查看更多>>摘要：Friction properties of rock are closely connected with the anisotropy.The anisotropy of rock friction can provide a valuable assessment for geotechnical and geological engineering.In this study,the rotary friction tests were conducted to analyze the water effect on the friction property and the friction anisotropy of the four types of rock.The drilling response model(DD-model)was employed to characterize the rotary friction behavior of the rocks.The parameters of this model include the three types of friction parameters:1/ς,μ,and f,where 1/ς and μ are constant,and f is a variable.A quantitative method is proposed for assessing the anisotropy of rock friction.The results of the rotary friction tests indicate that the relation between torque force and thrust force conforms to the DD-model.The changes of two friction constants 1/ς and μ from dry state to water-saturated state suggest that the water effect on the friction strength of the rocks exhibits significant anisotropy.The friction strength determined by the friction variable f increases first,then decreases,and finally stabilizes with the increasing of depth.AIf is an anisotropy index calculated by the proposed method.The percentage difference of the average value of AIf between water-saturated and dry states shows the degree of the water effect on the friction anisotropy of the rocks,mudstone(MU)>granite(GR)>fine sandstone(FS)>argillaceous siltstone(AS).The quantitative model is hopefully constructed for characterizing the relation between the anisotropic friction strength of rock and the moisture state in future.
查看更多>>摘要：The paper shows that work in a quantum system is quantized with energy;the quantum work is equivalent to the highest eigenenergy(the Debye energy)of the system and the superlubricity of solids is derived from the quantum work.The prerequisite for the superlubricity is that the lateral force at contact surfaces in sliding is less than the Debye force so that the phonon of the solids is not excited.
查看更多>>摘要：This study focused on producing metal matrix composite(MMC)coatings on Ti-6Al-4V alloy through laser surface alloying using a novel combination of Inconel 625 and SiC precursor materials.Various ratios of alloying powders were examined to evaluate surface properties such as microhardness,wear resistance,and friction coefficient,along with analyzing the phase composition and microstructure of the coatings.The in situ synthesized MMC coatings exhibited the presence of α-Ti,NiTi,NiTi2,and TiC phases.Additionally,Ti5Si3 and α-Ti/Ti5Si3 eutectic structures were observed when the SiC content exceeded 20%.In comparison to the titanium substrate,the MMC coating significantly enhanced microhardness by over threefold and reduced wear by 95%.However,it was crucial to carefully select the appropriate combination of alloying powders to avoid a substantial decrease in friction performance and excessive formation of cracks.Through a comparative analysis of experimental results,the optimal precursor material composition was identified as 85%Inconel 625 and 15%SiC.This study demonstrated the effective utilization of Inconel 625 and SiC alloying materials to enhance the surface properties of titanium alloys,thereby expanding their application in challenging environments.
Juan RUIZ-ACEROFelipe KESSLERHenara COSTATiago COUSSEAU...
2108-2125页
查看更多>>摘要：Ethanol has emerged as a promising alternative to fossil fuels,but its use can lead to significant dilution in lubricants,particularly during cold start or heavy traffic.This dilution can affect the performance of additives,including friction modifiers like molybdenum dithiocarbamate(MoDTC),which are designed to reduce friction under extreme contact conditions.Prior research suggests that ethanol may impact the performance of MoDTC,prompting this study's goal to investigate the effects of ethanol on MoDTC tribofilms and their friction response under boundary lubrication conditions.Therefore,reciprocating tribological tests were performed with fully formulated lubricants containing MoDTC with varying ethanol concentrations.The results indicate that a critical ethanol dilution level inhibits friction reduction by MoDTC activation,resulting in friction coefficients(COFs)similar to the base oil.Surfaces tested with simple mixtures of polyalphaolefin(PAO)+MoDTC showed increased COFs with added ethanol.Analysis of tested surfaces using Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),and X-ray absorption spectroscopy near the edge structure(XANES)revealed the presence of sulfates,MoO3,MoS2,and MoSxOy compounds in the tribofilms formed on the surfaces,with and without ethanol diluted in the lubricant.However,the addition of ethanol increased the sulfates and MoO3 content of the tribofilms at the expense of friction-reducing compounds such as MoS2 and MoSxOy.These findings suggest that ethanol dilution in lubricants containing MoDTC creates an oxygen-rich interfacial medium that favors the formation of compounds with insufficient friction-reducing capabilities.
查看更多>>摘要：The coefficient of friction(CoF)between the deflection pulley and rope in a lift strongly affects the life span of the rope.Although surface roughness is a key factor affecting the metallic pulley-rope CoF,its effect on polymeric pulleys is unknown.The present study analyses the effect of roughness and working conditions on cast polyamide 6(PA6G)deflection pulley-thermoplastic polyurethane(TPU)-coated rope contacts.The statistical analysis revealed that the effect of surface roughness on the CoF for low-load tests was significant.The present study contributes significantly to parameter selection in deflection pulley machining to minimise friction between the pulley and rope.
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