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In this work, the effect of the addition of reduced graphene oxide (rGO) nanoflllers to UHMWPE was investigated. The UHMWPE/rGO nanocomposites were prepared at rGO contents of 0.010, 0.10, 0.25, and 0.50 wt%. The morphological, mechanical, and surface properties of the nanocomposites and the neat UHMWPE were evaluated and related with their tribological behavior. For that, DSC, SEM, contact angle, MO, and profilometry techniques, besides shore D hardness tests, instrumented indentation tests and pin-on-disc sliding wear tests were performed. The results showed that nanocomposites with rGO contents of 0.10 and 0.25 wt% exhibited higher crystallinity degree than the neat UHMWPE, which improved significantly their mechanical and tribological behavior through increases of around 40% in the instrumented hardness and the elastic modulus, and a significant reduction of up to 48% in the coefficient of friction when compared to the neat UHMWPE. Additionally, the presence of rGO decreased the work of adhesion of the nanocomposites/ counterface pairs, resulting in friction and wear mechanisms changes in comparison with the neat polymer. KEYWORDS friction, nanocomposites, reduced graphene oxide, sliding wear, UHMWPE, work of adhesion, 1 | INTRODUCTION Ultra-high molecular weight polyethylene (UHMWPE) has been extensively used in engineering applications that involve wear and friction due to their self-lubricity, lightweight, corrosion resistance, and low coefficient [...]

Moving mechanical interfaces are commonly lubricated and separated by a combination of fluid films and solid 'tribofilms', which together ensure easy slippage and long wear life (1). The efficacy of the fluid film is governed by the viscosity of the base oil in the lubricant; the efficacy of the solid tribofilm, which is produced as a result of sliding contact between moving parts, relies upon the effectiveness of the lubricant's anti-wear additive (typically zinc dialkyldithiophosphate) (2). Minimizing friction and wear continues to be a challenge, and recent efforts have focused on enhancing the anti-friction and anti-wear properties of lubricants by incorporating inorganic nanoparticles and ionic liquids (3,4). Here, we describe the in operando formation of carbon-based tribofilms via dissociative extraction from base-oil molecules on catalytically active, sliding nanometre-scale crystalline surfaces, enabling base oils to provide not only the fluid but also the solid tribofilm. We study nanocrystalline catalytic coatings composed of nitrides of either molybdenum or vanadium, containing either copper or nickel catalysts, respectively. Structurally, the resulting tribofilms are similar to diamond-like carbon (5). Ball-on-disk tests at contact pressures of 1.3 gigapascals reveal that these tribofilms nearly eliminate wear, and provide lower friction than tribofilms formed with zinc dialkyldithiophosphate. Reactive and ab initio molecular-dynamics simulations show that the catalytic action of the coatings facilitates dehydrogenation of linear olefins in the lubricating oil and random scission of their carbon-carbon backbones; the products recombine to nucleate and grow a compact, amorphous lubricating tribofilm., Transportation vehicles account for about 19% of the world's energy consumption and some 23% of total greenhouse-gas emissions every year (6). With ever-increasing mobility, these numbers will undoubtedly surge and [...]

The erosion and wear in the gun barrel will get worse with an increase in the number of projectiles fired. Generally speaking, the ballistic performance of the gun, measured through indicators such as the maximum pressure [p.sub.m] and the muzzle velocity [v.sub.0], will decrease gradually due to gun barrel erosion. However, the above analysis does not agree with the firing test data of certain types of guns, especially of some small-caliber guns. The ballistic performance of such guns will exhibit an increase to their peak values followed by a gradual decrease with the number of rounds fired. This is the so-called interior ballistic peak phenomenon, also named as the hump effect. Taking several kinds of guns as examples, such as a 76 mm gun and a 100 mm gun, we calculated the engraving pressure Po of the guns by an approximate method and built a lumped-parameter interior ballistic model of the guns that exhibits the effect, according to the interior ballistics theory of guns with erosion and wear. The results of the modeling of the guns under different wear conditions are close to the test data, showing the existence of the peak values of [p.sub.m] and [v.sub.o]. The simulation results of some of the other guns that exhibit this phenomenon also show good agreement. Furthermore, it can explain the double-peak phenomenon for some types of guns with double driving bands. It was proven that the mismatch of the structure and the dimensions of the gun bore with those of the projectile driving band is the fundamental cause of this effect. Due to the mismatch, the engraving pressure will first increase and then decrease with the enlargement of the bore dimensions caused by barrel erosion and wear. The variation in the engraving pressure Po will inevitably lead to the variation in interior ballistic performance in the life cycle of the gun. This observed process appears to explain the interior ballistic peak phenomenon. [DOI: 10.1115/1.4001561] Keywords: erosion and wear, structure mismatch, gun barrel, driving band, engraving pressure

Two efficient methods for time-dependent fatigue reliability analysis are proposed in this paper based on a random process representation of material fatigue properties and a nonlinear damage accumulation rule. The first method is developed by matching the first two central moments of the accumulated damage to a well-known probability distribution, thus facilitating a direct analytical solution of the time-dependent fatigue reliability. The second method uses the first-order reliability method to calculate the reliability index based on a time-dependent limit state function. These two methods represent different tradeoffs between accuracy and computational efficiency. The proposed methods include the covariance structure of the stochastic damage accumulation process under variable amplitude loading. A wide range of fatigue data available in the literature is used to validate the proposed methods, covering several different types of metallic and composite materials under different variable amplitude loading.

The objective of this paper is to present physical and quantitative models for the rate of tool flank wear in turning under flood cooling conditions. The resulting models can serve as a basis to predict tool life and to plan for optimal machining process parameters. Analytical models including cutting force analysis, cutting temperature prediction, and tool wear mechanics are presented in order to achieve a thermo-mechanical understanding of the tool wear process. The cutting force analysis leverages upon Oxley's model with modifications for lubricating and cooling effect of overhead fluid application. The cutting temperature was obtained by considering workpiece shear deformation, friction, and heat loss along with a moving or stationary heat source in the tool. The tool wear mechanics incorporate the considerations of abrasive, adhesion, and diffusion mechanisms as governed by contact stresses and temperatures. A model of built-up edge formation due to dynamic strain aging has been included to quantify its effects on the wear mechanisms. A set of cutting experiments using carbide tools on AISI 1045 steels were performed to calibrate the material-dependent coefficients in the models. Experimental cutting data were also used to validate the predictive models by comparing cutting forces, cutting temperatures, and tool lives under various process conditions. The results showed that the predicted tool lives were close to the experimental data when the built-up edge formation model appropriately captured this phenomenon in metal cutting. Keywords: predictive models, tool wear, coolant [DOI: 10.1115/1.2714589]

This paper describes the influence of lubrication on wear during testing of materials for artificial knee joints in a rolling/sliding tribotester built to simulate contact conditions in a total knee replacement. The test configuration consists of parallel cylinders (pucks) of ultrahigh molecular weight polyethylene (UHMWPE) and polished cobalt-chrome alloy in oscillatory rolling/sliding contact in a bath of dilute (25%) bovine serum. Wear tests' of three different UHMWPE materials were run under constant load at 40% sliding for 1.5 million oscillation cycles at 1.5 cycles/s. Wear of the UHMWPE was determined by measuring the profile of the cylindrical contact surface of the puck before and after each test. Profile measurements were repeated after at least 53 days to eliminate the contribution from creep. Differences between initial and final profiles were attributed to wear of the UHMWPE. It was found that the largest wear depth in the lubricated tests occurred near the ends of the oscillatory contact area, while dry (unlubricated) tests of the same materials showed a peak wear depth near the center of the contact area. In the lubricated tests, the worn depth was lowest for the most heavily irradiated material. Analysis of the elastohydrodynamic lubrication in the rolling/sliding contact was carried out assuming a line-contact situation with smooth cylindrical surfaces. The time-dependent modified Reynolds equation and the elasticity equation with initial conditions were solved numerically using a multigrid technique with full approximation scheme, and using a Newton Raphson method to solve the highly nonlinear system of equations. The thickness of the lubricating film of bovine serum was determined for points along the length of the wear track. B was found that the smallest film thickness ([h.sub.min]) occurs very close to the location in the oscillating contact where the greatest wear occurs, owing to the very low entraining velocity near the ends of the oscillation cycle. The coefficient (K) for wear of the UHMWPE was found to be relatively constant over the central section of the oscillatory motion, but increased to a higher value where [h.sub.min] decreased to near zero. Thus, the important influence of lubrication on wear of artificial knee bearings was demonstrated [DOI: 10.1115/1.2464130] Keywords: knee prosthesis, oscillatory contact, wear, UHMWPE, elastohydrodynamic lubrication

M50 steel was implanted with nitrogen at elevated temperatures ranging from 260 [degrees]C to 420 [degrees]C using plasma-based ion implantation. The effect of implantation temperature on surface microstructure, hardness, and wear resistance was investigated. It is observed that nitrogen penetrates very deeply from the surface as a result of implantation and thermal diffusion at elevated temperatures. The amount of nitrides and their distribution depth as well as the hardness and the wear resistance in the surface layer increase with the processing temperature. As the implantation temperature increases, the wear mechanism changes from adhesive wear to abrasive wear. Index Terms--Elevated temperature ion implantation, plasma-based ion implantation (PBII), structure, wear.

Very hard and wear-resistant layers are formed after energetic nitrogen insertion into stainless steel. Here, a systematic investigation of the influence of the microstructure is presented. Nitrogen implantation was performed in austenitic, martensitic, and ferritic steels with the samples investigated with respect to formation of expanded phase, nitrogen depth distribution, hardness, and wear. Microstructure strongly affects the diffusion in austenite and has negligible effect in the case of martensitic/ferritic transformations. Index Terms--Microstructure, nitrogen implantation, stainless steel, wear.

To synthesize good diamond-like carbon (DLC) films on the inner surface of a cylinder, [C.sub.2][H.sub.2] plasma should be generated uniformly in the cylinder. In this study, glow discharge [C.sub.2][H.sub.2] plasma was generated by a high pulsed bias voltage applied on the cylinder, and ions were accelerated and implanted into the sample by the same bias. The effect of pulse frequency of the bias and working pressure on the discharge characteristics was investigated. In addition, the ball-on-disk test and Raman spectroscopy were used to characterize the as-deposited DLC films. The test results show that wear resistance of samples increases with the applied voltage, and the friction coefficient of DLC films lies in the range of 0.15-0.20. Index Terms--Diamond-like carbon (DLC) film, inner surface modification, plasma immersion ion implantation (PIII), wear resistance.

An investigation is reported on the wear of single-layer electroplated cubic boron nitride (CBN) grinding wheels and how the wear process affects the wheel topography and grinding behavior. Internal cylindrical and straight surface grinding experiments were conducted over a wide range of conditions on hardened bearing steel with wheels conraining different abrasive grain sizes. The radial wheel wear was characterized in each case by an initial transient at a progressively decreasing rate to a steady-state wear regime at a nearly constant rate until the end of the wheel life. Wheel wear during the initial transient was found to be mainly due to pullout of the most protruding weakly held grains, and the radial wheel wear in the steady-state regime was dominated by grain fracture. The wear rate in the steady-state regime for various grinding conditions and grain sizes was found to be directly related to the undeformed chip thickness. Dulling of the grain tips by attrition and fragmentation caused an increase in the grinding power. Wheel wear was accompanied by a progressive increase in the active grain density and a corresponding decrease in surface roughness. The surface roughness was found to depend mainly on the active grain density and is insensitive to the operating parameters. [DOI: 10.1115/1.2122987]

Accurate wear modeling has always been desired, but has also been difficult and elusive. Most useful wear models have relied on experimental calibration because the physical wear mechanisms are not fully understood. This is particularly true in machining, where contact stresses and temperatures can be extremely high. In machining, the two wear modes most frequently discussed are crater wear and flank wear. Flank wear receives much more attention because it is easier to measure and the mechanism of material loss is thought to be better understood for most machining situations. This work focuses on flank wear for the same reasons. In hard turning, tool life is relatively short and both crater wear and flank wear influence the cutting process substantially. Understanding the progression of flank wear at various cutting conditions is beneficial in itself but the ability to predict this progression will be extremely valuable. This work addresses both. Experimental flank wear progression is shown for uncoated and ceramic-coated polycrystalline cubic boron nitride (PCBN) tools at a range of cutting conditions. These data are used to calibrate a proposed mechanical wear model that predicts the progression of flank wear and tool failure points based on the cutting speed, feed, and cutting depth. The model was validated by additional experiments, which show good agreement with the predictions. [DOI: 10.1115/1.2039097]

Electrode wear is inherent in the resistance spot welding process. It determines the electrical and mechanical contact condition and thus strongly affects the resistance spot weld quality. A practical approach to minimizing the electrode wear effect is to compensate the welding current as the electrodes wear. However, the existing methods for welding current compensation rely on either a predetermined stepper schedule or an expulsion detection algorithm. These methods are not reliable since the welding current is not determined based on the contact condition for each weld made in the welding process. This paper presents an on-line electrode wear estimation approach to determining the contact condition and the welding current needed to make every weld a good weld during the entire life of the electrodes. In the study, an incrementally coupled finite element simulation was first formulated to analyze the contact area behavior in the resistance spot welding process. A lumped parameter model was then developed to characterize the contact area change with the dynamic resistance measurement. A calibration and an estimation algorithm were subsequently devised for on-line applications. The proposed approach has been validated with experimental data. The results have shown that the estimation algorithm is robust under various process conditions including both welding current and electrode force. [DOI: 10.1115/1.2034516]

The impact of frictional forces on the overall forces when drilling with a PDC bit has previously been implied by models and by single cutter and bit tests. This report describes new experiments to measure friction between three different bit surface materials and two different rocks over a wide range of normal stresses in up to four different fluids. Polished PDC cutters are shown to have lower frictional forces on the face of the cutter than standard cutters in both water and mineral oil. The measured friction coefficients were generally higher than reported in previous studies. [DOI: 10.1115/1.1485745]

Pavement surface texture significantly contributes to tire wear and tire-pavement friction. Currently available relationships quantify tire wear and tire-pavement friction simply in terms of empirical pavement texture parameters. The objective of this paper is to present correlations with which the tire wear rate and tire-pavement friction on smooth concrete pavements can be predicted using actual texture properties. Using a laboratory tire wear simulator and an aircraft tread-rubber block, a number of wear and friction tests are performed on pavement samples having different fine aggregate sizes. Frequency characteristics of the texture of the pavements are achieved by decomposing the profilometer measurements using the fast Fourier transform technique and constructing power spectral density plots of texture over surface spatial frequency. Then the tire wear rates as well as dry friction and wet friction of the tire-pavement interface are correlated to microtexture and macrotexture components of the texture power spectral density. The developed correlations indicate that both tire wear and dry friction are significantly affected by pavement microtexture. The developed wear correlations can be also useful for predicting the wear index of a pavement based on conventional Mu-meter and grease patch test results. This is illustrated by an example in which the wear index for a concrete runway pavement at Luke Air Force Base, Ariz., is computed using the new relations.

This paper investigates a flank wear estimation technique in turning through wavelet representation of acoustic emission (AE) signals. It is known that the power spectral density of AE signals in turning is sensitive to gradually increasing flank wear. In previous methods, the power spectral density of AE signals is computed from Fourier transform based techniques. To overcome some of the limitations associated with the Fourier representation of AE signals for flank wear estimation, wavelet representation of AE signals is investigated. This investigation is motivated by the superiority of the wavelet transform over the Fourier transform in analyzing rapidly changing signals such as AE, in which high frequency components are to be studied with sharper time resolution than low frequency components. The effectiveness of the wavelet representation of AE signals for flank wear estimation is investigated by conducting a set of turning experiments on AISI 6150 steel workpiece and K68 (C2) grade uncoated carbide inserts. In these experiments, flank wear is monitored through AE signals. A recurrent neural network of simple architecture is used to relate AE features to flank wear. Using this technique, accurate flank wear estimation results are obtained for the operating conditions that are within in the range of those used during neural network training. These results compared to those of Fourier transform representation are much superior. These findings indicate that the wavelet representation of AE signals is more effective in extracting the AE features sensitive to gradually increasing flank wear than the Fourier representation.

Exponential growth in both capacity and performance has been exhausting a lot of existing technologies in magnetic hard disk drive industry, one of them being laser zone texturing. Maintaining such a rapid growth requires innovative technologies. Adding landing pads to a slider's air bearing surface (ABS) appears to be able to further stretch the glide/stiction envelope into the ultra-low glide and stiction regime. To materialize this new technology, the pad wear needs to be minimized, underlying the importance of the fast take-off air bearing characteristics. This paper analyzes the slider's landing pad designs for fast take-off performance through the partial contact air bearing simulation of a take-off process. Two landing pad designs (3-pad and full texture) are created on a subambient pressure ABS. The contact force and its center profiles as well as the evolution of the contact pressure contour are used to characterize the movement of the contact location during the take-off process. The effects of the absolute and relative pad heights as well as the rear pad location on both the transition of the contact location and the rate of contact force decrease are calculated. While raising leading pads delays the transition of the contact location from the leading pads to rear pad, distancing the rear pad from the trailing edge greatly facilitates the movement of the contact location from the rear pad to the trailing edge. A fully textured ABS with a reasonably low and uniform pad height as well as rear pads being well distanced from the trailing edge offers a fast take-off performance.

In our study, we investigated the wear, mechanical and tribological properties of plasma and pulse plasma nitrided AISI 4140 steel compared to hardened steel. Contact surfaces of the samples were fully characterized using metallographic, SEM microscopic, microhardness, and profilometric techniques, before and after wear testing. Wear tests were performed on a pin-on-disk wear testing machine in which nitrided pins were mated to hardened ball bearing steel disks under dry sliding conditions. Results show only slight improvement of the tribological properties of AISA 4140 steel after plasma and pulse plasma nitriding compared to hardening. However, improvements become more evident when testing conditions become more severe. It was also found that compound layer should be removed from the nitrided surface to avoid impairment of the tribological properties by fracture of hard and brittle compound layer followed by the formation of hard abrasive particles.

Experiments were conducted using a gear-cam adapter to simulate line-contact lubrication and wear in a lubricant with various additive concentrations. In this study, the growth of an adsorption film and a chemical film in oil lubrication can be detected by the electrical contact resistance (ECR) apparatus of a wear testing machine. A constant current source was applied; the electrical voltage is thus obtained if the ERC is available. Roller wear rate and wear loss are formulated in terms of roller-lower specimen contact temperature and several relevant parameters. In addition, wear loss is also related to the rise of electrical voltage during the period of lubrication. The experimental data for wear rate and wear loss can be regressed by the models proposed for various additive concentrations. The roller's wear rate can be predicted through the investigation of the combined effect of growth in electrical voltage and its commencement. For lowering wear rate, the optimum additive concentration in a lubricating oil is determined under various operating conditions.

Flow-induced vibration of steam generator (SG) tubes may sometimes result in fretting-wear damage at the tube-to-support locations. Fretting-wear damage predictions are largely based on experimental data obtained at representative test conditions. Fretting-wear of SG materials has been studied at the Chalk River Laboratories for two decades. Tests are conducted in fretting-wear test machines that simulate SG environmental conditions and tube-to-support dynamic interactions. A new high-temperature force and displacement measuring system was developed to monitor tube-to-support interaction (i.e., work-rate) at operating conditions. This improvement in experimental fretting-wear technology was used to perform a comprehensive study of the effect of various environment and design parameters on SG tube wear damage. This paper summarizes the results of tests performed over the past 4 yr to study the effect of temperature, water chemistry, support geometry, and tube material on fretting-wear. The results show a significant effect of temperature on tube wear damage. Therefore, fretting-wear tests must be performed at operating temperatures in order to be relevant. No significant effect of the type of water treatment on tube wear damage was observed. For predominantly impacting motion, the wear of SG tubes in contact with 410 stainless steel is similar regardless of whether Alloy 690 or Alloy 800 is used as tubing material or whether lattice bars or broached hole supports are used. Based on results presented in this paper, an average wear coefficient value is recommended that is used for the prediction of SG tube wear depth versus time.

An analytical model for the chatter frequency of a turning cutter considering system compliance and flank wear of the tool is presented in this research. The fundamental mechanism of self-excited vibration at the presence of tool wearland is examined, and a mathematical model is developed to describe the frequency characteristics of the vibration. In the paper a comparison of the chatter frequencies for afresh cutting tool and a worn cutting tool is provided to demonstrate the coupling between wearland and chatter. The theoretical model of chatter frequency is validated by experimental observations over a range of turning conditions.

This paper completes previous studies concerning the mechanisms governing friction and wear of a steel/graphite couple under an external applied magnetic field. Friction tests were performed in a controlled chamber with a magnetised steel pin sliding against a graphite disk exposed to oxygen, argon, and vacuum environments. Wear debris and friction tracks generated by reactions with the gases after sliding, with and without magnetic field, were identified ex situ by scanning electron microscopy and energy-dispersive X-ray analysis. It shows that the magnetic field modifies the third body behavior which depends on the gases surrounding the contact; this governs the friction state, the type of graphite wear (fatigue or abrasive wear), and the surface reactivity.

The friction and wear properties of unmodified ultra-high molecular weight polyethylene (UHMWPE) were investigated experimentally. Disks of semicrystalline UHMWPE were slid against polished CoCrWNi pins in bovine serum at ranges of contact pressure and sliding speed typical of those encountered in total joint replacements. The coefficient of friction was monitored continuously during testing, and the wear rate was determined from surface profilometry measurements of worn disk surfaces accounting for strain relaxation. Scanning electron microscopy (SEM) results demonstrated that surface deterioration comprises adhesion, third-body abrasion by polyethylene wear debris, and delamination wear. The contribution of these mechanisms to the overall wear rate and the formation of wear debris depends predominantly on the contact pressure and secondarily on the sliding speed. Transmission electron microscopy (TEM) yielded new insight into the evolution of the microstructure morphology of UHMWPE during sliding. Cross sections parallel to the wear tracks obtained from various depths were analyzed with the TEM to develop a spatial mapping of the subsurface microstructure as a function of contact pressure. Alignment of crystalline regions (lamellae) in the polyethylene microstructure parallel to the sliding surface was found to occur during sliding even at relatively low contact pressures. SEM observations suggested that the highly oriented microstructure is the precursor to delamination wear, leading to the formation of wear particles larger than those produced by adhesion and third-body abrasion at the contact interface.

To explore the feasibility of 'oil-free' pressworking, we investigated the effects on the life of SKD11 steel dies and the quality of phosphor bronze workpieces under lubricated and unlubricated or dry conditions. In addition, the performance of SKD11 dies coated with TiN as well as cemented tungsten carbide dies were also examined under dry conditions. Results show that the life of unlubricated SKD11 dies is about half of that under lubricated conditions. The cemented tungsten carbide die gives superior die life and workpiece quality even under dry use conditions.

It is generally known that the humidity in the surrounding atmosphere influences wear processes in general. For fretting wear several authors examined the influence of humidity on the wear scar morphology and the composition of the wear debris. No agreement between the different results has been found, yet. In the present study, a distinction is made between running-in and steady-state fretting wear. Especially for the running-in stage, the influence of the humidity in ambient air on the friction and wear behavior and material transfer of steel surfaces subjected to contact vibrations has been investigated. The fretting experiments were conducted with a spherical against a fiat specimen under gross-slip regime. The fretting wear and accompanying material transfer between the contacting specimens quantitatively are measured with Thin Layer Activation method. It has been observed that high ambient humidity has a beneficial influence on the running-in fretting wear of steel surfaces. It has also been found that the results of several authors concerning the influence of humidity on the fretting wear of steel have to be treated with great care, as classical wear measuring techniques can give erroneous wear results.

The friction and wear micromechanisms of amorphous hydrogenated carbon films were investigated experimentally using commercially available thin-film rigid disks with sputtered carbon overcoats and [Al.sub.2][O.sub.3]-TiC magnetic recording heads. Continuous sliding tests demonstrated the existence of two distinct friction and wear regimes characterized by different dominant micromechanisms. Scanning electron microscopy and Raman spectroscopy revealed that the evolution of friction in the first regime is due to changes of the surface microtopography and the film structure from amorphous carbon to polycrystalline graphite. Atomic force microscopy showed that the topography changes result from asperity nanofracture leading to the gradual removal of carbon material and the generation of ultrafine wear debris. The friction behavior in the second regime is due to various wear processes arising on the carbon film surface. High friction promotes surface micropitting and the formation of significantly deeper and wider texture marks. The erratic fluctuations of the friction force and microplowing of the carbon film at steady state are attributed to the relatively large wear particles generated by micropitting.

A model for the steady-state wear behavior of polymer composite materials, including the effects of preferential load support by and surface accumulation of wear-resistant filler particles, is further developed. It is shown that the resultant inverse rule-of-mixtures description of steady-state composite wear rate behavior is independent of the assumed form of filler contact pressure, though preferential load support does affect the degree of surface accumulation of filler particles that occurs. The validity of these descriptions of steady-state wear behavior and surface accumulation as functions of bulk filler volume fraction are investigated by experiments with copper particle-filled PTFE composites for bulk filler volume fractions from 0 to 40 percent. The applicability of the description of surface accumulation for this composite system was limited to bulk filler volume fractions less than 20 percent, a hypothesized result of transition in load-sharing between filler and matrix. The inverse rule-of-mixtures description of steady-state wear rate, however, was maintained over the full range of volume fractions investigated.

Pin-on-disk wear tests of carbon steels in saline solution were carried out at high loads to study the effects of mechanical and chemical factors on the transition between severe and mild wear. The factors were load, presliding time, concentration of saline solution, dissolved oxygen content, and applied potential for cathodic protection. Severe wear and seizure appear at low concentration levels of saline solution and the transition takes place at a certain concentration level of saline solution. The concentration level for the transition is higher under argon-saturated condition than under air-saturated condition. Mild wear is predominant over the whole range of dissolved oxygen content from 0.5 to 18 ppm in 0.5 wt percent saline solution and the wear rate decreases with decreasing dissolved oxygen content. The mild wear occurs in the range from 2 to 18 ppm in 0.01 wt percent saline solution, whereas the wear mode moves to severe wear below 2 ppm. Mild wear predominates under incomplete cathodic protection between -0.50 and -0.80 V (versus Ag/AgCl) in 0.5 wt percent saline solution. The applied potential for the transition from initial to steady wear is more negative under higher dissolved oxygen content condition. Complete severe wear occurs below -0.90 V (versus Ag/AgCl) with a risk of seizure.

The mechanical properties of SiC films grown via [C.sub.60] precursors were determined using atomic force microscopy (AFM). Conventional silicon nitride and diamond-tipped steel AFM cantilevers were employed to determine the film hardness, friction coefficient, and elastic modulus. The hardness is found to be 26 GPa by nanoindentation of the film with a Berkovich diamond tip. The friction coefficient for the silicon nitride tip on the SiC film is about one half to one third that for silicon nitride sliding on a silicon substrate. By combining nanoindentation and AFM measurements an elastic modulus of [approximately]300 GPa is estimated for these SiC films.

Acoustic emission (AE) has previously been shown to be a useful technique in monitoring the state of wear of cutting tools. The piezo-electric transducers conventionally used for AE detection are contacting devices with a limited bandwidth. This paper describes the use of a robust fiber optic interferometer for the in-process measurement of AE during the face milling of annealed En24 steel to provide tool wear information via analysis of the rms AE signal. The interferometer displayed an improved diagnostic capability over a conventional piezoelectric sensor due to its advantages of being non-contacting, broadband with a fiat frequency response to displacement, and providing absolute calibration.

In this paper, a unified method for constructing dynamic models for tool wear from prior experiments is proposed. The model approximates flank and crater wear propagation and their effects on cutting force using radial basis function neural networks. Instead of assuming a structure for the wear model and identifying its parameters, only an approximate model is obtained in terms of radial basis functions. The appearance of parameters in a linear fashion motivates a recursive least squares training algorithm. This results in a model which is available as a monitoring tool for online application. Using the identified model, a state estimator is designed based on the upperbound covariance matrix. This filter includes the errors in modeling the wear process, and hence reduces filter divergence. Simulations using the neural network for different cutting conditions show good results. Addition of pseudo noise during state estimation is used to reflect inherent process variabilities. Estimation of wear under these conditions is also shown to be accurate. Simulations performed using experimental data similarly show good results. Finally, experimental implementation of the wear monitoring system reveals a reasonable ability of the proposed monitoring scheme to track flank wear.

A procedure is formulated to model impact and abrasion wear of surfaces exposed to a fluidized bed. A methodology adapting a single-particle wear model and the kinetic theory of gases to granular flows is used to develop a model accounting for impact wear from all possible particle collisions. Abrasive wear is modeled using a single-particle abrasion model adapted to describe the effects of many abrading particles. Parameters describing granular flow are necessary for evaluation of the resulting wear expressions. They are determined by numerical solution of the conservation equations describing fluidized-bed hydrodynamics. Additional parameters appear in the wear expressions which describe the contact between individual fluidized particles and the wearing surface. These are determined by an optimization procedure which minimizes error between predicted and measured wear rates. The modeling procedure was used to analyze several bubbling and turbulent fluidized bed experiments with single-tube and tube bundle configurations. Quantitative agreement between the measured and predicted wear rates was found, with some exceptions for local wear predictions. This work demonstrates a methodology for wear prediction in fluidized beds.