The fatigue strength of additive manufacturing (AM) materials has been severely compromised by inherent nonuniform microstructures (printing defects, element segregation). In this contribution, we innovatively explored a hot-isostatic pressing (HIP) process above the austenitizing temperature and a low-temperature austenitizing (LTA) process for enhancing the fatigue resistance of selective laser melting (SLM) 18Ni(300) steels. The above HIP process could synchronously shrink printing defects and homogenize elements, and its fatigue strength (663 MPa) is similar to or even higher than the traditional cast and forged (TC&F) steels. Meanwhile, the martensite blocks were significantly refined by the LTA process, but the fatigue strength did not increase simultaneously with tensile strength. It is found that the block boundaries are the preferred location for reversed austenite nucleation and growth accompanied by enrichment of elements, and the more precipitate-free zones (PFZs) generated by block refinement, which accelerate the initiation and propagation of microstructurally small cracks (MSCs).

Fatigue crack growth (FCG) behavior governs the safety and remaining life assessment of engineering structures and thus represents a central issue in fatigue fracture research. In conventional Paris-type models, the exponent m is commonly obtained by fitting FCG data, with limited explicit linkage to intrinsic mechanical properties of materials. This limits the model generalizability across materials and loading conditions. To address this issue, this study proposed a coupled framework integrating a theoretical model with machine learning (ML) for predicting FCG in steels. First, a theoretical FCG model incorporating an instability constraint was formulated, in which the fatigue crack growth rate (FCGR) is explicitly related to loading variables (stress intensity factor range Delta K and stress ratio R) and material properties (ultimate tensile strength sigma b, fracture toughness KIC, and elastic modulus E). Subsequently, four supervised learning algorithms were employed, including feedforward neural network (FNN), support vector regression (SVR), extreme gradient boosting (XGBoost), and k-nearest neighbors regression (K-NNR), to learn a nonlinear mapping from sigma b and KIC to m. Finally, the m predicted by ML was embedded into the theoretical model to enable rapid prediction of da/dN as a function of Delta K. The proposed approach was validated against FCG experiments on GCr15 bearing steel. The results show that FNN and XGBoost achieve higher accuracy and more robust generalization, with most predictions falling within an error band of +/- 10%. This framework offers a practical route for fast prediction of the FCG behavior and remaining life assessment of steels when the experimental data are limited.

Aiming at abnormal emission of floor oil-type gas in No.2 Coal Mine, Huangling Mining Area, this study combines field measurement and FLAC3D numerical simulation to analyze emission laws and disaster-causing mechanisms. Results show that oil-type gas mainly emits from floor heave fractures 5–10 m ahead of the working face, with a maximum concentration of 95%. Borehole emission follows a power-law pattern and attenuates rapidly within one week, with an attenuation coefficient of 1.24–2.14 d−1 and a fitting correlation coefficient R2 of 0.89–0.99. Emission intensity decreases with an increasing distance between the gas reservoir and coal seam. In-situ stress, geological structures, and gas pressure are the three main controlling factors, and 72% of abnormal emission points are located in anticline structures. Mining forms an approximately 40 m pressure-relief gas conduction zone ahead of the working face. Oil-type gas emission occurs only when the reservoir is within this zone. The results provide a key quantitative basis for the prevention and control of oil-type gas hazards in coal-oil-gas symbiotic mines.

To explore the potential for improving the 500℃ rotating bending fatigue performance (RBF) of carburized ultra-high-strength gear steel, three shot peening (SP) intensities (0.2, 0.3, and 0.4 mmA) were applied for surface treatment. The microstructure, surface roughness, microhardness, residual compressive stress (RCS), and high-cycle 500℃ RBF performance of specimens with and without SP were systematically investigated. The results show that SP refines the surface microstructure and significantly increases the surface roughness, microhardness, and RCS of the specimens. The 500℃ RBF strength first increases and then decreases with increasing the SP intensity, with the highest value of 887 MPa obtained at an SP intensity of 0.2 mmA. The increased microhardness and RCS shift the fatigue crack initiation location toward the interior of the specimen and are the main factors responsible for the improvement of 500℃ RBF strength. In contrast, microstructural defects induced by high-intensity SP change the crack initiation mode and lead to a reduction in 500℃ RBF strength.

ABSTRACT The effects of mean stress and stress biaxiality under complex loading conditions pose significant challenges in engineering design, and few studies bridge the multiaxial and stress ratio effects in a unified framework. This work addresses these gaps by proposing a fatigue damage model that synergistically integrates the variations in multiaxial stress and stress ratio. The model leverages critical plane concepts to capture failure mechanisms while incorporating stress ratio dependencies through physically informed parameters. Experimental validation using two steels (AISI 4340 and BG801) demonstrates the model's capability to predict both fatigue life and crack initiation planes under multiaxial and variable stress ratio conditions. Furthermore, the approach provides insights into material behavior transitions under varying stress states, offering a practical tool for engineering applications that require the simultaneous consideration of complex loading scenarios.

Recently, and have been proposed as new isogeny-based key exchange protocols to resist torsion point attacks. In this work, we propose two novel types of isogeny-based key exchange protocols based on and . Firstly, we propose ^ and ^ using different forms of primes in and . Secondly, we introduce a similar hardness assumption that reveals an image of torsion point of small order based on the assumption of . We show that this assumption is sufficient to build parallel isogenies and construct two key exchange protocols called ^ and ^ . Finally, we provide the corresponding parameters for the new protocol proposed at different security levels and develop a Sagemath implementation of these protocols. For example, compared to the original , when the security strength is 128 bits, ^ and ^ achieve speeds that are 2.2 × and 28.5 × faster in the key generation phase and 2.0 × and 19.1 × faster in the key exchange phase. The size of the public key is reduced by factors of 1.1 × and 2.7 × , respectively.

Bearings typically undergo rolling contact fatigue (RCF) failure during service, characterized by extensive spalling, which poses significant challenges for capturing crack initiation behavior and elucidating the underlying mechanism. Thus, the stress field under RCF was simulated and utilized as an applied load in 90 degrees out-of-phase non-proportional compression-torsion fatigue tests in this work, enabling the crack initiation characterization. A modified multiaxial fatigue prediction model was developed with a quadratic relationship between the shear stress amplitude and equivalent normal stress on the critical plane, which was determined by introducing a material parameter to quantify the different effects of the amplitude and mean normal stress on fatigue damage. Based on the quantitative relationship demonstrated by the material parameters, the contribution of mean normal stress to fatigue damage is 0.32 times that of the amplitude. The equivalent normal stress on the critical plane is tensile, elucidating that bearings actually experience tension-torsion fatigue failure under RCF, although it manifests as compression-torsion fatigue macroscopically.

Defects affect fatigue performance of high-strength steels significantly, which can be quantitatively enunciated from the perspective of defect size, but not from the perspective of defect shape and type to date. In this work, fatigue crack initiation behaviors at various kinds of high-strength steels containing defects with different shapes and types are comprehensively analyzed. Based on Murakami's model quantitatively expounding the effect of defect size on the fatigue cracking behaviors of high-strength steels, the damage factors considering defect shape and type, which reflect the intrinsic characteristics of defects, are rationally proposed and introduced. Accordingly, the effects of defect size, shape and type on the fatigue cracking mechanisms of high-strength steels are revealed quantitatively. Finally, a unified fatigue cracking criterion induced by defects in high-strength steels is established, achieving the normalized quantitative description of fatigue cracking behaviors induced by different kinds of defects. The critical size criterion for different kinds of defects inducing the fatigue crack initiation behaviors of high-strength steels is revealed, and a reasonable design strategy for enhancing the fatigue resistance of high-strength steels with multiple kinds of defects is proposed. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

The microstructures, basic mechanical properties, and high-cycle fatigue behaviors of aged X00CrNiMoCoTi13-7-3-8 maraging stainless steel with different solution treatments were investigated in the present study. Herein we demonstrated that the blocky retained austenite is a restrictive factor in improving the fatigue strength of aged X00CrNiMoCoTi13-7-3-8 maraging stainless steel with different aging treatments, prompting this study to explore the regulation of fatigue properties by controlling the size of blocky retained austenite. Lower solution temperatures result in a reduction in grain size, martensite block dimensions, and blocky retained austenite, as confirmed by optical microstructure, electron backscatter diffraction (EBSD) and transmission Kikuchi diffraction (TKD) analyses. The weakest link microstructure leading to fatigue cracking of specimens with different solution treatments is still the blocky retained austenite, and refining the blocky retained austenite by lowering solution temperature from 1100 degrees C to 1000 degrees C can effectively obtain a significant fatigue strength enhancement from 621 to 713 MPa.

Double-base chain (DBC) has been extensively studied for speeding up scalar multiplication, which significantly impacts the execution efficiency of ECC. In this paper, we estimate the theoretically optimal upper bound and lower bound for the leading term of a canonic DBC. Firstly, we develop a new method to estimate the bounds and prove its correctness, based on Yu et al.’s work in EUROCRYPT 2020. Secondly, we obtain the new bounds by applying this new method. Thirdly, we compare the efficiency improvements of canonic DBC generation algorithms and scalar multiplication algorithms using the new theoretically optimal upper bound. Compared to NAF algorithm, our new scalar multiplication algorithm achieves about 13% efficiency gains. Finally, we analyze the bounds for the leading term proposed by Eom et al., identify their limitations and provide counterexamples to demonstrate the issues.

Since detecting fatigue strength requires considerable time and economic cost, exploring its prediction models is of great scientific and engineering importance. In this work, by collecting and analyzing the plastic deformation characteristics and dynamic-static mechanical properties for different metallic materials, an intrinsic response mechanism in dynamic-static strength was discovered, and a quasi-intrinsic model for predicting fatigue strength was subsequently constructed. From the perspective of strengthening mechanisms, although increasing the content of crystal defects (CDs) can enhance static strengths, it also reduces the microstructure homogeneity and deformation uniformity, resulting in a monotonic decrease in fatigue ratios. We found that as the strengthening level increases, the strain-hardening capacity (SHC), reflected by the ratio of yield strength to tensile strength, exhibits either an increasing or decreasing trend. Depending on whether the CD content is the main influencing factor for SHC, either the yield or tensile strength is adopted to characterize CD content. This approach defines a theoretical condition where the fatigue ratio equals 1, representing the state of non-local plastic damage (N-LPD). By integrating this theoretical fatigue ratio of 1 with a single experimentally measured fatigue ratio at a given strengthening level, the trend of fatigue ratios across the entire strengthening range can be accurately depicted. This enables rapid prediction for fatigue strength of metallic materials with varying strengths, thereby substantially reducing the need for extensive fatigue tests.

This study presents four principles for enhancing metallic fatigue resistance, achieving record-high fatigue strength in cold-drawn pearlitic steel with oriented nano-scale lamellar microstructure and extremely small inclusions.

In the present study, variability in high-cycle fatigue lives has been studied in AISI 52100 high-strength steel containing TiN inclusions at two heat treatment states. It is found that the spatial orientations of TiN inclusions in the samples are randomly distributed, and have no significant effect on their cracking behavior under cyclic stress. All the examined samples revealed that the fracture planes of TiN inclusion are approximately vertical to the loading axis. Accordingly, a fatigue life prediction model is proposed by taking into account the cracking behaviors of TiN inclusions, ultimately reducing the prediction error of fatigue lives to within 2.5 times of the experimental values. The model demonstrates that the size and shape of TiN inclusions significantly affect fatigue lives of the samples. Specifically, TiN inclusions in samples with longer fatigue life either has a small area perpendicular to the loading direction or is thin parallel to the loading direction. Overall, the comprehensive results regarding the effect of TiN inclusions on fatigue life highlight the strategies to minimize uncertainty in fatigue life predictions for high-strength steels.

With the increasing demand for high-performance metallic materials, the improvement of fatigue strength (FS) has become a crucial issue. This study focuses on the AISI 52100 steel, a material with leading fatigue performance and low-cost raw material, aiming to further improve its FS. It is found that the fatigue damage mechanism of 52100 steels with different tensile strengths has undergone significant changes, and the inclusions, mainly nitride and oxide, are key factors limiting the further improvement of FS. Therefore, the size reduction and modification of inclusions were attempted through the rare earth addition and strict control of harmful elements. Combining targeted microstructure adjustment, the FS of the 52100 steel has been further enhanced to similar to 1.6 GPa, exceeding that of other metallic materials (performed in uniaxial tension with a stress ratio of R = 0.1), and thus establishing it as a standout for its exceptional performance-to-cost ratio. By clarifying the influences of different types of inclusions on fatigue performance and establishing the correlation between micro-hardness (or strength) and FS, an optimization strategy for FS improvement of the 52100 steel was proposed. The FS has been improved by approximately 187 MPa at most by implementing this strategy. These achievements provide feasible technical approaches and theoretical foundations for the anti-fatigue design of metallic materials. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Improving the fatigue strength of engineering materials is the most important strategy to ensure the safety of key components. Regrettably, although a large number of high-strength materials have tensile strengths over 3 GPa, their fatigue strengths do not exceed 1 GPa under push-pull loading. Here, we report the highest fatigue strength for steels to date (of 1103 MPa) under push-pull loading with the stress ratio of R =-1 in a GCr15 bearing steel, achieved by precisely controlling the microstructure and defects. First, the plasticity of the inclusions is improved by adding minute rare-earth elements, which efficiently prevents their brittle fracture. Second, a new shearable inclusion/matrix interface structure is formed, further improving their collaborative deformation ability. Third, an excellent synergy between tensile strength and plasticity is achieved by adjusting heat treatment to reduce the fatigue cracking tendency at inclusions. These new findings provide insight into how the fatigue strength of highstrength steels can be improved, through microstructural adjustment and defect control. This strategy can be readily achieved with current industrial technologies and provides a promising and effective procedure to improve the fatigue properties of other high-strength metallic materials.

In this study, the microstructures and high-cycle fatigue behaviors of high-titanium maraging stainless steel under different aging treatments were investigated. It is interesting to find that the fatigue strength of the high-titanium maraging stainless steel under different aging treatments does not change obviously with the increment of tensile strength, displaying the fatigue strength plateau phenomenon. The fatigue crack originated from the material matrix in the subsurface of specimen. It is deduced that the fatigue strength of high-titanium maraging stainless steel under different aging treatments is dominated by the blocky retained austenite, resulting in the fatigue strength plateau due to the "short-plate" effect on the fatigue cracking.

The strength, toughness, and fatigue crack growth (FCG) resistance of high‐strength steels are the key performance indexes concerned in the material selection of engineering components. It is considered that the FCG resistance of high‐strength steels can be optimized by simultaneous strengthening and toughening. In order to make clear whether the above view is correct or not, the strength–toughness combination and FCG resistance of AISI 4340 steel under different heat treatments are investigated and compared with those of 18Ni maraging steel in the present study. Meanwhile, the major fatigue damage mechanism of the AISI 4340 steel is analyzed and discussed. It is found that the FCG resistance of AISI 4340 steel enhances rapidly at first and then remains approximately the same with the decrement of strength (the improvement of toughness). Moreover, it is detected that simultaneously upgrading the strength and toughness of high‐strength steels cannot improve the FCG resistance. Finally, it is believed that the microscopic fatigue damage mechanism is the major factor determining the FCG resistance rather than the macroscopic strength–toughness combination, and the factors affecting the FCG resistance of AISI 4340 steel are mainly the pre‐existing dislocations and carbide precipitates.

To propose a time-saving method for evaluating the fatigue strength of carburized steel, the fatigue behavior and fracture mechanism of carburized 14Cr14Co13Mo5 steels are studied by the rotary bending fatigue tests. It is found that the fatigue crack initiation site changes from surface to internal after carburizing due to the residual compressive stress and carbide cluster caused by the carburization. Besides, a notable correlation between the stress intensity of the cracked carbides at fatigue crack initiation site and fatigue life is observed in the carburized samples. This correlation allows for the estimation of fatigue strength at long conditional life based on samples tested at relatively high stress amplitudes with short lives, achieving a prediction error within 10% for the material studied. A significant time saving of approximate to 65% compared to the staircase method is achieved. The proposed method has significant implications for improving the efficiency fatigue strength evaluation in carburized steels containing carbides.

It is the principal means to optimize the service performance of wheel steels by controlling the microstructure through composition design. The traditional regulation of adjusting alloy elements is mainly based on some empirical methods only strengthening the static mechanical properties of materials; while the optimization mechanism under the actual service condition of rolling contact fatigue (RCF) still lacks a reasonable explanation. In this work, the entire process of RCF failure in wheel steels was first analyzed to reveal the failure mechanism, proposing that the accumulation during severe plastic deformation (SPD) in the early stage was the major cause for the RCF crack initiation. Then, the effects of alloy elements on the intrinsic microstructures and mechanical properties were studied, and the optimization mechanism of the RCF performance was elucidated that strengthening the static properties of wheel steels reduced the SPD accumulation, thereby restraining the initiation and propagation of the RCF cracks. Finally, through the analogy and analysis of the RCF failure mechanism, it is suggested that the shakedown map and the fatigue index (FI) appropriately reflect the effect of SPD accumulation on the RCF crack initiation, and can serve as powerful criteria for rapid predicting the RCF performance of wheel steels.

Cracking resistance is vital to the practical application of spring steels, which consists of fracture toughness ( K IC ) under the quasistatic loading condition and fatigue crack propagation (FCP) resistance under the cyclic loading condition. In the present study, the relation between the K IC /FCP resistance and microstructure of the 50CrMnSiVNb spring steel tempered at various temperatures is studied. In the results, it is shown that the dislocation density is the main factor influencing the K IC and FCP resistances, and the carbide size/quantity and morphology can also affect the K IC and FCP resistances. Thus, reducing the dislocation density is the most effective method to enhance the cracking resistance of the investigated steel. Moreover, decreasing the aspect ratio and obtaining a moderate size of tempered carbides are also beneficial to the cracking resistance. In addition, free hydrogen atoms can cause intergranular fracture on the fracture surface, worsening the FCP rate. To enhance the FCP resistance, smelting processes need to be improved to reduce the hydrogen content of the investigated steel.