基于弹流润滑理论的深沟球轴承动态虚拟仿真

实践研究表明,润滑油膜对轴承的胶合、擦伤和接触疲劳有重要影响。而以往对轴承的仿真均忽略了润滑油膜的存在,误差较大。本文首先在刚性套圈假设的前提下,基于Hertz接触理论,运用拟动力学法建立球轴承在径向、轴向载荷作用下的力学模型,以Newton-Raphson法为主要计算工具对模型进行求解,获得轴承在联合载荷作用下的接触载荷和变形,并求取了各个滚珠与内、外圈之间的接触刚度。基于EHL理论考虑润滑油膜对轴承动态特性的影响,求取滚动轴承油膜刚度。最后提出等效综合刚度的概念并求其值,在此基础上运用ADAMS软件对轴承进行准确的动力学仿真。该方法使仿真更接近实际工况,为准确了解轴承的动态性能提供了重要的理论依据。     

A New Approach for Modeling Mixed Lubricated Piston-Cylinder Pairs of Variable Lengths in Swash-Plate Axial Piston Pumps

The swash-plate axial piston pump is one of the most widely used pumps due to its simplicity and compactness in structure. In such a pump, the piston-cylinder system plays a crucial role, with its lubrication characteristics greatly affecting the overall pumping performance. A new numerical approach is proposed in this study for modeling mixed lubricated piston-cylinder interfaces of variable lengths in swash-plate axial piston pumps in the framework of multibody dynamics. The approach couples the hydrodynamic mixed lubrication model of the piston-cylinder interface with the multibody dynamics model of the piston pump. The lubrication model is established with a transient average Reynolds equation considering asperity contacts and is solved with the finite element method to derive the hydrodynamic forces of the lubricated pair, while the multibody dynamics model is established with Lagrangian formalism by considering hydrodynamic forces as external forces. Results for piston-cylinder interfaces of variable lengths in swash-plate axial piston pumps are presented, and the impacts of cylinder length and the tilt angle of the swash plate on the tribological performances of the interface are discussed. The results indicate that increasing the cylinder length can improve the stability and wear resistance of the piston, but it can exacerbate the frictional power loss. Moreover, although enlarging the tilt angle of the swash plate can effectively increase pump displacement, it can easily lead to serious friction, wear, and leakage problems. Consequently, the tilt angle of the swash plate should be carefully selected in practical applications.     

Friction and Wear Characteristics of Polydimethylsiloxane under Water-Based Lubrication Conditions

In this study, the friction and wear characteristics of polydimethylsiloxane (PDMS) were evaluated when using lubricants created by adding surfactants at various ratios to deionized (DI) water. When pure DI water is used as a lubricant, the repulsion of water from the hydrophobic PDMS surface is large and the interfacial affinity is low; thus, the lubrication properties cannot be significantly improved. However, when a lubricant with a surfactant is added to DI water, the interfacial affinity with the PDMS surface increases to form a lubricating film, and the friction coefficient is greatly reduced. In this study, under dry and pure DI water conditions, severe wear tracks were formed on the PDMS surface after 10,000 cycles of reciprocating sliding motion under a vertical load of 100 mN, whereas in the case of the surfactant-based and water-based lubricant, no severe wear tracks occurred. The friction and wear characteristics of the PDMS were evaluated by increasing the normal loads and sliding cycles with a water-based lubricant containing 1 wt % surfactant. Under normal loads of 300 mN and 500 mN, only minor scratches occurred on the PDMS surface up to 10,000 and 100,000 cycles, respectively, but after 300,000 cycles, very severe pit wear tracks occurred.     

Water versus Oil Lubrication of Laser-Textured Ti6Al4V Alloy upon Addition of MoS2 Nanotubes for Green Tribology

A Nd-YAG laser was used for texturing the Ti6Al4V surface with dimples of diameter 50 and 100 µm and centre-to-centre distance 100, 200 and 400 µm, defining the surface texture density. The tribological evaluation was conducted to analyse and compare the behaviour of un-textured and laser-textured samples under water in comparison to oil (PAO6) lubrication without and with the addition of MoS₂ nanotubes into the lubricant. MoS₂ nanotubes had a positive effect on friction in both media for laser-textured Ti6Al4V. Evaluation of friction and wear in water and PAO6 showed a comparable tribological response in water to oil for specific laser-textured configurations, proving the novel concept of green tribology for laser texturing in combination with MoS₂ nanotubes/water lubrication.     

Communicating Tabular Data Using ORACLE

“You see but you do not observe.”

Sherlock Holmes to Watson

Arthur Conan Doyle

A Scandal in Bohemia     

胃镜润滑胶浆联合超细活检钳在三腔二囊管置入中的应用

目的 探索一种简便、快捷、安全而人性化的三腔二囊管置管方法,进一步提高三腔二囊管的应用水平.方法 将60例肝硬变合并食道胃底静脉曲张破裂大出血病人,随机分为常规组和胃镜润滑胶浆联合超细活检钳组(即联合组)各30例,对两组置管方法进行临床对比研究.结果 置管时联合组反应小,置管时间短(平均1.82 min),一次置管成功率达100％,两种置管方法比较差异有显著意义(P＜0.05).结论 胃镜润滑胶浆联合超细活检钳在三腔二囊管置入中的应用,可减轻病人痛苦,缩短置管时间,提高一次置管成功率,为病人赢得抢救时机.     

盐酸达克罗宁胶浆在上消化道内镜诊疗中的应用效果

目的观察盐酸达克罗宁胶浆在上消化道内镜诊疗中的应用效果。方法于本院消化内科收治的上消化道内镜诊疗患者中随机选取200例作为研究对象,采用随机数字表法将其分为观察组(100例)与对照组(100例)。对照组采用常规上消化道内镜诊疗,观察组在对照组基础上给予盐酸达克罗宁胶浆。比较两组的诊疗效果。结果观察组患者的一次检查成功率、疾病检出率、麻醉效果满意度、祛泡效果满意度均高于对照组,检查时间短于对照组(P<0.05);观察组患者的不良反应总发生率显著低于对照组(P<0.05);观察组患者的舒适度评分高于对照组,疼痛评分低于对照组(P<0.05)。结论将盐酸达克罗宁胶浆应用于上消化道内镜诊疗中,可有效减轻患者的痛苦、提升舒适度、改善麻醉润滑效果及祛泡效果、提高一次检查成功率及疾病的检出率、减少不良反应。     

球轴承窗式保持架兜孔与滚珠间润滑性能

以球轴承窗式保持架与滚珠间的流体动压润滑问题为研究对象,建立了滚珠 兜孔运动关系和力学分析的计算模型,建立了滚动轴承启动阶段和稳定运转阶段滚珠 兜孔油膜压力分布和油膜厚度的数值计算方法。以SKF61928MA轴承为研究对象,计算出轴承内圈转速、保持架角加速度,并研究了保持架兜孔尺寸对滚珠 兜孔润滑油膜的性能影响规律。结果表明,在稳定运转阶段,滚珠 兜孔间最小油膜厚度基本保持不变;在启动加速阶段,保持架加速度越大,油膜厚度越小。     

An Improved Modeling and Numerical Analysis Method for Tooth Surface Wear of Double-Arc Harmonic Gears

Tooth surface wear is one of the most common failure modes of harmonic gears, especially in space drive mechanisms. Due to difficulty accurately modeling its wear failure model and the complex mechanism, its dynamic behavior and wear mechanism have not been deeply investigated, and study of the double-arc tooth profile wear model is relative lacking. Therefore, an improved wear modelling and analysis method that is more in line with actual conditions for double-arc harmonic gears is here proposed. Firstly, a tooth surface wear model under mixed elastohydrodynamic lubrication (EHL) was established based on the Archard formula, which combines the Reynolds equation and double-arc tooth profile equation, and considering the meshing offset caused by elastic deformation. Then, the wear analysis method combined with mixed EHL was derived, and numerical simulation analysis of the wear characteristics in lubrication state was carried out, including wear depth calculation and wear output comparison of different tooth profiles. Furthermore, the influence of main working parameters and design parameters on the wear quantity was analyzed. The results show that wear depth for mixed EHL is significantly less than at dry contact. The double-arc tooth profile can withstand more wear cycles than the involute tooth profile, and the input torque and the number of cycles significantly affect the amount of tooth wear. This study further reveals the tooth wear mechanism for harmonic gears, and provides a theoretical basis for the structural optimization design, wear reduction, and life prolonging of harmonic gears.     

Nucleation of Frank Dislocation during the Squeeze-Out Process in Boundary Lubrication: A Molecular Dynamics Study

Liquid–vapor molecular dynamics (LVMD) simulations are performed to reinvestigate the phase transition and solvation force oscillation behavior of a simple argon liquid film confined between two solid surfaces. Our simulations present a novel scenario in which the n → n − 1 layering transitions are accompanied by the formation, climb, and annihilation of Frank partial dislocations during the squeeze-out process under compression. This is indicated by the splitting of the repulsive peaks in the solvation force profile. The detailed analysis reveals that the formation–climb–annihilation mechanism of Frank dislocation occurs during approach and disappears during receding, which would result in force hysteresis. In combination with our recent works, this study provides new insights into the physical property of nanoconfined lubricant films in boundary lubrication.