Textured surfaces offer the potential to promote friction and wear reduction by increasing the hydrodynamic pressure,fluid uptake,or acting as oil or debris reservoirs.However,texturing techniques often require additi...Textured surfaces offer the potential to promote friction and wear reduction by increasing the hydrodynamic pressure,fluid uptake,or acting as oil or debris reservoirs.However,texturing techniques often require additional manufacturing steps and costs,thus frequently being not economically feasible for real engineering applications.This experimental study aims at applying a fast laser texturing technique on curved surfaces for obtaining superior tribological performances.A femtosecond pulsed laser(Ti:Sapphire)and direct laser interference patterning(with a solid‐state Nd:YAG laser)were used for manufacturing dimple and groove patterns on curved steel surfaces(ball samples).Tribological tests were carried out under elasto‐hydrodynamic lubricated contact conditions varying slide‐roll ratio using a ball‐on‐disk configuration.Furthermore,a specific interferometry technique for rough surfaces was used to measure the film thickness of smooth and textured surfaces.Smooth steel samples were used to obtain data for the reference surface.The results showed that dimples promoted friction reduction(up to 20%)compared to the reference smooth specimens,whereas grooves generally caused less beneficial or detrimental effects.In addition,dimples promoted the formation of full film lubrication conditions at lower speeds.This study demonstrates how fast texturing techniques could potentially be used for improving the tribological performance of bearings as well as other mechanical components utilised in several engineering applications.展开更多
With the increased use of automotive engine start-stop systems,the numerical prediction and reduction of frictional losses in sliding bearings during starting and stopping procedures has become an important issue.In e...With the increased use of automotive engine start-stop systems,the numerical prediction and reduction of frictional losses in sliding bearings during starting and stopping procedures has become an important issue.In engineering practice,numerical simulations of sliding bearings in automotive engines are performed with statistical asperity contact models with empirical values for the necessary surface parameters.The aim of this study is to elucidate the applicability of these approaches for the prediction of friction in sliding bearings subjected to start-stop operation.For this purpose,the friction performance of sliding bearings was investigated in experiments on a test rig and in transient mixed elasto-hydrodynamic simulations in a multi-body simulation environment(mixed-EHL/MBS).In mixed-EHL/MBS,the extended Reynold’s equation with flow factors according to Patir and Cheng has been combined on the one hand with the statistical asperity contact model according to Greenwood and Tripp and on the other hand with the deterministic asperity contact model according to Herbst.The detailed comparison of simulation and experimental results clarifies that the application of statistical asperity contact models with empirical values of the necessary inputs leads to large deviations between experiment and simulation.The actual distribution and position of surface roughness,as used in deterministic contact modelling,is necessary for a reliable prediction of the frictional losses in sliding bearings during start-stop operation.展开更多
A new CVT(continuously variable transmission) design which is a traction drive variator has been introduced. Analytical predictions and experimental results of the steady state which demonstrate higher efficiencies an...A new CVT(continuously variable transmission) design which is a traction drive variator has been introduced. Analytical predictions and experimental results of the steady state which demonstrate higher efficiencies and power capacities of the new design are presented. The traction and power loss are then predicted by using models including evaluation of creep and spin in the contact patch. Analytical predictions of the transmission reach reasonable agreement with the experimental data, and the transmission efficiency of the system increases as the input torque increases while the input speed is certain. The research results can be further used in hydraulic traction drive CVT design and optimization.展开更多
The rolling contact fatigue(RCF)model is commonly used to predict the contact fatigue life when the sliding is insignificant in contact surfaces.However,many studies reveal that the sliding,compared to the rolling sta...The rolling contact fatigue(RCF)model is commonly used to predict the contact fatigue life when the sliding is insignificant in contact surfaces.However,many studies reveal that the sliding,compared to the rolling state,can lead to a considerable reduction of the fatigue life and an excessive increase of the pitting area,which result from the microscopic stress cycle growth caused by the sliding of the asperity contact.This suggests that fatigue life in the rolling-sliding condition can be overestimated based only on the RCF model.The rubbing surfaces of spiral bevel gears are subject to typical rolling-sliding motion.This paper aims to study the mechanism of the micro stress cycle along the meshing path and provide a reasonable method for predicting the fatigue life in spiral bevel gears.The microscopic stress cycle equation is derived with the consideration of gear meshing parameters.The combination of the RCF model and asperity stress cycle is developed to calculate the fatigue life in spiral bevel gears.We find that the contact fatigue life decreases significantly compared with that obtained from the RCF model.There is strong evidence that the microscopic stress cycle is remarkably increased by the rolling-sliding motion of the asperity contact,which is consistent with the experimental data in previous literature.In addition,the fatigue life under different assembling misalignments are investigated and the results demonstrate the important role of misalignments on fatigue life.展开更多
为了研究表面形貌对线接触弹流状态下摩擦副摩擦特性的影响,采用激光微造型技术,通过控制微造型的形状、深度、间距和面积占有率等参数制造了两组表面高度算术平均值Sa分别相同的试件.使用Talysurf CCI Lite非接触式三维光学轮廓仪对表...为了研究表面形貌对线接触弹流状态下摩擦副摩擦特性的影响,采用激光微造型技术,通过控制微造型的形状、深度、间距和面积占有率等参数制造了两组表面高度算术平均值Sa分别相同的试件.使用Talysurf CCI Lite非接触式三维光学轮廓仪对表面进行测量,采用ISO25178参数及连通性系数Us对测量表面进行表征,最后在JPM-1型双盘摩擦磨损试验机上对试件进行富油摩擦试验,得到不同转速、不同载荷工况下的摩擦系数.结果表明:线接触状态下,微造型形状、方向及深度均会对表面的摩擦特性产生影响,顺向箭头微造型表面表现出了最优的摩擦特性;试件摩擦系数随着转速的增大呈线性增长趋势,随着载荷的增大而减小,减小的幅度随载荷的增大逐渐变得缓慢;表面形貌三维表征参数Ssk、Sku、Vvv、Vvc、Us与摩擦特性均有一定的关联性.展开更多
In this paper, the effect of surface roughness on sealing clearance, pressure distribution, friction torque and leakage is studied by the thermal-elasto-hydrodynamic mixed lubrication model. A convergent nominal clear...In this paper, the effect of surface roughness on sealing clearance, pressure distribution, friction torque and leakage is studied by the thermal-elasto-hydrodynamic mixed lubrication model. A convergent nominal clearance is formed by the pressure de- formation and thermal deformation of the seal faces. This causes more serious wear in the inner side than that of the outer side of the contact area. Mass leakage increases with the growing of the surface roughness. The temperature and thermal defor- mation on the seal surface increases substantially if the roughness is reduced. The contact mechanical seals have consistent performance when the standard deviation of surface roughness is approximately 0.2 pm. In order to validate the theoretical analysis model, a method combining the measurement of three-dimensioned profile and Raman spectrum is proposed.展开更多
基金This project was generously financed by the State of São Paulo Research Foundation,Brazil(FAPESP Grant Nos.2016/25067‐9 and 2017/21151‐8)the Brazilian National Council for Scientific and Technological Development(CNPq)+1 种基金G.BOIDI thanks the Austrian Research Promotion Agency(FFG)for the funding obtained by the Austrian COMETProgram(Project K2,InTribology,No.872176)carried out at the“Excellence Centre of Tribology”(AC2T research GmbH)The government of Lower Austria is gratefully acknowledged for financially supporting the endowed professorship tribology of Prof.C.GACHOT at the TU Wien(Grant No.WST3‐F‐5031370/001‐2017)in collaboration with AC2T research GmbH.D.DINI also acknowledges the support received from the Engineering and Physical Sciences Research Council(EPSRC)via his Established Career Fellowship EP/N025954/1.
文摘Textured surfaces offer the potential to promote friction and wear reduction by increasing the hydrodynamic pressure,fluid uptake,or acting as oil or debris reservoirs.However,texturing techniques often require additional manufacturing steps and costs,thus frequently being not economically feasible for real engineering applications.This experimental study aims at applying a fast laser texturing technique on curved surfaces for obtaining superior tribological performances.A femtosecond pulsed laser(Ti:Sapphire)and direct laser interference patterning(with a solid‐state Nd:YAG laser)were used for manufacturing dimple and groove patterns on curved steel surfaces(ball samples).Tribological tests were carried out under elasto‐hydrodynamic lubricated contact conditions varying slide‐roll ratio using a ball‐on‐disk configuration.Furthermore,a specific interferometry technique for rough surfaces was used to measure the film thickness of smooth and textured surfaces.Smooth steel samples were used to obtain data for the reference surface.The results showed that dimples promoted friction reduction(up to 20%)compared to the reference smooth specimens,whereas grooves generally caused less beneficial or detrimental effects.In addition,dimples promoted the formation of full film lubrication conditions at lower speeds.This study demonstrates how fast texturing techniques could potentially be used for improving the tribological performance of bearings as well as other mechanical components utilised in several engineering applications.
基金This work was funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-GRK 1856.
文摘With the increased use of automotive engine start-stop systems,the numerical prediction and reduction of frictional losses in sliding bearings during starting and stopping procedures has become an important issue.In engineering practice,numerical simulations of sliding bearings in automotive engines are performed with statistical asperity contact models with empirical values for the necessary surface parameters.The aim of this study is to elucidate the applicability of these approaches for the prediction of friction in sliding bearings subjected to start-stop operation.For this purpose,the friction performance of sliding bearings was investigated in experiments on a test rig and in transient mixed elasto-hydrodynamic simulations in a multi-body simulation environment(mixed-EHL/MBS).In mixed-EHL/MBS,the extended Reynold’s equation with flow factors according to Patir and Cheng has been combined on the one hand with the statistical asperity contact model according to Greenwood and Tripp and on the other hand with the deterministic asperity contact model according to Herbst.The detailed comparison of simulation and experimental results clarifies that the application of statistical asperity contact models with empirical values of the necessary inputs leads to large deviations between experiment and simulation.The actual distribution and position of surface roughness,as used in deterministic contact modelling,is necessary for a reliable prediction of the frictional losses in sliding bearings during start-stop operation.
基金Project(A2220060029)supported by the National Ministries of Basic Scientific Research Fund Project,ChinaProject(9140C340201113403)supported by the Foundation of the National Key Laboratory of Vehicular Transmission,China
文摘A new CVT(continuously variable transmission) design which is a traction drive variator has been introduced. Analytical predictions and experimental results of the steady state which demonstrate higher efficiencies and power capacities of the new design are presented. The traction and power loss are then predicted by using models including evaluation of creep and spin in the contact patch. Analytical predictions of the transmission reach reasonable agreement with the experimental data, and the transmission efficiency of the system increases as the input torque increases while the input speed is certain. The research results can be further used in hydraulic traction drive CVT design and optimization.
基金National Science Foundation of China(No.51875369)General Projects of Basic Science and Frontier Technology Research of Chongqing(Nos.cstc2016jcyjA0511,cstc2018jcyjAX0451)Wei PU would like to thank Fundamental Research Funds for the Central Universities(No.YjJ201752).
文摘The rolling contact fatigue(RCF)model is commonly used to predict the contact fatigue life when the sliding is insignificant in contact surfaces.However,many studies reveal that the sliding,compared to the rolling state,can lead to a considerable reduction of the fatigue life and an excessive increase of the pitting area,which result from the microscopic stress cycle growth caused by the sliding of the asperity contact.This suggests that fatigue life in the rolling-sliding condition can be overestimated based only on the RCF model.The rubbing surfaces of spiral bevel gears are subject to typical rolling-sliding motion.This paper aims to study the mechanism of the micro stress cycle along the meshing path and provide a reasonable method for predicting the fatigue life in spiral bevel gears.The microscopic stress cycle equation is derived with the consideration of gear meshing parameters.The combination of the RCF model and asperity stress cycle is developed to calculate the fatigue life in spiral bevel gears.We find that the contact fatigue life decreases significantly compared with that obtained from the RCF model.There is strong evidence that the microscopic stress cycle is remarkably increased by the rolling-sliding motion of the asperity contact,which is consistent with the experimental data in previous literature.In addition,the fatigue life under different assembling misalignments are investigated and the results demonstrate the important role of misalignments on fatigue life.
文摘为了研究表面形貌对线接触弹流状态下摩擦副摩擦特性的影响,采用激光微造型技术,通过控制微造型的形状、深度、间距和面积占有率等参数制造了两组表面高度算术平均值Sa分别相同的试件.使用Talysurf CCI Lite非接触式三维光学轮廓仪对表面进行测量,采用ISO25178参数及连通性系数Us对测量表面进行表征,最后在JPM-1型双盘摩擦磨损试验机上对试件进行富油摩擦试验,得到不同转速、不同载荷工况下的摩擦系数.结果表明:线接触状态下,微造型形状、方向及深度均会对表面的摩擦特性产生影响,顺向箭头微造型表面表现出了最优的摩擦特性;试件摩擦系数随着转速的增大呈线性增长趋势,随着载荷的增大而减小,减小的幅度随载荷的增大逐渐变得缓慢;表面形貌三维表征参数Ssk、Sku、Vvv、Vvc、Us与摩擦特性均有一定的关联性.
基金supported by the National Basic Research Program of China(Grant No.2009CB724304)the National Natural Science Foundation of China(Grant No.51275268)the National Science and Technology Support Plan(Grant No.2011BAF09B05)
文摘In this paper, the effect of surface roughness on sealing clearance, pressure distribution, friction torque and leakage is studied by the thermal-elasto-hydrodynamic mixed lubrication model. A convergent nominal clearance is formed by the pressure de- formation and thermal deformation of the seal faces. This causes more serious wear in the inner side than that of the outer side of the contact area. Mass leakage increases with the growing of the surface roughness. The temperature and thermal defor- mation on the seal surface increases substantially if the roughness is reduced. The contact mechanical seals have consistent performance when the standard deviation of surface roughness is approximately 0.2 pm. In order to validate the theoretical analysis model, a method combining the measurement of three-dimensioned profile and Raman spectrum is proposed.
