针对目前带自由边的双参数弹性地基板的边界条件及基本方程在使用上的混乱情况,为了板与地基动力相互作用理论的严密性和计算的可靠性,将板和地基作为一个总系统,利用H am ilton动力变分原理,重新系统地审视了双参数弹性地基上板动力问...针对目前带自由边的双参数弹性地基板的边界条件及基本方程在使用上的混乱情况,为了板与地基动力相互作用理论的严密性和计算的可靠性,将板和地基作为一个总系统,利用H am ilton动力变分原理,重新系统地审视了双参数弹性地基上板动力问题的基本理论,给出了地基附加质量影响的明确计算公式,建立了考虑地基附加质量影响的基本方程和边界条件,并对边界条件的简化进行了讨论.所得的结果还可推广到位于层状地基上的板的分析.展开更多
In this study we present a mechanism for the elastohydrodynamic(EHD)friction reduction in steel/steel contacts,which occurs due to the formation of oleophobic surface boundary layers from common boundary-lubrication a...In this study we present a mechanism for the elastohydrodynamic(EHD)friction reduction in steel/steel contacts,which occurs due to the formation of oleophobic surface boundary layers from common boundary-lubrication additives.Several simple organic additives(amine,alcohol,amide,and fatty acid)with different molecular structures were employed as the model additives.It was found that the stronger chemisorption at 100℃,rather than the physisorption at 25℃,is more effective in friction reduction,which reaches 22%.What is more,EHD friction reduction was obtained in steel/steel contacts without use of the diamond-like carbon(DLC)coatings with their wetting or thermal effect,which was previously suggested as possible EHD friction reduction mechanism;yet about the same friction reduction of about 20%was obtained here—but with much simpler and less expensive technology,namely with the adsorbed oleophobic surface layers.A small variation in the additive’s molecular structure results in significant changes to the friction,indicating good potential in future EHD lubrication technology,where these additives could be designed and well optimised for notable reduction of the friction losses in the EHD regime.展开更多
The emerging use of two-dimensional(2D)nanomaterials as boundary lubricants in water offers numerous benefits over oil-based lubricants;whereas the friction reduction varies significantly with nanomaterial type,size,l...The emerging use of two-dimensional(2D)nanomaterials as boundary lubricants in water offers numerous benefits over oil-based lubricants;whereas the friction reduction varies significantly with nanomaterial type,size,loading,morphology,etc.Graphene oxide(GO)and Ti_(3)C_(2)T_(x)MXene,a relatively new 2D material,are investigated as boundary lubricants in water in this study.The contact pair mainly includes Si3N4 balls and Si wafer.The results found(1)monodispersed GO offers better lubricity than monodispersed MXene under identical concentration and testing conditions;and(2)the mixed dispersion of GO and MXene(0.1 mg/ml:0.1 mg/ml)produced the lowest friction coefficient of~0.021,a value 4×and 10×lower than that produced by comparable mono-dispersions of GO or MXene,respectively.Wear track analysis,focused ion beam microscopy,in-situ contact observation,and atomic force microscopy(AFM)characterization suggest(1)GO nanoflakes have higher adhesion than MXene and are more easily adsorbed on the tribopairs’surfaces,and(2)GO/MXene tribofilm has a layered nanostructure constituting GO,MXene,amorphous carbon,and TiO_(2).We further hypothesized that the high lubricity of GO/MXene results from the synergy of GO’s high adhesiveness,MXene’s load support ability,and the low shear strength of both constituents.The present study highlights the key role of tribofilm stability in water-based boundary lubrication using state-of-the-art 2D nanomaterials.展开更多
Neodymium dialkylthiophosphate （NdDDP） with alkyls of isopropyl and isooctyl were synthesized by exchanged reaction respectively. The structures of the two NdDDPs were determined using IR and XRD. Properties of anti...Neodymium dialkylthiophosphate （NdDDP） with alkyls of isopropyl and isooctyl were synthesized by exchanged reaction respectively. The structures of the two NdDDPs were determined using IR and XRD. Properties of anti-wear and friction-reducing of the two additives were investigated with four ball experiment and the commercial anti-wear additive ZDDP was selected as control. The elemental analysis of the wear scars after 10 s friction at low stress were investigated by EDXA （Energy Dispersion Analysis of X-ray）. Primary results showed that the NdDDPs possess better lubrication ability than ZDDP. This might mainly be contributed to the formation of a boundary film containing Nd2O3, FeS and sulphate, phosphate, organo-sulfide, etc., and a neodymium-rich diffused layer which changes the crystal structure of the surface of friction materials.展开更多
文摘针对目前带自由边的双参数弹性地基板的边界条件及基本方程在使用上的混乱情况,为了板与地基动力相互作用理论的严密性和计算的可靠性,将板和地基作为一个总系统,利用H am ilton动力变分原理,重新系统地审视了双参数弹性地基上板动力问题的基本理论,给出了地基附加质量影响的明确计算公式,建立了考虑地基附加质量影响的基本方程和边界条件,并对边界条件的简化进行了讨论.所得的结果还可推广到位于层状地基上的板的分析.
基金The authors acknowledge the financial support from the Slovenian Research Agency(Research Core Funding No.P2-0231).
文摘In this study we present a mechanism for the elastohydrodynamic(EHD)friction reduction in steel/steel contacts,which occurs due to the formation of oleophobic surface boundary layers from common boundary-lubrication additives.Several simple organic additives(amine,alcohol,amide,and fatty acid)with different molecular structures were employed as the model additives.It was found that the stronger chemisorption at 100℃,rather than the physisorption at 25℃,is more effective in friction reduction,which reaches 22%.What is more,EHD friction reduction was obtained in steel/steel contacts without use of the diamond-like carbon(DLC)coatings with their wetting or thermal effect,which was previously suggested as possible EHD friction reduction mechanism;yet about the same friction reduction of about 20%was obtained here—but with much simpler and less expensive technology,namely with the adsorbed oleophobic surface layers.A small variation in the additive’s molecular structure results in significant changes to the friction,indicating good potential in future EHD lubrication technology,where these additives could be designed and well optimised for notable reduction of the friction losses in the EHD regime.
基金The authors acknowledge support from the financial support from the National Natural Science Foundation of China(Grant Nos.51875153,51875152,and 51975174)the Fundamental Research Funds for the Central Universities(JZ2021HGPA0062)。
文摘The emerging use of two-dimensional(2D)nanomaterials as boundary lubricants in water offers numerous benefits over oil-based lubricants;whereas the friction reduction varies significantly with nanomaterial type,size,loading,morphology,etc.Graphene oxide(GO)and Ti_(3)C_(2)T_(x)MXene,a relatively new 2D material,are investigated as boundary lubricants in water in this study.The contact pair mainly includes Si3N4 balls and Si wafer.The results found(1)monodispersed GO offers better lubricity than monodispersed MXene under identical concentration and testing conditions;and(2)the mixed dispersion of GO and MXene(0.1 mg/ml:0.1 mg/ml)produced the lowest friction coefficient of~0.021,a value 4×and 10×lower than that produced by comparable mono-dispersions of GO or MXene,respectively.Wear track analysis,focused ion beam microscopy,in-situ contact observation,and atomic force microscopy(AFM)characterization suggest(1)GO nanoflakes have higher adhesion than MXene and are more easily adsorbed on the tribopairs’surfaces,and(2)GO/MXene tribofilm has a layered nanostructure constituting GO,MXene,amorphous carbon,and TiO_(2).We further hypothesized that the high lubricity of GO/MXene results from the synergy of GO’s high adhesiveness,MXene’s load support ability,and the low shear strength of both constituents.The present study highlights the key role of tribofilm stability in water-based boundary lubrication using state-of-the-art 2D nanomaterials.
文摘Neodymium dialkylthiophosphate （NdDDP） with alkyls of isopropyl and isooctyl were synthesized by exchanged reaction respectively. The structures of the two NdDDPs were determined using IR and XRD. Properties of anti-wear and friction-reducing of the two additives were investigated with four ball experiment and the commercial anti-wear additive ZDDP was selected as control. The elemental analysis of the wear scars after 10 s friction at low stress were investigated by EDXA （Energy Dispersion Analysis of X-ray）. Primary results showed that the NdDDPs possess better lubrication ability than ZDDP. This might mainly be contributed to the formation of a boundary film containing Nd2O3, FeS and sulphate, phosphate, organo-sulfide, etc., and a neodymium-rich diffused layer which changes the crystal structure of the surface of friction materials.
