The effect of slip amplitude and test time on fretting wear in metal-metal contact

A study was conducted to determine the effect of amplitude and test time on surface damage in metal-to-metal contact under lubricated conditions. The test set up consisted of a ball loaded against a flat disc, with an external drive imparting a linear oscillatory motion to the ball on the flat. The materials were steel AISI 52100/AISI 52100, and the lubricant was ISO VG 220. Damage characteristics were defined for amplitudes in the range of 5 to 50 microns and for test times of 10 to 360 min.     

A theoretical model for the prediction of initial growth angles and sites of fretting fatigue cracks

The crack initiation mechanisms under fretting fatigue conditions are investigated. Fretting fatigue tests have been conducted on an aluminium alloy. Two major crack initiation mechanisms are experimentally observed. They are theoretically identified by employing a simple dislocation dipole model and taking into consideration the reverse sliding along dislocation layers and the influence of the distance between these layers. It is shown that cracks may initiate either by an extrusion-intrusion mechanism or a fatigue tensile process. Two parameters respectively linked to each of these initiation mechanisms are proposed to predict crack location. The theoretical crack initial growth directions and locations are shown to correlate very well with the experimental ones. With regards to these initiation processes, a spall detachment mechanism is proposed considering the interaction of microcracks.     

A thermodynamic approach for predicting fretting fatigue life

This paper extends the application of the theory of continuum damage mechanics (CDM) to predict the occurrence of fretting fatigue failure. It is concerned with the application of thermodynamic theory of CDM for predicting crack formation in fretting. This is done by calculating subsurface shear stress distribution due to fretting loading conditions and obtaining corresponding principal plane location. For given fretting conditions such as the load, the coefficient of friction and the bulk material properties, the present model predicts the number of cycles to failure. The results are validated with published experimental data.     

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.     

Friction behavior of quenched and tempered steel in partial and gross slip conditions in fretting point contact

Tangential traction caused by friction in contacting surfaces is a major factor in fretting fatigue that increases stress levels and leads to a reduction in fatigue life. Friction in fretting contact was studied in partial, mixed and gross slip conditions on quenched and tempered steel. Measurements were made with sphere-on-plane contact geometry for polished and ground surfaces. Friction was evaluated from on-line energy ratio and, after the tests, from wear marks. A maximum friction coefficient of over 1.0 was measured at mixed slip zone with polished surfaces, whereas ground surfaces promote lower values in similar operating conditions. The friction coefficient dependence on load cycles and loading frequency is also presented and briefly discussed. The friction data and understanding thus gained is to be used for evaluation of crack initiation with the numerical fretting fatigue model.     

Laboratory evaluation of anti‐fretting lubricants

To characterise the friction and wear behaviour of materials and lubricants under a variety of operating conditions, laboratory models are frequently used to provide useful information. For example, during the development and/or selection of tribomaterials and lubricants, laboratory ranking of candidate products can save many hours of field testing. A reciprocating ball‐on‐flat wear test rig has been developed to rank the performance of materials, surface coatings, and lubricants under boundary, extreme‐pressure, or fretting conditions in a variety of environments and at various temperatures. The rig design is based on ASTM G133–1995. The friction force and wear are measured on both specimens while the load, stroke length and frequency, test temperature, lubricant type, test duration, surface topography of both ball and flat specimens, specimen materials, and environmental conditions are noted. The results presented in this paper refer specifically to a series of tests performed to evaluate various anti‐fretting lubricants. Two lubricants are compared in terms of friction coefficient and wear volume over time. A clear difference is shown between the two products.     

Utility of a fretting device working under free displacement

Relative movements of low amplitudes between two materials in contact are generally reproduced on fretting devices with imposed displacement or imposed tangential force. The damage kinetics observed (cracking, wear) is established under such conditions. In this article, a fretting device working under free displacement is used to characterize the damages generated by seizure and wear. The conditions of seizure are analyzed from the total sliding distance and the discussion is focused on a correlation established with Dupre's work of adhesion. The wear behavior of materials has been characterized from an energetic wear coefficient taking into account the wear volume of contact, the total sliding distance and the dissipated energy.     

Application of the solution of the contact wear problem to modeling wear during fretting corrosion

Fretting corrosion wear was modeled using the deformation model of Winkler and the assigned elementary law of wear. The obtained theoretical results were compared with the available experimental data. It is demonstrated that the proposed model is adequate for the actual process of fretting corrosion.     

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.     

Development of a laboratory test device for electrorheological fluids in hydrostatic lubrication

Electrorheological (ER) fluids exhibit changes in their rheological behaviour in the presence of an external electric field. Research and development activities related to ER fluids and their applications have increased dramatically during the last few decades. If commercialised, ER fluids could have a significant impact on hydraulic equipment, and be utilised in the automotive, marine, aerospace, robotics, and machinery industries. The objective of the present study is to demonstrate the feasibility of using ER fluids to produce ‘smart’ lubricants that can control friction and wear of sliding components. The ER lubricant effect is demonstrated using a unique test machine that utilises hydrostatic lubrication. It is found that the friction torque increases by as much as 30% when a voltage of 2000 V is applied to an ER fluid in the newly developed test machine.     

A fatigue endurance criterion in two stages with application to fretting contact

In this paper we propose a fatigue endurance criterion suitable for mechanical components under high stress gradients. It is composed of two stages in order to predict both short and long crack arrest. In the first stage, a non-local multiaxial fatigue criterion measures the potential for crack initiation/short crack arrest. In the second stage, linear elastic fracture mechanics is used to evaluate the possibility of long crack arrest. The predictions of the fatigue criterion are compared with available experimental data obtained with cylinder-flat contacts under partial slip, fretting wear conditions. The results show that the proposed criterion can describe the endurance mechanisms observed in the experimental data.     

二次压缩机填料盘微动失效研究

对茂名石化乙烯工业公司低密度聚乙烯装置二次压缩机填料盘过度磨损和开裂的原因进行了分析和研究。结果表明。相邻两块填料盘之间存在着微动磨损,同时填料环的腐蚀和磨损加速了填料盘的微动,大大降低了填料盘的疲劳寿命,使填料盘疲劳开裂。     

圆弧端齿结构微动疲劳试验加载装置的设计及实现

针对圆弧端齿结构三维微动疲劳试验难度大、成本高等问题,提出了一种二维等效加载方案,设计并实现了微动疲劳试验加载装置,建立了二维结构微动疲劳试验模型。对典型圆弧端齿结构的二维等效试件进行了微动疲劳试验,发现疲劳裂纹萌生于接触面的接触边缘,接触面出现大量微动磨屑,为典型的微动疲劳失效形式。试验结果表明,该微动疲劳试验加载装置可满足端齿结构微动疲劳试验要求,为微动损伤机理分析和微动疲劳寿命预测提供了试验数据支持。     

LCU逻辑控制单元试验台的研制

针对用户使用特点,研制了一种台式、实用的逻辑控制单元试验台;该产品采用工业计算机技术、硬件电路模块化设计技术,实现了逻辑控制单元的整机测试、手动测试试验;阐述了该系统的硬件、软件实现方法,系统结构简洁,使用方便、安全、可靠、抗干扰性强,具有很好的扩展性和升级空间。     

虚拟仪器在触点分断电弧性能测试系统中的应用

本文采用虚拟仪器技术,研制了一套触点分断电弧性能测试系统,该系统基于触点材料试验机、工业控制计算机和高速数据采集卡,用于研究分断电流、电极分断速度、触头材料等参数对电弧性能的影响。系统操作简便,自动化程度高,测量准确度高。     

基于能量密度法预测微动疲劳寿命

通过接触界面的应力应变场和临界平面法计算了能量密度损伤参数,结合疲劳试验得到了能量密度损伤参数-寿命关系曲线中的材料常数,建立了LZ50钢微动疲劳寿命的预测公式。根据裂纹萌生寿命预测效果,将Chen损伤值作为裂纹萌生控制参数。分析了摩擦因数、微动桥半径、循环载荷和微动桥压力对LZ50车轴钢的Chen损伤值的影响,以及CRH2型动车组空心车轴裂纹萌生的位置及寿命。     

钢丝微动疲劳裂纹萌生寿命预测研究*

钢丝微动疲劳过程中,钢丝裂纹萌生特性直接影响其裂纹扩展特性,进而制约钢丝微动疲劳寿命,因此开展钢丝微动疲劳裂纹萌生寿命预测研究具有重要意义。基于有限元法、摩擦学理论和断裂力学理论,运用Smith-Watson-Topper（SWT）多轴疲劳寿命准则建立考虑磨损的钢丝微动疲劳裂纹萌生寿命预测模型,基于多种不同的钢丝疲劳参数估算方法对钢丝的微动疲劳裂纹萌生寿命进行了预测,并探究接触载荷、疲劳载荷、交叉角度及钢丝直径等微动疲劳参数对钢丝微动疲劳裂纹萌生寿命的影响规律。结果表明：基于中值法的预测结果最接近实际值;在微动疲劳过程中,钢丝微动疲劳裂纹萌生寿命主要与接触载荷和疲劳载荷相关。通过引入微动损伤参数建立简化的适用于钢丝绳的钢丝微动疲劳裂纹萌生寿命预测模型,通过与考虑磨损的预测模型计算结果进行对比验证了该模型的准确性。     

超高压压缩机填料盘的微动磨损

对茂名乙烯超高压压缩机的填料盘异常磨损和开裂进行分析和计算,发现填料盘的磨损是由于填料盘在工作时有微动磨损而引起的,并且造成填料盘微动疲劳,形成微动疲劳裂纹。     

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.