Search Results (621)

Electric-shovel top sheave bearings with sensor-embedded slots operate under harsh service loads, making them prone to fatigue crack initiation and propagation. Accurate predictions of crack growth within the bearing body are therefore essential for intelligent bearing design and reliability assessments because the bearing integrity directly affects shovel service life and safety. This paper presents a sub-modeling-based method that embeds initial cracks while preserving actual roller-ring boundary conditions and ensuring computational efficiency via adaptive mesh refinement. A global model first identifies critical crack-prone zones, after which the sub-model systematically examines the effects of the initial crack angle and sensor-embedded slot depth on the propagation behavior. The results indicate that both factors significantly increased the stress intensity factor (SIF). Among the evaluated designs, the 15 mm -deep slot produced the highest SIFs and the shortest predicted crack-propagation life, indicating that slot depth was a key design parameter under the investigated conditions. The findings provide theoretical support for the structural design and fatigue evaluation of intelligent electric-shovel top sheave bearings. Full article

SBS-modified asphalt is widely used in high-grade pavements for its excellent rutting and fatigue resistance; however, how its friction behavior evolves under submerged conditions with surface distress remains poorly understood. To address this gap, we developed a rubber–asphalt friction tester to characterize quasi-static rubber–asphalt friction under submerged conditions with three typical distresses: pothole, crack, and surface void. Our results show that friction increases with roughness, load, and water temperature, but degrades progressively under cyclic loading. Among the three distresses, surface void offers the most stable friction performance, whereas pothole exhibits the largest friction loss under repeated loading, identifying them as high-priority repair targets. The positive temperature–friction correlation further implies that wet-skid risks are higher at lower temperatures, providing a basis for seasonal maintenance scheduling. Three-dimensional wear analysis reveals distinct mechanisms: pothole causes localized deep-pit wear, while surface void generates uniform roughening, explaining their contrasting durability. These findings directly support distress prioritization, friction-performance evaluation, and maintenance planning for SBS-modified pavements in rainy environments. Full article

Fatigue crack propagation prediction plays a critical role in structural health monitoring and remaining useful life (RUL) assessment of engineering structures. However, conventional particle filter (PF) algorithms may suffer from particle impoverishment and insufficient particle diversity, which can adversely affect prediction accuracy and stability. To address these limitations, a hybrid genetic algorithm–particle filter (GA-PF) is developed for fatigue crack propagation prediction by incorporating genetic operations, including selection, crossover, and mutation, into the PF framework to optimize particle distribution and enhance global search capability. The proposed method is evaluated using fatigue crack growth experimental data, and its performance is compared with that of the conventional PF algorithm. The results show that the GA-PF method achieves improved prediction performance for fatigue crack propagation and remaining useful life estimation. At 255,000 cycles, the GA-PF algorithm predicted a median RUL of 22,500 cycles, with a relative RUL error of 9.04%, whereas the conventional PF algorithm resulted in a relative RUL error of 45.41%. These results indicate the potential benefit of introducing genetic optimization into the particle filter framework for fatigue crack propagation prediction. The findings further suggest that the hybrid GA-PF method can improve predictive performance compared with conventional PF on the tested dataset. Full article

Predicting the fatigue lives of high-performance alloys, specifically aluminum 7075-T6 and Inconel 718, is essential for ensuring structural integrity in applications such as aerospace and energy. While Poisson’s ratio is typically treated as a constant within fracture mechanics and finite element analysis, it has been found to vary significantly with increased temperatures and substantial amounts of plastic deformation. Variations in Poisson’s ratio can, therefore, have a significant impact on local stress fields around cracks and the behavior at crack tips. This study introduces a novel approach by systematically isolating the effects of varying Poisson’s ratios on fatigue life cycles, stress distributions, and fatigue crack growth using finite element analysis with the robust ANSYS SMART crack growth feature. The results indicate a stark difference in the effects of Poisson’s ratio on the fatigue life of aluminum 7075-T6 compared to Inconel 718. A strong negative correlation exists between Poisson’s ratio and fatigue life cycle numbers for aluminum 7075-T6, whereas a more linear trend is observed for all fatigue life cycle numbers of Inconel 718. The underlying reasons for these trends lie in the differing sensitivities of elastic, shear, and bulk moduli between the two alloys. Overall, a higher Poisson’s ratio intensifies the maximum principal stress for both alloys. Additionally, an increase in Poisson’s ratio leads to a decrease in von Mises stress for both metals. Furthermore, these numerical results demonstrate that an increase in Poisson’s ratio corresponds to a decrease in the cyclic plastic zone size at the crack tip for both alloys, indicating enhanced hydrostatic constraint and reduced shear deformation. The findings presented herein underscore the necessity of eliminating the use of static values for Poisson’s ratio when evaluating the structural performance of high-performance alloys under extreme operational environments. Additionally, this research highlights several key areas where existing modeling approaches are lacking and establishes a framework for developing improved constitutive models for fatigue life prediction. Full article

In ultra-supercritical (USC) power plants, P92 steel welded joints are continuously subjected to creep-fatigue (CF) loading, rendering them susceptible to premature cracking during service. To investigate the CF interaction behavior, CF tests were performed on P92 steel welded joints at 650 °C under various dwell times. The results indicate that prolonged dwell periods progressively shorten the cycle life. Scanning electron microscopy (SEM) observations reveal that with increasing dwell time, the fracture mechanism of the P92 steel gradually transitions from a fatigue-dominated failure mode to one governed by creep-fatigue interaction damage. Subsequently, nanoindentation was employed to evaluate the hardness (H), elastic modulus (E), and creep deformation, based on which the strain rate sensitivity (m) was estimated and the underlying damage mechanisms were thoroughly discussed. Full article

Asphalt serves as the core binder for heavy-load high-modulus pavements, and its viscoelasticity across a wide temperature range directly governs pavement-rutting resistance, low-temperature crack resistance and service life. Virgin asphalt contains abundant light fractions and exhibits insufficient stiffness at high temperatures. Modification with single styrene–butadiene–styrene block copolymer (SBS) fails to meet the anti-deformation requirements under heavy loads, while separate incorporation of nano-silica (nano-SiO₂) aggravates low-temperature brittleness. Existing studies lack comprehensive investigations into the rheological evolution laws and synergistic microscopic mechanisms of asphalt modified by combined SBS and nano-SiO₂. In this paper, virgin asphalt was adopted as raw material to prepare composite modified asphalt with gradient dosages. Integrated macroscopic performance tests and multi-scale microscopic characterizations were conducted for systematic analysis. High-temperature, low-temperature and fatigue performances were evaluated via conventional physical property tests, temperature sweep tests, multiple stress creep recovery (MSCR), linear amplitude sweep (LAS) and bending beam rheometer (BBR) tests. Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC) and thin-layer chromatography–flame ionization detection (TLC-FID) were utilized to analyze variations in functional groups, molecular weight and four fractions, to elaborate the two-phase synergistic modification mechanism. The results demonstrate that the combined incorporation of SBS and nano-SiO₂ synchronously optimizes the comprehensive performances of asphalt. Compared with single-SBS-modified asphalt, the sample with optimal dosages achieves elevated high-temperature modulus and rutting factor, reduced permanent deformation, improved low-temperature stress relaxation capacity and remarkably decelerated fatigue damage accumulation rate. Microscopic characterizations verify that only physical interactions occur during modification without generating new substances. The nano-filler facilitates the aggregation of small molecules and increases the proportion of macromolecules; meanwhile, it physically adsorbs light fractions and induces apparent redistribution of asphalt components, raising the relative proportion of resins and asphaltenes in the organic asphalt phase, realizing moderate heavy-fraction enrichment of the asphalt system. This study clarifies the internal correlation between molecular fraction evolution characteristics and macroscopic rheological performances of asphalt co-modified by nano-SiO₂ and SBS, which can provide theoretical references for formula design and engineering application of modified asphalt materials. Full article

To explore the high-value utilization of liquid recovery products from waste wind turbine blades in road binders, a liquid-rich fraction obtained from subcritical acetic acid degradation and subsequent vacuum distillation of waste wind turbine blade epoxy composites was introduced into styrene–butadiene–styrene (SBS)-modified asphalt to prepare composite-modified asphalt. Conventional property tests, dynamic shear rheological tests, bending beam rheological tests, steady shear tests, master curve analysis, Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC) were conducted to systematically evaluate the influence of the liquid-rich fraction on the properties and structural characteristics of the composite-modified asphalt. The results showed that, with increasing liquid-rich fraction content, the softening point increased, while penetration and ductility decreased, and the rotational viscosity at 135 °C increased, indicating enhanced overall stiffness and high-temperature flow resistance. High-temperature rheological results showed that the liquid-rich fraction increased the storage modulus, loss modulus, and rutting factor, while decreasing the phase angle improved the high-temperature deformation resistance of the composite-modified asphalt. Low-temperature rheological results indicated that the creep stiffness S increased, the m-value decreased, and the S/m ratio increased, suggesting weakened stress relaxation capacity and reduced cracking resistance at low temperature. Fatigue factor and steady shear results revealed that the liquid-rich fraction enhanced structural stability and flow resistance but also increased fatigue damage sensitivity at intermediate temperature. Master curves, Black diagram, and Cole–Cole plots further demonstrated that the liquid-rich fraction increased the modulus level over a wide frequency domain and strengthened the structural stability of the asphalt system. FTIR and GPC results indicated that the introduction of the liquid-rich fraction increased the relative contents of aromatic structures and polar oxygen-containing groups and promoted molecular association and increased the apparent molecular weight level of the system. Overall, the liquid-rich fraction acted as a structure-enhancing modifier in SBS-modified asphalt, improving its high-temperature performance while causing a certain trade-off in low-temperature and fatigue properties. Therefore, the dosage should be selected by balancing high-temperature stability, low-temperature cracking resistance, and fatigue durability, and the practical sustainability of this recycling route still requires dedicated economic and environmental evaluation. Full article

Cyclic high-pressure gas impact is a promising waterless stimulation method for enhancing permeability in deep low-permeability coal seams. However, the nonlinear fracture evolution, cumulative fatigue damage, and coupled fracturing mechanisms during repeated gas impacts remain insufficiently understood. In this study, cyclic high-pressure gas impact tests were conducted on unconfined synthetic rock-like specimens under gas pressures of 5 MPa and 7.5 MPa. The macroscopic crack networks induced by repeated impacts were quantitatively characterized using digital image processing and box-counting fractal analysis. Ultrasonic P-wave velocity measurements were used to reconstruct the spatial evolution of internal damage after each impact, and an empirical Weibull statistical damage model was established to describe the nonlinear fatigue degradation process. In addition, two-dimensional LS-DYNA numerical simulations were performed to reveal the transient stress wave propagation and stress-field evolution during cyclic impacts. The results show that fracture propagation under cyclic gas impacts exhibits a distinct nonlinear pattern, characterized by slow early-stage damage incubation followed by rapid late-stage crack coalescence. The fractal dimension of the surface crack network increased markedly after repeated impacts, reaching a maximum of 1.51 under the 7.5 MPa condition. Ultrasonic damage analysis further indicates that, based on path-averaged evaluations, apparent damage is more pronounced near boundaries at the lower pressure, whereas higher pressure induces severe structural degradation along the central measurement paths, with a maximum damage value of 0.47. The combined experimental and numerical results suggest that the initial impacts generate transient stress waves and cumulative microcracking, thereby progressively weakening the rock matrix. This progressive degradation subsequently enables quasi-static gas wedging to drive macroscopic crack propagation and coalescence. These findings provide a preliminary phenomenological baseline for understanding cyclic gas-induced cracking, providing a preliminary basis for understanding waterless reservoir stimulation by cyclic gas impacts. Full article

This study examines how reclaimed asphalt pavement (RAP) dosage, virgin-binder grade, and virgin-binder content govern the cracking response of Marshall-designed mixtures. The experimental matrix comprised four RAP levels (30%, 40%, 50%, and 60%), two modified virgin binders (PG 76-22 and PG 88-34) evaluated at their respective optimum asphalt contents (OACs), and two binder-rich PG 76-22 variants (OAC + 0.3 and OAC + 0.5 percentage points); virgin mixtures served as controls. Cracking behavior was characterized by low-temperature semi-circular bending (SCB), the Illinois Flexibility Index Test (I-FIT), and direct-tension cyclic fatigue (DTCF). Fracture and fatigue indicators were subsequently integrated into cracking balance design diagrams, and k-means clustering was used to derive provisional, dataset-specific performance boundaries for long-term oven-aged mixtures. The results show that the higher-performance binder improved long-term cracking resistance at moderate RAP contents. By contrast, mixtures with 50% or 60% RAP and PG 76-22 displayed a distinctly brittle response. Increasing the PG 76-22 content above OAC produced only limited gains. These findings demonstrate that binder quality, rather than a small increase in binder dosage, is the more effective lever for balancing fracture and fatigue resistance in mixtures with substantial RAP contents. Full article

Increasing plastic waste and limited recycling rates underscore the need for value-added recycling applications. Polymers commonly present in plastic waste streams, including packaging films, bottles, caps, and rigid containers, may provide a practical pathway for developing plastic-modified asphalt binder (PMAB) systems. In this study, virgin high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) were selected as reference modifiers to evaluate their intrinsic effects on performance grade (PG) 58-28 and PG 67-22 base binders. Conventional high-, intermediate-, and low-temperature gradings were complemented by $\Delta T_c$, the Christensen–Anderson R-value (R-value), the Glover–Rowe (G-R) parameter, Linear Amplitude Sweep (LAS) fatigue analysis modeled via Viscoelastic Continuum Damage (VECD), rheological master curves, and extended Bending Beam Rheometer (BBR) testing. Modification improved high-temperature grading and LAS-based fatigue response while increasing master-curve stiffness. However, $\Delta T_c$, G-R parameter, and extended BBR results indicated increased low-temperature cracking susceptibility. High-temperature grades increased by 3.4 °C, 2.8 °C, and 2.3 °C per percent HDPE, LDPE, and PP, respectively, whereas low-temperature grade losses reached 7.8 °C; HDPE produced the highest high-temperature grade improvement, while LDPE showed the greatest extended BBR grade loss, and PP exhibited the fastest physical hardening rate. These results provide a controlled binder-level baseline for evaluating HDPE, LDPE, and PP as modifiers for future PMAB development. Full article

This study investigates adhesively bonded composite patch repair to enhance the load-carrying capacity of damaged metallic structures, introducing a novel FE-augmented machine learning (ML) framework that addresses the limited availability of experimental data in structural repair applications. To evaluate this approach, aluminum and steel specimens with central fatigue cracks were repaired using glass-fiber/epoxy and carbon-fiber/epoxy composite patches and tested under quasi-static loading at room ($70 \mathrm{F} °$), high ($145 \mathrm{F} °$), and low (−$60 \mathrm{F} °$) temperatures. Finite element (FE) models were then developed in ABAQUS© to predict the failure loads of the patched specimens under varying temperature conditions, showing excellent agreement with the experimental data. The high accuracy of the FE predictions enabled their use as additional training data, effectively augmenting the limited experimental dataset and allowing the development of more robust regression models. Ten machine learning (ML) regression models, including linear regression (LR), polynomial regression (PR), support vector regression (SVR), random forest (RF), gradient boosting (GB), XGBoost (XGB), LightGBM (LGBM), Gaussian process (GP) regression, artificial neural networks (ANNs), and Kolmogorov–Arnold networks (KANs), were trained to predict the failure load of both unpatched and patched specimens as a function of material type, temperature, specimen thickness, crack length, and, for patched specimens, patch type and thickness. The datasets combined a limited set of physical results (75 patched samples: 63 experimental and 12 finite-element; 72 unpatched samples: 27 experimental and 45 theoretical) with Gaussian-mixture-model synthetic samples used only to augment the training data up to 300 samples per case. Under a configuration-grouped, leakage-free nested cross-validation (entire configurations held out for testing, hyperparameters tuned on inner folds only), the best models predicted the failure load of unseen configurations with mean absolute percentage errors of 2.78% (Gradient Boosting, patched, $R^2=0.87$) and 3.33% (Gaussian Process, unpatched, $R^2=0.98$). A paired ablation showed that Gaussian-mixture-model augmentation did not improve accuracy and, for several models, actually reduced it; the final models therefore rely on the real multi-source (experimental, FE, and theoretical) data, with the synthetic pipeline reported as a validated but non-beneficial component for these datasets. Overall, this study provides a novel, data-efficient framework combining experimental testing, FE simulation, and validated regression modeling to predict the performance of adhesively bonded composite patch repairs under varying thermal and mechanical conditions. Full article

Contact fatigue, bending fatigue, and wear failures in gears are governed by the stress state, hardening gradient, microstructural stability, and surface topography within the near-surface and subsurface regions. For tooth flanks, rolling–sliding contact, asperity interaction, lubricant-film disturbance, and subsurface shear stress control micropitting, pitting, and spalling. For tooth-root fillets, local stress concentration and surface or near-surface defects dominate bending-fatigue crack initiation. Laser shock peening (LSP) introduces deep compressive residual stress, gradient hardening, and microstructural refinement, and is therefore relevant to gears when these effects are matched to the critical damage zones. This review examines LSP of gear steels and related load-bearing steels from the viewpoint of tooth-flank and tooth-root damage control. It links laser parameters, shock-induced plastic deformation, residual-stress depth, hardening response, surface roughness, and profile accuracy to bending fatigue, rolling contact fatigue, and wear behavior. LSP is most effective when the compressive residual-stress layer and hardened layer reach the contact- or bending-damage depth while lubrication compatibility, flank form accuracy, and subsequent finishing are preserved. Excessive pulse energy, overlap, or unstable absorbing/confining conditions may increase roughness, produce ablation or micropitting-sensitive defects, and compromise tooth profile accuracy. Thus, LSP for gears should be evaluated together with carburizing, nitriding, shot peening, surface rolling, polishing, coatings, and laser texturing rather than as an isolated treatment. The central task is to define gear-specific process windows that balance residual-stress depth, surface integrity, dimensional accuracy, and manufacturing repeatability. Full article

The present study is situated within the broader research context of optimizing the use of C60 steel in industrial applications, with a particular emphasis on enhancing durability and fatigue resistance, two critical factors in the field. C60 steel is renowned for its exceptional combination of strength and hardness. However, a critical evaluation is necessary to ascertain the impact of thermal and thermochemical treatments on its performance under fatigue conditions. An investigation was conducted into the crack formation process and the early stages of fatigue in C60 steel. The effects of heat treatment (hardening and tempering) were compared with those of thermochemical treatments (oxidation) on the steel’s microstructure. Furthermore, the performance of C60 steel under fatigue conditions was evaluated based on the applied treatments. The insights gained from this research can optimize the use of this steel in industries requiring high resistance and durability. The study’s methodology encompassed the execution of fatigue tests on a four-point bending machine, a procedure that was meticulously employed to ascertain the onset of microcracking. The C60 steel samples were processed in accordance with SR ISO 1099:2017, entitled “Fatigue testing. Axial load method”. To ensure consistency and comparability of results, the samples were fabricated from the same material charge and machined under identical conditions. A total of 26 samples were utilized, with 13 samples allocated to each treatment type: heat treatment by hardening, tempering, and thermochemical treatment by oxidation. To ensure comparability and scientific interpretability of the results, an identical applied force level was utilized for both treatment conditions. The frequency changes were monitored to evaluate the behavior of the materials under repeated stresses. Finally, the frequency changes were correlated with the number of cycles to identify when microcracks appeared and their evolution. The primary findings of this study indicate substantial disparities between the longevity of thermally and thermochemically modified specimens and the onset of microcrack formation in the material. Full article

This study investigates hydrogen-assisted fatigue crack growth (FCG) in vintage pipeline steels to quantify grade-dependent degradation under hydrogen–natural gas blending conditions. Fatigue behavior was evaluated using compact-tension specimens extracted from API X52 and X70 pipeline steels and tested in natural gas–hydrogen mixtures at a total pressure of 6.9 MPa and ambient temperature. Hydrogen concentration was systematically varied from 0% to 100% H₂ to assess its influence on crack-length evolution, fatigue crack growth rate, and fracture morphology. Crack propagation was characterized as a function of the stress-intensity-factor range, and scanning electron microscopy was used to examine hydrogen-induced changes in fracture mechanisms. The results demonstrate that FCG accelerates as hydrogen concentration increases, with a strong dependence on steel grade. X70 exhibited substantially greater hydrogen-induced FCG acceleration than X52, despite showing better fatigue resistance under hydrogen-free conditions. Fatigue life reductions approached 60% for X70 at 100% hydrogen, compared with approximately 30% for X52 under the same conditions. Significant early-life sensitivity was observed in X70 even at low hydrogen concentrations, whereas X52 showed more pronounced acceleration during later stages of crack growth. The influence of hydrogen was nonlinear and tended to stabilize at elevated blend fractions, indicating a saturation-type response once hydrogen-assisted crack growth became dominant. Fractographic analyses revealed a transition from ductile tearing in natural gas environments to terrace- and facet-controlled crack propagation in hydrogen-rich environments, accompanied by secondary cracking and river-pattern features. These findings demonstrate that hydrogen–natural gas blending can significantly alter fatigue crack growth behavior and relative material performance in pipeline steels, highlighting the need for grade-specific integrity assessment of existing pipeline infrastructure. Full article

With increasing renewable energy penetration, hydropower units face more frequent load rejection transients, which impose severe hydraulic excitation on Francis turbine runners. Although extensive studies have investigated flow dynamics and stress concentrations during transients, quantitative fatigue damage assessments for runners with pre-existing cracks remain scarce. To fill this gap, this study conducts CFD simulations coupled with one-way FSI to analyze a Francis turbine runner during load rejection, comparing uncracked and cracked configurations. Fatigue damage is evaluated using rain-flow counting, a modified S-N curve with Goodman mean stress correction, and the Palmgren–Miner linear damage rule. Results show that stress concentrations shift from the band-side to the crown-side T-junction during load rejection, with 4.5 times higher fatigue damage at the crown (D = 1.62 × 10⁻⁴) than at the band (D = 3.57 × 10⁻⁵). Pre-existing cracks increase local stress and reduce the allowable number of load rejection events from 6173 to 514 cycles. Reducing residual stress from 200 MPa to 100 MPa lowers fatigue damage by approximately 42%. This study provides a quantitative framework for transient fatigue assessments. Full article