Effect of surface texturing on rolling contact fatigue within mixed lubricated non-conformal rolling/sliding contacts

The rolling contact fatigue (RCF) life of highly loaded machine components is significantly influenced by the surface roughness features so that there is a continuous effort to design the topography of rubbing surfaces to enhance lubrication efficiency and prolong the operation of machine components. It can be suggested from the recent experimental results that lubricant emitted from shallow micro-dents could effectively lift off the real roughness features and reduce the asperities interactions within rolling/sliding mixed lubricated contacts. Thereby the additional supply of lubricant from surface features could help to reduce the risk of surface damage through the reduction of the interaction of rubbing surfaces during start-up or starvation. However, the introduction of such roughness features into the rubbing surfaces of highly loaded non-conformal contacts should consider not only the effects on lubrication film thickness but also on RCF.That is why this study is focused on the effects of surface texturing on RCF within non-conformal rolling/sliding contacts operated under mixed lubrication conditions. The principal task has been whether possible beneficial effect on film thickness is not accompanied by the reduction in RCF life. Textures with various sizes of micro-dents and their arrangement within the contacts have been considered. It has been found that results obtained with textured surfaces have exhibited no obvious reduction in RCF. Conversely, some increase in RCF using textured surfaces was observed that could be attributed to the positive contribution of micro-dents working as lubricant micro-reservoirs that reduce asperities interactions. Nevertheless, further experiments are necessary to confirm this possible beneficial contribution of surface texturing on RCF.     

激光加工多孔端面气体密封的临界静压开启特性

研究激光加工多孔端面干式气体密封的临界静压开启特性。建立控制端面气膜压力的Reynolds方程;在静压开启条件下,分析机械密封端面从接触到非接触的临界开启密封性能,研究周向开孔比、径向开孔比、深径比、面积密度等微孔几何参数对临界开启力以及气膜刚度的影响规律。结果表明:面积密度在0.5～0.6内取值,深径比在0.004～0.006范围内取值,周向开孔比和径向开孔比均取0.7时,密封可获得最佳静压临界开启特性。     

Effective solution for the tribological problems of Ti-6Al-4V: Combination of laser surface texturing and solid lubricant film

Titanium alloys are characterized by poor tribological properties, and the traditional use of titanium alloys has been restricted to nontribological applications. Surface texturing has been recognized as an effective means of surface engineering to improve tribological properties of sliding surfaces. In this study, the patterns of micro-dimple with different dimples density were fabricated on the surface of Ti-6Al-4V by using laser. The effect of dimples density on the friction behavior of the titanium alloy was investigated under dry friction and coated MoS₂. The results showed that the textured surface with higher dimples density had lower friction coefficients only at low load and speed under dry friction. When combining the solid lubricant with dimples, some textured samples showed excellent tribological performance for all applied loads. The optimum surface pattern was found, and the mechanisms for friction reduction and anti-wear were discussed.     

高速加弹机网络压空系统的改造

通过在各型号高速加弹机上对网络压空系统进行改造,将原先的一级减压变为二级减压,从而提高了网络压空系统的稳定性,减少了网络降等产品数量及压空故障停机次数,降低了生产成本。     

保暖发热聚酯纤维的开发

将电气石母粒添加到聚酯中,纺制成中空形聚酯预取向丝,再经假捻变形加工使其具有三维卷曲形态,开发出保暖发热聚酯纤维。假捻变形时第一热箱温度控制在180~190℃,纤维断裂强度为3.2 c N/dtex,卷曲收缩率为24%。经测试表明:该纤维的远红外法向发射率为88%,温升为2.9℃,中空形状保持完好。     

Status of surface modification techniques for artificial hip implants

Surface modification techniques have been developed significantly in the last couple of decades for enhanced tribological performance of artificial hip implants. Surface modification techniques improve biological, chemical and mechanical properties of implant surfaces. Some of the most effective techniques, namely surface texturing, surface coating, and surface grafting, are applied to reduce the friction and wear of artificial implants. This article reviews the status of the developments of surface modification techniques and their effects on commonly used artificial joint implants. This study focused only on artificial hip joint prostheses research of the last 10 years. A total of 27 articles were critically reviewed and categorized according to surface modification technique. The literature reveals that modified surfaces exhibit reduced friction and enhanced wear resistance of the contact surfaces. However, the wear rates are still noticeable in case of surface texturing and surface coating. The associated vortex flow aids to release entrapped wear debris and thus increase the wear particles generation in case of textured surfaces. The earlier delamination of coating materials due to poor adhesion and graphitization transformation has limited the use of coating techniques. Moreover, the produced wear debris has adverse effects on biological fluid. Conversely, the surface grafting technique provides phospholipid like layer that exhibited lower friction and almost zero wear rates even after a longer period of friction and wear test. The findings suggest that further investigations are required to identify the role of surface grafting on film formation and heat resistance ability under physiological hip joint conditions for improved performance and longevity of hip implants.     

Effect of ultrasonic vibration-assisted laser surface melting and texturing of Ti-6Al-4V ELI alloy on surface properties

Ultrasonic vibration-assisted laser surface processing that involves application of vertical ultrasonic vibrations to the Ti-6 Al-4 V alloy substrates while being irradiated with a CO_2 laser was performed for the development of laser melted and textured surfaces with potential applications in biomedical implants.The laser processing resulted in very consistent repeating undulating grooved surfaces, and the undulations were significantly more pronounced in the samples processed with higher ultrasonic power outputs.The phase evolution, studied by x-ray diffraction, confirmed that the laser processing triggered transformation of globular α→ acicular α and martensitic α' as well as increased amounts of retained α phases,which were also reflected in the microscopic analysis. The surface texture developed by laser processing resulted in increased surface wettability with increasing ultrasonic power output. The textured surfaces exhibited marked decrease in coefficients of friction during sliding wear testing performed under simulated body fluid due to lubricant entrainment within the textured grooves. The texturing also resulted in significant reduction in surface contact area during the wear process, which considerably reduced the overall wear rates due to abrasive wear.     

Monolithic Perovskite/Silicon Tandems with >28% Efficiency: Role of Silicon-Surface Texture on Perovskite Properties

Textured silicon wafers used in silicon solar cell manufacturing offer superior light trapping, which is a critical enabler for high-performance photovoltaics. A similar optical benefit can be obtained in monolithic perovskite/silicon tandem solar cells, enhancing the current output of the silicon bottom cell. Yet, such complex silicon surfaces may affect the structural and optoelectronic properties of the overlying perovskite films. Here, through extensive characterization based on optical and microstructural spectroscopy, it is found that the main effect of such substrate morphology lies in an altering of the photoluminescence response of the perovskite, which is associated with thickness variations of the perovskite, rather than lattice strain or compositional changes. With this understanding, the design of high-performance perovskite/silicon tandems is rationalized, yielding certified power conversion efficiencies of >28%.     

微细旦假捻变形丝加工与应用

讨论了从ＰＯＹ加工细旦和微细旦假捻变形丝的一些主要工艺参数的控制，以及参数之间的关系。为微细旦假捻变形丝加工生产提供了参考数据。