Metallic wear — a review with special references to vibration-induced wear in power plant components

Some of the major processes that are likely to be involved in wear — namely, adhesion, abrasion, fatigue, delamination and oxidation — are described. An outline of the Systems Concept in the analysis of wear processes is given. Some wear theories and various factors that affect wear, such as distance of travel, speed, applied load, material and temperature, are also discussed. The latter part of the paper reviews recent literature pertinent to vibration-induced wear, eg impact and fretting of power plant components — more specifically, heat exchangers. Several predictive models for tube wear are described.     

Fretting fatigue considerations in holistic structural integrity based design processes (HOLSIP)—A continuing evolution

Fretting fatigue has become one of the most significantly recognized failure mechanisms in engineering applications of critical components of many joined sub-systems or systems. It is one of the major areas of concern in fixed wing aircraft connections, rotary wing gearboxes, clutches, bearings, bushing, lugs, and engines of all types in the aviation industry. For many years the power generation industry has recognized the importance of fretting fatigue and some major failures have been attributed to fretting fatigue over many years. It has been of concern in many other industries in recent years. As the knowledge on fretting corrosion, fretting wear, and fretting fatigue has expanded it has been recognized as a major source of the failure of engineering components in a myriad of applications. This has led to recent standards for testing and terminology related to fretting fatigue in Japan, the USA/Canada (ASTM), and France.     

Progress in standardization of fretting fatigue terminology and testing

This paper reviews the current ASTM, ISO, and other standards that pertain in part to fretting fatigue and fretting wear testing. A historical perspective gives some background on why there still are relatively few standards for fretting fatigue and fretting wear testing. Current standards on the books tend to be application specific. In the past few years, there have been some new activities in standardization. These developments along with future needs in standardization are discussed.     

汽车关键零部件的寿命定量设计

汽车关键件疲劳寿命定量设计是一种现代设计方法,它把定量疲劳寿命理论和试验相结合,使疲劳寿命由定性设计提高到定量设计,提高了设计水平,对于汽车制造商来说极具经济价值。     

Fretting wear behaviour of hypereutectic P/M Al–Si in oil environment

The fretting wear behaviour of forged hypereutectic P/M Al–Si in contact with hardened steel and Cu–Sn–Pb bearing material is investigated. Fretting tests are performed with a view to the movement in the contact between the small end of the connecting rod and the piston pin in a car engine. Therefore, the tests are carried out under engine oil lubrication at temperatures up to 150°C. The behaviour of the Al alloy is compared to that of steel, the current connecting rod material. Some tests under non-lubricated conditions are also performed. The correlation between the friction coefficient, the wear volume and the microscopic wear mechanisms is discussed. After the running-in wear, a stable wear condition is reached for the Al–Si/steel contact.     

Fretting fatigue properties of plasma nitrided AISI 316 L stainless steel: Experiments and finite element analysis

This study investigates the effects of thickness, hardness and composition of modified layer on the plain and fretting fatigue properties of the nitrided 316 L steel plasma nitrided under various processing conditions. Fretting fatigue behaviour of untreated and nitrided material is also analysed with the finite element method. Experimental and theoretical fatigue life results are compared. The result indicates that the nitriding process improved the fretting fatigue properties of 316 L stainless steel. The experimental test results are close to theoretical fretting fatigue life results, thus it yields that the established model in the numerical analysis is consistent in this regard.     

Measurement, analysis and prediction of fretting wear damage in a representative aeroengine spline coupling

A methodology to predict fretting wear in complex couplings is described and validated against results obtained from a reduced scale aeroengine-type spline coupling subjected to complex cyclic load cases. The methodology uses three-dimensional finite element analysis, together with coefficient of friction data obtained from stroke controlled round-against-flat fretting tests, to determine spline tooth contact pressure and slip distributions; the latter as a function of number of loading cycles. A modified Archard equation is used to calculate wear depths from the contact pressure and slip distributions using wear coefficients obtained from the round-against-flat fretting tests. The slip distributions, and, concomitantly, the wear distributions, are found to depend strongly on the coefficient of friction, which, in turn, depends on the state of lubrication and number of loading cycles. For constant coefficient of friction, the slip distributions stabilise quickly with increasing numbers of loading cycles. The methodology predicts greater wear under lightly lubricated conditions than without added lubrication for the essentially load-controlled tests on the reduced scale aeroengine-type coupling. The wear depth trends are predicted correctly, both axially along the spline teeth and around the tooth flank, and the predicted wear depths bracket the measured values, dependent on the lubrication conditions considered; the latter attributable to the sensitivity of spline wear to the evolving coefficient of friction during testing. The methodology provides a basis for further development.     

Fretting fatigue behaviour of Ti–6Al–4V alloy under plane bending stress and contact stress

Fretting fatigue tests for Ti–6Al–4 V alloy were conducted by use of the plate fatigue specimen with bolt-tightened shoe on both sides of the plate. It was clarified that the repeated bending stress at the contact area where fretting fatigue failure starts linearly decreased as stress over the contact area increased. Fretting fatigue crack starts from the pit where stress concentrate. The pit initiates when fretting debris were removed from the surface striation formed due to the contact slip movement. The fretting fatigue crack initiation mode was transgranular, while the fretting fatigue crack propagation mode was striation.     

Progression of fretting fatigue damage in Ti–6Al–4V

An investigation was conducted to explore the nature of fretting fatigue damage in the stages prior to crack formation. In the unique experimental apparatus employed in this study, where total slip never occurs, several locations on each test specimen exist where cracks can develop due to local contact conditions. Under the test conditions used, not all of the sites had cracks upon test completion. This study evaluated the condition of non-cracked sites on several fretted specimens in an effort to identify differences between these and sites where small cracks were observed.A single test condition of 620 MPa average applied static clamping stress and 250 MPa applied axial fatigue stress for R=0.5 was selected, which corresponds to a fretting fatigue life of 10⁷ cycles based on prior work. For specimens tested to 10⁶ cycles, or 10% of life, several destructive and non-destructive characterization methods were chosen: scanning electron microscopy (SEM), residual stress measurement and transmission electron microscopy (TEM). Each site at which crack nucleation could be expected was inspected in the SEM and was then characterized using surface X-ray diffraction to quantify the residual stresses field near that location. Then TEM foils were cut from one area on a specimen with tiny cracks and dislocation densities were observed. A novel technique was used which permitted TEM samples to be obtained from regions in close proximity on the original specimen.Comparisons were made between as-received (AR) and stress-relief annealed (SRA) specimens, on which the stress-relief was applied prior to fretting fatigue testing. SEM inspection was useful for qualitative analysis of wear debris and identification of cracks as small as 20 μm, but was unable to provide quantitative data on the level of fretting fatigue damage beyond crack size. Although differences were noted in the residual stresses for the SRA versus the AR specimens, no residual stress peaks were noted in the edge of contact regions where cracks would eventually develop. TEM observations in the vicinity of the crack nucleation region showed that the dislocation structure decayed rapidly into the specimen thickness. The cause of the dislocations was attributed to plastic deformation caused by the clamping stresses.     

Influence of load and speed on wear characteristics of grey cast iron in dry sliding — selection for minimum wear

The wear of grey cast iron in dry sliding conditions has been studied with the aims of (1) finding the influence of working conditions on the wear rate, and (2) determining the region of speed and load where low wear is accomplished. Grey cast iron with flake and nodular graphite was submitted to investigation using a pin-on-disc machine. The results indicate that the flake graphite cast iron is more suitable for applications at speeds greater than 4 m s⁻¹ and lower loads, while nodular cast iron has greater wear resistance at lower speeds in the range of loads investigated - from 50 N cm⁻² to 200 N cm⁻²     

核电厂闸阀锅炉效应的危害与防治

论述了核电站用阀门锅炉效应的危害及其产生的机理。结合阀门的功能结构、核电厂的运行以及事故工况、概率安全分析和利益代价比分析等因素,给出待改进阀门的判断方法。针对阀门的不同情况,提出了相应的改进方案。以大亚湾核电厂和岭澳核电厂为实例,介绍了防治阀门锅炉效应的良好实践。