The wear and friction of short glass-fibre-reinforced polymer composites in unlubricated rolling-sliding contact

The wear and friction behaviour of short glass-fibre-reinforced polyamide 66 composites running against each other, unlubricated, in non-conformal, rolling-sliding contact has been investigated. Both a wide range of loads and slip ratios and a range of samples with different fibre concentration and different crystallinity have been examined. Short glass-fibre reinforcement makes the polyamide 66 exhibit unique tribological behaviour. There is a high resistance to wear and friction which results from a significant self-lubricating property. A thin film layer exists on the contacting surfaces when two discs run against each other within the range of the test conditions. It is this thin film that plays a dominant role in the self-lubricating property of the composite. The formation of the thin film and the life of the composite depend on a complex of interactions between structure, strength and fibre concentration, and the specific conditions of load and slip ratio imposed. Under identical loading conditions, either lower fibre concentration or lower crystallinity cause the thin film to form continuously during the wear process so that the life of the composite may reach 6×10⁶–10⁷ cycles. It is suggested that the self-lubricating property may be used in the working period of engineering components rather than only during the temporary running-in period of machine elements.     

Role of micro/nano fillers on mechanical and tribological properties of polyamide66/polypropylene composites

The objectives of this research article is to evaluate the mechanical and tribological properties of polyamide66/polypropylene (PA66/PP) blend, graphite (Gr) filled PA66/PP, nanoclay (NC) filled PA66/PP and NC plus short carbon fiber (NC + SCF) filled PA66/PP composites. All composites were fabricated using a twin screw extruder followed by injection molding. The mechanical properties such as tensile, flexure, and impact strengths were investigated in accordance with ASTM standards. The friction and sliding wear behaviour was studied under dry sliding conditions against hard steel on a pin-on-disc apparatus. Scanning electron micrographs were used to analyze the fracture morphologies. From the experimental investigation, it was found that the presence of NC and SCF fillers improved the hardness of PA66/PP blend. Further, the study reveals that the tensile and flexural strength of NC + SCF filled PA66/PP was higher than that of PA66/PP blend. Inclusion of micro and nanofillers reduced the wear rate of PA66/PP blend. The wear loss of the composites increased with increasing sliding velocity. The lowest wear rate was observed for the blend with nanoclay and SCF fillers. The wear rates of the blends with micro/nanofillers vary from 30–81% and lower than that of PA66/PP blend. The wear resistance of the PA66/PP composites was found to be related to the stability of the transfer film on the counterface. The results have been supplemented with scanning electron micrographs to help understand the possible wear mechanisms.     

Synthesis of ionic liquid functionalized graphene oxides and their tribological property under water lubrication

Ionic liquid functionalized graphene oxides (GOs-IL) were synthesized by the amidation and cation-π stacking, and their tribological property as the water-based lubricant additives was investigated. The GOs-IL exhibited superior friction-reducing and antiwear performance. Specifically, under the same test conditions, the mean friction coefficient and wear volume of 0.02 wt% GOs-IL/base liquid suspension were 57% and 76% lower than that of base liquid. The worn surface analyses revealed that the boundary tribofilm composed of the GOs-IL deposition film and chemical reaction film should formed on the wear scar lubricated by the GOs-IL/base liquid suspension. The proposed lubrication mechanism illustrated that the IL functional groups of GOs-IL improved their absorption and embedded stability on the rubbing surfaces by the electrostatic interactions, and then promoted the formation of the above boundary tribofilm. The tribofilm directly prevented the rubbing surfaces from the immediate contact and hence greatly reduced the friction and wear.     

Effect of testing conditions and microstructure on the sliding wear of graphite fibre/PEEK matrix composites

The sliding friction and wear behaviour of unreinforced polyetheretherketone (PEEK) matrix and its unidirectional continuous and two-dimensional woven graphite fibre-reinforced composites were investigated. The operating wear mechanisms, as evinced by scanning electron microscopy of the worn surfaces, and the coefficients of friction and the wear rates changed considerably with the fibre reinforcement form and orientation. Sliding wear rates, on account of their extreme sensitivity to the microstructure of the interacting surfaces at the sliding interface, were found to be a function of not only the surface roughness, but also of the sliding time. Complex interactions arising due to the effects of the testing parameters such as fibre orientation, sliding velocity, contact pressure and interface temperature were characterized for the neat matrix and the two composite systems. The wear rates of the two-dimensional woven composites were almost an order of magnitude lower than those of the unidirectional fibre composite or the unreinforced matrix.     

Finite element hydrodynamic friction model for metal forming

The complex contact conditions on the three-dimensional (3-D) tooling-workpiece interface, such as non-penetrations, slip–stick phenomena and friction forces due to the relative motion of contacting surfaces, are of vital importance in metal forming operations. Usually, a lubricant is provided as an interface medium between the tool and the workpiece to avoid strain localization, wear and surface damage. Hence, a simple friction law such as Coulomb friction, involving only a constant friction coefficient, cannot model the contact phenomena accurately. In this research, a realistic friction model, which accounts for the tribological behaviour, and most importantly, the effect of surface roughness on the lubricated contact, is developed. This model has been implemented in a 3-D arbitrary Lagrangian Fulerian finite element code for metal forming analysis. The applicability of the proposed model is demonstrated by the simulation of fluid-lubricated thrust bearing and sheet metal stretch forming.     

Experimental investigation on tribological behaviours of PA6, PA6-reinforced Al<Subscript>2</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>3</Subscript> and PA6-reinforced graphite polymer composites

This article reports on the preparation, characterization and experimental investigation of polyamide 6 (PA6) reinforced with alumina oxide (Al₂O₃) and graphite composites. The test specimens were prepared in an injection-moulding machine by varying the weight proportions of Al₂O₃ and graphite particles blended with PA6. The tribological properties of the composites were observed by using pin-on-disc wear test rig under dry sliding conditions. The worn surfaces of the composites were examined using scanning electron microscope. The addition of Al₂O₃ and graphite significantly enhanced the tribological properties of PA6. The PA6 containing 30 wt% Al₂O₃ and 20 wt% graphite revealed the best tribological behaviours due to the stronger interfacial bonding characteristics with improved wear resistance. Further, the thermal stability of Al₂O₃ and graphite particles was studied through thermogravimetric analysis test. It was also found that further addition of Al₂O₃ and graphite in PA6 had no significant improvement in wear resistance, the co-efficient of friction and heat generation.     

Sliding behaviour of nanophased AISI M2 tool steel obtained by mechanomaking and hot isostatic pressing

Abstract

The friction and wear behaviour of a nanophased AISI grade M2 tool steel was studied under dry sliding conditions and compared with that of a conventional AISI M2 steel. The nanocrystalline steel was produced by mechanosynthesis followed by cold and hot isostatic pressing. Slider-on-cylinder tests were performed against a ceramic coated countermaterial under loads of 10, 20, and 30 N and sliding speeds of 0.3 and 1.2 m s^-1 up to 10 km sliding distance. The nanocrystalline material underwent mild wear with low coefficient of friction under all testing conditions. The commercial M2 steel displayed distance dependent transitions from a regime of mild wear with low coefficient of friction, to a regime of severe wear with high coefficient of friction. The first tribological regime was due to the formation of a layer of iron oxides on the worn surfaces. In this regime, the wear resistance of both steels is mainly dominated by the mechanical properties of the carbides which have high load carrying capability. The second tribological regime, observed in the commercial steel, was due to the formation of cracks both on the mechanically mixed layer and at a depth beneath this layer, which also led to the detachment of carbides from the matrix. This abrasive ‘third body’ produced high wear damage of the commercial steel under high applied loads.     

直流稳恒磁场对45钢摩擦磨损性能的影响

大气条件下,研究不同强度的直流稳恒磁场对45钢干滑动摩擦磨损性能的影响.结果表明:与无磁场条件下相比,材料的摩擦系数降低,磨损量明显减少,磨损表面光滑,磨屑细化.微观分析表明,45钢在磁场条件下磨损后,表面生成更多的氧,认为氧化磨损及磨屑的润滑作用是磁场降低摩擦系数、减轻磨损的主要原因.     

新型填料对高摩复合材料摩擦磨损性能影响及机制

采用干法热压成型工艺制备高摩复合材料,研究了基体材料腰果壳油改性酚醛树脂(CPR)与丁晴橡胶(NR)的质量比和新型高性能填料(主要成分为石墨粉Al2O3、MoS2、Fe粉)含量对高摩复合材料摩擦磨损性能的影响规律。在摩擦磨损试验机上测试了高摩复合材料的摩擦磨损性能,利用激光共聚焦显微镜、扫描电镜对摩擦表面形貌、磨屑进行观察和分析,借助EDS测定摩擦表面成分的变化。结果表明,随着CPR与NR质量比的增加,高摩复合材料的耐热性能、结合性能大幅提高,且具有较好的摩擦磨损性能。当高性能填料含量较低时,磨损表面出现大量连续的真实接触面,磨损机制为磨粒磨损和黏着磨损;当高性能填料含量较高时,真实接触面积减少,磨损表面剥落严重,并出现较多的裂纹,其主要磨损形式转变为磨粒磨损和疲劳磨损。随着高性能填料含量的增加,摩擦表面的元素从均匀分布逐渐转变为局部富集,磨粒的尺寸逐渐变大。     

The preparation and characteristic of maleic anhydride grafted polyethylene (PE-g-MA) filled CNT/PMMA composite film

ABSTRACT

In order to improve the tribological properties of PMMA, the PMMA composites incorporated with CNT powders were prepared. The effect of CNT content on tribological properties of the composites was investigated. When CNT content is 0.5 wt%, the friction coefficients of the 0.5%CNT/PMMA composite are the smallest, which are about 0.15 and are 67% less than those of the pure PMMA composite, and its wear resistance remains the same as the pure PMMA composite. Incorporating 0.5 wt% CNT into the PMMA composite may develop a continuous transferred film on the worn surface. As a result, the friction coefficients of the composite are reduced and its wear mechanism is mainly fatigue spalling. The addition of PE-g-MA improved the friction and wear properties of CNT/PMMA composite.     

Tribological properties of solid lubricants filled glass fiber reinforced polyamide 6 composites

The main purpose of this paper is to further optimize the tribological properties of the glass fiber reinforced PA6 (GF/PA6,15/85 by weight) for high performance friction materials using single or combinative solid lubricants such as Polytetrafluroethylene (PTFE), ultra-high molecular weight polyethylene (UHMWPE) and the combination of both of them. Various polymer blends, where GF/PA6 acts as the polymer matrix and solid lubricants as the dispersed phase were prepared by injection molding. The tribological properties of these materials and the synergism as a result of the incorporation of both PTFE and UHMWPE were investigated. The results showed that, at a load of 40 N and a velocity of 200 rpm, PTFE was effective in improving the tribological capabilities of matrix material. On the contrary, UHMWPE was not conductive to maintain the structure integrity of GF/PA6 composite and harmful to the friction and wear properties. The combination of PTFE and UHMWPE showed synergism on further reducing the friction coefficient of the composites filled with either PTFE or UHMWPE only. Effects of load and velocity on tribological behavior were also discussed. To further understand the wear mechanism, the worn surfaces were examined by scanning electron microscopy.     

Einfluß von Luftfeuchte und Werkstoffgefüge auf das tribologische Verhalten von Siliciumcarbid‐Keramik unter einsinniger Gleitbeanspruchung

Influence of humidity and microstructure on the tribological behaviour of silicon carbide ceramic in unidirectional sliding contact Tribological tests were carried out on self‐mated SiC in a laboratory tribometer (system: flattened ball‐on‐disc) to characterize the behaviour of silicon carbide ceramic under unidirectional sliding at relative humidities between 5% and 80%. Furthermore the influence of distilled water in the contact zone was investigated on friction and wear. The microstructures of the SiC ceramics variied concerning size and shape of the crystallites, pores and graphite particles. The results show that the friction coefficient increased with increasing relative humidity while the amount of linear wear tended to decrease simultaneously. The smallest friction coefficient and also a relatively small amount of linear wear were measured at the presence of distilled water compared to sliding contact in humid air. Tribological mechanisms could be explained based on studies of the worn surfaces by scanning electron microscopy and atomic force microscopy as well as considering the experimental data recorded during and after the tests.     

石墨/聚四氟乙烯/玻璃纤维改性PA6的力学和摩擦磨损性能

采用石墨(Gr)、聚四氟乙烯(PTFE)和玻璃纤维(GF)改性聚酰胺6(PA6),以提高PA6的摩擦磨损性能和力学性能。重点研究了填料组合、配比、载荷和转速对复合材料摩擦磨损性能的影响,通过磨损表面形貌分析探讨了摩擦磨损机理。结果表明:Gr/PTFE/GF混杂改性PA6能明显降低摩擦系数并提高耐磨性,PA6/Gr/PTFE/GF质量比为70/5/10/15时摩擦系数和磨损率最低,且在高转速(40N,1500r/min)下摩擦磨损性能更好,摩擦系数为0.08,比PA6降低了27%,磨损率为5.5×10~(-6) mm~3/(N·m),比PA6降低了1个数量级,且该复合材料的拉伸强度、冲击强度、储能模量和损耗模量都高于PA6。     

莫来石与碳纤维协同填充的聚四氟乙烯基复合材料及其摩擦学性能

为了提高聚四氟乙烯（PTFE）的摩擦学性能,采用机械混匀、带温预压及烧结等工艺制备了莫来石和碳纤维填充的PTFE基复合材料,并通过FTIR、XRD、万能材料试验机、洛氏硬度计、DSC及热机械分析分别表征了PTFE基复合材料的显微结构、力学性能和热学性能;然后,使用MRH-3 型高速环块磨损试验机测定了复合材料的摩擦系数和磨损率,通过自制的硅油砂浆磨损装置测定了复合材料在不同温度下的耐砂浆磨损性能;最后,借助3D测量激光显微镜研究了复合材料摩擦面形貌,并分析了摩擦磨损机制。结果表明:莫来石和碳纤维在PTFE体系中起到填充增强作用,20wt%莫来石-10wt%碳纤维/PTFE复合材料的弹性模量由364 MPa增加至874 MPa;20wt%莫来石-10wt%碳纤维/PTFE复合材料的干摩擦系数较大,但其磨损率与纯PTFE相比降低了3个数量级以上,且此复合材料在水摩擦条件下仍能保持较好的摩擦系数和磨损率,摩擦系数为0.157,磨损率为7.40×10-6 mm3·N-1·m-1;此外,20wt%莫来石-10wt%碳纤维/PTFE复合材料在较高温度下仍能表现出良好的耐砂浆磨损性能。所得结论表明改性得到的PTFE 基复合材料的摩擦学性能显著提高,复合材料可用于有杆抽油井防偏磨。      

玻璃纤维增强PA66复合材料与Al2O3陶瓷的摩擦磨损行为

研究了25%(质量分数)玻璃纤维增强PA66复合材料(25%GF/PA66)在干摩擦和水润滑条件下与Al₂O₃陶瓷之间的摩擦磨损行为。采用激光共聚焦扫描显微镜、 扫描电子显微镜、 傅里叶变换红外光谱仪和X射线光电子能谱分析仪对25%GF/PA66的组织、 磨损形貌和磨损表面的化学结构变化进行分析。结果表明: 相同实验载荷时,润滑条件下25%GF/PA66的摩擦系数小于干摩擦条件下的摩擦系数,但磨损体积却远远大于干摩擦条件下的磨损体积。在有水存在的条件下,机械微切削作用持续发生,温度的升高使25%GF/PA66试样变形,同时引起酰胺基团发生水解,C—C键大量断裂,导致磨损体积增加。采用扩展表面一般导热模型计算本实验所用材料的热软化温度为105.9℃。     

Microhardness,compression performance and high-temperature tribological properties of Ti2AlNb-silver self-lubricating composite

The Ti₂AlNb-based self-lubricating composite material reinforced with silver particles of 0 wt% to 15 wt% was prepared by spark plasma sintering, and the microhardness, compression performance and high-temperature tribological properties were investigated. The results show that the silver is distributed in the Ti₂AlNb matrix as small islands. The microhardness reaches the maximum at 5 wt% silver content but then decreases sharply. The compressive strength is reduced due to the silver-rich areas have become the initiation points of cracks, and the softening of silver at high temperatures intensifies the process. The friction coefficient and wear rate of the composite material at 500 °C are significantly reduced by silver, and the lubrication mechanism is attributed to the synergistic effect of silver and oxides.     

Dynamic contact characteristics between hoisting rope and friction lining in the deep coal mine

Dynamic contact characteristics between hoisting rope and friction lining in the deep coal mine were analyzed in the present study. Dynamic rope tension and tension differences were obtained using Simulink simulation models. Evolutions of slip states and stress distributions along the groove bottom of friction lining during hoisting, and the effect of coefficient of friction on those evolutions, were explored employing finite element analyses. The results show that fluctuating rope tensions and tension differences during hoisting exhibit three stages. The wear failure is more likely to occur along contacting surfaces between the rope and friction lining. Contact arcs between the rope and friction lining consist of two frictional arcs with severe damage and a sticking arc with slight damage. Dynamic contact status during hoisting consists of a slip regime and a mixed regime. Larger tension difference results in larger relative slips, contact pressure and equivalent stress. Frictional arcs exhibit more serious wear due to higher stress levels as compared to the sticking arc. An increase of coefficient of friction reduces the possibility of gross slip and wear between the rope and friction lining.     

Effect of water absorption on erosive wear behaviour of polyamides

Two polyamides (PAs) viz. PA 6 and PA 12 were selected for investigating the influence of water absorption on some physical, mechanical and tribological properties. Erosive wear studies on water treated and untreated samples were carried out at two impact angles viz. 30° and 90°. Tests on tensile strength of untreated and treated polyamides revealed that the water treatment resulted in enhancement for PA12 and reduction for PA 6. Exactly similar trends were reflected in their erosive wear performance also. The water absorption deteriorated the wear performance of PA 6 at both the angles, whereas the erosion wear behaviour of PA 12 improved at both the angles due to water absorption. The improvement was more significant at the angle of 30° rather than 90°. Scanning electron microscopic (SEM) investigations were done to study the topography of worn surfaces and to understand the wear mechanisms.     

铜-石墨复合材料的摩擦学性能和磨损机理

采用机械合金化后冷压成型和放电等离子烧结两种不同工艺分别制备铜-石墨复合材料,在销盘式实验机上进行材料的摩擦实验,并通过扫描电镜、X射线光电子能谱仪(XPS)分析摩擦表面的形貌和化学性质。结果表明:随着石墨含量的增加,复合材料的摩擦系数与磨损率显著下降;随烧结温度的升高,摩擦系数与磨损率都呈下降趋势。摩擦系数与磨损率的显著改善是由于在磨损过程中形成一层覆盖表面的润滑膜。当形成的润滑膜几乎覆盖住整个磨损表面时,该润滑膜能够抑制滑动界面处金属与金属接触,使摩擦磨损特性得以改善。     

The role and effects of the third body in the wheel–rail interaction

This paper focuses on the presence of the third body, a solid interfacial layer in the wheel–rail contact. This third body is studied from different viewpoints: its presence including composition, thickness and morphology; and its role with respect to its load‐carrying capacity, shearing behaviour, transfer of material and finally global friction coefficient. The general approach is phenomenological and is carried out as closely as possible of the real tribological behaviour of this contact. This paper presents a synthesis of different studies coming from: analysis of specimens taken out periodically from rails and wheels in service, and thus under real contact conditions; and test laboratories, allowing us to impose rolling–sliding conditions with very high precision. From all these studies and results, a better understanding of the role of the third body and its influence on friction, adhesion and damage mechanisms (wear, pits, cracks …) is reached and this is the first step for including its effect in numerical models.