Search Results (361)

Additive manufacturing has huge development potential in the aerospace field. The hot-end components of aeroengines work in harsh environments, facing high temperatures and a demand for long service life. In this paper, high-cycle fatigue (HCF) tests of Ti6Al4V alloy at 400 °C by selective laser melting (SLM) under different stress ratios (−1, 0.1, 0.3, 0.5, and 0.8) were carried out, and the fracture surfaces were observed. The results show that the defects existing on the surface or subsurface are prone to become the origin of fatigue cracks. There is a large dispersion of the high-cycle fatigue life of the samples, especially at a low stress ratio. With the increase in the stress ratio, the fatigue failure area on the fracture surface gradually decreases, and the fracture surface gradually presents a mixed pattern of tensile endurance fracture and fatigue failure. Considering the influence of creep damage due to mean stress, models were established, respectively, for the fatigue behavior and time-related rupture behavior to predict fatigue life and conduct an assessment. Then, the two models were combined and the composite models were proposed using the linear damage law. Finally, the single fatigue model and rupture models, as well as the composite models, were evaluated, respectively, and compared with the actual fatigue life, and the best model was obtained for the high-cycle fatigue prediction of SLM Ti6Al4V at 400 °C. Full article

This study investigates the effects of multiple laser shock peening (LSP) treatments on the low-cycle fatigue performance and fracture mechanisms of laser-melted, additive-manufactured Ti-6.5Al-1Mo-1V-2Zr (TA15) titanium alloy. The primary objective is to systematically evaluate how different LSP impact numbers (0, 1, and 2 impacts) enhance fatigue life and alter fracture behavior. Low-cycle fatigue life was determined via tensile-compression fatigue testing. Microfracture morphology was examined using scanning electron microscopy (SEM), surface residual stresses were measured by X-ray diffraction (XRD), and microhardness tests were conducted concurrently. Results indicate that LSP significantly enhances fatigue life: fatigue life increased by 2.34 times and 2.56 times after one and two LSP impacts, respectively, compared to the untreated state. As impact cycles increased, the microhardness of the material surface rose by 8.51% and 14.53%, respectively, with residual compressive stresses reaching −145 MPa and −183 MPa. Concurrently, LSP-2 treatment formed a refined microstructure featuring coexisting lamellar α and acicular martensite in the surface layer. This strengthening effect is attributed to LSP-induced surface residual compressive stress, grain refinement, and the resulting migration of fatigue crack initiation from the surface to subsurface regions. These findings provide critical insights for optimizing fatigue-resistant designs of additively manufactured titanium alloy components. Full article

It is difficult to achieve ultra-precision machining (UPM) on semiconductor materials like single-crystal silicon because of their hardness and brittleness. To solve this issue, numerous field-assisted machining systems and their combinations have been suggested and developed. However, the difficulty in directly observing the physical variables limits our comprehension of the in-depth machining mechanisms of field-assisted machining. In this work, we investigated the machining mechanism of single-crystal silicon under the combination of laser heating and tool vibration using molecular dynamics (MD) simulations. The effect of tool vibration trajectory determined by different tool edge radii is discussed under the condition of raising temperature. The simulation results indicate that the surface morphology is closely related to vibration and heating parameters. Raising the cutting temperature causes a reversed relation between tool edge radius and surface roughness. While the subsurface damage and internal stress are also determined by the tool edge radius and cutting temperature. The findings in this simulation could help to improve the understanding of machining mechanics in multi-field-assisted machining. Full article

Oil and gas fields in subsidence-prone regions face multiple hazards that threaten the resilience of their infrastructure. This study presents an integrated risk mapping framework for the Yibal field in the Sultanate of Oman, utilizing remote sensing and geophysical data. Multi-temporal PS-InSAR analysis from 2010 to 2023 revealed cumulative surface deformation and tilt anomalies. Micro-seismic and fault proximity data assessed subsurface stress, while a flood risk map-based surface deformation-adjusted elevation captured hydrological susceptibility. All datasets were standardized into five risk zones (ranging from very low to very high) and combined through a weighted overlay analysis, with an emphasis on surface deformation and micro seismic factors. The resulting risk map highlights a central corridor of high vulnerability where subsidence, seismic activity, and drainage pathways converge, overlapping critical infrastructure. The results demonstrate that integrating geomechanical and hydrological factors yields a more accurate assessment of infrastructure risk than single-hazard approaches. This framework is adaptable to other petroleum fields, enhancing infrastructure protection (e.g., pipelines, flowlines, wells, and other oil and gas facilities), and supporting sustainable field management. Full article

Land subsidence caused by groundwater withdrawal remains a significant challenge in urbanized regions, requiring robust predictive models to manage its impact effectively. In this study, a set of coupled partial differential equations is formulated using Biot’s poroelasticity theory and Darcy’s law to model the hydro-mechanical behavior of a multi-aquifer system. The numerical models capture the coupled dynamics of fluid flow and subsurface deformation induced by groundwater table depression. Hydraulic head reductions, vertical compaction, and lateral deformation patterns over a 10-year pumping period are systematically examined. The results manifest that greater hydraulic gradients near geological discontinuities, such as bedrock steps, induce localized deformation and stress redistribution. While Terzaghi’s model effectively predicts vertical compaction in simple systems, Biot’s model accounts for lateral strain and coupled feedback mechanisms, providing a more comprehensive analyses and understanding of subsidence phenomena. This study highlights the importance of coupled hydro-mechanical modeling for accurately predicting land subsidence and offers insights into managing groundwater extraction in geologically complex regions. Full article

Laser additive manufacturing shows great promise for repairing high-value carburized gears, but the underlying relationships among thermal history, microstructure, and properties remain insufficiently quantified. This study uniquely integrates finite-element modeling with microstructural mapping to decipher thermo-mechanical coupling during gear repair. A thermal simulation model that combines a double-ellipsoidal heat source with phase-transformation kinetics achieves 91.1% accuracy in predicting melt pool depth and hardened-layer depth. The cladding process induces a substantial increase in subsurface hardness, primarily due to phase-transformation-induced refinement and regeneration of martensite during rapid thermal cycling. This results in a peak hardness of 64 HRC and a tensile strength of 2856 MPa in the secondary-hardened layer, both exceeding those of the original carburized substrate. The presence of beneficial compressive residual stresses further improves fatigue resistance. Spatial gradients in elastic modulus, strength, and hardness, measured by flat indentation and microhardness testing, are quantitatively correlated with simulated peak temperatures and predicted phase distributions. These correlations establish a causal link from the thermal history to phase transformations, microstructural evolution, and the resulting local hardness and strength. These findings provide a mechanistic foundation for precision repair and service-life prediction of high-carbon gear steels using laser additive manufacturing. Full article

This paper assesses the contributions of induced tensile stress in the behavior of foundations in order to make a case that tensile stress induced by foundation loading needs to be considered in geotechnical analysis for foundations that apply high loading and are sited on sloping ground, subsurface materials with complex geometry, or other conditions that do not conform to the assumption of shear-dominant failure that is the basis for foundation analysis used in current practice. The assessment uses numerical simulations using fracture-based continuum modeling (FBCM), which models mechanical damage of subsurface materials in terms of the initiation and propagation of shear and tensile failure surfaces (fractures). FBCM models fractures explicitly in a continuum framework using fracture transformation matrices to encapsulate, thus automating the creation and use of fracture geometry. The assessment shows that tensile and shear damage mechanisms contribute to behavior of foundations on sloping ground, with the tensile mechanism increasing as setback from the slope crest decreases. For a large setback, failure is shear-dominated but tensile mechanisms occur at the ultimate state. In contrast, tensile mechanisms dominate the failure of foundations at a small setback. Additionally, the paper provides verification of FBCM for foundation analysis by comparing model calculations against published results. Full article

Groundwater resources in Jordan are under severe stress due to rapidly increasing water demand and over-abstraction that far exceeds natural replenishment. In addition, water quality is threatened by pollution from the misuse of fertilizers and pesticides, leakage from septic tanks, and illegal waste disposal. This study focuses on the Aqeb, Corridor, and Special Economic Zone wellfields, where hydrological and hydrochemical investigations were carried out. A total of 36 groundwater samples were collected and analyzed for hydrochemical composition, stable isotopes of oxygen (δ¹⁸O) and hydrogen (δ²H), and trace elements. In addition, two exploration 2D seismic profiles crossing the study area were interpreted, providing critical insights into the activity of the subsurface Fuluk Fault zone and its relationship with the wellfields. The hydrochemical results reveal elevated total dissolved solids and nitrate concentrations, accompanied by more depleted δ¹⁸O and δ²H values in wells located in the central part of the study area. Three distinct hydrochemical groups were identified within the same aquifer, indicating heterogeneity in groundwater chemistry that reflects variations in recharge conditions, flow paths, and geochemical processes. The first group (high Na/Cl with low salinity) likely represents recently recharged waters with limited rock–water interaction. The second group (intermediate Na/Cl and moderate salinity) may be influenced by evaporation, irrigation return flow, or cation exchange. The third group (low Na/Cl with high salinity) suggests the dissolution of sulfate minerals or mixing with deeper mineralized groundwater, possibly facilitated by structural features such as the Fuluk Fault. Seismic interpretation indicates several active near-surface fault systems that are likely to serve as preferential pathways for salinity and nitrate enrichment, linked to intensive agricultural activities and wastewater leakage from nearby septic tanks. The findings emphasize the combined influence of geochemical processes, excessive groundwater abstraction, and structural features in controlling water quality in the region. Full article

To investigate the impact of subsurface karst cavities on the stability of pipe jacking construction, this study utilizes the Yunnan Central Water Diversion Project as a real-world case. Employing ABAQUS finite element software to establish a numerical model, it systematically analyzes construction stability under the specific condition of “karst cavities present ahead of the excavation direction” in karst formations. The research focuses on examining the effects of four key scenarios on the displacement and stress response of surrounding rock and pipe segments. These conditions specifically include the following: tunnel burial depth (10 m, 15 m, 20 m, 25 m), cavity diameter beneath the tunnel (1–4 m), cavity filling status, and distance between the cavity and the tunnel (1–4 m). The study reveals that in composite stratum tunnel construction, when cavities exist in the strata ahead, multi-area displacements increase progressively with cavity size. Displacement changes accelerate and magnify when the cutting face of the jacking machine approaches within approximately 2.5 m of the cavity. However, no significant difference is observed between soft plastic clay reinforcement and slurry reinforcement effects. When composite stratum tunnels traverse beneath karst caves, the maximum upward bulge at tunnel bases occurs at 1-meter diameter caves, reaching approximately 2.5 mm. When the diameter of the cave increases to 4 m, the arching settles to a maximum. As tunnel burial depth increases, the arch base rises while the crown sinks, with settlement magnitude exceeding bulge amount. The displacement and stress fields from the initial excavation phase become disturbed, intensify, and then stabilize. When the jacking machine reaches directly above the cavern, stress at the crown base increases while stress at the crown top decreases. The pipe bottom exhibits uplift, and the pipe top shows reduced settlement directly above the cavern. Cavern filling has a minor effect on pipe-segment displacement, with segments deforming into an approximate elliptical shape. At the completion stage of excavation, the maximum Mises stress occurs at the top of the launch-end pipe segment. While cavern-related factors have a limited influence on the pipe-segment Mises stress, this stress gradually increases as excavation progresses. Full article

Sinkholes caused by historical underground mining operations are significant geotechnical and safety hazards for new residential developments. This paper presents a case study concerning the assessment of the condition of the foundations of a planned multi-family residential building located within a former mining operations area in southern Poland, which is exposed to the risk of discontinuous ground deformation. This study aimed to identify potential voids within the rock mass and develop safe structural solutions for building foundations. To this end, a comprehensive site investigation was conducted, including two-dimensional electrical resistivity profiling to detect zones of high-resistivity anomalies. High-resistivity anomalies were identified beneath several building segments, suggesting the presence of voids or loose soil resulting from shallow coalmining operations. Based on these findings, a finite element analysis (FEA) of the reinforced concrete foundation slab was performed to simulate the presence of subsurface cavities. The results indicated local tensile stress in the slab of up to 0.34 MPa, which necessitated subsequent design adjustments. Consequently, the use of additional bottom reinforcement and continuous reinforced concrete ribs was proposed to enhance structural safety. This study highlights the necessity of detailed geotechnical and geophysical analyses of planned development zones located in former mining operation areas to address the risks related to sinkholes and ensure the long-term safety of new buildings. Full article

Laser polishing represents a promising post-processing method for FDM-printed parts, enabling targeted manipulation of their surface topography and the associated functional properties. Despite extensive research in this field, no experimental investigation has yet addressed the configuration with vertical build orientation, which is critical in terms of interlayer stress transfer. Therefore, this study focuses on CO₂ laser polishing of vertically printed PLA specimens at power levels of 10 and 12 W and polishing speeds of v_f = 200, 400, and 600 mm·s⁻¹, with a constant transverse displacement of 0.1 mm. The results showed that both laser power and polishing speed have a significant influence on the surface topography and mechanical properties of the samples. The lowest roughness values, R_a = 10.24 ± 0.14 µm at 10 W and R_a = 12.20 ± 0.43 µm at 12 W, were achieved at the highest polishing speed of v_f = 600 mm·s⁻¹; however, these still exceeded the roughness of the reference unpolished sample (R_a = 9.02 ± 0.21 µm). The increase in roughness was attributed to the formation of relief structures caused by insufficient overlap of laser passes, orthogonal to the printing-induced surface orientation. These reliefs further acted as local stress concentrators, resulting in a decrease in mechanical performance of up to 9% in comparison with the reference specimen. At 10 W, the surface profile was dominated by R_v > R_p, similar to the reference sample, whereas at 12 W, the opposite trend (R_p > R_v) was observed—attributed to more intense subsurface melting and valley filling by the melt pool. Therefore, the findings clearly confirm that the critical factor is the energy distribution and transverse displacement of the laser polishing paths, where improper parameter settings may visually improve the surface while structurally weakening it. These findings highlight the need for further research, focused on the precise optimization of the polishing trajectory and the energy distribution for vertically oriented samples. Full article

This study investigated the physicochemical properties and nutrient dynamics on the Romanian shelf of the northwestern Black Sea in July 2024, collecting data across 36 stations (13–1116 m depth) heavily influenced by Danube discharges. Vertical CTD profiling revealed a pronounced seasonal thermocline and a deep-lying permanent halocline. The Cold Intermediate Layer (CIL) boundary, defined by the 8 °C isotherm, was absent, indicating warmer subsurface waters. Surface nutrient concentrations, particularly for nitrate (NO₃) and phosphate (PO₄), were considerably lower than peak eutrophication periods, approaching pre-1970s values, suggesting a positive trend due to reduced anthropogenic loading. They are also comparable to or lower than other coastal regions in the Black Sea. Vertical nutrient profiles confirmed the typical anoxic Black Sea structure, but with regional specifics: the PO₄ maximum was slightly deeper, and the NO₃ maximum position and concentration mirrored the pre-eutrophication period, further supporting reduced anthropogenic nitrogen input. Silicate (SiO₄) concentrations were consistently low throughout the water column, suggesting the northwest shelf functions as a SiO₄ sink compared to the southeastern Black Sea. Overall results indicate a shift towards a less eutrophic state on the Romanian shelf while highlighting the continued dominance of Danube-driven hydrodynamics. In addition to those investigations, this study assessed nutrient preservation techniques, finding that pasteurization was significantly superior to freezing for maintaining the stability of PO₄ and NOx (losses up to 20% and 47% for frozen samples, respectively) over six months. Though SiO₄ was stable under both methods, the freezing produced lower concentrations, possibly from incomplete depolymerization during thawing. These findings stress that pasteurization could be taken into consideration as a reliable preservation technique for long-term storage of nutrient samples. Full article

Residual stress plays a critical role in the durability and structural integrity of steel rolls and bars. Proper analysis helps prevent defects like warping or cracking, ensuring the steel meets quality standards and performs reliably in critical applications. This paper presents a methodology for analysing residual stresses using electromagnetic acoustic transducer (EMAT) based nonlinear ultrasonics. It compares its effectiveness with established techniques such as X-ray diffraction (XRD) and coercive force measurements. The results demonstrate that nonlinear ultrasonics provides more detailed insights into stress distribution, particularly in subsurface regions where traditional methods like XRD face limitations. It also shows good sensitivity to stress-induced microstructural variations than coercive force measurements. This research study is the first to perform a comparative analysis using XRD, EMAT, and coercive force techniques on industrial samples, followed by the implementation of EMAT nonlinear technology at an industrial production site. The findings indicate a positive trend observed in XRD and coercive force results, and those from nonlinear ultrasonics, further validating its accuracy. Moreover, the technology has been successfully applied in steel manufacturing industries through the project named STEEL components assessment using a novel non-destructive residual stress ultrasonic technology (STEELAR), funded by the Research Fund for Coal and Steel (RFCS). These findings underscore the potential of nonlinear ultrasonics as a powerful, fast and complementary tool for comprehensive residual stress monitoring in steel components, enhancing both theoretical understanding and practical industrial application. Full article

Rhizosphere hypoxia, caused by soil compaction and waterlogging, is a major constraint on agricultural productivity. It severely impairs crop growth and yield by inhibiting root aerobic respiration, disrupting energy metabolism, and altering the rhizosphere microecology. Micro-nano bubbles (MNBs) show significant potential for alleviating rhizosphere hypoxia due to their unique physicochemical properties, including large specific surface area, high oxygen dissolution efficiency, prolonged retention time, and negative surface charge. This paper systematically reviews the key characteristics of MNBs, particularly their enhanced mass transfer capacity and system stability, and outlines mainstream preparation methods such as cavitation, electrolysis, and membrane dispersion. And the multiple alleviation mechanisms of MNBs—including continuous oxygen release, improvement of soil pore structure, and regulation of rhizosphere microbial communities—are clarified. The combination of MNBs aeration and subsurface drip irrigation can increase soil aeration by 5%. When applied in soilless cultivation and conventional irrigation systems, MNBs enhance crop yield and nutrient use efficiency. For example, tomato yield can be increased by 12–44%. Furthermore, the integration of MNBs with water–fertilizer integration technology enables the synchronized supply of oxygen and nutrients, thereby optimizing the rhizosphere environment efficiently. This paper sorts out the empirical effects of MNBs in soilless cultivation and conventional irrigation, and provides directions for solving problems such as “insufficient oxygen supply to deep roots” and “reactive oxygen species (ROS) stress in sensitive crops”. Despite these significant advantages, the industrialization of MNBs still needs to overcome challenges including high equipment costs and insufficient precision in parameter control, so as to promote large-scale agricultural application and provide an innovative strategy for the management of rhizosphere hypoxia. Full article

Monitoring groundwater dynamics and basin-scale water budget closure is critical for sustainable water resource management, especially in regions facing climate stress and overexploitation. This study examines the temporal variability of total water storage and groundwater trends in Türkiye’s Kızılırmak River Basin by integrating GRACE/GRACE-FO satellite gravimetry, GLDAS-Noah land surface model outputs, ERA5-Land reanalysis products, and local meteorological observations. Groundwater storage anomalies (GWSAs) were derived from the difference between GRACE-based total water storage anomalies (TWSAs) and GLDAS-modeled surface storage components, revealing a long-term groundwater depletion trend of −9.55 ± 2.6 cm between 2002 and 2024. To investigate the hydrological drivers of these changes, lagged correlation analyses were performed between GRACE TWSA and ERA5-Land variables (precipitation, evapotranspiration, runoff, soil moisture, and temperature), showing time-shifted responses from −3 to +3 months. The strongest correlations were found with soil moisture (CC = 0.82 at lag −1), temperature (CC = −0.70 at lag −3), and runoff (CC = 0.71 at lag 0). A moderate correlation between GRACE TWSA and ERA5-based water storage closure (CC = 0.54) indicates partial alignment. These findings underscore the value of satellite gravimetry in tracking subsurface water changes and support its role in basin-scale hydrological assessments. Full article