A Functional Form for Wear Depth of a Ball and a Flat Surface

Formulae are derived from first principles which predict the wear depth of a ball and a flat surface through time as they slide against each other, in relation to any phenomenological law for wear volume, and taking into account the effect of component geometry. The equations can be fit using experimental wear volume data from ball-on-flat tribometers. The formulae remove previous limiting approximations made in the literature and extend to the prediction of the wear depth of both contacting surfaces. The wear model accords with a previous model that is validated by pin-on-disc testing of a steel/steel contact. The current paper uses the formulae derived to predict the wear depth of a diamond-like carbon (DLC) coating and a steel ball as they slide against each other in deionised water. An Archard equation is used to predict the wear volume of each surface; however, a DLC coating is known to form a transfer layer which reduces the rate of wear, and since this scenario does not obey Archard’s law directly, a time-dependent-specific wear rate is used to fit a semi-empirical model to experimental results. The final model predicts the wear depth of the ball and flat accurately.     

Comparison of two test methods for evaluation of forming tool materials

Two test methods often used to simulate the tribological performance of forming tool materials are compared in this investigation through an evaluation of the friction and wear properties of four tool steels in dry sliding. One test (slider‐on‐flat‐surface (SOFS)) utilises a vertical disc sliding on a horizontal flat test surface, and the other (load scanner (LS) tests) utilises two crossed cylindrical rods. The test conditions were selected as equal as possible for the two tests, and the following conclusions are made. Somewhat unexpectedly, the friction and wear results differed substantially between the two tests. The SOFS test showed a better potential to evaluate wear resistance since one test sample is in continuous contact with the other. The LS test can generate higher contact pressures since the two rods contact each other in an unworn condition throughout the whole test stroke. LS indicate that two hard and smooth tool steels tested against each other generally give low friction and good galling resistance. The two hard couples tested sustained the highest loads without any detectable surface damage. For the same combinations of hard steels, SOFS gave a higher friction due to the wear of the disc. The carbides in the disc material resist wear better than the matrix and will consequently wear the disc by abrasion, which adds to the friction. The above conclusions are drawn from a rather limited examination using only one set of test parameters. In fact, the two tests are both very flexible as to the way they can be used, and they both have advantages and limitations in tribological studies. They should rather be considered complementary than competitive. Copyright © 2008 John Wiley & Sons, Ltd.     

The dry wear of metals as a process in an open system

The wear of metals is considered as a number of possible processes occurring in an open system, containing the wear objects and the interfacial volume containing debris.It is shown for non-identical wear objects, for instance the pin and disc configuration where often only the pin wears continuously, that the net oxidation rate of the pin is not necessarily equal to the wear rate, since account must be taken of inevitable metal transfer between the two objects.Only for identical wear objects is it possible to equate the wear of each object to the net oxidation rate of that object.     

Modeling transient adhesive wear of tungsten carbide inserts tested with an angular setting

The standard transient adhesive wear equation had been used for modeling pins tested with a full contact with a counter disc. The wear volume against distance curve (wear curve) obtained from such a test can be divided into two regimes: the curvilinear transient regime and the linear steady-state wear regime. The slope of the wear curve at the beginning is a lot higher, and it gradually decreases with sliding distance towards the steady-state wear regime. On the other hand, for inserts tested with an angular setting, generally, the wear curve is in the form of a straight line with a constant slope. This is due to the limited volume of asperities available for wear initially, but as wear progresses, the volume of asperities available will also increase. Generally, the volume loss of inserts with an initial angular setting with the counter disc is lower, as compared with those obtained with a full contact setting. The wear volume also increases with load, speed and temperature. As the wearing conditions for both cases are different, a new exponential transient adhesive wear equation has, therefore, been developed to model the transient wear volumes of tungsten carbide inserts tested with an angular setting. Excellent results with an average correlation coefficient of 0.9964 and an average deviation of about 10% are obtained. Inferior results are obtained when the standard transient adhesive wear equation is used for modeling the inserts with an angular setting, as the assumption made in its derivation is no longer applicable. The modeling results obtained from using both equations, as well as some evidence obtained from SEM and optical examinations of the worn inserts and wear tracks will be discussed in details in this paper. The experimental wear data used to support this modeling work are obtained earlier from a high temperature wear testing rig, in which Sandvik tungsten carbide inserts are tested with an angular setting with a hot work tool steel counter disc. The experimental parameters used are: (i) Applied loads of 40 and 50 kgf, (ii) speeds of 100 and 130 m/min, (iii) temperatures of 25, 200, 400 and 600 °C, and (iv) distances from 1000 m to 16,000 m.     

Analysis of the friction and wear mechanisms of multilayered plasma-sprayed ceramic coatings

Wear tests were conducted on a rotor-vane-disk adaptor where three rotating vanes were pressed against a disk. Vanes were coated by WC and used as the upper specimen while the disk was coated by Cr₂O₃ and used as the lower specimen. A buffer layer of various thicknesses and contents was placed between the top coating and the bulk steel of the disk to alleviate the effects of the large difference in thermal properties of the two materials. The experimental results reveal that correct placement of a buffer layer can indeed improve the wear resistance. Factors such as the temperature to which the specimen was heated before testing, the proportion by weight of each individual constituent in the buffer layer, and the thickness of each coating layer, were also important for the volume of wear of the lower specimen. As the specimens were heated to higher temperatures, the wear volume decreased with increasing proportions of Cr₂O₃ in the buffer layer. Elevating the preheating temperature of the specimens can diminish the wear volume but increases the friction coefficient. The steady-state wear rate is not much influenced by the constituents of the buffer layer and the coating thickness. Brittle fracture, abrasion, adhesion and oxidation were found to be the primary wear mechanisms in the tests.     

Condition monitoring of industrial machinery through lubricant oil analysis

A number of techniques exist that can be used to determine the condition of a machine by analysing a sample of the lubricant. However, there are only a few available techniques that can be used to determine the effect of more than one cause of deterioration with a single method of analysis. By sensing changes in the dielectric of the lubricant, it is possible to obtain information relating to both the deterioration of the machine by means of wear products, and the influence of any solid and liquid contaminants present in the lubricant. In this paper, the principle of operation for this method is described, and the results of some controlled tests are reported in which comparisons are made with results obtained using other types of ‘health’ monitor.     

基于表面灰度图像的植物磨料磨损表面分形维数计算

以磨损表面SEM灰度图像为研究对象,采用变分法、双毯法、差分盒计数法和盒计数法4种方法计算植物磨料对不同金属材料磨损表面的三维分形维数。结果表明:植物磨料对金属材料磨损表面具有分形特征,分形维数与体积损失有着密切关系,体积磨损越大,分形维数也越大。4种算法中,变分法计算的分形维数稳定性最好,其次是双毯法和差分盒计数法,盒计数法对表面噪声最为敏感。     

Quantitative estimation of wear amounts by real time measurement of wear debris in lubricating oil

A diagnostic technique that can estimate quantitatively wear amounts under lubricated condition was developed using our developed on-line particle counter. Wear tests were carried out by rubbing a bearing metal against a carbon steel in paraffin oil. The size and number of wear debris in the circulating oil could be measured in real time. The volume of each debris was calculated and, additionally, the total wear amount during a given duration was calculated by accumulating all debris volume. The wear amounts obtained by the quantitative estimation were fairly similar to the measured values of mass loss of the specimen.     

Sliding wear resistance of Al-alloy particulate composites: An assessment on its efficacy

One of the advantages reported in Al-base alloy particulate composites is its improved sliding wear properties over its base alloy by several investigators. Much of the improvement depends on the experimental conditions, alloy composition as on the particulate size, shape and distribution in the matrix. The present paper will make an attempt to assess the improvement in sliding wear properties attained in a few Aluminium base alloys with different size, quantity and distribution of SiC-particulates and bring out the efficacy of making composites if any in the different alloy systems over other methods of property improvement like homogenisation, secondary processing, etc. In some cases remarkable improvements have been achieved, such as the composites have sustained much harsher conditions whereas the base alloy has seized at much milder conditions; whereas in other alloy systems the improvement is only comparable to that obtained by secondary processing. Properties attained on homogenisation, extrusion and making composites would be compared with the base alloys. In this paper an attempt will be made to draw a line as to the conditions under which composites can been used to make engineering products where improved sliding wear resistance is demanded and where more prevalent methods like ageing could serve the purpose.     

Biological reactions to wear debris in total joint replacement

The vast majority of total hip prostheses currently implanted consist of a hard metal or ceramic femoral head articulating against an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup. Over the last 10 years, evidence has accumulated to show that these prostheses are prone to failure due to late aseptic loosening and few survive beyond 25 years. With an increasing need to implant hip prostheses in the younger, more active patient the need to understand the mechanisms of failure and to develop artificial hip joints using alternative materials have become major issues in the orthopaedic community. This review focuses initially on our current understanding of the biological reactions to UHMWPE prosthetic wear debris in vivo and in vitro since this is believed to be the main cause of late aseptic loosening. While the precise mechanisms of osteolysis induced by UHMWPE wear debris have not been elucidated, the major message to emerge is that it is not the wear volume that determines the biological response to the debris, but the concentration of the wear volume that is within the critical size range (0.2-0.8 micron) for macrophage activation. The review then considers whether the problem of wear-debris-induced osteolysis may be overcome with the use of new generation metal-on-metal or ceramic-on-ceramic prostheses. For metal-on-metal prostheses, the prospects for increasing the osteolysis free life of the implant are good but additional biological problems associated with the nanometre size and reactivity of the wear particles in vivo may emerge. For the ceramic-on-ceramic prostheses, although initial prospects are encouraging, more data are needed on the characteristics of the wear particles generated in vivo before predictions can be made. It is concluded that the pre-clinical testing of any new materials for joint replacement must include an analysis of the wear particle characteristics and their biological reactivity in addition to the usual assessment of wear.     

A new method to investigate the sliding wear behaviour of materials based on energy dissipation: W–25 wt%Cu composite

A new method is proposed to explain and monitor wear behaviour based on energy dissipation. The wear of a W–25 wt%Cu composite against 52100 steel was used to demonstrate this approach with pin-on-disc tests conducted under three normal loads. An energy-dependent criterion, namely, specific wear volume (wear volume/dissipated energy (mm³/J)), was defined to evaluate the wear of the composite. The specific wear volume can be used as a substitute for the traditional wear rate due to the simultaneous expression of several wear parameters and because of its strong dependence on the wear mode. The specific wear volume appears to be constant in any particular “wear mode” regardless of the active “wear processes”. In the wear of this composite, processes such as particle pull-out, mechanically mixed layer (MML) formation, crack propagation and delamination were observed. But, combination of these processes in each test had identical specific wear volumes. Thus, all of these wear processes were considered to be consecutive stages of the same wear mode: fatigue wear. The amount of dissipated energy and the volumetric loss increased with increasing normal load. Also, changing the normal load changed the rate of energy dissipation per unit sliding distance.     

Wear mechanisms in materials with granitic textures—Applicability of a lateral crack system model

In petreous materials, the mechanisms causing wear are several depending on which system we need to focus in. This work describes how it is possible to employ the lateral crack system, initially outlined to explain the wear of ceramic materials, to understand the wear of materials with granitic textures (granite, granodiorite, gabbro, quartzite,…) while being processed by diamond tools. For assessing the wear parameters of ten types of stones a new experimental procedure was developed and optimised to provide accurate measurements of specific energies and resultant forces as, at the same time, considers the impact that each stone has in the wear of a standard tool. The experimental results show the applicability of the lateral crack system in stones. Following a lateral crack system model, it was possible to attain a relation between the volume loss caused by a diamond tool and the macro-mechanical properties of the stone (hardness, Young's modulus and fracture toughness) while knowing the normal force applied during the erosive wear.     

The abrasive wear of alumina: correlation with electron triboemission

This study reports the measurements of wear volume and the cumulative triboemission of electrons that are a consequence of multi-pass abrasion of alumina by a diamond indenter in vacuum. The interpretation of these measurements is facilitated by an analysis of the wear scar surface morphology. Wear volume measurements and the examination of the wear scar surface by SEM are necessarily post hoc and, therefore, provide limited insight into the time dependence of wear processes. In this study, the feasibility of using triboemission as a real-time probe (on the order of seconds) of the abrasive wear of ceramics is discussed. A severe-to-mild wear transition is observed after approximately 20 passes with 10 N load. No wear transitions are observed with 30 N load up to 18 passes. A transition in the fraction of plastic debris coated on the wear scar appears to occur concurrently with the wear transition at 10 N load. The wear volume and the fraction of plastic debris film are measured at discrete pass numbers (the ends of the abrasion period) and, therefore, the temporal evolution of the wear process transition is not known. The triboemission, on the other hand, is measured quasi-continuously (separation between measurements is 1 s) and displays an abrupt change in the slope of the cumulative triboemission with respect to the number of passes, at a pass number that is consonant with the transitions in wear rate and fraction of plastic debris film. Evidence is provided that in fact the transitions in wear rate, plastic debris fraction, and cumulative triboemission slope are concurrent. An interpretation of these results is discussed.     

Wear of wheel-rail surfaces

The interactions between the tribological stress parameters and the measurable wear quantities during rolling with slip are examined with the help of experimental results already published and the results of some new investigations by the authors of this paper.It is from these that the following model for wear behaviour is derived.

• 1.(1) The wear quantities (wear volume and mass loss due to wear) are first of all proportional to the frictional work.
• 2.(2) The factor of proportionality between frictional work and wear volume depends on (a) the structure of the tribological system (material pairing and environment) and (b) the temperature of the contacting surfaces. This temperature is a function of the stress collective, the influence of which may be approximated as the relation of frictional power to contact area, the surface temperature thus governing the transitions between mild and severe wear.

     

高水基液压阀陶瓷摩擦副摩擦学性能研究

为选择适合的高水基乳化液液压阀摩擦副材料,探讨ZrO2与不同结构陶瓷组成的摩擦副在高水基乳化液润滑状态下的摩擦磨损特性。采用摩擦磨损试验机,在不同载荷和滑动速度下,研究在高水基乳化液介质中4种不同陶瓷材料（ZrO2、Al2O3、Si3N4和SiC）分别与ZrO2配副的摩擦学性能,并探讨不同组合陶瓷摩擦副的磨损机制。结果表明：在高水基乳化液中,各陶瓷的摩擦因数均随着滑动速度的增大而降低,其中Al2O3陶瓷的摩擦因数最小;ZrO2、Al2O3和Si3N4陶瓷的摩擦因数受载荷的影响较小,SiC陶瓷的摩擦因数则随着载荷的增大而骤增;各陶瓷的磨损体积都随着速度和载荷的增大而增大,其中Al2O3/ZrO2陶瓷摩擦副的磨损体积最小,其磨损机制以磨粒磨损和微疲劳磨损为主。研究表明,在不同工况下,Al2O3与ZrO2陶瓷配副的摩擦因数和磨损体积均为最低值,更适合作为高水基乳化液液压阀的摩擦副材料。     

Studies of Wear and Load-Carrying Capacity in the Pin and Disk Machine

A pin and disk machine has been used to investigate the influence of load and stress on the wear of steel specimens lubricated with a plain mineral oil and two blends containing typical commercial EP additives.

Under constant load conditions it was found that, contrary to the wear law of Archard et al., the volume wear rate decreased asymptotically to zero throughout each test. With each additive blend the final stress was found to be a constant irrespective of the load applied, whereas with the base oil the final stress increased as the applied load was increased. It is suggested that for the additive blends the mechanism of lubrication is boundary, but that with the base oil a hydrodynamie oil-film is formed.

The importance of these results is that they show that, under such lubricated conditions, the equilibrium slate is not one of steady wear, as previously thought, but one of zero wear and that wear should properly be thought of as a transient process. It is shown that once the existence of the equilibrium stale is recognized this transient wear can be expressed to a good approximation by a simple modification of the dry wear law.     

A Model for Potential Adhesive Wear Particle at Sliding Inception of a Spherical Contact

A new approach for adhesive wear modeling based on physical principles that eliminate the use of any empirical wear coefficient has been presented. The model predicts dimensionless volume of a potential wear particle that can be detached from an elastic-plastic sphere in contact with a rigid flat at sliding inception. An explicit relation between the dimensionless potential wear volume, material properties, and dimensionless normal load is obtained. An empirical expression for predicting wear coefficient which depends on the normal load and material properties is also presented. Some recommendations for a dynamic modeling to allow actual detachment of wear particle rather than prediction of a potential wear particle are indicated.     

Cavitation Erosion and Sliding Wear to Assess Carbide Integrity in AISI D2 Tool Steel

Ultrasonic cavitation and ball-on-disk wear tests were conducted in order to assess the carbide integrity in AISI D2 steel specimens with different heat treatments and carbide orientations on the exposed surface. The response of the tested materials under cavitation erosion was clearly distinguishable for each carbide orientation and heat treatment. Particularly, carbide predominant orientation can be successfully associated with the incubation period of cavitation damage. Validity of the cavitation erosion tests as a useful characterization technique in materials with reinforcement phases is discussed based on the small contact areas associated with the microjets generated in the ultrasonic cavitation test. On the other hand, ball-on-disk tests in conjunction with conventional wear analysis (coefficient of friction graph, wear volume) did not provide a clear relationship between research variables. However, by using discrete Fourier analysis from friction coefficient data, it was possible to establish a correlation between integrity of primary carbide, its orientation and matrix hardness.     

The abrasive wear of silica sand agglomerates

Processing of agglomerated particulate products can lead to attrition by abrasive wear as the agglomerates move relative to one another. In order to investigate this damage mechanism under controlled conditions, bar-shaped silica sand agglomerates of a range of strengths have been formed by addition of appropriate proportions of polyvinylpyrrolidone binder (molecular weight 44 000). These were then tested for wear resistance against various grades of abrasive paper and by rubbing against each other. In common with many materials, it was found that the wear rate is proportional to total sliding distance and to normal load, and independent of relative velocity. A simple Coulombic interlocking wear model is advanced to account for the dependence of wear rate on the size of abrasive particle forming the countersurface. In sustained (multi-pass) sliding, the presence of the debris reduces the attrition rate significantly. This phenomenon has been exploited by various workers who introduced solid lubricants into particle-processing devices in order to reduce attrition. The wear rate of agglomerates of different strengths has been found to be approximately proportional to the reciprocal of K_c, the critical stress intensity factor measured for the same bar agglomerates using the three-point bend test. This relationship between attrition rate and K_c has also been found for attrition in fluidized beds.