROM AUTHOR]

Grade 91 steel is widely used in the boilers and piping of thermal power plants. There has been significant research interest in understanding the variations in creep characteristics among different heats of this steel for effective plant management. In recent years, thermal power plants have been subjected to frequent load changes and startup/shutdown to adjust power supply and demand and stabilize frequencies. These operational shifts have raised concerns regarding the potential for creep-fatigue damage in high-temperature components. Therefore, this research focuses on creep-fatigue properties of Grade 91 steel and their predictability. Tensile, creep, strain-controlled fatigue, and strain-controlled creep-fatigue tests were performed on six Grade 91 steels with different heats and/or histories, and the characteristics in each test were compared. As a result, the variations in creep-fatigue life among the materials were found to be correlated with the difference in creep characteristics and stress level during stress relaxation. Furthermore, the study involved a comparative assessment of the predictive performance of creep-fatigue life using five different approaches: time fraction, classical ductility exhaustion, modified ductility exhaustion, energy-based, and hybrid approaches. Among these approaches, the hybrid approach, based on inelastic strain energy density at fracture formulated as a function of inelastic strain rate, exhibited the most accurate predictive performance. [ABSTRACT FROM AUTHOR]

In order to accurately assess the fatigue performance of semi-rigid base layers, this paper proposes a novel fatigue testing method for semi-rigid base layers that takes into account the spatial stress state. Based on this method, the fatigue performance of three types of reinforced semi-rigid base-layer materials (steel wire mesh, plastic geogrid, and fiberglass) was tested and compared with unreinforced materials. The fatigue strain evolution patterns of these materials were analyzed, and a fatigue strain characteristic value at the limit state was proposed as an evaluation index for the fatigue failure of base layer materials. The results showed that in terms of fatigue performance, plastic geogrid > steel wire mesh > fiberglass > unreinforced specimens. The development of tensile strain can be approximately classified into a three-stage growth pattern, consisting of "curve + straight line + curve". For the unreinforced specimens, the three stages of bending strain accounted for 10%, 70%, and 20% of the total fatigue life, respectively. The fatigue failure stages of the three types of reinforced materials had similar proportional ranges, representing 5%, 75%, and 20% of the total fatigue life, respectively. The fatigue strain characteristic values for plastic geogrid, steel wire mesh, fiberglass, and unreinforced specimens were 371 με, 280 με, 280 με, and 195 με, respectively. In summary, the use of reinforced materials within semi-rigid base layers enhances their fatigue performance, providing new insights and methods for extending the service life of road surfaces and offering scientific guidance for the practical application of reinforced materials in semi-rigid base layer road surfaces' fatigue performance. [ABSTRACT FROM AUTHOR]

Prestressed concrete composite girder bridges with corrugated steel webs (PCCGBCSWs) are extensively employed in bridge construction because of their low dead weight, fast construction, and high prestressing efficiency. Moreover, PCCGBCSWs will experience deformation and failure of the corrugated steel webs, including steel fatigue and fracture, during earthquakes. These changes will introduce safety hazards, which can be addressed via bridge disaster prevention and mitigation. Because near-fault pulse-like ground motions (NFPLGMs) have high peak accelerations, these motions can easily cause damage to a bridge. Therefore, in this study, a seismic fragility assessment is performed for long-unit PCCGBCSWs subjected to NFPLGMs considering spatial variability effects, and a sensitivity evaluation of the seismic fragility is conducted considering girder type, bearing type, ground motion type, and apparent wave velocity to offer a point of reference for seismic design. The results show that PCCGBCSWs are less vulnerable than concrete bridges. The shock absorption effect of the friction pendulum bearing is better than that of the viscous damper. The impact of NFPLGMs on bridges is greater than that of near-fault non-pulse-like ground motions (NFNPLMs) and far-fault ground motions (FFGMs). The seismic fragility under nonuniform excitation conditions is greater than that under uniform excitation conditions, showing an increasing trend with decreasing apparent wave velocity. [ABSTRACT FROM AUTHOR]

An isolation layer composed of isolators and steel dampers in base-isolated tall buildings can dissipate wind-induced energy via repeated elasto-plastic deformation. Its energy dissipation can be used to estimate its wind-induced responses and the fatigue damage in the steel dampers. Computationally costly time history analyses using multi-degree-of-freedom (MDOF) models suggest that some structural parameters influence the isolation-layer energy dissipation. However, using common single-degree-of-freedom (CS) models cannot fully capture such influences (e.g., those caused by the damping ratio and the natural period of the upper structure). Hence, this paper proposes a more accurate new equivalent single-degree-of-freedom (ES) model to estimate the isolation-layer energy dissipation in base-isolated tall buildings under strong winds. The ES model considers the influence of structural parameters and uses the first mode shapes of the MDOF models. It is as computationally efficient as, but is more accurate than, the CS model. The results indicate that it can estimate the isolation-layer energy dissipation as closely as MDOF models of base-isolated tall-building under strong winds. [ABSTRACT FROM AUTHOR]

The motivation of this work is to investigate cyclic deformation behaviors of 42CrMo steel performed under uniaxial stress-controlled cyclic-loading. The cyclic deformation (i.e., ratchetting behaviors induced by near-yield mean stress) is positively correlated to the increases in mean stress and stress amplitude. However, the increase in loading frequency has an opposite influence on the cyclic accumulation deformation. This is mainly because increasing loading frequency contributes to dynamic strain strengthening, thus evidently inhibiting ratchetting evolution. [ABSTRACT FROM AUTHOR]

In this study, the refinement of two microstructures was controlled in medium carbon 25Cr2Ni3MoV steel via multi-step tempering and partition (MTP) to achieve high cryogenic strength–ductility combinations. Microstructure evolution, the distribution of stress concentration, and microcrack formation and propagation during cryogenic Charpy impact testing were investigated. Compared with their performance in the quenching and tempering states (QT), the MTP steels showed a significant improvement in yield strength (1300 MPa), total elongation (25%), and impact toughness (>25 J) at liquid nitrogen temperature (LNT). The strengthening contributions mainly originated from the high dislocation density and refinement cementite (size: 70 nm) in the martensite lath (width: 1.5 μm) introduced by refined reversed austenite and its latter decomposition. The instrumented Charpy impact results indicated that cracks nucleated in the primary austenite grain (PAG) boundary for two steels due to the strain concentration band preferring to appear near PAGs, while cracks in the QT and MTP samples propagated along the PAGs and high-angle grain boundary (HAGB), respectively. The crystallized plasticity finite element simulation revealed that the PAG boundary with cementite precipitates of large size (>200 nm) was less able to dissipate crack propagation energy than the HAGBs by continuously forming a high strain concentration area, thus leading to the low-impact toughness of the QT steel. [ABSTRACT FROM AUTHOR]

This paper shows the relationship, in steel fiber-reinforced concrete, between fiber orientation and fatigue response through the combined use of computed tomography (CT), digital image processing (DIP) software and wedge splitting test (WST). The WST cubes were extracted from conventional 150 × 150× 600 concrete prisms and a groove and notch were carved on different faces in such a way that in half of the test specimens the fibers are oriented mostly perpendicular to the breaking surface and, in the other half, the fibers are mostly oriented parallel to the breaking surface. Fiber orientation was obtained using a CT device and DIP software from a miniprism extracted from the previously mentioned concrete prisms. The results show that there is a strong correlation between the crack-sewing fiber orientation on the one hand and fatigue life and crack opening rate per cycle on the other hand. Cubes with a higher percentage of fibers perpendicular to the crack surface (i.e., with a higher efficiency index) show a longer fatigue life and a lower crack opening rate per cycle, while cubes with a lower efficiency index show a shorter fatigue life and a higher crack opening rate per cycle. [ABSTRACT FROM AUTHOR]

Existing semantic segmentation methods for fatigue cracks in steel bridge girders are fully supervised and thus demand manual annotation of pixel-level labels, which is time-consuming. Recently, there have been remarkable developments in semantic segmentation under image-level tag supervision. However, these weakly supervised approaches are still inferior to the fully supervised manner in terms of accuracy. To mitigate this gap, this paper commits to improving the correlation between high-level semantics to low-level appearance. A two-stage training manner with a segmentation refinement module for progressively refining pseudolabels and training the segmentation network was proposed. First, an activation modulation and recalibration scheme was recommended, which leverages a spotlight branch and a compensation branch to locate both the discriminative and less-discriminative object regions. Then, the generated pseudolabels were used as supervision to train the segmentation network in the proposed two-stage manner. In the first stage, the network was pretrained to learn all essential information and provide a basic segmentation performance, aiming to facilitate network convergence in the following training. To develop the inference quality, in the second stage, the pretrained network was further trained recursively with the designed segmentation refinement module to improve the labels using two postprocessing algorithms between each iteration. Overall, our method achieves comparable inference results to fully supervised approaches while significantly reducing annotation workload, which improves the efficiency of routine bridge inspection. [ABSTRACT FROM AUTHOR]

The low cycle fatigue properties of Q355B structural steel subjected to different levels of corrosion were investigated in the present study. The corroded Q355B steel coupons were obtained by means of cyclic wet–dry immersion corrosion, and the low cycle fatigue tests of coupons with different corrosion degrees, featuring both constant and variable strain amplitudes, were carried out. The cyclic stress response, cyclic skeleton curve, and hysteretic curve of the corroded steel were analyzed. The low cycle fatigue life of the corroded steel was predicted, and a constitutive model of the corroded steel was proposed. The results show that corrosion reduced the low cycle fatigue life of Q355B structural steel. Finite-element (FE) models were developed, and the FE results were in good agreement with the experimental curves, indicating the accuracy of the constitutive model proposed in this paper. The findings from the present research provide a valuable reference for the accurate assessment of the low cycle fatigue properties of steel structures with varying degrees of corrosion. [ABSTRACT FROM AUTHOR]

Large infrastructure projects can efficiently use large diameter bars as longitudinal reinforcement in reinforced concrete elements. In earthquake-prone zones, critical regions of these elements must be detailed for ductility and hysteretic energy dissipation. Longitudinal bars in these regions are expected to sustain large-amplitude strain cyclic reversals before bar fracture occurs, in a mode of failure defining the collapse prevention limit state. To date, no successful large strain-amplitude cyclic loading testing has been reported on large-diameter reinforcing bars to observe the large-strain amplitude fatigue life of such bars, which often involves plastic bar buckling. This paper describes a test program designed to determine the plastic buckling/straightening fatigue life of ASTM A706 Grade 60 No. 18 bars (Ø57 mm) reinforcing bars subjected to cycles of reversed plastic strains. The design and implementation of the loading apparatus, critical for the gripping of the bars, the metallurgical characterization of the bars, and several key test results are discussed in the paper. Finally, the paper discusses a general unidimensional fatigue damage index precursor to bar fracture following a few plastic buckling and straightening cycles. [ABSTRACT FROM AUTHOR]

White etching area (WEA) is a primary damage in rolling contact fatigue (RCF) of bearing steels. In spite of extensive investigations, there is a large discrepancy in the existing mechanisms of WEA formation. We attempt to unify the mechanisms from the perspective of shear localization and plastic damage accumulation based on ductile damage. RCF tests were conducted to generate WEAs with various microstructures and compositions. A thermodynamically consistent model of the ductile damage evolution from an inclusion was established by developing the phase field damage coupled with the crystal elastic‐viscoplastic constitutive relationship under RCF. The model was implemented into the FE framework through a user materials subroutine. The results indicated that the WEA is the shear band resulting from shear localization. The large inhomogeneity and scatter in WEA's microstructure are due to the influence of the crystal orientation. The development and orientation of SBs predicted by the model and the experimental observation of the WEA are in good agreement. The large micro‐shear strain in the WEA provides the driving force for mechanically controlled austenite phase transformation. The shear band center, which has the largest strain and the least stress, is where cracks initiate. This demonstrates that contrary to earlier reports that WEA is induced by previously formed crack faces friction, cracks actually initiate from the interior of the WEA. Highlights: WEA presents the form of shear band as a result of shear localization.WEA's orientation is significantly influenced by the crystal orientation.Large micro‐shear strain in WEA is the driving force for phase transformation.Instead of WEA being induced by friction of crack faces, cracks begin in WEA. [ABSTRACT FROM AUTHOR]

Fatigue resistance of steel containing non-metallic inclusions (NMIs) varies widely, depending on many criteria; therefore, finding the most compromised types of NMIs is a sober objective that may significantly reduce severe damage and premature failure in many applications, such as bearings, gears, transmission shafts, etc. The multiple criteria decision-making methodologies have been used in this study to assess the more effective NMI types using the analytical hierarchy process by expert choice software. The five most common types of non-metallic inclusions selected are oxides, sulfides, carbides, silicates, and nitrides, based on different criteria: size, shape, distribution, mechanical properties, and quantity. The results showed that the oxide NMIs are the optimum type relative to the other four options regarding the fatigue resistance of about 35%, probably due to their spherical shape and small size. The most dominant criterion is mechanical properties, which have an effective percentage of 34.6% among the other criteria. It means that the reduction of other types rather than oxide NMIs probably enhances the fatigue resistance of the steel. [ABSTRACT FROM AUTHOR]

The steel–concrete joint (SCJ) of a railway hybrid girder–cable-stayed bridge transmits tremendous internal forces, resulting in complex structure and stress. The existing complex SCJs lead to difficulties in on-site concrete construction, and the complex stress of the SCJ under train load is prone to diseases such as steel concrete fatigue detachment and cracking. To investigate the complex fatigue performance of a novel SCJ for a long-span high-speed railway hybrid box girder–cable-stayed bridge with a main span of 672 m, finite-element analysis (FEA) and a 1:2 scaled fatigue model test with 2.15 million cycles were conducted. The results showed that the numerical fatigue stresses of the SCJ exhibited a significant shear lag effect in the transverse direction with unfavorable fatigue stresses at the side box. After 1.70 million loading cycles, all the steel plates of the test model remained intact, indicating good fatigue resistance during the design life. Cracks appeared at the junction between the horizontal diaphragm and the web of the steel transition segment (STS) after 1.85 million cycles, showing a fatigue life of 118 years. The measured fatigue crack life of the concrete deck over the postanchor position of the prestressed tendons in the STS was 30.5 years for the local concentrated tensile stress, which can be improved by casting the concrete after the tendons are prestressed. No fracture or other abnormalities occurred in the shear studs and perforated rib (PBL) rebars, and the deflection of the test model and the slip between the steel and concrete were insignificant during the fatigue tests, indicating the good fatigue performance of the SCJ, which was better than that of the STS. The thickness of the bearing plate and diameter of the shear studs for the actual SCJ were suggested to be 40–60 and 16–25 mm, respectively, based on a parametric study. [ABSTRACT FROM AUTHOR]