Design and manufacture of intelligent Cu-based wet friction materials

The friction sheets working process was analyzed. It is found that its characteristic is microregion instantaneous high temperature and the current cooling method, making the sheets cooled by the lubricating oil flowing through the friction surface, is not very efficient. Then, intelligent materials concept was introduced, the component and microstructure of intelligent Cu-based friction materials were designed, and the intelligent Cu-based wet friction materials as well as sheets were manufactured. And the intelligent friction materials working principle, i.e. the materials cooling the friction microregion in real time or the friction sheets cutting the peak value of microregion instantaneous high temperature during friction process, was given depending on the characteristics of the materials’ and friction sheets’ working process. Finally, it is indicated that the intelligent friction sheets excell the currently used friction sheets in properties, including anti-heating property, anti-wearing property as well as friction characteristic.

Optimization of pore structure and wet tribological properties of paper-based friction materials using chemical foaming technology

Paper-based friction materials are porous materials that exhibit anisotropy;they exhibit random pore sizes and quantities during their preparation,thereby rendering the control of their pore structure difficult.Composites with different pore structures are obtained by introducing chemical foaming technology during their preparation to regulate their pore structure and investigate the effect of pore structure on the properties of paper-based friction materials.The results indicate that the skeleton density,total pore area,average pore diameter,and porosity of the materials increase after chemical foaming treatment,showing a more open pore structure.The addition of an organic chemical foaming agent improves the curing degree of the matrix significantly.Consequently,the thermal stability of the materials improves significantly,and the hardness and elastic modulus of the matrix increase by 73.7%and 49.4%,respectively.The dynamic friction coefficient increases and the wear rate is reduced considerably after optimizing the pore structure.The wear rate,in particular,decreases by 47.7%from 2.83×10^(−8) to 1.48×10^(−8)cm^(3)/J as the foaming agent content increases.Most importantly,this study provides an effective method to regulate the pore structure of wet friction materials,which is conducive to achieving the desired tribological properties.

A new kind of resin-based wet friction material:Non-woven fabrics with isotropic fiber networks as preforms

As an alternative to short fibers,non-woven fabrics(NWFs)were made using different types of long fibers to optimize the performance of paper-based friction materials and their technology.In this investigation,the fillers and resin were impregnated into these NWFs to prepare three kinds of wet friction material.The tribological,mechanical,and thermal properties of the new wet friction material were studied.The results indicate that the dynamic friction coefficient of the new friction material is approximately 0.12 and the static friction coefficient is approximately 0.15;the better wear rate is 0.81334×10^(-14)m^(3)·(N·m)^(-1).In addition,the temperature for 10%mass loss yielded 100°C enhancement and the tensile strength was improved by 200%,compared to previously reported values.Most importantly,the advantages include a simple preparation flow,low cost,and resource conservation.This is a promising approach for the future development of paper-based friction materials.

Regulation and control of wet friction of soft materials using surface texturing:A review

Surface texturing is a smart strategy that is commonly used in nature or industry to improve the tribological properties of sliding surfaces.Herein,we focus on the recent research progress pertaining to the wet friction modification of soft elastomers via texturing.To consider the pertinent physical mechanisms,we present and discuss the fundamentals of wet sliding on soft surfaces(including dewetting and wetting transitions in compliant contacts).Subsequently,we consider the methods in which the characteristic textures regulate and control wet sliding behaviors on soft surfaces;these textures range from conventional patterns of dimples to bioinspired architectures and can either positively or adversely impact the interfacial friction force.Furthermore,we briefly address the perspectives,potential applications,and challenges of texture design for modifying the friction characteristics of soft materials.

Modeling and analysis of wet clutch engagement characteristics

A mathematical model was developed to analyze the characteristics of the wet clutch during engagement. The lubricant squeeze action was simulated with Patir and Cheng average flow model in which the permeability of friction material is taken into account, and the asperity load is calculated according to the Greenwood and Tripp approach. In this model, effects of friction material permeability, applied load and driving velocity on the engagement characteristics of the wet clutch were studied. The results show that friction material with high permeability reduces the film thickness rapidly and increases the torque peak; the applied load increases the asperity contact pressure and the friction torque, and reduces the engagement time; the driving velocity mainly increases the engagement time. The theoretical torque and relative velocity curves agree qualitatively with the experimental ones, which verifies the wet clutch engagement model.

湿式纸基摩擦材料研究进展及其国产化

湿式纸基摩擦材料广泛应用于汽车制动器和各种主流自动变速器中,是汽车传动的核心零部件材料,其主要组分包括增强纤维、粘结剂和填料。由于其组分多样且生产工艺复杂,只有少数国家如美国、日本等具备自主生产乘用车自动变速器湿式纸基摩擦片的能力。该行业在我国发展较晚,受关注程度较低,国外企业长期占据该领域主要市场。国内摩擦材料相关产品配方相对单一,稳定性和使用寿命等方面正处于追赶国际同类产品的阶段,相关研发工作仍有待深入。本文介绍湿式纸基摩擦片的制备、组成、结构、相关机理以及影响摩擦性能的参数,并展望了中国湿式纸基摩擦片国产化的发展方向。

铝对铜基粉末冶金材料摩擦磨损性能的影响

采用粉末冶金工艺制备了含铝和石墨的铜基粉末冶金摩擦材料,利用定速摩擦试验机,分别在干、湿状态下,探讨了各摩擦速度条件下铝对材料摩擦磨损性能的影响规律。结果表明,铝有利于稳定摩擦因数,提高材料的耐磨性,原因在于铝提高了材料的硬度,从而降低摩擦面微凸体的变形程度。在干摩擦状态下,低速条件下的摩擦因数随铝含量增加而减小,高速条件下的摩擦因数变化不明显;湿摩擦状态,水膜的润滑作用降低了摩擦因数,铝含量增加,有利于提高低速摩擦条件的摩擦因数。高速摩擦条件下,由于离心作用和水分的加热蒸发,水膜的润滑作用降低,摩擦因数波动不显著。

铜基粉末冶金摩擦材料的湿式摩擦性能

采用粉末冶金方法制备铜基湿式摩擦材料,利用金相技术分析材料表面的微观结构,并用MM-1000摩擦试验机研究制动条件对动摩擦因数影响的变化规律。研究结果表明:添加短切炭纤维增强的材料能有效提高材料的能量许用负荷和摩擦因数;摩擦副的制动速度为1 500 r/min和2 500 r/min时,摩擦因数随制动压力的增加而减小;摩擦副的制动速度为3 500 r/min时,摩擦因数随制动压力的增大呈现先降低而后增大的趋势;当制动压力为1.0 MPa和1.5 MPa时,摩擦因数随制动速度的提高而缓慢减小;当制动压力为2.0 MPa和2.5 MPa时,摩擦因数随制动速度的增加呈现先减小而后急剧增大的趋势。

树脂含量对湿式离合器碳质摩擦材料摩擦磨损性能的影响

探讨了树脂含量对湿式离合器碳质摩擦材料摩擦磨损性能的影响。结果表明:树脂含量在20%～30%之间时,随着树脂含量的减少,摩擦系数的压力稳定性和转速稳定性都提高;当摩擦剂含量相同时,树脂含量对摩擦材料磨损量的影响很小;当树脂含量为20%时,在高转速、高比压条件下,没有出现明显的热衰退现象,摩擦材料的摩擦磨损性能较为理想。

不同摩擦条件下铜-铁基粉末冶金材料的摩擦性能

采用粉末冶金技术制备铜-铁基复合材料,在制动压力0.5～1.2MPa范围内,通过定速摩擦试验机研究干、湿条件下,速度、压力与材料摩擦磨损性能的关系。结果表明,干摩擦系数随摩擦速度增加而降低,湿摩擦明显降低了低速摩擦系数而对高速摩擦系数影响不大。低速摩擦系数随摩擦压力增加而增加,摩擦压力对高速摩擦系数影响不明显。

水分对铜基摩擦材料摩擦磨损性能的影响

采用粉末冶金工艺制备了含二氧化硅和石墨的铜基粉末冶金摩擦材料,利用定速摩擦试验机,分别在摩擦速度为7.8~47.1 m/s的范围内,探讨了干、湿摩擦条件下材料摩擦磨损性能的变化情况.结果表明：摩擦表面第三体的状态与干、湿摩擦条件密切相关,并影响材料的摩擦磨损性能.摩擦速度低时,材料的干摩擦系数高于湿摩擦情况,原因在于水起到隔离和润滑作用;摩擦速度提高,干摩擦系数低于湿摩擦条件,这归因于水分对表面的冷却作用降低了基体高温软化程度.

C/C-SiC复合材料的制备及其湿式摩擦磨损性能研究

采用1700炭纤维针刺毡，经超声振动渗硅、化学气相沉积（CVD）、硅化处理及液相浸渍／炭化新工艺制备SiC呈“岛状”分布的C／C—SiC复合材料，利用偏光显微镜和扫描电子显微镜观察其微观组织结构并分析其形成机制，在MM-1000型湿式摩擦磨损试验机上研究C／C—SiC复合材料的摩擦磨损性能、结果表明：在初始转速恒定的条件下，动摩擦系数随制动比压的增加而逐渐减小；当制动比压恒定时，摩擦系数随初始转速的增加呈现出先增大而后降低的趋势；在本文试验条件下，摩擦系数稳定在0．088～0．126之间；在300次磨损试验后，其磨损量检测值为0．

粗粒料单向压缩湿化变形试验研究

采用高压单向压缩仪,对糯扎渡堆石坝的坝壳反滤料进行了不同相对密度的粗粒料湿化变形试验研究.分析试验结果,揭示了粗粒料在单向压缩条件下的湿化变形规律,探讨了不同干密度下粗粒料的湿化变形性质,发现湿化变形仅在高压下随粗粒料干密度的增大而增加,低压下干密度的影响不明显.另外,还分析了压力对湿化变形的影响,得出了湿化变形随竖向压力的增大而增加的规律,并用一指数函数进行了拟合.试验中,研究了一种减小侧壁摩擦力的方法,并通过是否减轻摩擦的对比试验,论证了方法的有效性.

含炭纤维湿式铜基摩擦材料的性能

采用粉末冶金方法制备含短炭纤维的湿式铜基摩擦材料,研究炭纤维含量对湿式摩擦材料的摩擦磨损性能和力学性能的影响,以及制动条件对动摩擦因数的影响。结果表明:随着炭纤维含量及材料的孔隙率增加、硬度及密度均降低,摩擦因数呈先增加后减小的变化趋势,磨损量呈先减小后增大的趋势。炭纤维含量为(质量分数)1%时材料的摩擦磨损性能最好,摩擦因数最大且最稳定,磨损量最小。材料摩擦因数随着载荷增大而增大,随炭纤维含量增加磨损率呈先减小后增大的趋势。炭纤维的加入提高了材料的能量许用值。

酚醛树脂对芳纶复合纸基摩擦材料的影响

本文采用高性能芳纶纤维和剑麻纤维为原料制备湿式纸基摩擦材料。初步探讨了酚醛树脂的种类和上胶量对纸基材料的强度性能和摩擦系数的影响。

芳纶复合纸基摩擦材料的初步研究

本文采用高性能芳纶纤维和剑麻纤维为原料制备湿式成型纸基摩擦材料。初步探讨了原纸中两种纤维的配比、剑麻打浆度、芳纶纤维的长度和形态以及作为粘结剂的酚醛树脂的种类和上胶量等对纸基材料的力学性能和摩擦性能的影响,为进一步研究湿式成型纸基摩擦材料奠定基础。

MoS_2改性碳布湿式摩擦材料的摩擦学性能

基于碳布优异的耐热性能、摩擦磨损性能和纳米MoS2的自润滑特性,采用纳米MoS2改性处理碳布摩擦材料以适用于高载荷、高转速或润滑不充分等特殊的工况条件。通过在树脂浸渍液中加入不同质量分数的纳米MoS2对摩擦材料进行改性处理。采用扫描电子显微镜、光学显微镜和湿式摩擦实验机等对材料的表面形貌以及摩擦磨损性能进行分析。实验结果表明,纳米MoS2的加入有利于提高材料的致密性,改善表面粗糙度;当MoS2含量小于5%时,样品的动摩擦系数变化较小,约为2.6%,但当MoS2含量为8%时,动摩擦系数降幅较大,达到14.2%;纳米MoS2的加入有效减少磨损过程中纤维的拔出与断裂,大幅度降低磨损率。

烧结压力对湿式铜基烧结摩擦材料性能的影响

研究了烧结压力对湿式铜基烧结摩擦材料性能的影响,探讨了这些影响的作用机理。研究结果表明:在一定范围内,随烧结压力增大,材料的硬度增大,能量负荷许用值增大,磨损大幅度下降,平均动摩擦因数(μ_d)则略有降低。

湿式铜基摩擦材料的磨损图研究

磨损图研究是1种能够系统分析材料的摩擦性能、直观反映材料摩擦学特性变化，以达到评估、预知材料摩擦磨损性能的研究方法。本文作者依据相似性原理，通过对摩擦因数、摩擦表面及磨屑的测试及分析，获得不同工况条件下湿式铜基摩擦材料的摩擦学信息，建立磨损图。进一步研究表明：随制动初速度增加（从8m/s增加到20 m/s）和载荷增大（由1 MPa增大到2 MPa），铜基湿式摩擦材料的摩擦因数都逐渐非线性增加，并保持在0.070～0.100之间；其磨损图可划分为轻微磨损区（质量磨损率W〈10-5 mm/次）、严重磨损区（W〉10-4 mm/次）和过渡区（10-5 mm/次〈w〈10-4 mm／次）3个区域，轻微磨损的主要机制为塑性变形和显微犁削，严重磨损的主要机制为疲劳磨损，过渡区域为磨料磨损向疲劳磨损转变的区域。

土石坝工程领域的若干创新与发展

我国高土石坝数量居世界之首,保证高坝大库建设与长期运行安全是国家经济和公共安全保障的重大需求。系统总结了长江科学院近年来在土石坝工程领域的若干创新与发展。提出了基于“旁压模量当量密度法”的粗粒料级配相似理论试验方法;介绍了研发的系列CT三轴仪,实现了粗粒料组构要素的定量测量;提出了三轴试验中加载板与试样之间由滑动摩擦变为滚动摩擦、整体式接触变为分散式接触的减摩新方法,研发了相关减摩装置;研制了大尺寸、高压力、微摩擦、刚柔复合加载的土工真三轴仪;揭示了粗粒料真实三维应力条件下的强度与变形变化规律、湿化与蠕变变形特性;构建了粗粒料三参量非线性K-K-G剪胀模型、六参数湿化模型、九参数蠕变数学模型及相应的参数确定方法;基于当量密度法的原创思想,提出了利用旁压试验间接确定超百米级深厚覆盖层现场密度的试验方法。上述研究成果可为高土石坝工程建设提供重要科技支撑。