Wet friction performance of C/C-SiC composites prepared by new processing route

C/C-SiC composites with SiC island distribution Were prepared via a new processing route. The fabrication process mainly included silicon infiltration by ultrasonic vibration, chemical vapor deposition （CVD）, siliconizing, liquid phase impregnation and carbonization. The wear and friction properties were tested by an MM-1000 wet friction machine. The results show that SiC phases are mainly distributed between carbon fibers and pyrocarbons as well as among the pryoearbons. The dynamic friction coefficient of the composites decreases gradually from 0.126 to 0.088 with the increase of the surface pressure from 0.5 to 2.5 MPa at the same rotary speed. Furthermore, under the constant surface pressure, the dynamic friction coefficient increases from 0.114 to 0.126 with the increase of the rotary speed from 1 500 to 2 500 r/min. However, the coefficient decreases to 0.104 when the rotary speed exceeds 4 500 r/min. During the friction process, the friction coefficient of C/C-SiC composite is between 0.088 and 0.126, and the wear value is zero after 300 times brake testing.

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.

An Optimal Wet Friction Plate Inspired by Biological Surface Patterns

It is found that many biological organisms exhibit superior adhesion characteristics in wet environments. It has been observed that the foot pads of tree frogs and katydids are consist of a number of closely arranged polygons, most of them are hexagonal. In this paper, the common structure of two kinds of biological foot pad was extracted to model the bionic surface structure of friction plates. The friction plate prototypes were also prepared. Through the multivariate orthogonal regression design, the optimum parameter combination of the friction performances of the prototypes of the bionic plates has been obtained. The hexagonal circumcircle size is 10 mm, the groove width is 1 mm, and the hexagonal diagonal angle is 90~. Then the maximum static friction coefficient, dynamic friction coefficient and wear amount of the optimal friction plate were tested and compared with the control group friction plates. The comparative analysis of the experiment findings demonstrated that the bionic structure with hexagonal ring grooves can significantly improve the friction performance of the friction plates.

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.

Inspired by Tree Frog:Bionic Design of Tread Pattern and Its Wet Friction Properties

The wet grip of tire has always been the focus because it is related to the personal safety of passengers directly.Many methods were employed to improve the wet grip of tire.Researchers paid more attention on bionics method recent years.In nature,tree frogs have high adhesion ability in wet environment,which is mainly due to their footpads having fine polygon grooves(mainly hexagon grooves).To improve the performance of wet grip of tire,from the perspective of bionics,inspired by the footpad of tree frog,the bionic hexagon tread pattern was designed.The friction test was carried out to compare with the common tread patterns such as serrated,striped and square patterns.The results showed that the bionic hexagon tread pattern generally had high friction coefficient and directional stability of friction.The main reason was that the hexagon tread block was less affected by the friction-induced torque and the groove of bionic hexagon tread pattern had better drainage characteristic.The bionic hexagon tread pattern provides new idea and method for the design of tires with high wet grip.

Effect of Rotational and Sliding Motions on Friction and Degeneration of Articular Cartilage under Dry and Wet Friction

Understanding the tribological properties of articular cartilage allows scientists to evaluate degenerative joint diseases and develop new treatment techniques. The objectives of this study are to demonstrate the detrimental effect of rotational motion under both dry and wet friction and to evaluate the friction and wear behavior of bovine articular cartilage with sliding and rotational testing configurations that represent fluid film and boundary lubrication mechanisms, respectively. The articular cartilage pin and plate samples were harvested from healthy adult bovine and then tested on a self-made friction and wear simulator. Cartilage samples were subjected to sliding and rotational motions under constant load. Friction coefficients and wear factors were calculated under three conditions： using bovine serum, phosphate buffered saline and with no lubricant present. The friction coefficient and wear factor of the articular cartilage were significantly increased with rotational motion under both dry and wet friction. Using bovine serum as lubricant in the sliding testing configuration the friction coefficient and wear factor of articular cartilage were both decreased. A similar decrease in the tribological properties of cartilage was initially observed for the rotational testing configuration with bovine serum; however, the friction coefficient and wear factor were increased after 150,000 cycles. In the absence of lubricant, the articular cartilage was entirely worn on contact area in both sliding and rotational testing configurations. Bovine serum proved an effective fluid film lubricant for articular cartilage surfaces.

Wear Calculation Model Considering the Effect of Porosity and Wear Properties of Wet Clutch Friction Disc

This paper aims to investigate the effect of porosity percentage on the wear performance of a wet clutch. A wear calculation model for the relationship of porosity and wear mass loss is established. The results of experiments conducted verify the wear coefficient expression used in the model. The influence of porosity on the wear performance of a friction disc was also analyzed for various pressures and speeds. Specifically,the 80 min sliding test was performed with three different friction disc porosity percentages using a wet clutch test rig. Comparison of the model calculation results with the measured values confirmed the accuracy of the calculation model. The test results show that the calculated and detected data fit well,which indicates that the wear calculation model can be used to estimate the wear mass loss of wet clutch friction plates. These research results will help to improve the anti-abrasion properties and employment lifespan of wet clutch friction discs.

Wet and Dry Tribological Behaviors of Circular Islandic Protrusion Patterns on M2 Steel Discs under Spinning Condition

Under spinning conditions, lubricant on islandic spot patterned M2 steel disc experiences centrifugal and tangential force components. Depending upon the relative position of the spots and the flow of lubricant, accumulation of lubricant in front of patterned islandic spots creates thrusting to mating part and subsequently reduces contact between the mating couple. Whilst wear debris is likely to be spun off the plateau of the spots to their neighbouring valleys so as to reduce wear. Hence, it gives favorable tribological characteristics. Aiming at verifying such mechanisms, studies were performed on M2 steel disc specimens slid with ASSAB 17 tool steel pin. The M2 steel disc specimens were respectively （i） machined with non-patterned （NP）, （ii） etched to produce in-lined （INE） islandic patterns, and （iii） etched to produce staggered （STE） islandic spot patterns. Results indicated that the INE patterned discs gave most favorable wear characteristics, the NP of the worse characteristics whilst the STE ranged in the middle. However, the actual contact mechanism leads to the descending sequence of favorable friction behaviors nominally as： NP, INE and STE.

Dynamic Engaging Characteristics of Wet Clutch in Automatic Transmission

Wet clutch is an important shifting component in automatic transmission,and its properties will affect the gear shift performance. By comparing the calculated and test results,the static friction torque model was proved to be capable of describing the real pressure and torque only in the situation of high-energy engagement.Therefore,a dynamic torque model was proposed on basis of hydrodynamic properties between friction surfaces, in which the clutch engagement was divided into three phases for hydrodynamic lubrication, mixed lubrication, and mechanical contact. The proposed dynamic torque model was validated by comparing the calculated and test results. The effects of temperature,pressure,and pressure changing rate of automatic transmission fluid( ATF) on the clutch torque were analyzed. Based on these results,the clutchto-clutch torque control during shifting in automatic transmission was optimized,and as a result,the shifting comfort was significantly improved since the problems such as the fluctuation and sudden drop of the engine rotating speed during shifting were eliminated.

干湿循环下节理砂岩细观能量演化规律研究

为探究干湿循环作用下的节理砂岩的细观损伤劣化规律,采用颗粒流软件开展了节理砂岩细观数值模拟,研究了不同干湿循环下节理砂岩的细观力学特性和能量演化机制。研究表明:随着干湿循环次数的增大,颗粒间的接触力和平行黏结力最大值呈线性递减规律;干湿循环下节理砂岩裂纹演化主要经历缓慢增加、均匀增加、阶梯增加及突变增加4个阶段,且裂纹数目(总裂纹、拉伸裂纹及剪切裂纹)与干湿循环次数呈正相关;细观边界能、平行黏结应变能及线性黏结应变能随干湿循环次数的增加呈逐渐减小趋势,节理砂岩中耗散能与微裂纹数大致呈正相关;干湿循环作用导致颗粒间抗断裂能力弱化,使岩样能量储存能力降低,这是造成节理砂岩干湿损伤劣化的能量机制。

基于空化效应的带排转矩模型优化及试验测试

某重型车辆混合动力传动系统湿式制动器在非制动作业时,由于油液的黏滞作用,摩擦副产生了带排转矩,造成功率损失。为能实现含有复杂沟槽结构流场的带排转矩精准预测,针对空气提前进入流场造成预测误差的问题,提出了一种通过空化数预测空化效应体积分数来优化带排转矩模型的方法。首先,通过不同工况下的模型计算,分析了转速、流量和间隙对空化效应体积分数的影响:随着转速提升,空化效应体积分数先增大后减小;更大的流量和更小的间隙都会使空化效应体积分数的最大值增大。接着,对湿式制动器带排转矩进行了试验测试,对比分析结果显示,优化后模型的预测误差小于6%,相比未考虑空化效应的模型,平均误差减小了55%。此外,还研究了空化效应后沟槽的复杂程度对带排转矩的影响。结果表明,沟槽结构越复杂,带排转矩越小。其中,径向槽的加入对带排转矩的影响最大,可使带排转矩减小约25.9%。研究可为湿式制动器的带排转矩精准预测和摩擦片结构优化提供支持和工程实践指导。

混合动力汽车湿式离合器摩擦副温度场及其影响因素研究

热失效是混合动力汽车湿式离合器发生故障的主要原因之一。摩擦副滑摩过程中具有高度非线性,同时摩擦副温度场受到多个参数影响。为深入研究混合动力汽车离合器摩擦副温度场分布情况,通过搭建混合动力汽车离合器热结构耦合分析模型,对滑摩过程进行仿真计算。在此基础上,深入研究初始转速、接合油压、对偶钢片厚度和摩擦衬片材料等因素对摩擦副温度场的影响。

基于工况参数信息的摩擦界面形貌反演

为优化湿式离合器设计,增强传动系统可靠性,并为工程研究与应用提供基础数据,以湿式离合器为研究对象,设计通用机械性能测试仪(universal mechanical testing machine,UMT)摩擦磨损试验机盘-盘实验,在给定工况下应用循环神经网络(recurrent neural network,RNN)算法,构建了湿式离合器摩擦元件三维微界面形貌反演模型。通过对比11组工况下的真实值和反演值,验证了RNN反演模型的准确性,其中测试工况的平均绝对百分比误差为4.04%,决定系数为0.9806。最后,借助反演模型分析了转速和压力2个工况参数对界面形貌特征的影响,湿式摩擦副界面形貌受压力的影响较为显著。

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。

湿滑状态下飞机轮胎与道面摩擦特性试验

湿滑道面会造成飞机制动性能下降,影响起降安全。通过搭建污染跑道摩擦特性测试装置,根据飞机在湿滑道面滑跑的实际情况,对飞机轮胎在不同水膜厚度、速度、载荷条件下运行的接触力、滑移距离进行研究,分析了湿滑条件下道面摩擦特性与影响因素间的关系。实验结果表明:水膜厚度对道面摩擦特性影响显著,水膜厚度为13 mm时,轮胎与道面之间的接触应力变化明显,滑移距离大幅度增加。随着速度的增加,轮胎与道面之间的接触应力呈线性增加趋势,过高的速度会增加滑水风险。轮胎载荷的增加会减少湿滑道面上的滑移距离,在一定程度上提高飞机轮胎的载荷,能有效改善湿滑道面上的摩擦特性。

湿式离合器局部润滑与摩擦特性的温升影响研究

针对湿式离合器因局部润滑工况恶化而加速失效的问题,本文中建立带有表面微凸峰接触的摩擦副微观润滑摩擦计算模型,并结合小试样销-盘试验,研究温升对湿式离合器润滑油膜承载力、微凸峰接触力和接触面积、载荷承担比、局部温升和摩擦系数等的影响规律,揭示湿式离合器局部润滑与摩擦特性的温升影响机理.结果表明:随着温度从30℃升高到150℃,虽然湿式离合器摩擦副间润滑油膜的载荷承担比由约97%减小至约57%,但其仍是摩擦副间载荷的首要承担者,此外,温升过程中实际接触面积率快速增大,局部摩擦温度快速升高,摩擦系数从不足0.04快速增大到约0.11,当温度高于90℃时,摩擦系数的增大速度与实际接触面积的增大速度基本一致.

考虑离合器摩擦性能衰减的湿式DCT车辆起步控制研究

建立了考虑离合器摩擦系数变化及离合器性能衰减的湿式双离合变速器(dual clutch transmission,DCT)车辆起步过程动力学模型,以车辆起步过程冲击度、滑摩功和起步滑摩时间为优化目标,采用线性二次型最优控制方法获得了车辆起步过程离合器最优传递转矩。针对离合器摩擦系数变化及离合器性能衰减对车辆起步过程离合器压力控制的影响,提出了一种离合器压力非线性鲁棒控制策略,以实现对离合器最优传递转矩的跟踪。结果表明,所提出的非线性鲁棒控制策略能够在离合器摩擦系数变化的情况下实现对离合器最优传递转矩的有效跟踪,跟踪误差不大于0.02 N·m,且能够适应摩擦性能衰减导致不同寿命阶段摩擦系数的不同变化规律,与比例-积分-微分(proportion-integral-differential,PID)控制策略相比具有更精确的控制效果和更强的鲁棒性。

干湿循环作用下黄土厚度对其裂隙发育的影响

黄土体长期处于降雨和蒸发的湿热耦合环境,极易诱发土体裂隙产生,显著弱化土体的结构性和完整性,从而影响工程区域的建设。因此,对干湿循环作用下不同厚度的黄土开裂特性研究十分必要。该文通过室内干湿循环试验,记录试样的含水率变化和裂隙发育情况,利用数字图像处理技术,结合分形维数对裂隙网络进行分析。试验结果表明,蒸发路径和含水量的不同导致土体水分蒸发速度不同,土体越厚,水分蒸发速度越慢。界面摩擦力影响土体开裂过程,土体越厚,裂隙发育越慢,裂纹网络复杂性越低。随着干化的进行,界面摩擦力逐渐降低,土体收缩明显,干湿循环效应导致土体颗粒重新组合,加快水分蒸发过程,土体表面会不断劣化。研究结果可为地质灾害防治提供指导。

变速箱离合器设计及性能测试

如今自动变速箱的应用越来越广,对于离合器也有了新的需求,为了探究湿式离合器的自主化设计,对湿式离合器的结构与原理进行了分析,并对其特点进行了研究,对变速箱的摩擦副以及回位弹簧进行了设计分析,最后对离合器的循环耐久进行测试,为变速箱离合器的进一步研究奠定了基础。

湿式离合器摩擦片孔隙及油槽结构对摩擦特性的影响分析

湿式离合器通过主从动片的摩擦力矩传递动力,在接合过程中经常因摩擦系数的变化而带来接合过程的抖动冲击,严重影响车辆的乘坐舒适性,因此研究湿式离合器摩擦片的油槽结构及离合器摩擦材料气孔特性,对维持良好的动态摩擦特性至关重要。通过试验对比验证,增加油槽数量(多段化)和加大摩擦材料平均气孔直径,都能够提升离合器结合时摩擦材料初期的接触性,从而能够得到更稳定的动态摩擦特性。