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.
At present, research on wheel wear for special freight vehicles, such as humpback vehicles, remains limited and lacks a systematic approach. The specific wear characteristics of wheels on humpback freight vehicles are not yet well understood. In this study, a dynamic simulation model of a humpback freight vehicle with small-diameter wheels was developed. Using the Jendel wear model, the progression of wheel wear on such vehicles was calculated, and the effects of primary suspension parameters, secondary suspension parameters, and curved track geometry on wear evolution were examined. Wheel wear under varying friction coefficients was also analysed via the Polach model. The findings indicate that wheel wear is strongly affected by longitudinal and lateral stiffness in the primary suspension. Additionally, wear accumulates continuously as superelevation increases. Asymmetric rail cant and gauge widening on curved tracks are shown to effectively reduce wheel wear, with a 15 mm gauge widening resulting in a 21.9% reduction in wear on the left wheel. Furthermore, wear is notably mitigated under wet, low-coefficient friction (LCF), and oil-contaminated conditions. This study offers practical insights to support the operation and maintenance of humpback freight vehicles in railway systems.
ABSTRACT In view of the promising application potential of two‐dimensional MXenes (Ti 3 C 2 T x ) in lubrication, along with the challenge of their poor dispersibility in non‐polar base oil, this work reports the surface functionalisation of Ti 3 C 2 T x through the covalent grafting of alkylphosphonic acid (TDPA). TDPA grafting converts the surface properties of Ti 3 C 2 T x from polar to non‐polar, significantly enhancing its dispersion stability in non‐polar PAO20 base oil. Tribological performance tests showed that as an additive, TDPA‐Ti 3 C 2 T x improved the anti‐wear performance of PAO20 by 38.1%. Its excellent performance is mainly attributed to the high mechanical strength, easy interlayer shear characteristics of the modified nanosheets, and the synergistic effect of the protective tribochemical film formed in situ during the friction process. The TDPA functionalisation strategy is an effective way to realise the efficient application of Ti 3 C 2 T x in non‐polar lubricating systems, and provides a new idea for the design of high‐performance lubricating additives.
The structural, mechanical and tribological properties of UHMWPE reinforced with clinoptilolite microparticules (Clino) at various concentrations (0%, 5%, 10%, and 20%), under dry sliding, were investigated. The biocomposites were processed by compression moulding and their microstructure was characterized by Fourier Transform Infrared Spectroscopy (FTIR). Friction and wear tests were performed against M30NW stainless steel using a reciprocating pin-on-disc tribometer. The wear morphology was evaluated by the Scanning Electron Microscopy (SEM). Rockwell hardness was used to investigate the mechanical properties of the biocomposites. Results showed that crystallinity, hardness and wear resistance of all biocomposites were improved compared to neat UHMWPE. SEM micrographs revealed an improvement in the wear behaviour by adding clinoptilolite in UHMWPE. It was found that, the 10 wt.% clinoptilolite biocomposite exhibited the best wear behaviour.
