Fretting-induced friction and wear in large flat-on-flat contact with quenched and tempered steel

Fretting may cause severe surface damage and lead to unexpected fatigue failure. Our test apparatus was designed based on reciprocating, large, annular flat-on-flat contact without any edge effects in the direction of the fretting movement. Fretting wear tests were run with quenched and tempered steel with different normal pressures and sliding amplitudes under gross sliding conditions. The development of the friction coefficient and total wear mass depended mostly on the accumulated sliding distance. Initially, friction and wear were highly adhesive but gradually changed to abrasive due to third body accumulation in the interface.     

Failure analysis of aluminum cable steel reinforced (ACSR) conductor of the transmission line crossing the Paraná River

The failure of the conductor of the 460 kV overhead transmission line located along the crossing of the Paraná River was investigated. As a result of this failure, a blackout took place in the southern states of Brazil in January of 2002, reaching approximately 67 million inhabitants. Investigation of the external aluminium layer of the ACSR conductor near the fracture showed typical static deformation marks and dynamic fretting wear tangential marks, both associated with the presence of Al₂O₃ debris. Additionally, encrusted silicon particles were observed on the external surface of the strands. The internal Al layer showed elliptical deformation marks also associated with Al₂O₃ debris. Both Al₂O₃ and Si particles are efficient abrasive material, which associated with slight relative motion of metallic surfaces (clamp/strand and strand/strand) can promote fretting wear. Two types of fracture surface of the Al strands were identified: 45° and quasi-normal surfaces, the former being the predominant type. Delamination and particle detachment were the mechanisms of superficial degradation observed on the Al strands, indicating that the rupture of the strands occurred under a gross slip fretting regime induced by sub-conductor oscillation. Inspection of the internal surface of as-cast Al–10%Si spacer clamps revealed different stages of intense circumferential wear caused by the preferential cracking and particle detachment of the eutectic constituent of the as-cast microstructure. This intense wear reduces the clamping contact pressure, which allows higher displacement amplitude and leads to the critical fretting regime. Finally, a few suggestions are discussed to minimise the occurrence of future failures.     

Fatigue Delamination Characteristics of Plasma Sprayed Coatings under Fretting

FRETTING is referring to a reciprocating motion withthe small displacement between two components incontact[1].Fretting wear is superficial materialremoval during the fretting.It severely reduces theperformance,efficiency and service lifetime of thecomponents[2],Thermal spraying has been employedto enhance the fretting wear resistance of components,and the fretting wear behavior of the coatings has beenalso explored.However,the experimental results wereoften contradictive and confusing.On …     

Prediction of the crack extension under fretting wear loading conditions

Fretting is associated with small amplitude oscillatory movements between two surfaces in contact. One possible consequence of fretting is the formation and subsequent growth of cracks at the edges of the contact. This paper presents an experimental investigation of the cracking behaviour under fretting loading of two different aluminium alloys: 2024-T351 and 7075-T651. Systematic and controlled experiments with a cylinder-flat contact under partial slip fretting conditions were carried out. A model which combines both crack nucleation and propagation processes is used to predict the crack extension throughout the life of the component. The direction of crack propagation experimentally observed was taken into account by the model. Furthermore, an analytical prediction of crack nucleation based on the process volume approach is made. The predictions of both crack extension and nucleation are compared with the experimental results, and show good agreement.     

Recent developments in the understanding of fretting fatigue

Considerable progress has been made in the understanding of fretting fatigue over the last decade. Experiments have become more standardised and carefully controlled and this has provided the data necessary for development of methods for predicting fretting fatigue performance. This paper reviews a number of recent developments, starting with attempts to apply multiaxial initiation criteria to the fretting problem. The importance of the size effect is highlighted and an analogy is made between fretting and notch fatigue. Methods for characterising crack initiation using asymptotic analysis are discussed, together with short crack arrest concepts which provide a means of predicting fretting fatigue limits from plain fatigue data.     

TiC/Ti(C,N)/TiN复合涂层在滑移区的高温微动磨损特性

采用化学气相沉积（CVD）技术，在1Cr13不锈钢基体上制备TiC／Ti（C，N）／TiN复合涂层，研究了该涂层从室温（25℃）到400℃的微动磨损特性，并与无涂层的1Cr13不锈钢基材比较。结果表明：在滑移区．温度对1Cr13不锈钢微动磨损影响较显著；随着温度上升1Cr13不锈钢摩擦系数减少，磨损体积下降；而温度对TiC／Ti（C，N）／TiN复合涂层磨损体积影响不大．且磨损量均很小．TiC/Ti（C，N）／TiN涂层表现出比1Cr13不锈钢优异的抗微动磨损性能。但当该涂层被磨去后，产生的硬质磨屑形成磨粒磨损，反而对基体造成更大的损伤。     

The tribological performance of DLC coatings under oil-lubricated fretting conditions

Whether or not the process of fretting occurs is to a large extent dependent on the coefficient of friction, because the coefficient of friction directly affects the amount of shear stress. As a result, the key factor when it comes to reducing the amount of fretting damage is to reduce the coefficient of friction. Various surface coatings, and especially hard, diamond-like carbon (DLC) coatings, are known to be able to produce surfaces with a low level of friction. Despite some such attempts in the past, which did not result in major improvements, the developments and improvements in DLC coatings in recent years suggest the need for a re-evaluation of these coatings for fretting applications. Another way to reduce the amount of friction in mechanical components is to apply lubricants, and recent studies on the lubrication of DLC coatings suggest that this combination could be very successful in preventing failures under boundary-lubrication conditions. Therefore, in this work we present the results of friction and wear measurements from three types of fretting contacts: steel/steel, steel/DLC and DLC/DLC. Boundary oil-lubrication conditions were investigated and a wide range of displacement amplitudes, i.e., from 25 to 500 μm, were selected to assess the fretting and sliding behaviours. The results show a significant difference between the fretting and sliding regimes. In the fretting regime, the DLC-containing contacts, and especially the self-mated DLC/DLC contacts, performed much better than the steel/steel contacts, and significantly reduced both the wear (a 3–10 times reduction with steel/DLC and DLC/DLC) and the friction (a more-than-two-times reduction with DLC/DLC). In the sliding regime, the lubrication effects governed the tribological performance, making the results for all three material combinations very similar.     

Wear characteristics of commercial gas turbine components

Wear is one of the common degradations in a commercial gas turbine. A stainless steel grade 304 (SS 304) fuel nozzle and its collar made of nickel-based superalloy (Hastelloy X) are two vital components that normally suffer from rapid wear. During an installation, the fuel nozzle is slotted into the collar of the combustion liner. In operation, these two surfaces are subjected to high pressure from the fuel combustion, hence continuously rubbing against each other causes vibrations. During the start–stop operation, these surfaces had undergone a large relative motion. The vibration is the main cause of the wear occurrence on the surfaces. Physical properties of the worn surfaces were obtained through visual observations: wear measurement, hardness and microstructure examination. Through visual observations, fretting wear was mainly suspected as the dominant wear mode, particularly after 8,000 of running hours at high temperature and vibration. In short, this paper discusses the preliminary findings of wear on the fuel nozzle and its collar. It also discusses the changes in the mechanical properties before and after the operation. Solutions for mitigating the problem were discussed.     

Fretting fatigue crack initiation behavior using process volume approach and finite element analysis

This study investigates crack initiation behavior by incorporating fretting fatigue process volume. Three critical plane based fretting fatigue crack initiation parameters are characterized by computing their averaged values over the process volume and then comparing with their counterparts obtained from the localized approach. Two approaches are used: first one involves the computation of parameter at several points over a rectangular region and then its average, and second approach computes the average state of stress/strain over a radial region from which the averaged parameter is calculated. Both approaches require pre-determination of a critical location at or around which the process volume needs to be placed. Effects of size and location of process volume on the averaged value of parameters are studied in detail. Two radii of cylindrical pad are analyzed to investigate the effect of severity of stress gradient on process volume approach. Effects of finite element mesh refinement are also investigated. Averaged value of parameter decreases with the increase of process volume size. This decrease is higher when the process volume is located in the region that is away from the contact zone. Further, a parameter based on normal stress on the critical plane shows more dependence on the size of process volume than that based on shear stress or on a combination of both shear and normal stresses. Orientation of crack initiation changes within a range that is well within the scatter band of experimental observations as the process volume size increases. Averaged value of parameter for a pad with higher stress gradient has a larger reduction with the increase of process volume size than that with a lower stress gradient. Process volume size has less effect on the averaged value of parameter with coarser finite element mesh. Finally, the localized approach provides a conservative value of fretting fatigue crack initiation parameter compared to its counterpart based on the process volume.