Observed Wear Rates Research Articles

A Phenomenological Model for Estimating the Wear of Horizontally Straight Slurry Discharge Pipes: A Case Study

When a slurry TBM advances in pebble and rock strata, large rock particles are carried in pipelines out of a tunnel by moving slurry. To estimate the wear of horizontally straight slurry discharge pipes, a phenomenological model was proposed that was mainly based on knowledge gained by means of direct and indirect in situ observations. The proposed model applies an equation composed of three variables, namely, the wear rate (λ), the central angle (2α), and the excavated tunnel length (L), to estimate the wear distribution along a pipe’s internal surface. The results indicated that wear mainly occurred on the bottoms of pipes. In addition, linear relationships between the maximum pipe wear amount (δmax) and the excavated tunnel length (L) were found for specific pipes and specified types of ground. The observed wear rates of different pipes in different types of ground had varied constants. The wear rates were higher for pipes in rock ground than for those in a pebble layer. For horizontally straight pipes, the observed wear rates were 0.0045 mm/m in a pebble layer and 0.0212 mm/m in rock ground. Lastly, to improve the proposed model, more field monitoring will be necessary to determine the pipe wear rates in different types of ground in the future.

Experimentation and optimization of wear behavior on polytetrafluoroethylene composites using response surface methodology and bald eagle search optimization

AbstractIn Industries, polytetrafluoroethylene (PTFE) is used as a solid lubricant due to its excellent toughness, lack of reactivity, high‐thermal stability, and so forth. However, the abrasive resistive behavior is minimal for the virgin PTFE polymer. In this study, the wear and coefficient of friction (COF) of PTFE composite prepared by the combination of 10% halloysite, 10% graphite, and 10% bronze are investigated. The investigations are performed on a pin‐on‐disc test rig and analysis is done by response surface methodology (RSM), especially in Box‐Behnken Design (BBD). The experimentation is performed by varying the sliding distance (Ds), sliding velocity (Vs), and applied load (L). In the analysis of COF, the load is considered as a significant parameter, and sliding distance is an influencing parameter for wear rate. From the experimentation, the proposed PTFE composite promotes COF of 0.0052 and a wear rate of 0.62 × 10−5 mm3/Nm. Such observed wear rate and COF are 2.8 times and 1.5 times better than the pure PTFE. The experimented outcomes are validated using hybrid DBN‐based bald eagle search optimization (DBN‐BESO), and RSM. From the validated results, the proposed hybrid DBN‐BESO prediction process using the Matlab platform promotes closer values to the experimented outcomes. Besides, the parametric optimization is conducted using RSM and BESO approaches with the objective of minimum wear rate and COF. The optimized BESO results are superior to the RSM. BESO‐based optimized wear rate is 0.0317 × 10−5 mm3/Nm and COF is 0.0352.

Comparison of long-term kinematics and wear of total knee arthroplasty implant designs

We sought to evaluate wear and kinematics in well-established implants of posterior stabilized (PS) and cruciate retaining (CR) designs. Ninety-one knees implanted for at least five years were examined. The implants were Genesis II PS (Smith & Nephew, Memphis, TN), Sigma PS (DePuy Synthes, Warsaw, IN), or Sigma CR. Radiostereometric analysis (RSA) images were acquired at multiple flexion angles and the 3D positions of the implant components were determined using model-based RSA software. The location of the center of the contact area between the femoral and polyethylene components was used to obtain contact kinematics, and the magnitude of the virtual intersection between the components indicated linear wear. All three groups had paradoxical anterior motion on both condyles, experienced similar net external rotation, and exhibited instances of internal rotation during flexion. The maximum observed wear rate was significantly greater for the Sigma PS than the Genesis II PS on the medial condyle (mean difference = 0.032 mm/year, p = 0.044), but not the lateral condyle, while there was no difference between the Sigma PS and Sigma CR for either condyle. Knees with lateral condylar separation had greater maximum wear rates on the medial condyle (mean difference = 0.033 mm/year, p = 0.001), while those with medial condylar separation had greater maximum wear rates on the lateral condyle (mean difference = 0.044 mm/year, p = 0.014). At long term follow-up in patients with well-functioning implants, there were differences in kinematics and wear resistance between implants. These results suggest that implant design affects long-term kinematics and wear in well-functioning implants and that condylar separation should be avoided to minimize wear.

Understanding and modelling wear rates and mechanisms in fretting via the concept of rate-determining processes - Contact oxygenation, debris formation and debris ejection

A new framework which describes the role of three key processes in fretting wear of metals is proposed, with these three processes being: (i) oxygen transport into the contact; (ii) formation of oxide-based wear debris in the contact and (iii) ejection of the wear debris from the contact. Based upon a physical understanding, rate equations for the three key processes are proposed, which provide a basis for the influence of test parameters (such as contact geometry, applied load, slip amplitude, fretting frequency etc) on the three rates to be understood. To maintain system equilibrium in steady-state fretting, the three processes must operate at the same rate as each other (debris cannot be ejected from the contact faster than it is formed, and debris cannot be formed faster than it is ejected). Accordingly, the observed wear rate is the rate of the process with the lowest rate of the three processes, with this process being termed the rate-determining process. The effect of test parameters on the three key processes differs, and thus the effect of changes in any test parameter on the observed rate of wear will itself be dependent upon which of the three processes is rate-determining.A number of assumptions have been made in deriving the equations which describe the key processes and it is recognised that these equations themselves may be refined in light of future research; however, any such revised equations can simply replace those proposed as part of the rate-determining process framework.The framework can be applied to both conforming and non-conforming contact geometries. In tests with non-conforming contact geometries, the contact size increases with wear; since it is proposed that the rates of two of the three processes (oxygen transport and debris ejection) are dependent upon the size of the contact, the rate determining process can change during such a test and the rate of wear will continually fall when either of these processes are rate-determining. This complexity means that the evolution of the wear volume can only be evaluated numerically through the use of a time-marching analysis in such cases. In contrast, in tests with conforming contact geometries, the contact size does not change as wear occurs, and so there will be no changes in the rate-determining process as wear proceeds.It is recognised that this framework addresses wear under steady-state conditions and does not consider the initial period of exposure where steady-state conditions are being developed. In the case of conforming contacts where the contact size is large, the duration of the initial transient period may be substantial and may form a significant proportion of the test duration or component lifetime. This needs to be recognised both in the design of tests and in the application of this framework.

Quantitative ultrahigh-molecular-weight polyethylene wear in total elbow retrievals

The purpose of this study was to evaluate ultrahigh-molecular-weight polyethylene (UHMWPE) wear and damage from retrieved total elbow arthroplasty components and compare invivo wear with wear produced invitro. Explanted total elbow components were collected at revision surgery. UHMWPE damage was characterized visually, whereas penetration and wear were quantified using micro-computed tomography and gas pycnometry. Volumetric wear rates were compared with historical hip data, and wear data were compared with reported invitro wear test data. Humeral bushing damage primarily occurred in the form of burnishing, scratching, and pitting at the articular face in the region of contact with the ulnar component. Wear of the ulnar bushings was concentrated on the edge of the component at the point of contact with the axis pin. Pitting and embedded debris were dominant damage modes, in addition to burnishing and delamination. Backside wear was negligible. The median linear penetration rates of the lateral, medial, and ulnar bushings were 0.14 mm/yr (range, 0.01-0.78 mm/yr), 0.12mm/yr (range, 0.03-0.55 mm/yr), and 0.11 mm/yr (range, 0.01-0.69 mm/yr), respectively. The volumetric wear rates of the lateral, medial, and ulnar bushings were 5.5 mm3/yr (range, 0.7-37.2 mm3/yr), 5.9 mm3/yr (range, 0.6-25.5 mm3/yr), and 5.5 mm3/yr (range, 1.2-51.2 mm3/yr), respectively. The observed wear rates were similar to those reported in well-functioning total hip replacement patients with conventional UHMWPE bearings. We found limitations in reported invitro testing resulting in wear that was not consistent with our retrieval data. We recommend further investigation to clinically validate invitro simulation to provide appropriate loading protocols for elbow wear simulation.

Effect of Y2O3 addition on tribological properties of plasma sprayed Al2O3-13% TiO2 coating

The effect of Y2O3 addition on structure, mechanical properties and tribological properties of Al2O3-13 wt% TiO2 coating was investigated. The addition of 20 wt% Y2O3 resulted in better densification, stabilization of alpha (α) alumina phase and improvement in fracture toughness of Al2O3-13 wt% TiO2 coating. Abrasive wear tests were performed over a range of loads and sliding speeds. The stabilization of α alumina phase further increased with an increase in severity of wear test conditions, as noted from X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) analysis of worn coatings. Al2O3-13 wt% TiO2-20 wt% Y2O3 coating displayed lower friction coefficient and lower abrasive wear rate than Al2O3-13 wt% TiO2 coating, which was due to synergistic effect of α alumina phase and formation of magneli phase oxide of titanium; Ti2O3. Friction energy map was used to rationalize observed wear rates, to identify different regimes of wear and degradation modes of coatings.

Water content, effective stress, and rotation speed impact on the abrasivity of granular soils in LCPC test results

The development of mechanized tunneling technology and the extent of its application in the soft grounds have revealed the importance of soil abrasivity studies more. As one of the first methods of soil abrasivity assessment, LCPC test is widely used in predicting the wear of cutting tools in soft grounds. In this study, the effect of water content, rotation speed, and applied stress on the abrasivity of crushed silica particles are investigated with the LCPC tests. The results showed that water content has a considerable effect on the abrasive behavior of silica particles. The occurrence of drainage during the tests considerably changed the dominant conditions of moisture and affected the observed wear rates. The obtained correlation between the effective stress levels and recorded wears showed that the theory of granular soils compaction can be used to describe the variations of soil abrasivity with water content changes. Moreover, the results showed a direct linear correlation between the rotation speed of steel propellers and measured wears. The same correlation was also found between effective stress levels and wear amounts. However, in the samples with higher water content than 10 percent, the effect of stress on the wear rates increases with the increase of propeller rotation speed.

Estimation of wear rate in dual phase steel on the basis of the load sharing between constituent phases

Model has been for proposed for estimating the wear rate in dual phase (DP) steel for the run-in and the steady state of wear based on estimated load sharing between the constituent phases i.e., ferrite and martensite. The model has been checked by conducting pin-on-disc sliding wear tests on DP steel, Armco (pure) iron and fully martensitic steel (FMS) samples at normal loads of 14.7, 19.6, 24.5, 29.4 and 34.3 N and at a fixed sliding velocity of 1.15 m/s. Armco iron and FMS simulate the constituent phases in DP steel i.e., ferrite and martensite. The wear rates predicted by the proposed model have been found to match well with the experimentally observed wear rates in the regime of lower loads for the steels containing relatively lower volume fraction of martensite. However, wear rates have increasingly larger difference at higher loads. The difference in the estimated and the observed wear rates has been attributed to the flow of the softer phase of ferrite over the hard martensite islands and its relatively higher rate of wear.

Impact of Free Glasses and a Teacher Incentive on Children's Use of Eyeglasses: A Cluster-Randomized Controlled Trial.

To study the effect of free glasses combined with teacher incentives on in-school glasses wear among Chinese urban migrant children. Cluster-randomized controlled trial. Children with visual acuity (VA) ≤6/12 in either eye owing to refractive error in 94 randomly chosen primary schools underwent randomization by school to receive free glasses, education on their use, and a teacher incentive (Intervention), or glasses prescriptions only (Control). Intervention group teachers received a tablet computer if ≥80% of children given glasses wore them during unannounced visits 6 weeks and 6 months (main outcome) after intervention. Among 4376 children, 728 (16.7%, mean age 10.9 years, 51.0% boys) met enrollment criteria and were randomly allocated, 358 (49.2%, 47 schools) to Intervention and 370 (50.8%, 47 schools) to Control. Among these, 693 children (95.2%) completed the study and underwent analysis. Spectacle wear was significantly higher at 6 months among Intervention children (Observed [main outcome]: 68.3% vs 23.9%, adjusted odds ratio [OR] = 11.5, 95% confidence interval [CI] 5.91-22.5, P < .001; Self-reported: 90.6% vs 32.1%, OR = 43.7, 95% CI = 21.7-88.5, P < .001). Other predictors of observed wear at 6 months included baseline spectacle wear (P < .001), uncorrected VA <6/18 (P = .01), and parental spectacle wear (P = .02). The 6-month observed wear rate was only 41% among similar-aged children provided free glasses in our previous trial without teacher incentives. Free spectacles and teacher incentives maintain classroom wear in the large majority of children needing glasses over a school year. Low wear among Control children demonstrates the need for interventions.

Studies on wear rate and micro-hardness of the Al/Al2O3/Gr hybrid composites produced via powder metallurgy

Micro-structural characterization of the composites has revealed fairly uniform distribution and some amount of grain refinement in the specimens. Further, it was observed that the micro-hardness improve when increasing the milling time and the reinforcement content due to presence of hard Al2O3 particles. Was also observed a low wear rate exhibited by the Al/Al2O3/Gr hybrid composites due to presence of Al2O3 and Gr which they acted as load bearing elements and solid lubricant respectively. The observed wear rate and micro-hardness have been correlated with microstructural analyses.

Synthesis and Characterization of Al/Al3Fe Nanocomposite for Tribological Applications

Aluminum based composites find diverse applications due to their superior mechanical and physical properties. Aluminum matrix nanocomposites have been synthesized with Al3Fe nanocrystalline intermetallics reinforcement using the powder metallurgy route. The prepared composites have been characterized for various physical and mechanical properties such as density measurement, bulk hardness, compressive strength, and tribological properties. The theoretical coefficient of the linear thermal expansion has also been predicted. The composite shows a high strength to weight ratio and excellent wear resistance, along with a low coefficient of friction. The observed wear rate is superior to other composites irrespective of the load and sliding velocity chosen for the study and it continuously decreases withan increasing amount of dispersoid.

Polycrystalline diamond bearing testing for marine hydrokinetic application

Polycrystalline diamond (PCD) bearings are ideally suited for use in extreme environments because of their extraordinary thermal and mechanical properties. Past use of PCD in process-fluid-lubricated down-hole tool applications, such as those in oil and gas drilling turbines, have proven them to be robust, long lasting, and rugged. Another harsh environment where the use of PCD bearings makes sense is underwater in marine hydrokinetic (MHK) energy machines. Through a grant from the United States' Department of Energy (DOE), contract #DE EE0003633, US Synthetic performed tests to evaluate a PCD thrust bearing operating in a water environment. This paper discusses the data collected and the lessons learned from this testing. Laboratory tests that measured bearing capacity, hydrodynamic properties and diamond wear rates are presented that can help predict the performance of PCD in MHK applications. Three important results were discovered. First, when compared to bearings tested in oil, the bearing capacity was increased by using water as a cooling medium due to its higher convective heat transfer coefficient. Second, the PCD thrust bearings were able to endure 6000 stops and starts in a test imitating years of life of a tidal power generator with no signs of damage or failure. Third, the small observed wear rate of the diamond would extend the life of a typical bearing in MHK applications. In addition, it was observed that the wear rate decreased as the surface finish of the bearing improved. These key points and other subjects discussed herein illustrate that PCD thrust bearings can provide a robust, long lasting, and low maintenance bearing in MHK applications.

Defect Structures in Diamond Composite Coated Cemented Tungsten CarbideSubstrates

Variability in the abrasive wear of PCD coatings on cemented WC substrates has been investigated. Six samples of PCD coated carbides were tested in a wear testing rig. The PCD coated element was used to turn an industry standard vitrified bonded corundum grinding wheel. The wear rate was measured as the weight loss of the cutting element per cubic metre of grinding wheel machined during the test. Two grades of cutting elements were observed. One grade had wear rates between 6 and 7.3 g/m³ but of the three poor quality samples, only one valid test was made realising wear rate of ~7,800 g/m³. The microstructures of the samples were studied using SEM, X-ray imaging, neutron diffraction and XRD. SEM images revealed differences in the volume percentage of diamonds in the two grades and the XRD scans highlighted the variable distribution of the diamond phase in the coating. Estimates of the residual stresses in a good and poor quality samples indicated significantly higher compressive stresses in the good quality versus poor quality coating. These results have revealed two extremes in the wear rates of these PCD coated carbides. It is suggested that the difference in diamond content between the two grades is not sufficient to account for the 3 orders-of-magnitude difference in the observed wear rates. However, the presence of intrusive veins of carbide material in the coatings, especially around the curved cutting tip, suggested that the macroscopic defects observed in the x-ray and SEM images were the major cause of the high wear rates in the poor quality sample.

Comparison of sliding wear behaviour of pulse electrodeposited Ni–Cu nanocrystalline alloys and Ni–Cu/Cu multilayers

This study presents a comparison of tribological properties of electrodeposited nanolayered Ni–Cu/Cu multilayers and nanocrystalline Ni–Cu alloys. In this work, nanocrystalline Ni–Cu alloys containing 35·8 and 26·0 wt-%Cu with grain sizes of 12·8 and 6·6 nm respectively were chosen for wear tests in which the tribological performances of these alloys were compared with Ni–Cu/Cu multilayers: [Ni–Cu (4·5 nm)/Cu (1·97 nm)]n (30·4 wt-%Cu) and [Ni–Cu (7·8 nm)/Cu (1·97 nm)]n (20·2 wt-%Cu) respectively. All the test samples were electrodeposited under pulsed current conditions on polished stainless steel substrates keeping total thickness fixed at ∼10 μm. Reciprocating dry sliding experiments of these samples at a constant normal load in the range 3–11 N were performed in ball on plate geometry keeping the amplitude fixed at 0·001 m. The obtained average coefficient of friction of nanocrystalline alloys was found to be slightly inferior compared to that of multilayers. On the other hand, the wear rate of nanocrystalline alloys was lower than that of multilayers under identical conditions. Higher hardness and lower elastic modulus of nanocrystalline alloys compared to that of multilayers was found to be responsible for the observed wear rate variation.

The predictive Power of Surface Profile Parameters on the Amount of Wear MeasuredIn Vitroon Metal-On-Polyethylene Artificial Hip Joints

Various studies report a weak correlation between the average surface roughness R(a) of metallic ballheads and the observed wear rate of the polyethylene cups coupled to them. The aim of this study is to verify, with controlled in vitro experiments, whether other parameters such as the total roughness R(t), and the skewness R(sk) are better predictors of the polyethylene wear when the metallic heads present a surface conditioning that varies substantially from specimen to specimen, as is usually the case with retrieved specimens. Twelve CoCrMo (cobalt-chromium-molybdenum) ballheads were intentionally damaged in order to reproduce a wide spectrum of surface conditioning and were then subjected to the standard wear test against polyethylene cups, using a hip joint wear simulator. After 2 x 10(6) cycles the weight lost by the cups was assessed with a gravimetric procedure, and the surface roughness of the metallic ballheads was qualified in terms of R(a), R(t), and R(sk). The various parameters were correlated to the weight loss using a linear regression analysis. The skewness R(sk) showed a coefficient linear regression R2 = 0.80, while the average roughness R(a), used in most previous studies, presented an R2 = 0.56. It was concluded that when specimens with substantially different surface conditioning are compared, as in retrievals analysis, it is also important to report the skewness R(sk) so that qualify the surface roughness of the specimens can be qualified.

Tribochemical wear of sodium trisilicate glass at the nanometer size scale

We report measurements of single-asperity wear on sodium trisilicate glass in basic solution using atomic force microscopy (AFM), where the silicon nitride tip was used both to tribologically load and image the surface. Single-asperity micron-square polishing was performed by rastering the AFM tip in a square pattern. More localized, “nano”-machining was performed by drawing the AFM tip back and forth across the substrate in a linear fashion. In both modes, the wear rate gradually slowed during prolonged scanning. Changes in contact stress due to the wear of the AFM tip dramatically affect the observed wear rates. The changes in surface elevation for both the tip and the substrate display the same dependence on true stress and time for the case of square-raster scanning over micron dimensions. In the case of linear reciprocal scanning, conformal wear substantially modifies the rates and morphology of the wear of both the tip and the substrate.

Evaluation of the Reciprocating-Wear Behavior of Unlubricated Hypereutectic Al-Si Alloys

The reduction of abrasive and scuffing wear between aluminum and cast-iron wear-pairs is an important goal for the automotive industry given the implications for improved engine performance and reliability. Hypereutectic aluminum-silicon alloys such as B390 may help lead the way towards this goal because of their potential for wear resistance and durability. Yet, despite this potential, B390 has not been evaluated under the severe reciprocating conditions typical of automotive applications. Moreover, the influence of various manufacturing and processing steps on the resulting wear resistance of the alloy has not been studied at all. To help fill this void, a series of unlubricated tests were conducted using cast, spray-formed, spray-formed then extruded, and semi-solid formed variations of B390 reciprocated against gray cast-iron under a constant contact-stress. Originally, the weight-loss per reciprocating distance was measured and converted to volume-loss to determine the steady-state wear rates for each alloy variation. However, it was determined that debris from the mating cast-iron surface was adhering to the B390 and obscuring the actual material lost to wear. To compensate for the trapped iron debris, the volume-loss was directly calculated from the changing contact area or “flat” originally measured for the loading adjustments. After this correction, the data indicated that the spray-formed, spray-formed then extruded, and semi-solid formed all experienced measurable, albeit modest decreases in their wear rates relative to the cast B390. However, there were not any significant disparities in the observed wear rates between the spray-formed, spray-formed then extruded, and semi-solid formed hypereutectic alloy despite their processing and microstructural differences.

Slide track analysis of the relative motion between femoral head and acetabular cup in walking and in hip simulators

Joint simulators are important tools in wear studies of prosthetic joint materials. The type of motion in a joint simulator is crucial with respect to the wear produced. It is widely accepted that only multidirectional motion yields realistic wear for polyethylene acetabular cups. Multidirectionality, however, is a wide concept. The type of multidirectional motion varies considerably between simulators, which may explain the large differences in observed wear rates. At present, little is known about the relationship between the type of multidirectional motion and wear. One illustrative way to compare the motions of various hip simulators is to compute tracks made on the counterface by selected points of the surface of the femoral head and acetabular cup due to the cyclic relative motion. A new computation method, based on Euler angles, was developed, and used to compute slide tracks for the three-axis motion of the hip joint in walking, and for two hip simulators, the HUT-3 and the biaxial rocking motion. The slide track patterns resulting from the gait waveforms were found to be similar to those produced by the HUT-3 simulator. This paper is the first to include a verification of the computed simulator tracks. The tracks were verified in the two simulators using sharp pins, embedded in acetabular cups, engraving distinct grooves onto the femoral heads. The engravings were identical to the computed tracks. The results clearly differed from earlier computations by another research group. This study is intended to start a thorough investigation of the relationship between the type of multidirectional motion and wear.

The effect of minimum load on the fluid uptake and wear of highly crosslinked UHMWPE total hip acetabular components

Thirteen total hip replacement acetabular components of the same design (32mm diameter, cup liners made of highly crosslinked ultra-high molecular weight polyethylene (UHMWPE)) were tested in an AMTI hip simulator (six in wear stations and seven in load-soak stations). Two additional liners were immersed in undiluted bovine calf serum but not loaded. The test conditions were otherwise similar for all wear and load-soak samples, with the following exceptions: (a) no motion was applied onto load-soak liners; (b) the minimum load during the swing phase was set at 40N for three of the wear liners and four of the load-soak liners (group A: low minimum load), and 230N for the remaining three wear liners and three load-soak liners (group B: high minimum load). It was found that: (a) load-soak liners gained about 10 times more weight than no-load soak liners; (b) load-soak liners in the low minimum load group gained twice as much weight as those in the high minimum load group, and (c) the observed wear rates were low for both groups; surprisingly, however, the wear rates of the low minimum load liners were also higher than those of the high minimum load liners. This study showed for the first time that the fluid uptake and wear rates of highly crosslinked UHMWPE are sensitive to small differences in the loading pattern.

Brake Wear Particulate Matter Emissions

Current particulate matter (PM) emission factor models estimate brake wear particulate matter emission rates using data derived from asbestos brakes. However, most brake pads are now produced from nonasbestos materials. Little work has been performed on emissions from brakes using these materials. Therefore, a brake wear study was performed using seven brake pad formulations that were in high volume use in 1998. Included were semi-metallic brakes, brakes using potassium titanate fibers, and brakes using aramid fibers. Brakes were tested on a brake dynamometer under four wear conditions. On average, 35% of the brake pad mass loss was emitted as airborne PM. The observed wear rates correspond to vehicle emission rates of 5.1−14.1 mg/mi. On average, 86 and 63% of the airborne PM was smaller than 10 μm in diameter (PM10) or 2.5 μm in diameter (PM2.5), respectively. The large number of particles observed in some wear tests was attributed to condensation, a process that is highly dependent on dilution condition...