An X-ray diffraction study of the triaxial normal residual stresses in worn aluminum bronze surfaces

In metallic systems subjected to sliding wear material loss often results from the formation and subsequent delamination of a transfer layer. This phenomenon has previously been observed in copper-rich aluminum bronzes. The evidence obtained indicates that wear occurs by the delamination of the layer parallel to the surface in the vicinity of the layer-substrate interface.In general, copper-rich aluminum bronzes exhibit increasing wear rates with increasing aluminum content. Since wear results from the failure of the transfer layer, it is expected that factors which affect the stability of the layer should be related to the observed wear rate. One factor could be the residual stress pattern induced during the wear process. In a previous study the in-plane residual stresses were measured on worn copper-rich aluminum bronze samples. The residual stresses were found to be compressive and of increasing magnitude for increasing wear rate (increasing aluminum content). In this investigation the stresses normal to and at some distance below the surface were measured on samples of compositions similar to those used previously. The normal stresses were found to be tensile and increased in magnitude with increasing wear rate. It is suggested that the development of residual stresses normal to the surface may be an important wear-controlling parameter.     

Contact stresses in the glenoid component in total shoulder arthroplasty

Several studies of retrieved glenoid components from total shoulder arthroplasty show an erosion of the rim, surface irregularities, component fracture and wear resulting from polyethylene deformation in vivo. Particles resulting from polyethylene wear might be one of the reasons for the very high rate of glenoid component loosening found clinically. Because wear can be the result of high contact stresses, the aim of this study is to find out whether or not contact stresses are high enough to cause wear of the glenoid component and what influence the component type and geometry have on polyethylene contact stresses for different humerus abduction angles. Elasticity theory is used in a parametric study of contact stresses in several glenoid component designs. A finite element method is used to confirm the accuracy of the analytical solution. The analysis shows that the peak stress generated in glenoid components under conditions of normal living can be as high as 25 MPa; since this exceeds the polyethylene yield strength, wear and also cold flow of the components can be expected. It is predicted that more conforming components have lower contact stresses, which might result in lower wear rate and less cold flow. It is also found that a metal-backed component promotes higher contact stresses than an all-polyethylene component with the same total thickness, therefore it can be expected that metal-backed components have inferior wear properties.     

The role of stacking fault energy and induced residual stresses on the sliding wear of aluminum bronze

An analysis was made of the residual stresses induced during sliding contact of a series of Cu-Al alloys of various stacking fault energies (SFEs) using the conventional two-exposure X-ray technique. Compressive residual stresses were found in all alloys which increased with decreasing SFE in a manner analogous to the strain-hardening behavior. The macroscopic wear rate was found to be linearly related to the compressive stresses induced during the wear process. The increase in wear rate associated with increasing hardness and residual compressive stresses is attributed to the presence of a residual tensile stress normal to the surface.     

陶瓷磨削残余应力对表面性能的影响

陶瓷零件的磨削表面必然要附加一层残余压应力 ,其对零件的使用性能影响较大。本文主要针对陶瓷材料磨削表面残余应力对疲劳磨损和表面硬度的影响进行实验研究。试验结果表明 :与金属材料相比 ,Zr O2 陶瓷材料的磨削残余应力对零件的摩擦磨损性能的影响要小得多。磨削、研磨及加热三个试件组的磨损量随摩擦时间呈现一定的变化规律。残余拉应力在一定程度上加速陶瓷零件的磨损 ,残余压应力可适当减缓陶瓷零件的磨损 ,其数值变化对零件性能的影响很小。随着残余压应力值的增加 ,表面硬度值也在逐渐增加 ,当残余压应力增加到一定值后表面硬度值开始下降。     

Modelling the Effect of Steady State Wheel Temperature on Rail Wear

A moving train subjects a rail cross section to many wheel passes and heat generation at the interface from bulk friction and microslip. Frictional heating at the interface causes the temperature of the contacting rail surface and wheel surface to rise. After the train has passed, the rail temperature drops to ambient till the next train arrives. Wheels, on the other hand, pick up the frictional heat input continuously and hence their steady state temperature could be much higher than that of the rail. A hot wheel provides an additional temperature rise at the rail surface. The accompanying thermal stresses and thermal softening may enhance the rail wear rate. This has been investigated in the present study. A ratchetting failure-based computer simulation has been employed to assess the wear rate of a pearlitic rail steel. It is found that the thermal stress effect on wear rate is only the modest, but thermal softening can enhance the wear rate by up to an order of magnitude for the conditions considered.     

The Wear of PTFE-Containing Dry Bearing Liners Contaminated by Fluids

The influence of fluid contamination on the wear of a number of aircraft dry bearing liners has been examined using a recently developed, accelerated test procedure. It is shown that fluids generally increase wear to an extent depending on the level of stress, the type of fluid and the structure and composition of the liner material. Water is invariably deleterious but, at low stresses, mineral and diester oils can sometimes reduce the wear rate below that obtained in dry conditions. Explanations for the trends observed are deduced from a detailed examination of worn surfaces by X-ray photo-electron spectroscopy (XPS) and scanning electron microscopy (SEM). The relevance of the results to current specification requirements for aircraft dry bearings is discussed, and a number of inadequacies exposed.     

Wear and friction of 6061-T6 aluminum alloy treated by laser shock processing

Laser shock processing (LSP) is becoming an important surface treatment to induce a compressive residual stress field, which improves fatigue and fracture properties of components. In this work, we examine the effect of laser shock processing on the wear and friction behavior of 6061-T6 aluminum alloy. Wear rate and friction coefficient evolution are investigated for different process parameters of LSP. Roll-on-flat tribometer is used with different loading conditions. Hardness and residual stresses are assessed as well. It is observed that wear rate decreases as pulse density increases; this is explained in light of residual stress distribution.     

Severe wear of rolling/sliding contacts

The wear of wheel flanges against the sides of rails is shown to be caused by rolling/sliding contacts sustaining high cyclic stresses at low slide/roll ratios. When these conditions are reproduced in the laboratory severe metallic wear is initiated when the resultant shear stress, which is dependent on both normal (pressure) and tangential (friction) forces, exceeds a critical value. The results are discussed in terms of Johnson's shakedown limit and the material's stress/strain characteristics. It is concluded that the severe wear of contacts at low slide/roll ratios is caused by high resolved cyclic stresses that result in continual plastic deformation of the surface layers.     

Development of a wear equation for polymer-metal sliding in terms of the fatigue and topography of the sliding surfaces

A wear equation has been derived using the concept of fatigue failure due to asperity interactions in the contact region between sliding bodies. One of the three principal stresses that arise in the contact zone under the effect of a normal as well as a tangential load is of tensile nature. It is this principal stress that has been considered to be responsible for the initiation and propagation of fatigue cracks. It is assumed that the deformation in the contact zone is of elastic nature and that both the contacting surfaces are covered with asperities that have spherical tips. The wear equation involves the asperity height distribution φ(z). The particular distribution for a sliding situation is determined from experimental studies of the topography of sliding surfaces. The wear equation indicates that the wear rate depends upon the fatigue properties of the weaker material, normal load, sliding speed, coefficient of friction, moduli of elasticity of the contacting materials, asperity density, asperity radius of curvature and the distribution and standard deviation of asperity heights. The variation of wear with these parameters as indicated by the wear equation is in agreement with the experimental studies already reported in the literature.     

Influence of an additional elastic stress on dry wear behaviour in reciprocating tests

This paper is concerned with an experimental investigation to assess the influence of the additional elastic bulk stress state, as imposed by an external load, on dry reciprocating wear. Results obtained from dry reciprocating wear tests on an Al7175 alloy, in contact with a 34CrNiMo6 steel pin, are presented. It is shown that the additional elastic bulk stress has a substantial influence on the wear behaviour of the materials used in this study. It is, therefore, pertinent to take it into consideration in wear assessment. A physical model, based on micro and macro surface roughness, capable of interpreting the experimental obtained results has been developed. The model proposed is a modification of the Archard's model for the prediction of wear volume, in order to take into account elastic bulk stresses imposed by external loading.     

Microstructure and abrasive wear in silicon nitride ceramics

It is well known that abrasive wear resistance is not strictly a materials property, but also depends upon the specific conditions of the wear environment. Nonetheless, characteristics of the ceramic microstructure do influence its hardness and fracture toughness and must, therefore, play an active role in determining how a ceramic will respond to the specific stress states imposed upon it by the wear environment. In this study, the ways in which composition and microstructure influence the abrasive wear behavior of six commercially-produced silicon nitride based ceramics are examined. Results indicate that microstructural parameters, such as matrix grain size and orientation, porosity, and grain boundary microstructure, and thermal expansion mismatch stresses created as the result of second phase formation, influence the wear rate through their effect on wear sheet formation and subsurface fracture. It is also noted that the potential impact of these variables on the wear rate may not be reflected in conventional fracture toughness measurements.     

Experimental study on micro electrical discharge machining of porous stainless steel

Various cutter strategies have been developed during milling freeform surface. Proper selection of the cutter path orientation is extremely important in ensuring high productivity rate, meeting the better quality level, and longer tool life. In this work, finish milling of TC17 alloy has been done using carbide ball nose end mill on an incline workpiece angle of 30°. The influence of cutter path orientation was examined, and the cutting forces, tool life, tool wear, and surface integrity were evaluated. The results indicate that horizontal downward orientation produced the highest cutting forces. Vertical downward orientation provided the best tool life with cut lengths 90–380 % longer than for all other orientations. Flank wear and adhesion wear were the primary wear form and wear mechanisms, respectively. The best surface finish was achieved using an upward orientation, in particular, the vertical upward orientation. Compressive residual stresses were detected on all the machined surfaces, and vertical upward orientation provided the minimum surface compressive residual stress. In the aspect of tool wear reduction and improvement of surface integrity, horizontal upward cutter path orientation was a suitable choice, which provided a tool life of 270 m, surface roughness (R _a ) of 1.46 μm, and surface compressive residual stress of ?300 MPa.     

Microstructural modeling of adaptive nanocomposite coatings for durability and wear

Adaptive thin-film nanocomposite coatings comprised of crystalline ductile phases of gold and molybdenum disulfide, and brittle phases of diamond like carbon (DLC) and ytrria stabilized zirconia (YSZ) have been investigated by specialized microstructurally based finite-element techniques. One of the major objectives is to determine optimal crystalline and amorphous compositions and behavior related to wear and durability over a wide range of thermo-mechanical conditions. The interrelated effects of microstructural characteristics such as grain shapes and sizes, local material behavior due to interfacial stresses and strains, varying amorphous and crystalline compositions, and transfer film adhesion on coating behavior have been studied. The computational predictions, consistent with experimental observations, indicate specific interfacial regions between DLC and ductile metal inclusions are critical regions of stress and strain accumulation that can be precursors to material failure and wear. It is shown by varying the composition, resulting in tradeoffs between lubrication, toughness, and strength, the effects of these critical stresses and strains can be controlled for desired behavior. A mechanistic model to account for experimentally observed transfer film adhesion modes was also developed, and based on these results, it was shown that transfer film bonding has a significant impact on stress and wear behavior.     

The Behaviour of Sliding Contacts Between Non-Conformal Rough Surfaces Protected by 'Smart' Films

Many tribological contacts involve two components, each exhibiting finite roughness, sliding over one another for many repeated cycles of operation. Although the initial contact may be plastic, if low wear rate conditions are to be achieved, the steady state situation should be one of predominantly elastic stresses in each surface. When lubrication is present, the stress fields in the components must be consistent with the presence of a low shear strength film separating the surfaces. Commercial lubricants invariably contain a chemically complex additive package with one of the aims of the formulation being the production of boundary layers, which beneficially influence both friction and wear when conditions are not conducive to the formation of either a hydrodynamic or an elasto-hydrodynamic film. These boundary layers must be physically robust enough to survive prolonged service but slippery enough to maintain acceptably low coefficients of friction. Reductions in friction are not necessarily synonymous with improvements in anti-wear behaviour. Recent experimental evidence from studies using both atomic force microscopy and micro-tribometry suggest that boundary films produced by the action of commercial anti-wear additives, such as ZDTP, can exhibit mechanical properties which are affected by local values of pressure – the film is tribologically 'smart' becoming more robust just where it is needed at the most heavily loaded points of the conjunction. These effects have been explored in a numerical model of rough surface contact and the implications for the mechanisms of wear of real devices is discussed.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.     

Observations of In-Service Wear of Railroad Wheels and Rails Under Conditions of Widely Varying Lubrication

Some of the wheel and rail wear results from the current test at the Facility for Accelerated Service Testing are analyzed in the light of both adhesive and fatigue wear theories. This analysis suggests that the wheel: rail wear processes occurring in the unlubricated state contain one or more components other than adhesive wear alone. Whether or not increases in the hardness of one component will cause an increase or decrease in the wear rate of the mating component appear possibly to be related to the mechanism of wear, the magnitude in the change in hardness and the relative change in the wear rate of the component which is changed in hardness. A metallurgy: lubrication interaction which has been observed to occur when lubrication is applied has been found to be consistent with a concept of friction-dependent alteration of surface contact stresses when modified by the inclusion of a material sensitive parameter.     

硬质合金刀具高能离子源增强多弧镀AlCrTiSiN梯度涂层制备及性能研究

采用离子源增强的多弧离子镀新技术,在硬质合金刀具表面制备了不同含Si层梯度结构的AlCrTiSiN梯度涂层,并对涂层组织结构、残余应力、结合强度、摩擦磨损以及铣削和钻削加工灰铸铁性能进行了详细的研究。结果表明：不同含Si层梯度结构的AlCrTiSiN涂层主要由固溶的(Al,Cr) N、(Al,Ti) N相和非晶态Si₃N₄相组成。其中,含Si层梯度变化最缓和的G3(Gradient 3)涂层具有较高的结合强度,较低的残余压应力、摩擦因数和磨损率。铣削和钻削试验显示,涂层刀具的切削磨损机理主要表现为磨粒磨损和粘着磨损。G3涂层降低了磨粒磨损,其刀具的铣削和钻削寿命均最高,这主要得益于其含Si层的梯度设计、适当的压应力(-3.8 GPa)以及良好的膜基结合强度。研究结果表明,通过对含Si层进行梯度设计可显著提高涂层刀具的切削性能。     

ANALYTICAL MODELING OF THE EFFECT OF THE TOOL FLANK WEAR WIDTH ON THE RESIDUAL STRESS DISTRIBUTION

Tool flank wear has significant effects on the cutting process, as it affects cutting forces, temperature and residual stresses. In this article, analytical models are developed to predict the cutting temperature and residual stresses in the orthogonal machining of a worn tool. In these models, measured forces, cutting conditions, tool geometry, and material properties are used as inputs. Stresses resulting from thermal stresses, fresh tool stresses and stresses due to tool flank wear are used in this analytical elasto-plastic model, and the residual stresses are determined by a relaxation procedure. The analytical model is verified experimentally with X-ray diffraction measurements. With the analytical model presented here, accurate residual stress profiles in worn tools are shown, while the computational time is significantly reduced from days, typical for finite-element method (FEM) models, to seconds.     

Parametric study of solid-lubricant composites as ball-bearing cages

The performance of two polymer-based materials (polyimide/MoS₂ and ptfe/ glass fibre/MoS₂) as self-lubricating cages for ball bearings has been comprehensively evaluated. The two composites emerged as the most promising for operating at elevated temperatures during screening tests in a thrust-bearing geometry and were then tested in four sizes of 440C stainless steel single-row radial ball bearings at a range of loads, speeds and temperatures.Two regimes of operation were observed: the first with essentially zero steel wear when the lubricant transfer film is complete and bearing life is dictated by cage wear; the second with finite steel wear when the transfer film is only partially effective and bearing life is dictated by increase in internal clearance. The ball/raceway stress at which steel wear starts to occur is very low (< 1.2 × 10³ MN m^?2) compared to the stress implied by the catalogue load capacity of the bearings. The ball/raceway stress also has an important effect on both steel wear rate and cage wear rate.Overall, the ptfe-based composite gave lower steel and cage wear than did the polyimide-based composite, but the latter could be operated at higher temperatures (up to 360° C) and at slow speeds it gave a higher load capacity before the onset of steel wear.Using the wear results as a basis, a Bearing Performance Guide has been produced which provides a convenient means of approximately predicting the bearing life over a wide range of operating conditions     

An investigation into the effect of train curving on wear and contact stresses of wheel and rail

Some important papers concerning the studies on rail wear and wheel/rail contact stresses are briefly reviewed. The present paper utilizes a numerical method to analyze the effect of railway vehicle curving on the wear and contact stresses of wheel/rail. The numerical method considers a combination of Kalker's non-Hertzian rolling contact theory, a material wear model and a vertical and lateral coupling dynamics model of the vehicle/track. In the analysis, the important factors influencing on the wear and the contact stresses are, respectively, the curving speed, the curved track super-elevation and the rail cant. Compared to the present model, some concerned models and results in the published papers are in detail discussed. Through the detailed numerical analysis, it is found that the difference between the normal loads of the left and right of the wheelset increases linearly with increasing the vehicle curving speed. The material wear volume per length along the rail running surface has a tendency to grow. However, the variation of the maximum normal contact stress has a large fluctuation as the curving speed increases. The increase of the maximum contact stress depends greatly on not only the normal load but also the profiles of the wheel/rail. Increasing the track super elevation efficiently lowers the normal load difference of the left and right of the front wheelset, and the contact stresses and the wear. The rail cant has a great influence on the low rail wear of the curve track. An increase in rail cant results in a great increase in the low rail wear of the curved track, and a decrease in the outside rail wear. These conclusions are very useful in the maintenance of the track.