ABSTRACT This paper deals with the numerical simulation of texture surface thrust bearing utilizing a Newtonian lubricant. Reynolds' equation is applied to model the lubricant flow within these bearings, which feature square and rectangular micro‐depressions oriented in both circumferential and radial directions. The finite element method is employed to solve Reynolds' equation, enabling the calculation of film pressure, load‐supporting capacity, and frictional power loss. To optimum bearing performance the texture shapes are optimized based on dimple size, depth, and number of dimples. It was found that square dimples outperform rectangular dimples in terms of both load‐carrying capacity and frictional power loss. The performance enhancement of the thrust bearing was achieved by identifying optimal texturing parameters through a fuzzy logic‐based optimization framework. A multi‐objective genetic algorithm (MOGA) is utilized to identify the optimal design parameters of the bearing system, with the objectives of maximizing load‐carrying capacity and minimizing frictional power loss concurrently.
ABSTRACT In mechanical lubrication systems, grease can become contaminated with water due to seal failure and high ambient humidity. Water can alter the fibrous network of the thickener in grease, leading to base‐oil separation, reduced consistency and abnormal oil bleeding. In this study, experiments were combined with molecular dynamics (MD) simulations to investigate the tribological behaviour of lubricating systems with different water contents, together with changes in parameters such as density distribution and system height. The aim was to clarify the short‐term effects of water on grease structure and lubrication performance. The results show that the system with 5% water exhibits the best lubrication performance. Compared with the anhydrous system, the maximum wear‐scar depth decreased by 0.142 μm and the maximum stress decreased by 29%. These findings suggest that a moderate amount of water forms hydrogen bonds with the polar groups of the lithium soap thickener, strengthening the soap‐fibre network. This interaction stabilizes the emulsion formed by water, base oil and thickener, resulting in the highest resistance to compression. In contrast, excessive water increases the intermolecular spacing between thickener molecules, weakens the structural integrity of the thickener network, promotes lubricant‐film rupture and reduces load‐carrying capacity. The experimental results are consistent with the MD simulations.
ABSTRACT The growing demand for titanium alloys with low elastic modulus for bone‐integrated implants has driven the development of novel β‐type alloys. This study examines the corrosion and tribocorrosion behaviours of a Ti15Zr15Mo alloy produced by arc melting, with and without heat treatment at 600°C for 6 h, benchmarked against Ti6Al4V. Corrosion behaviour was evaluated in phosphate‐buffered saline (PBS) at 37°C using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). Tribocorrosion tests were performed under reciprocating sliding against a 10 mm alumina ball (1 N, 1 Hz, 600 μm) in PBS, with simultaneous monitoring of open‐circuit potential (OCP) and coefficient of friction (COF). x‐Ray diffraction (XRD) showed a predominance of β phase in the Ti15Zr15Mo alloys, while Ti6Al4V exhibited a dual‐phase structure, with the as‐cast and heat‐treated Ti15Zr15Mo alloys exhibiting microhardnesses of 399 ± 2 HV 0.25 and 433 ± 3 HV 0.25 , respectively, compared to 337 ± 5 HV 0.25 for the Ti6Al4V benchmark. When benchmarked against Ti6Al4V, the Ti15Zr15Mo alloys exhibited lower passive film resistance ( R ox of 0.74 ± 0.05 MΩ cm 2 for as‐cast and 0.60 ± 0.02 MΩ cm 2 for heat treated versus 1.36 ± 0.68 MΩ cm 2 for Ti6Al4V), with heat treatment slightly further impairing the passive layer stability. Furthermore, significantly higher wear volume losses of (4.58 ± 0.46) × 10 −3 and (4.42 ± 1.44) × 10 −3 mm 3 were observed for the as‐cast and heat‐treated Ti15Zr15Mo alloys, respectively, relative to (1.41 ± 0.28) × 10 −3 mm 3 for the Ti6Al4V reference, highlighting the interplay between mechanical properties and tribocorrosion mechanisms.
A unified constitutive model for friction is developed using a generalised power-law framework that captures rate, load, temperature and state dependencies across granular, cohesive, soft-material interfaces and geological faults. Grounded in an energy-balance derivation and state-evolution tribology, the model defines the interface velocity (strain-rate) as the fundamental constitutive property. The inverted kinetic friction formulation utilises a power-law representation, successfully reproducing static-to-dynamic transitions, direct velocity-strengthening effects and evolutionary velocity-weakening behaviours. Representative systems: rock penetration, cohesive soil sliding, high-speed machining and fault friction are systematically mapped. The explicit incorporation of Arrhenius temperature kinetics corrected to couple the activation energy with the rate-and-state exponent () proves that the model captures macroscopic thermal weakening. Furthermore, numerical sensitivity analyses of the real area of contact evolution confirm sublinear growth under confining pressure, successfully predicting pressure-induced friction drops. This robust formulation bridges classical empirical laws with modern rate-and-state mechanics. The framework is parsimonious, physically coherent and demonstrates powerful predictive capabilities across tribological and Earth science contexts.
Regulating pore structure by using pore-forming agents (PFAs) is an effective strategy for improving the self-lubricating performance of oil-containing materials. However, the application of conventional PFAs has been limited by their low decomposition temperatures and the release of toxic gases during decomposition. In this study, starch, a green and biodegradable biomass material, was employed as a PFA to prepare copper-based oil-containing materials with varying starch contents by powder metallurgy. Oil storage and release tests, sliding friction experiments, and mechanical property measurements were conducted to investigate the effect of starch on pore structure and tribological behaviour. The results show that increasing the starch content changes the pore morphology from isolated closed pores to interconnected network pores, thereby improving oil storage and release. However, with increasing starch addition, the friction coefficient and wear rate first decrease and then increase, whereas the mechanical properties gradually decline because of the development of the porous network. At 5% starch, the hardness, density, crushing strength, and impact toughness decreased by 20.0%, 19.9%, 22.4%, and 22.8%, respectively, compared with those of the starch-free material. At 3% starch, the moderately interconnected pores provide both effective oil release and sufficient matrix strength, resulting in the lowest friction coefficient and wear rate, which were reduced by 84.8% and 84.3%, respectively, relative to the starch-free sample. These findings clarify the mechanism by which starch regulates pore structure and tribological performance in copper-based materials and provide guidance for the use of biodegradable PFAs in the design of environmentally friendly self-lubricating materials.
