60Si2Mn钢复合微动磨损行为的研究

采用球／平面接触,研究了60Si2Mn钢在两种倾斜角(45°和60°)、三种载荷(Fmax=200 N、400 N、800 N)和恒定加载速度(6 mm／min)下的复合微动磨损行为。在详细分析该微动接触条件下的动力学特性的基础上,结合光学显微镜和激光共焦扫描显微镜对磨痕的分析,探讨了不同阶段的微动过程和机制。根据F-D曲线的三种形状,60Si2Mn钢的复合微动运行过程划可划分为三个阶段。第1阶段的磨损以滑移为主,第Ⅱ、Ⅲ阶段的颗粒剥落均按剥层机制进行,但损伤程度明显不同。     

An experimental study on radial fretting behaviour

A new test apparatus has been developed for radial fretting test. Main experimental conditions are as follows: the amplitude of normal load from 200 to 800N, the number of cycles from 1 to 3×10⁵ cycles. Three contact pairs (a 52100 ball against 52100, 1045, 1045 steel with TiN coating) were used for the test. Variations of normal load vs indentation depth between two contact surfaces have been analyzed as a function of cycles. Contact degradation was examined through metallographic expertise on the flat specimen and radial fretting behaviour was compared in the paper.     

Comparison between radial fretting and dual-motion fretting features of cortical bone

Fretting tests were carried out to compare the effect of radial and dual-motion modes on wear of cortical bone. A titanium ball was rubbed against fresh human cortical bone under controlled load and motion test conditions. Dual-motion fretting mode produced more severe damage than radial fretting, with more debris occurring at the worn surface. Cracks were abundant in radial fretting and they were significantly affected by the microstructure of cortical bone; this effect was not obvious in the case of the dual-motion fretting mode. Radial fretting test could be used to evaluate the anisotropy of material and crack propagation of brittle cortical bone.     

On the mechanisms of various fretting wear modes

According to relative motion directions for a ball-on-flat contact, there are four fundamental fretting wear modes, e.g., tangential, radial, torsional and rotational modes. In this paper, the mechanisms of these four fundamental fretting wear modes, particularly for the later three modes, have been reviewed from results obtained by the authors in combination with results from literature. Some general features have been reported. Differences both in running and degradation behavior have been discussed in detail. Results showed that some similar laws for three fretting regimes (partial slip regime, mixed regime and slip regime), fretting maps (running condition fretting map and material response fretting map), wear and cracking mechanisms obtained from the classic mode (i.e. tangential fretting) were also identified and useful to characterize the other modes. Nevertheless, the occurrence of relative slip for the radial fretting, the formation of mixed regime for the torsional fretting, the evolution of surface morphology for the rotational fretting were quite different compared to that of the classical fretting mode.     

Mechanical and experimental investigation on nuclear fuel fretting

A mechanical approach to the nuclear fuel fretting problem is studied in this paper to find a possible and efficient way of a wear restraint. Two different contours of the spacer grid spring and dimple were developed to increase the contact area. Fretting wear experiments were carried out for the developed springs and tube specimens. Contact forces of 10 and 30 N, and slip displacements of 50–100 μm were applied under the environment of air as well as water at room temperature. Wear scars on the rods were examined to observe the effect of the mechanical approach on the wear. Especially, the influence of a contour deviation which occurred during fabrication and the wear particle accumulation in the clearance region were investigated in detail. It was found that the contact shape influenced the feature and the behavior of the length, width and volumetric shape of the wear. For the model of fuel fretting wear, equivalent depth (D_e) is suggested as a new parameter that can represent the wear severity.     

Radial fretting fatigue damage of surface coatings

Radial fretting tests with a 52100 steel ball-on-flat contact have been carried out under different normal loads. TiN, MoS₂ and TiN+MoS₂ coatings on a 1045 steel flat were examined. The normal loads amplitude used were 200, 400 and 800 N at speeds of 12 and 1.2 mm/min. Dynamic analysis in combination with microscopic examinations by SEM and EDX have been performed. It was observed that the vertical stiffness increased with the increase of loading speed and number of cycles. The metallographic examinations showed that little damage was observed for the MoS₂ coating, which exhibited excellent radial fretting fatigue resistance. For the TiN coating, micro-cracks appeared at the lower load while delamination occurred at the higher load. For the TiN+MoS₂ composite coating, the vertical stiffness increased but accompanied by some micro-cracks. As a result of the study, the radial fretting test is proposed as one possible new method to evaluate coating life.     

Radial fretting behaviours of dental ceramics

Radial fretting tests on a Si₃N₄ ceramics ball opposite to the two dental ceramics flats (Vita VMK95 and Cerec Vita Mark II) have been carried out. The test apparatus was developed from a tension-compression hydraulic machine. Maximum normal load (F_max) was varied from 100 to 800 N with a speed of 6 mm/min, and the number of cycles from 1 to 10⁵. The fretting scars were examined by optical microscope and laser confocal scanning microscope (LCSM). The results of kinetics behaviours showed that all loading and unloading curves of load (F)–displacement (D) curves were almost superposed in the whole fretting process for two dental ceramics under a lower normal load (), and all F–D curves opened, correspondingly some micro-cracks initiated and developed in contact area, when the normal load increased to a higher level (). Under lower normal load, the fretting scars displayed the worn zones in shape of annulus. The cracks in shape of homocentric circularity can be observed for Vita VMK95 at and for Cerec Vita Mark II at . Therefore, there is better radial fretting damage resistance for Cerec Vita Mark II. In the microslip zone, the microscopic analysis showed that the particles detached by the mechanism of delamination. It the meantime, the competing mechanisms of fatigue cracks and wear also were discussed in this paper.     

An investigation of the fretting behaviour of low friction coatings on steel

Three different low friction coatings on steel (electrolytically deposited cadmium, PTFE solid lubricant in epoxy resin and PTFE solid lubricant in polyimide resin) were studied in order to relate their fretting behaviour with mechanical properties. Particular importance was given to adhesion which was measured using a scratch test. Fretting tests were carried out on the steel substrate and on the coatings under the same conditions. The major parameters of the tribological system were identified and then quantified. The values of the parameters obtained for each coating were compared with the corresponding values for uncoated steel. The mechanical characteristics of the coatings and their fretting parameters were plotted using a polar diagram in order to give an overview of the fretting behaviour of each coating. Differences were noted and the corresponding parameters were identified. The influence of the adherence of the coating and of the fretting test load on the lifetime of the coating was determined.     

An experimental study torsional fretting behaviors of LZ50 steel

Four simple fretting modes are defined according to relative motion: tangential, radial, rotational, and torsional fretting. This paper presents a new test rig that was developed from a low-speed reciprocating rotary system to show torsional fretting wear under ball-on-flat contact. Torsional fretting behavior was investigated for LZ50 steel flats against AISI52100 steel balls under various angular displacement amplitudes and normal loads. The friction torques and dissipation energy were analyzed in detail. Two types of T–θ curves in the shape of quasi-parallelograms and ellipticals were found that correspond to gross and partial slips, respectively. The experimental results showed that the dynamic behavior and damage processes depend strongly on the normal loads, angular displacement amplitudes, and cycles. In this paper, the debris and oxidation behaviors and detachment of particles in partial and gross slip regimes are also discussed. Debris and oxidation are shown to have important roles during the torsional fretting processes. The wear mechanism of torsional fretting was a combination of abrasive and oxidative wear and delamination before third-body bed formation. The mechanism was then transformed into third-body wear after a great amount of debris formed.     

Investigation of micro-cracking behaviors of human femur cortical bone during radial fretting

Radial fretting tests on human femur cortical bone with a ball-on-flat configuration were carried out in vitro under different normal contact loads. The kinetics behaviors and damage characteristics of the cortical bone were analyzed using the load versus displacement (F-D) curves. The fretting scars were examined using laser confocal scanning microscopy (LCSM) and scanning electron microscopy (SEM). A nano-indenter was used to characterize the mechanical property of the osteon of the cortical bone. Morphologies showed that the primary damage form was due to micro-cracking. Around the osteon, three kinds of micro-crack configurations were observed; i.e. annular cracks—located at the concentric lamellae; radial cracks—initiated from the Harversion canal; and interstitial cracks—initiated and propagated between the interstitial lamellae. Plenty of interstitial cracks occurred in the wear scar, which indicated that the interstitial tissue was the weak zone in the structure of cortical bone. In addition, the contact stresses under the radial fretting condition were calculated by the finite element method analysis (FEMs) and the behaviors of cracking were explained. The results demonstrated that the stress concentration that occurred around the Harversian canal and osteon system resulted in a better resistance than that from the interstitial tissue. The concentric lamellae presented a better radial-fretting resistance and contact fatigue resistance than that from the interstitial lamellae.     

Design effects on the fretting wear behaviour of ball bearings

A change in design of a ball bearing is described based on the results of numerical and experimental analysis to reduce fretting wear. Increasing the radii of curvature of the inner and outer races by a small amount reduces the product of the relative slip δ and the tangential traction τ at the contact region, both of which are caused by Heathcote slip. This results in the consequent reduction in fretting wear because there is a good correlation between the amount of fretting wear and τδ. This prediction is confirmed experimentally by increasing the groove radius of the inner race from 4.02 to 4.21 mm for a ball of radius 3.97 mm.     

表面粗糙度对微动摩擦特性的影响

通过实验研究,探讨了表面粗糙度对微动摩擦特性影响的作用。表面粗糙高时接触表面之间的摩擦系数会有明显增加,在微动状态下表面粗糙度对表面磨损影响不大。     

Development of a test device for the evaluation of fretting in point contact

Fretting wear and fatigue may occur between any two contacting surfaces, wherever short‐amplitude reciprocating sliding is present for a large number of cycles. A test device has been developed for the evaluation of fretting fatigue and wear in partial and gross slip conditions. Three similar sphere‐on‐plane contacts run at the same time. Normal force, tangential force or displacement amplitude and constant bulk stress can be controlled and measured separately. Reciprocating tangential displacement is produced with rotational motion, the amplitude and frequency of which can be adjusted and controlled accurately by an electric shaker. The number of load cycles for crack initiation and growth is determined with strain‐gauge measurements near the fretting point of contact. The contact surfaces are measured with 3D optical profilometer before fretting measurements to determine actual contact geometry. The measurements were done with quenched and tempered steel. The initial results indicate that cracks are mostly formed in partial slip conditions, whereas fretting wear is more heavily involved in gross slip conditions. The initiation of a crack occurs near the edge of the contact in the slip direction, where the calculated cracking risk has its maximum value in partial slip conditions. The number of cracks increases as the displacement amplitude, i.e. friction force, increases in partial slip conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

Fundamental investigations of electrical conductor fretting fatigue

Fretting is known to be the main factor leading to conductor individual wire breaks under aeolian vibration in the vicinity of a clamp. In this paper, previous studies on overhead electrical conductor bending fatigue are summarized. Results obtained with several conductor types and clamps are compared. A general fretting analysis as well as testing procedure are suggested. Influence of the main mechanical parameters on the occurrence of several types of degradation processes is discussed.     

Effect of the dynamic response of fretting devices on test results

The dynamic response of equipment and measurement systems can have a significant influence on results. These effects have a particular importance in experimental fretting studies owing to the frequency levels usual for these kinds of test. In the present work the measuring systems used in fretting rigs to measure friction force are modelled using a lumped mass system with a single degree of freedom. Correction factors are calculated for application to the amplitude and the phase of the measured friction force. The application of these factors to a case study is demonstrated. The distortion of the phase introduced by some filtration techniques is also discussed.     

Laboratory fretting tests with thin wire specimens

Wire ropes, due to their construction and application, are prone to fretting damages. In order to know the wear behaviour of individual wires under fretting conditions, laboratory tests are required. The present work describes the preliminary fretting tests accomplished with thin steel wires to optimise the testing procedure. The tests were carried out with ‘crossed‐cylinders’ configuration varying the stroke and normal load. Afterwards, the fretted surfaces were characterised by means of an optical and scanning electron microscope, and a diamond stylus. No significant influence of selected parameters was detected and a good correlation was proved for on‐line measured parameters and off‐line obtained values. Copyright © 2007 John Wiley & Sons, Ltd.     

690合金材料的微动磨损特性研究

利用微动磨损试验机,在载荷50N以及位移幅值为60μm、100μm、150μm的工况下,研究了690合金材料在常温下的微动磨损行为及其动力学特性,采用激光共焦扫描显微镜(LCSM)和扫描电子显微镜(SEM)观察磨痕微观形貌。结果表明,载荷和位移幅值对微动特征有很大的影响,微动运行完全处于滑移状态。在滑移区,滑移磨损严重、磨痕面积大。690合金材料的磨损机制主要表现为磨粒磨损与剥层的共同作用。     

A friction energy approach to quantifying lubrication under fretting sliding

The problem of a proper lubrication under low‐speed small oscillatory movement can be a decisive factor for the reliability of various components. There is a need to characterise the lubricious behaviour of the interface under oil‐bath fretting wear conditions for ball bearing applications. Fast and reliable methods to quantify this behaviour for broad range of mechanical conditions are proposed and validated. Pure sliding reciprocation induces mixed lubrication mode. It was found that transient film profiles depend on the non‐Newtonian response of the oils and the type of motion. Running‐in period has a crucial importance for the tribofilm formation, and is a result of the interplay of the oil‐sliding surfaces interface and is directly connected with the total energy dissipated from the contact region. The stability of structured tribofilm in steady‐state period relies on the balance between the competitive processes: replenishment of the oil to the contact and ejection of the oil pending the oscillatory movement. The phenomenon of starvation was observed when the system was moved away from dynamical equilibrium and the growth of the dissipated energy was spotted. A proposed methodology provides the evaluation of the lubrication properties of the oil in a quantitative way. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental and numerical investigation of the sliding behaviour in a fretting contact between poly (methylmethacrylate) and a glass counterface

The fretting conditions in a contact between poly (methylmethacrylate) and a rigid counterface have been investigated using both experiments and finite elements computations. The computation of the microdisplacements in the contact area during a tangential loading allowed the determination of the critical displacement for transition from partial sliding to gross sliding conditions. These conditions were mapped in friction maps as a function of the contact loading parameters (i.e., normal load and displacement amplitude) and the friction coefficient. This analysis was performed assuming that the polymer behaved elastically and that the friction obeyed Coulomb's law. Experimental results were found to be in accordance with the numerical predictions, despite the fact that some plastic deformation of the polymer surface occurred during tangential loading.     

Characterization of friction-induced local convex topography under dual-rotary fretting

Dual-rotary fretting (DRF) is a complex fretting wear mode combining torsional fretting with rotational fretting. Two different typical friction-induced convex topographies (Type I and Type II) in contact area were showed, which are under the control of torsional and rotational fretting components, respectively. To investigate their evolution characteristics and formation mechanism, the convex topographies were analyzed by SEM, XPS, a nano-hardness tester and surface profilometry, etc. The results show that the convex topographies significantly depended on the test parameters and environmental conditions. The initiation and propagation of fretting fatigue cracks were found related with the convex topography under the fretting wear.