Tribological Properties of Greases Based on Biogenic Base Oils and Traditional Thickeners in Sapphire-Steel Contact

Friction and wear tests were performed with a number of greases based on biogenic esters and thickened with two metal soaps and a highly dispersed silica acid gel. The series of experiments was performed on a Nonotribometer in material combination of sapphire ball on steel disks with a range of normal loads from 1 up to 500 mN. Results directly show influences of the bulk grease components on frictional and wear behavior. Comparison of frictional and wear results makes manifest that, while in most combinations of base oil and thickener, the highest influence is found in the thickening agent, some combinations are mainly influenced by the base oil. All frictional results along with wear widths and depths as well as micrographs of the prevailing wear mechanisms are presented and discussed.     

Effects of Fiber Diameter and Tribotest Conditions on Nonlubricated Frictional Behavior of a Microsized Metal Fiber

Experimental determination of the frictional properties of a microsized fiber wrapped around a cylinder has been of long-standing interest to the academic community. The purpose of the current experiments was to explore the diameter dependence of such microsized fibers in nonlubricated friction using a highly accurate tribometer. For this work, NbTi superconducting material was used for the fibers and polyvinyl chloride (PVC) was used as the cylinder material. Significant effects were observed in the kinetic friction coefficient for different fiber diameters, normal forces, and sliding speeds. Moreover, the effects of fiber diameter on the frictional stability were measured. Smaller fiber diameters and low sliding speeds both produced poor frictional stability. The most likely explanation for the observed stick–slip phenomena is hypothesized to be a combination of creep mechanics and plastic deformation of the junctions on the contacting surfaces.     

石油钻机盘式刹车副材料的摩擦磨损性能研究

为提高深井石油钻机盘式刹车副的摩擦学性能和使用寿命,研制开发了新型刹车盘表面堆焊材料和无石棉刹车块摩擦材料,并通过变温摩擦磨损性能实验,研究了刹车副的摩擦学性能。研究表明,刹车副具有良好的变温摩擦特性和高温抗热衰退性能,高温下的摩擦因数比较稳定;刹车块和刹车盘的磨损率均随温度的升高而增大,但刹车盘表现出相对稳定的耐磨性能。载荷对刹车副的摩擦因数影响不大,变化比较平稳;刹车块和刹车盘的磨损率均随载荷的增大而增大,但刹车块表现出相对稳定的耐磨性。刹车副的摩擦因数随滑动速度的增加而增大,并趋向平稳;但速度对刹车块和刹车盘的磨损率影响不大,变化相对稳定。研制的刹车副材料能够满足石油矿场钻机作业的要求。     

Fretting wear behaviors of mandibular condylar cartilage of nature temporomandibular joint in vitro

Torsional fretting tests of condylar cartilage against a ZrO₂ ball were carried out. The damage characteristics were discussed based on an analysis of frictional kinetics behavior, SEM observations, and histological stainings. The results indicated that fretting behaviors were strongly dependent on the angular displacement amplitudes and the number of cycles. The worn surface was characterized by netlike shape ridges along the radial direction, and three parts were detected. The wear mechanism of condylar cartilage performed mainly as delamination and micro-fracture of collagenous fibers. As the damage characters are very special, a model of the condylar cartilage surface damage was established.     

Adhesive wear and frictional characteristics of UHMWPE and HDPE sliding against different counterfaces under dry contact condition

Abstract

The current work evaluates the wear and frictional performance of ultrahigh molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE) sliding against different metal counterfaces, stainless steel(SS), mild steel (MS) and aluminium (Al), under dry contact condition. The experiments were conducted using pin on disc machine at different sliding distances (0–40·32 km), 15 N applied load and 2·8 m s^–1 sliding velocity. Interface temperatures and frictional forces were measured simultaneously during the sliding, while specific wear rates were determined for every 1·68 km sliding distance. Based on the optical microscopy of the worn surface and wear track, frictional and wear results were analysed and discussed. The experimental results showed that the type of counterface material significantly influences both frictional and wear performances of the selected polymers. This was mainly due to the film transfer characteristics. Higher temperature and friction coefficient for UHMWPE and HDPE were evident when sliding took place against Al counterface. Sliding the polymers against stainless steel showed low friction coefficients compared to other counterfaces.     

Contact and friction between catheter and blood vessel

Therapeutic vascular catheterization techniques are sometimes hampered by the frictional forces between the blood vessel and the catheter, when contact points of the vessel are changing and deforming during the movement of the catheter. The goal of the present study was to characterize frictional interactions between the blood vessel wall and the catheter using experimental and numerical analysis. First, the frictional force was measured with an experimental apparatus that uses a ball and flattened porcine aorta to simulate frictional forces between the catheter and the vessel. Second, catheter motion was characterized by two-dimensional numerical calculations based on the experimental results. Experimental analysis demonstrated that slip occurred and that friction coefficient between the vessel and the catheter and the deformation of the specimen were small when the contact between the ball and the aorta occurred at a small angle. The compliance of the specimen in the normal direction obtained by the experiment was by far larger than that calculated according to the Hertzian contact theory. Numerical analysis shows that this difference of the parameter of the vessel, which must be determined accurately in surgical simulator, could affect the trajectory of the catheter.     

Analysis of biphasic lubrication of articular cartilage loaded by cylindrical indenter

Combination of theoretical biphasic analyses and corresponding experimental measurements for articular cartilage has successfully revealed the fundamental material properties and time-depending mechanical behaviors of articular cartilage containing plenty of water. The insight of load partitioning between solid and fluid phases advanced the prediction of the frictional behavior of articular cartilage. One of the recent concerns about biphasic finite element (FE) analysis seems to be a dynamic and physiological condition in terms of mechanical functionality as a load-bearing for articular joint system beyond material testing, which has mainly focused on time-dependent reaction force and deformation in relatively small and low speed compression. Recently, the biphasic FE model for reciprocating sliding motion was applied to confirm the frictional effect on the migrating contact area. The results indicated that the model of a cylindrical indenter sliding over the cartilage surface remarkably sustained the higher proportion of fluid load support than a condition without migrating contact area, but the effectiveness of constitutive material properties has not been sufficiently evaluated for sliding motion. In our present study, at the first stage, the compressive response of the articular cartilage was examined by high precision testing machine. Material properties for the biphasic FE model, which included inhomogeneous apparent Young's modulus of solid phase along depth, strain-dependent permeability and collagen reinforcement in tensile strain, were estimated in cylindrical indentation tests by the curve fitting between the experimental time-dependent behavior and FE model simulation. Then, the biphasic lubrication mechanism of the articular cartilage including migrating contact area was simulated to elucidate functionality as a load-bearing material. The results showed that the compaction effect on permeability of solid phase was functional particularly in the condition without the migrating contact area, whereas in sliding condition the compaction effect did not clearly show its role in terms of the proportion of fluid load support. The reinforcement of solid phase, which represented the collagen network in the tissue, improved the proportion of fluid load support especially in the sliding condition. Thus, a functional integration of constitutive mechanical properties as a load-bearing was evaluated by FE model simulation in this study.     

Basic observations in the flat lapping of aluminum and steels using standard abrasives

This research studies the characteristics of aluminum 2024, 304 stainless steel, and 1018 steel during lapping with three different types of abrasives, namely, garnet, silicon carbide, and white aluminum oxide, through detailed experimental analysis. Specifically, the effects of different abrasives on material removal rate and surface finish were evaluated. It was found that silicon carbide and white aluminum oxide abrasives removed more material per minute than garnet. A higher mean frictional force and mean coefficient of friction were obtained in aluminum lapped with SiC and white Al₂O₃ abrasives, and a lower mean frictional force was obtained in 304 stainless steel lapped with SiC. From geometric and energy-dispersive spectroscopy analysis obtained using scanning electron microscopy, it was confirmed that some abrasives became embedded into the lapped metal substrates. No burn was observed on the lapped samples, and scratches and unfinished lapped parts were observed mainly in 304 stainless steel. In order to determine the quantitative influence of each variable, an analysis of variance was performed. It was found that the main effects of abrasive types, size of abrasives, and type of work material had statistically significant influence on material rate and surface finish. In addition, there was a highly significant two-way interaction between abrasives and workpiece.     

Experimental determination of the equivalent stress at the frictional surfaces of a slip bearing in a heavily loaded contact

The significant influence of the frictional forces on the bush deformation in a heavily loaded contact is shown. The results of comparative tests are presented. The coefficients for calculating the equivalent stress at the frictional surfaces of a slip bearing are determined.     

体内微机构与动物肠道摩擦实验研究

采用了一组不同材料、直径、长度、质量的微机构样本,在动物离体肠道中进行了摩擦实验。通过实验数据分析了微机构外壳的材料和尺寸对动物肠道摩擦力大小的影响。实验结果表明:在肠道中,密度较小的材料比密度大的材料具有更好的润滑性能,因此更适于作为医用微机构外壳的材料。另外,直径对于摩擦力也具有较为明显的影响,长度则影响不大。微机构的质量是影响负载的又一重要因素,在设计时应避开使负载达到最大值的微机构质量值。     

Study of the influence of ring misalignment in rolling bearings on frictional torque and the fatigue life of supports

The influence of ring misalignments on the torsional characteristics and fatigue life of rolling bearings was investigated. It was shown that ring misalignment increased frictional torque in rolling bearings, especially with the radial and axial forces. Ring misalignment in the radial-thrust bearings has a controversial influence on fatigue life of supports. Fatigue life increases at small misalignments angles and decreases with an increase in the misalignment angle.     

Hybrid Navigation System Based Autonomous Positioning and Path Planning for Mobile Robots

To improve the quality and efficiency of Z-directional 3D preform forming, the Z-yarn frictional force distribution model of the preform and its wear mechanism were investigated. In this study, a tensile force measuring device was designed to measure the force required to replace the guide sleeve, which is equivalent to the Z-yarn frictional forces. The frictional force is proportional to the number of preform layers and is applied to the preform decreased from the corner, edge, sub-edge, and middle in order. A back propagation neural network model was established to predict the friction at different positions of the preform with different layers, and the error was within 1.9%. The wear of Z-yarn was studied at different frictional positions and after different times of successive implantation into the preform. The results showed that with an increase in the number of Z-yarn implantations and frictional forces, the amount of carbon fiber bundle hairiness gradually increased, and the tensile fracture strength damage of the fiber was increasingly affected by the frictional forces. In the corner position of the preform, when the number of implantations was 25, the fiber fracture strength decreased non-linearly and substantially; in order to avoid fiber fracturing in the implantation process, the Z-yarn needs to be replaced in time after 20–25 cycles of continuous implantation. This study solves the problem of difficulty in measuring the force required for individual replacements owing to the excessive number of guide sleeves, puts forward the relationship between fiber wear, preform position, and implantation times, solves the phenomenon of fracture in the preform during Z-direction fiber implantation, and realizes the continuous implantation of fibers.     

Effect of phospholipidic boundary lubrication in rigid and compliant hemiarthroplasty models

Hemiarthroplasty may benefit from materials which produce lower friction and improved boundary lubrication protection during start-up conditions. The purpose of this study was to evaluate the effect of phospholipidic boundary lubrication in both rigid and compliant hemiarthroplasty. An in vitro model was designed to dissociate the relative contribution of implant material compliance and the presence of phospholipid to the overall friction of a hemiarthroplasty contact using bovine articular cartilage. Normal bovine articular cartilage was articulated against four flat materials using reciprocating motion: (a) borosilicate glass: (b) borosilicate glass coated with dipalmitoylphosphatidylcholine (DPPC); (c) polyurethane (PU) elastomer (Tecoflex SG93A, a medical-grade aliphatic thermoplastic PU, Thermedics Incorporated. Woburn, Massachusetts); and (d) surface-coated PU (Tecoflex SG93A substrate coated with lipid-attracting copolymer poly[methacryloyloxyethyl phosphorylcholine (MPC)-co-butyl methacrylate (BMA)]. Tests were conducted in physiologically simulated tribological conditions for a non-conformal point contact. Friction and lubrication analysis was performed using both static and kinetic coefficients of friction mu measured for each group as a function of time for a sliding distance of up to 60 m. Results showed that the inclusion of supplemental phospholipid, DPPC, on a rigid substrate significantly decreased mu in comparison with the control (cartilage-glass). Additionally, removal of phospholipid components from the articular cartilage surface produced a significantly greater start-up mu in comparison with normal cartilage at the test onset. The use of a material with a lower modulus resulted in lower mu for the entire duration of the test. Polyurethane elastomer coated with the lipid-attracting copolymer, poly(MPC-co-BMA), resulted in the lowest frictional response. As seen in this study, the improvement of low-modulus hemiarthroplasty may involve the optimization of chemical modification and incorporation of lipid-attracting MPC copolymers onto compliant materials. However, further tests are warranted to determine whether lipid-attracting MPC copolymers perform as well during long-time, in vivo wear studies.     

Internal stresses during rolling friction and their evaluation

The estimation of wear of materials intended for practical use demands a detailed knowledge of applied forces and internal stresses in materials. For a dry friction rolling-body model the relationship between the internal stresses and the normal force, slip and rolling length was determined. The evaluation of the internal stresses was carried out on the basis of a practical (wheel/rail) frictional system. X-ray determination of forces proved to be an efficient method of measuring forces in the surface of metallic rolling bodies. The purpose of internal stress measurements is to follow plastic deformation at frictional surfaces and consequently to establish new criteria for the deformation and resistance of materials and their application to frictional systems.     

三指力封闭抓取的内力存在性研究

针对指端与物体构成有摩擦固定点接触的情况，基于内力的特性分析，对三指力封闭抓取时的内力存在性进行研究，推导了摩擦扇存在条件和三指内力汇交条件。通过内力汇交多边形的构成特点分析，提出了根据摩擦扇边界线交点相互位置关系研究汇交多边形存在性的完整方法。在考虑内力平衡关系的基础上，给出了基于数学计算的内力存在性通用判别算法，并结合实例说明了方法的有效性。     

A study to estimate the tensile strength of friction stir welded AA 5059 aluminium alloy joints

The influence of strain rate on the frictional behaviour of AA7075 aluminium alloy, in the O-annealed temper state, was studied. Attention was focused on the evaluation of the mechanisms affecting friction at high strain rate. To this purpose, axisymmetric and ring compression tests were carried out using the split Hopkinson tension-compression bar in the direct version. The flow curves were investigated in a wide range of strain rates using cylindrical specimens characterised by different slenderness ratios. The results of the axisymmetric compression tests showed an appreciable strain rate sensitivity of the deforming material with a marked increase in flow stress with strain rate in the dynamic loading condition. As far as the ring compression tests are concerned, different strain rates were obtained using hollow cylinders with different initial sizes. The analysis of the results showed that strain rate affects the variation of the inner ring diameter, irrespective of the height reduction and frictional condition. Axysimmetric and ring compression tests were also performed under the quasi-static loading condition and the experimental results did not show any appreciable effect of strain rate on flow curves and frictional behaviour. Finally, the different frictional behaviour between the quasi-static and dynamic loading conditions was attributed both to the reduction in the lubricant film thickness and change in the viscous actions at the specimen-tool interface.     

Role of Rubber Stiffness and Surface Roughness in the Tribological Performance on Ice

The aim of this work is to investigate the effect of slider surface roughness and stiffness on the friction between rubber compounds and ice surfaces in order to provide insight into rubber–ice friction generation mechanisms. For this purpose, rubber compounds were designed to have different levels of macroscopic roughness and cured stiffness by modifying the filler system and plasticizer loading. In order to accurately evaluate the effects of surface and bulk rubber property on ice friction, linear friction tests were performed on laboratory ice with varied frictional heat buildup by modifying the friction test protocol. The results showed that the friction force was in general increased through the ploughing effect of a rough rubber block sliding on smooth ice. The increase in friction by ploughing was more pronounced when the contacting rubber block had sufficiently low stiffness and when the accumulation of frictional heat on ice was sufficiently high. It was also evidenced that a sufficiently hard rubber with test conditions leading to low heat buildup on ice could nevertheless lead to an opposite influence of roughness on rubber–ice friction; that is, lower friction force with a slider with a higher roughness.     

压力测试平台在燃料泵送系统中的应用

针对燃料泵送系统存在的水击压力过大、气液分离不足以及汽蚀等问题，采用压力传感器和数字信号采集系统建立燃料泵送系统压力测试平台。根据测得的压力信号，对燃料枪关闭瞬间流量、管长、溢流阀调定压力以及主阀弹簧刚度对水击效应引起的峰值压力的影响进行研究，并通过频率分析方法和小波分析方法较精确地获得系统的气液分离值和临界汽蚀压力点。该测试平台不仅能实时可靠地对系统压力进行定量诊断与识别，同时还可以为燃料泵送系统的性能优化提供依据。     

Anisotropic Friction of the Ventral Scales in the Snake Lampropeltis getula californiae

Since the ventral body side of snakes is in almost continuous contact with the substrate during undulating locomotion, their skin is presumably adapted to generate high friction for propulsion and low friction to slide along the substrate. In this study, the microstructure of ventral scales was analyzed using scanning electron microscopy, atomic force microscope and confocal laser scanning microscopy. Dynamic friction was investigated by a microtribometer. The ventral scales demonstrated anisotropic frictional properties. To analyze the role of the stiffness of underlying layers on the frictional anisotropy, two different types of scale cushioning (hard and soft) were tested. To estimate frictional forces of the skin surface on rough substrates, additional measurements with a rough surface were performed. Frictional anisotropy for both types of scale cushioning and rough surfaces was revealed. However, for both types of surface roughness, the anisotropy was stronger expressed in the soft-cushioned sample. This effect could be caused by (1) the stronger interaction of the microstructure with the substrate in soft-cushioned samples due to larger real contact area with the substrate and (2) the composite character of the skin of this snake species with embedded, highly ordered fiber-like structures, which may cause anisotropy in material properties.     

Experimental investigation on the effect of tangential force on wear and rolling contact fatigue behaviors of wheel material

The study aims to explore the effect of tangential force on wear and rolling contact fatigue (RCF) behaviors of wheel material using a JD-1 wheel/rail simulation facility. The normal, tangential and lateral forces between the wheel/rail rollers are controlled, and the magnetic power brake was used to generate the tangential forces (16–330 N). The results indicate that the surface hardness and wear loss of wheel rollers increase with the tangential force increasing. The surface cracks mouths are perpendicular to the resultant directions of the frictional forces. There are visible secondary cracks and multilayer cracks and the interlayer material of multilayer cracks are easy to break. The compositions of wear debris consist of Fe₂O₃, Fe₃O₄ and iron.