Search Results (642)

This paper comprehensively investigates the ultraviolet (UV) nanosecond laser fabrication of micro-groove textures on planar PEEK surfaces, as well as their surface performance in terms of wettability and frictional properties. Firstly, a three-dimensional finite element model, incorporating a moving Gaussian heat source, solid heat transfer and deformed geometry, was established to simulate the transient temperature field and ablation profile of PEEK during UV laser ablation. The predicted groove depth agreed with the experimental value with a low deviation of 11.19%. Based on the simulation and single-factor experiments, the optimized single-track laser parameters were determined as a laser power of 1.2 W, a scanning speed of 100 mm/s and a repetitive frequency of 100 kHz. Secondly, systematic single-factor and multi-pass laser ablation experiments of PEEK surfaces were conducted to fabricate micro-groove textures with precisely tailored geometric parameters. Furthermore, ablated surface characterization showed that the laser-textured surfaces exhibited increased roughness, apparent crystallinity up to 22.13%, and pronounced anisotropic wettability, with improved liquid spreading along the groove direction and restricted spreading across the grooves. Finally, fretting wear tests under simulated body fluid lubrication were carried out. The research findings reported in this paper provide a systematic theoretical and experimental basis for the application of UV nanosecond laser surface texturing in the fabrication of PEEK-based components. Full article

Developing Cu-based composites with excellent electrical and mechanical properties under multiphysics-coupled service conditions remains challenging. Novel Cu-Nb-Gr composites were fabricated by high-energy ball milling and High-pressure Multi-field Assisted Rapid Sintering. Experiments combined with computational fluid dynamics (CFD) and finite element method (FEM) simulations were used to investigate how Gr regulates material performance. The incorporation of 3 vol.% Gr promoted the formation of a semi-continuous Gr-rich structure coupled with an Nb-rich load-bearing structure. Under arc erosion, the semi-continuous Gr-rich structure provided efficient heat-conduction pathways, reducing the peak temperature and metal-vapor recoil force, while the Nb-rich load-bearing structure suppressed liquid–metal spattering and stabilized the molten pool. Simultaneously, Gr dynamically spread to form a continuous solid-lubricating film during sliding friction, significantly reducing the coefficient of friction and interfacial shear stress. Furthermore, under compressive loading, the semi-continuous Gr-rich structure coupled with the Nb-rich load-bearing structure alleviated interfacial elastic–modulus mismatch and extreme stress concentration, limiting macroscopic plastic deformation of the matrix. Consequently, Cu-Nb-3Gr achieved a favorable balance of arc-erosion resistance, wear resistance, and compressive performance, providing a new strategy for improving conventional Cu-based composites. Full article

ESG ratings are widely used in sustainable finance, yet disagreement among agencies may weaken their information role and relate to firms’ financing frictions. Using Chinese A-share non-financial listed firms from 2009 to 2024, this study examines whether ESG rating divergence is associated with an SA-based financing-constraint proxy, whether stock turnover provides a liquidity-related pathway, and whether digital transformation weakens the association. ESG rating divergence is measured by the dispersion of available rescaled ESG ratings from five agencies, and financing constraints are proxied by the absolute value of the SA index. Firm and year fixed-effects regressions show that greater ESG rating divergence is significantly associated with higher values of the SA-based proxy. The result remains positive and significant in a lagged-variable specification. Instrumental-variable estimates provide additional sensitivity evidence, although the exclusion restriction cannot be directly verified. The bootstrap results support a statistically significant but economically small partial mediation effect through stock turnover; however, lagged mediation checks do not establish a complete temporal sequence. A moderation analysis indicates that digital transformation weakens the positive association. The subsample estimates are reported as descriptive patterns. The findings suggest that inconsistent ESG signals are associated with an SA-based financing-constraint proxy, while internal information-governance capabilities may reduce this exposure. Full article

Cemented carbide is extensively applied in cutting tools. Surface laser micro-texturing alleviates tool surface wear and boosts cutting performance. This work adopts response surface methodology to investigate circular micro-texture parameters (diameter, spacing, offset) of YG8 carbide tools with average friction coefficient as the response, constructing a quadratic regression model to acquire optimal texture parameters: diameter 0.46 mm, spacing 0.93 mm, offset 0.31 mm. Friction tests reveal texture parameters greatly affect tribological properties, and the wear mitigation mechanism of optimized textures is analyzed. Turning experiments compare plain tools, air-ablation and liquid-phase laser textured tools. Cutting force and temperature models for smooth and liquid-phase textured cutters are built and validated. Results show air-textured tools reduce cutting force by 26.35% and average temperature by 13.42%, while liquid-phase counterparts achieve 30.07% force drop and 20.73% temperature reduction. Genetic algorithm optimization yields liquid-texture force attenuation coefficient 0.3646 and temperature coefficient 0.2961, offering theoretical support for high-performance textured cutter design. Full article

Mechanical seals in rotating machinery require sufficient liquid-film support while limiting leakage and temperature rise. This study proposes an equilateral-triangle-textured T-groove seal face and establishes a thermohydrodynamic CFD model incorporating cavitation to evaluate its lubrication and sealing behavior. The novelty lies in coupling equilateral triangular microtextures with T-grooves and assessing their combined effects on pressure generation, cavitation, thermal response, leakage, and film stability. The effects of medium pressure, rotational speed, film thickness, T-groove number, and texture depth were analyzed. The results show that the triangular textures and T-grooves jointly enhance local hydrodynamic pressure and load-carrying capacity. Higher medium pressure increases both load-carrying capacity and leakage, whereas higher rotational speed improves load support while reducing leakage. The maximum film temperature first increases and then decreases with medium pressure, peaking near 2 MPa. As film thickness increases, the load-carrying capacity reaches its maximum at approximately 8 μm, while the temperature and frictional coefficient decrease. Increasing the number of T-grooves improves load-carrying capacity and film stiffness but also increases leakage and machining complexity. Under the investigated conditions, 10–14 T-grooves provide a practical compromise among load support, leakage control, stiffness, and manufacturability. Full article

Ferrofluid seals provide non-contact operation, low friction, and strong sealing performance in high-speed rotating equipment and liquid-sealing systems. However, high speed, liquid contact, thermal loading, vibration, and eccentricity can cause ferrofluid loss, performance degradation, leakage, and premature failure. Here, intelligent reliability denotes a reliability-centered framework that integrates condition monitoring, physically interpretable health assessment, fault diagnosis, uncertainty-aware prognosis, condition-based maintenance, and feedback-driven active control. This structured review synthesizes centrifugal, thermal, liquid-medium, eccentricity-related, and material-degradation mechanisms and evaluates pressure, leakage, temperature, torque, vibration, and acoustic-emission signals. It also assesses health indicators, diagnostic methods, remaining useful life (RUL) prediction, maintenance decisions, and health-management strategies. Its principal contribution is a framework linking degradation physics with observable evidence, health assessment, diagnosis, prognosis, and maintenance and design feedback. The framework also distinguishes direct ferrofluid-seal evidence from transferable methods and supports sensor selection, indicator design, validation planning, and intervention development. Key limitations include scarce public degradation datasets, inconsistent evaluation protocols, weak physical consistency of health indicators, and limited closed-loop implementation. Future work should prioritize public run-to-failure data, physics-informed multisource assessment, uncertainty-aware RUL prediction, and experimentally validated condition-based interventions and active-control strategies. Full article

This study examines the possibility of plastic deformation in low-modulus gels and yielding liquids. The model systems were a gelatin-sodium alginate hydrogel and the same gel filled with nanoscale zinc oxide particles. The experiments involved short- and long-term observations of deformation development under a prescribed shear stress, followed by stress removal and monitoring of deformation recovery. The initial hydrogel is a typical soft-matter system with an elastic modulus of 63 Pa. At low stresses, residual deformations were observed in addition to elastic deformations; these residual deformations reached up to approximately one half of the total deformation. They appeared instantaneously, depended on the applied stress, and did not change during long-term observation. This behavior is characteristic of plastic deformation. The incorporation of 5% dispersed ZnO nanoparticles converted the gel into a yielding liquid. This transition is attributed to partial disruption of the physical network, as evidenced by a sharp decrease in the elastic modulus to 18 Pa and by comparison of the FTIR spectra of the unfilled gel and the nanoparticle-modified gel. The yield stress of the yielding liquid was 7 Pa. However, at stresses below this value, while the material remained in a gel-like state, steady-state flow with a very high viscosity, at the order of 10⁵–10⁶ Pa s, was detected. After the yield point was exceeded, steady-state flow with a much lower viscosity, at the order of 3 Pa s, occurred, as is characteristic of conventional liquids containing a solid filler. Nevertheless, a small fraction of plastic deformation was still observed. Thus, the experimental results show that physical gels can behave as elastic-plastic media and that yielding liquids may flow below the yield point with very high viscosity. All existing models of the mechanical behavior of gels represent various combinations of viscous and elastic elements, to which, for yielding liquids, a slider is added that begins to slide after overcoming static friction. This element models the yield point. However, no model includes plasticity as an independent mechanical phenomenon. The phenomenon of plasticity should therefore be taken into account when developing rheological models of yielding liquids. Full article

The escalating global accumulation of plastic waste (PW) poses a critical obstacle to environmental sustainability, necessitating the development of viable valorization strategies. Pyrolysis process offers a thermo-chemical conversion pathway capable of transforming waste plastics into a potentially functional liquid product. This work presents a systematic and comprehensive investigation of the physicochemical, wettability, thermal stability, rheological, and tribological properties of pyrolysis oil (i.e., pyro-oil) derived from virgin linear low-density polyethylene (LLDPE) pellets to mimic the behavior of common polymers in such thermo-chemical conversion processes. Pyro-oil was produced under controlled slow pyrolysis conditions in a fixed-bed reactor at 700 °C, and its properties were benchmarked against tire-derived pyro-oil and a commercial engine oil. Chemical and structural characterization was conducted via Fourier transform infrared spectroscopy (FTIR), wavelength dispersive X-ray fluorescence (WDXRF), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). Wettability was evaluated through temperature-dependent contact angle measurements, and thermal stability was assessed by thermogravimetric analysis (TGA). Rheological profiling of the plastic pyro-oil was investigated using a rheometer apparatus at different temperatures. Lastly, the tribological properties of plastic pyro-oils at various temperatures were examined using a tribometer instrument in a ball-on-disk configuration. Results demonstrate that plastic-derived pyro-oil exhibits a hydrocarbon-dominant chemical composition similar to that of tire pyro-oil and engine oil. Its absolute viscosity is nearly similar to that of the tire pyro-oil and is lower than that of engine oil across different temperatures. Tribological testing revealed that the plastic pyro-oil results in lower friction at elevated temperatures compared to both tire pyro-oil and commercial engine oil. However, the thermal examinations showed that plastic pyro-oil has lower thermal stability than tire pyro-oil and engine oil. Overall, these findings indicate that plastic pyro-oil holds promise as a functional lubricant for low-load and moderate-temperature industrial applications, positioning PW pyrolysis as a viable contributor to circular economy strategies in the lubricants sector. Full article

This study investigates the impact of tax avoidance on dividend policy in listed non-financial firms in Portugal, Italy, Greece, and Spain from 2018 to 2024. Using Refinitiv Eikon panel data for 368 firms—yielding approximately 2200 firm-year observations before lagging—and firm fixed-effects models, the study examines whether tax avoidance increases dividend payouts and whether board independence, financial constraints, and economic policy uncertainty condition this relationship. Tax avoidance is measured using reverse-coded effective tax rate proxies and book–tax differences, while dividend policy is proxied by the dividend payout ratio. The results reveal a positive association between tax avoidance and dividend payout, suggesting that tax planning can operate as a channel for generating additional distributable liquidity in classical double-tax systems. However, this pass-through is not mechanical. The effect of tax avoidance on dividends is weaker in firms with more independent boards and stronger among financially constrained firms. It is also attenuated under heightened policy uncertainty. These findings support a three-dimensional conditionality model in which tax avoidance creates the capacity for higher dividends, but governance quality, financing frictions, and macro-level risk jointly determine whether tax-generated liquidity is paid out, retained, or used for dividend smoothing. Full article

Forgings currently have long lead times, motivating technology developments that produce parts with forge-like properties and have shorter timelines. Solid-state processes such as additive friction stir deposition (AFSD) offer this potential; however, large-scale deposition of high-temperature materials remains limited by tool durability, thermal management, and process stability. In this study, new polycrystalline cubic boron nitride (PCBN) AFSD tools, integrated with a liquid-cooled tool holder, are developed and evaluated for bulk deposition of 316 L stainless steel. Tool geometry modifications, including increased puck diameter and a drafted feed exit orifice, enabled graphite-free deposition by mitigating feedstock swaging. A minimum deposition rate is identified that maintains stable material flow and avoids excessive actuator forces. Comparing the use of PCBN tools with different shank materials shows that tungsten carbide shanked tools have improved thermal management relative to tools with a nickel-based shank. This improved thermal regulation resulted in more stable deposition, reduced tool wear, and successful multi-layer builds. Additionally, the use of a fully enclosed inert gas environment reduces surface oxidation and interlayer oxide formation. Electron microscopy was used to reveal limited tool-related contamination in the deposition. The contamination observed was dispersed boron nitride particles rather than continuous interfacial layers of tool material as observed in other literature. These results demonstrate that PCBN tooling combined with active cooling can enable stable, bulk AFSD of high-temperature alloys. Full article

With the continuous increase in horizontal displacement during unconventional oil and gas drilling, drilling operations are commonly plagued by high frictional resistance, severe pipe sticking issues and difficulties in directional drilling. Conventional single-component water-based drilling fluid lubricants fail to satisfy multifunctional demands, including high-temperature resistance, salt tolerance and long-term lubrication. In this work, a novel microsphere lubricant, RB-Si, with high-temperature and high-salinity resistance was developed by combining the merits of solid and liquid lubricants. The product was synthesized using myristic acid and triethanolamine as raw materials via co-reaction with boric acid and nano-silica. Laboratory tests reveal that after aging at 180 °C, the lubrication coefficient reduction rates of based mud, saturated salinity-based mud and a high-density (2.0 g/cm³) drilling fluid gel system containing 1.0 wt% RB-Si reached 90.1%, 83.3% and 62.8%, respectively. Meanwhile, RB-Si can effectively plug the micropores in the filter cake, reduce fluid loss, inhibit shale hydration and swelling, and exhibit excellent compatibility with drilling fluids. RB-Si rapidly adsorbs onto the surfaces of metallic drill strings and formation rocks to construct a durable and high-strength lubricating film, accompanied by the rolling friction of the incorporated microspheres, thereby reducing frictional drag between the drill string/casing and the drill string/borehole wall. This lubricant effectively mitigates high frictional resistance under prolonged friction conditions, and is expected to provide technical support for long-horizontal-well drilling. Full article

Tribology is a growing field concerning reductions in the environmental footprint of tribological systems while increasing their operational efficiency by minimizing friction, wear and lubrication in an environmentally conscious manner. This review aims to discuss in detail sustainable lubrication strategies, with particular emphasis on surface modification and coating-based strategies for advanced tribological applications. The surface engineering techniques covered in this study are critically reviewed with regard to their ability to improve wear resistance, reduce friction and increase the durability of components, such as laser surface texturing (LST), nitriding, plasma treatment and advanced coating technologies such as DLC-, TiN-, CrN- and PVD-based coatings. Another key focus is on the synergy of sustainable lubricants and engineered surface coatings. The tribochemical compatibility of eco-friendly lubricants, bio-lubricants, ionic liquids and advanced coated surfaces is explained in detail, because they are essential for the formation of stable tribofilms, lubricant retention, reductions in surface degradation, and the minimization of tribological losses. They are an important component of environmental footprint, energy consumption and the thermal stability and service life of tribological components. Recent developments in coating-assisted green tribology, sustainable tribochemistry and circular sustainability concepts of the design of tribological systems are also included in the review. In addition, the review briefly outlines the use of Life Cycle Assessment (LCA) as a potential tool for the future evaluation of the environmental sustainability of tribological systems. The proposed expanded set of Green Tribology principles offers useful guidance for the implementation of tribology-based solutions toward more sustainable engineering systems and responsible resource utilization. Full article

Flow patterns in vertical wellbores are highly complex and variable. Classical theoretical models for pressure drop prediction frequently yield significant errors when applied to different geological blocks. However, existing correction models suffer from incomplete coverage of flow patterns. Therefore, it is necessary to develop new pressure drop prediction models specifically for gas–liquid two-phase flow in vertical wellbores under various flow patterns. This study conducted physical experiments on gas–liquid two-phase flow in vertical wellbores, successfully reproducing four typical flow patterns—bubbly flow, slug flow, churn flow, and annular flow—and determining their transition boundaries. Based on the experimental data, a systematic comparison was performed among four classic flow pattern discrimination models: Aziz, Beggs–Brill, Mukherjee–Brill, and Ansari. The results indicated that the Aziz model demonstrates superior applicability for identifying vertical flow patterns. To address the substantial prediction errors of the Aziz model in pressure drop calculations, the liquid holdup ratio and friction factor under different flow patterns were manually corrected using the experimental data, yielding a new pressure drop prediction model (Model 1). Furthermore, the particle swarm optimization (PSO) algorithm was introduced to further automatically optimize and fit the model parameters, thereby establishing another new pressure drop prediction model (Model 2) specifically tailored for different flow patterns. Validated against the experimental measured data, the new Model 2 achieved a Mean Absolute Percentage Error (MAPE) of 11.9% and a Root Mean Square Error (RMSE) of 1.9 kPa. Further verified by independent validation experiments outside the calibration dataset, Model 2 achieves an average prediction error of 12.0%, maintaining stable and high prediction accuracy. In comparison, the Aziz model and the new Model 1 yielded MAPE/RMSE values of 50.6%/5.3 kPa and 18.2%/4.9 kPa, respectively. The errors of the new Model 2 are markedly lower than those of the aforementioned models, demonstrating its superior accuracy in calculating pressure drops under various flow patterns. These findings provide a more accurate and reliable theoretical model for pressure drop calculation in gas–liquid two-phase flow within vertical wellbores, thereby laying a solid foundation for numerical simulation history matching and subsequent production forecasting. Full article

This study examines the moderating role of liquidity in the relationship between extreme capital structure and firm performance among listed firms in emerging markets. It is motivated by the need to better understand how financing constraints and liquidity management influence firm performance in environments characterised by high financial frictions and limited access to external capital. Extreme capital structure is defined as firms maintaining very low levels of debt, measured using thresholds of 1% (ultra-low debt) and 5% for both long-term debt and total debt. The analysis is based on a panel dataset of non-financial listed firms over the period 2006–2024 and employs a dynamic panel System Generalised Method of Moments (System GMM) complemented by a Random Effects model for robustness. Empirical results indicate that liquidity has a meaningful and predominantly positive moderating effect. This is observed when firms maintain extremely low long-term debt (1% threshold) and low long-term debt (5% threshold). Liquidity enhances firm performance. This effect is strongest for return on assets (ROA) and return on equity (ROE). The effect on Tobin’s Q is weaker but remains generally positive. These findings highlight the strategic importance of liquidity in improving profitability and financial resilience under conservative financing structures. However, the findings are limited to listed non-financial firms in emerging markets and may not be generalizable to SMEs or unlisted firms. Future research could explore the threshold at which liquidity ceases to generate benefits or begins to produce diminishing returns in ultra-low leverage contexts. Full article

Understanding the pricing of climate risks in bond markets is relevant to financial stability. The real estate sector, characterized by geographically fixed and long-duration assets, exhibits high exposure to environmental shocks; yet, empirical matching between specific climate channels and real estate bond pricing remains sparse. This analysis examines the impact of climate risks on corporate bond credit spreads within the real estate sector by constructing three thematic indicators: transition risk (CTRI), chronic physical risk (ChroCPRI), and acute physical risk (AcuCPRI). Initial feature selection via machine learning suggests all three risk categories as predictive covariates for bond pricing. Subsequent regression estimations indicate that climate transition risk and acute physical risk expand credit spreads, whereas chronic physical risk compresses them—with these statistical patterns being more pronounced among state-owned enterprises (SOEs). Mechanism analyses yield threefold insights: first, transition risk elevates spreads by tightening financing constraints and restricting corporate asset growth, a channel concentrated in short-term tranches and low-liquidity firms; second, the counterintuitive spread-compressing effect of chronic risk is localized among firms with lower credit ratings and lower profitability, consistent with institutional climate support frameworks and strategic green adaptations; third, acute physical risk widens spreads by compressing operational cash flows and exacerbating financing friction, particularly for smaller enterprises. These channels align with the structural attributes of SOEs, which are characterized by larger asset scales, superior capital liquidity, and a higher propensity to secure state guarantees. Full article