查看更多>>摘要：Traditional antifouling agents usually have a certain toxic effect on marine environments and non-target organisms.In this study,Dictyophora indusiata polysaccharide(DIP)was applied as a natural antifouling surface modifier to prepare the surface coating for marine antifouling.Three DIP coatings were prepared:D.indusiata spore polysaccharide(DISP),D.indusiata volva polysaccharide(DIVP),and D.indusiata embryonic body polysaccharide(DIEP).The antifouling,tribological,and anticorrosion behavior of the coatings were examined.Results revealed that the three kinds of DIP coatings had excellent antifouling properties,which could effectively prevent the adhesion of Chlorella and the attachment of water-based and oily stains on the surface.Additionally,the coatings showed great mechanical stability and could maintain an extremely low coefficient of friction(COF<0.05)after continuous wear.The drag reduction rate of the coated surfaces reached 5%,showing a powerful lubrication performance.Furthermore,the DIP coatings presented an outstanding corrosion resistance,where the equivalent circuit impedances were 4-9 orders of magnitude higher than the control groups.This research showed a promising prospect of surface coating fabrication with DIP for marine devices to achieve the purpose of antifouling and drag reduction.
查看更多>>摘要：Many rubber friction theories or some method combined theories and field-experiments are employed to evaluate the pavement skid-resistance deterioration due to the evolution of surface textures.However,these methods are difficult to be implemented in the analysis of situations with multi-factor coupling and some extreme conditions.This study developed a framework to evaluate the skid-resistance deterioration of asphalt pavements.In this framework,the portable laser scanning was used to create the digital worn pavement model,and a hydroplaning finite element(FE)model for these digital worn pavements was constructed to evaluate coupling effects of the texture evolution and factors of slip ratio,slip angle,velocity and water film on braking-cornering characteristics of tire.In this study,the deterioration of skid-resistance of five typical asphalt pavements due the surface texture wear was systematically investigated by this framework.Compared with previous works,this study established the rubber friction models for each digital worn pavement considering the energy hysteresis of rubber and the power spectrum density of surface texture.And the rubber friction model was used to define the interaction behaviors between the tire and corresponding wore pavements in the FE hydroplaning model,rather than using an empirical friction model or a fixed friction coefficient.
查看更多>>摘要：This work investigated the temperature changes inside the bulk of lubricating greases under controlled high-shear stress conditions(250-500 s-1).For this purpose,a newly developed temperature-measuring cell called Calidus was successfully tested.The temperature changes(ΔT)have been related to the greases'components(thickener,base oil-type,and composition)and the structural degradation of the lubricating greases.Furthermore,a theoretical approach was proposed for calculating the internal temperature change of lubricating greases during shear stress.All greases showed an internal temperature profile characterised by a sudden rise in ΔT within the first 4 h from starting the test and subsequent ΔT decay until it reaches the steady state value.Furthermore,it was found that greases C1 and C5,formulated with lithium and calcium soap,respectively,with different soap content(16.1 wt%and 9.7 wt%,respectively),but the same base castor oil,showed the highest value of the maximum ΔT,c.a.3.2 K,and the most drastic drop of ΔT.These greases showed both the highest specific densities and heat capacities.In addition,they showed the lowest ratio of expended energies(Rtee),which means more structural degradation in the stressed grease.On the contrary,the grease C3,with 13 wt%of Li-soap but the lowest base oil's viscosity,showed the lowest maximum ΔT and the temperature profile was characterised by a moderate variation of ΔT along the test.The biogenic grease B3 developed a low-temperature change in the group of pure bio-genic greases close to grease C3.
查看更多>>摘要：Leakage currents accelerate surface degradation of metal contacts via small scale arcing across lubricating films,but recent observations suggest that metallic nanoparticle additives in lubricants may be useful to improve contact performance.These findings prompted a study that examined electrically induced surface pitting of steel contacts in the presence of several lubricating greases including some containing nanometer-sized colloidal silver(Ag)particles.Reciprocating rolling sphere-on-disk experiments were conducted under electro-tribological loads employing polyurea greases derived from mineral and synthetic base oils with and without additives.Friction forces and electrical resistance were monitored continuously during the tests;surface changes were characterized by means of optical spectroscopy,stylus profilometry,and scanning electron microscopy(SEM)including compositional analysis using energy dispersive spectroscopy(EDS).The observations demonstrate that surface pitting induced by arcing occurs mainly at the points were the rolling motion changes direction and that eroded metal is deposited along the wear grove.Micron-sized pits are formed which contain carbon and oxygen indicating that arcing causes decomposition of the hydrocarbon lubricants.Numerous findings indicate a significant inhibition of pitting is induced by the Ag nanoparticles;some greases containing other additives exhibit a similar,although less pronounced,effect.
查看更多>>摘要：In hydrodynamic bearings traditional bearing alloys:Babbitts and bronzes are most frequently utilized.Polymer sliding layers are sometimes applied as a valuable alternative.Hard diamond-like carbon(DLC)coatings,which are also considered for certain applications may show some advantages,as well.Although material selection is of secondary importance in a full film lubrication regime it becomes important in mixed friction conditions,which is crucial for bearings with frequent starts and stops.Experimental research aimed at studying the performance of fluid film bearings in the specific operating regime,including the transition to mixed friction,is described in the paper.The tests were carried out on four tilting pad bearings of different material compositions:Steel/bronze,DLC/steel,steel/polyether ether ketone(PEEK),and steel/Babbitt.The tests comprised stopping under load and reproduction of the Stribeck curve by decreasing rotational speed to very low values,and observing the changes of friction force during the transition to mixed friction regime.Analysis of the transition conditions and other results showed clear differences between the tested bearings,illustrating the feasibility of less popular material compositions for bearings operating in specific conditions.More specifically,the DLC/steel bearing was demonstrating superior performance,i.e.lower friction,transition to mixed friction occurring at higher load,and more stable performance at start-stop regime over the other tested bearings.
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