Flat Wear Research Articles

On dental wear, dental work, and oral health in the type specimen (LB1) of Homo floresiensis

The claim that the lower left first mandibular molar of LB1, the type specimen of Homo floresiensis, displays endodontic work, and a filling is assessed by digital radiography and micro-CT scanning. The M(1) tooth crown is heavily worn and exhibits extensive dentine exposure that is stained white, but there is no trace of endodontic treatment or a dental filling in this Indonesian fossil dated to 17.1-19.0 kya. Dental calculus (commonly observed in foragers) is present on the teeth of LB1, but there are no observable caries. The pattern of dental attrition in the mandibles of both LB1/2 and LB6/1 (moderate to extensive flat wear across the entire arch) is consistent with that seen in Plio-Pleistocene Homo fossils and in modern hunter-gatherers, and is not typical of most agriculturalists. We conclude that the dental-work and farming hypotheses are falsified and therefore irrelevant to the debate over the taxonomy and phylogeny of H. floresiensis.

New Experimental Rig to Investigate Abrasive–Corrosive Characteristics of Metals in Aqueous Media

A new tribometer to investigate a conjoint effect of three-body abrasion and corrosion has been developed. In this design, a flat wear sample is loaded against a rotating cylindrical disc counterface and the abrasive slurry is delivered to the contact interface. Capabilities of the newly developed tribometer have been assessed through conducting abrasion–corrosion tests involving simultaneous electrochemical measurements. In this work, the stability of the passive layer on stainless steel under three-body abrasive wear in a near neutral electrolyte was investigated using potentiodynamic polarization tests. 316L Stainless Steel wear samples were abraded by coarse garnet particles in an aerated sodium sulphate electrolyte. The effects of load and speed on the polarization curves and passivity of 316L steel were determined. It was found that under abrasion–corrosion conditions 316L steel became more thermodynamically active and the passive corrosion rate has increased. Increasing the contact load resulted in a small increase in the passive corrosion current, while increasing the rotating speed had the opposite effect of decreasing the current. Linear polarization resistance method was used to analyse corrosion current changes with time during abrasion–corrosion testing. The existence of three distinct stages was explained by the third-body effect on the corrosion potential and current. First stage was revealed by continuous decrease of corrosion potential. Then, the potential reached a plateau for the second and third stages. In the first and second stages, particle constraint in the contact zone plays the major role and a linear rise in corrosion current with time has been recorded. After a certain amount of surface roughening, no further increase in particles entrapment is expected. Therefore, in the third stage steady-state corrosion current values are anticipated. The rig developed can also be used to simulate two-body abrasion–corrosion. The capabilities of the new rig have been compared against other experimental set-ups used in studies of combined abrasion–corrosion behaviour.

Adhesive wear of stir cast hypereutectic Al–Si–Mg alloy under reciprocating sliding conditions

This paper describes an attempt to enhance the wear properties of hypereutectic cast aluminium–silicon alloys produced by semi-solid metal (SSM) processing technique. The rheological experiments on SSM slurries were performed under continuous cooling condition from liquidus temperature. Wear characteristics of alloy under investigation were studied using pin on flat wear system over a range of normal load (10–40 N) at constant average sliding speed (0.2 m/s) against cast iron and stainless steel counter surface. Stir cast alloy showed lesser weight loss compared to conventional cast alloy. Stir cast and conventional cast alloys showed higher weight loss against the stainless steel as compared to that against cast iron counter surface. Optical microscopy of the conventional cast and stir cast hypereutectic alloy has shown that stir casting causes refinement of primary silicon particles and modification of eutectic silicon compared to conventional cast alloy. The scanning electron microscopy of wear surfaces was carried out to investigate the mode of wear.

Influence of WC addition in Co–Cr–W–Ni–C flame sprayed coatings on microstructure, microhardness and wear behaviour

In present paper the influence of the tungsten carbide (WC) particle addition on the microstructure, microhardness and abrasive wear behaviour of flame sprayed Co–Cr–W–Ni–C (EWAC 1006) coatings deposited on low carbon steel substrate has been reported. Coatings were deposited by oxy-acetylene flame spraying process. Wear behaviour of coatings was evaluated using pin on flat wear system against SiC abrasive medium. It was observed that the addition of WC particle in a commercial Co–Cr–W–Ni–C powder coating increases microhardness and wear resistance. Wear behaviour of these coatings is governed by the material parameters such as microstructure, hardness of coating and test parameters (abrasive grit size and normal load). Addition of WC in a commercial powder coating increased wear resistance about 4–9 folds. WC modified powder coatings showed better wear resistance at high load. Heat treatment of the unmodified powder coatings improved abrasive wear resistance while that of modified powder coating deteriorated the wear resistance. SEM study showed that wear of coatings largely takes place by microgroove, crater formation and scoring. Electron probe micro analysis (E.P.M.A.) of unmodified and WC modified powder coating was carried out for composition and phase analysis.

표면 마모결함을 고려한 증기발생기 세관의 구조건전성 평가

During the last two decades, several guidelines have been developed and used for assessing the integrity of a defective steam generator (SG) tube that is generally caused by stress corrosion cracking or wall-thinning phenomenon. However, as some of SG tubes are also failed due to fretting and so on, alternative failure estimation schemes are required for relevant defects. In this paper, parametric three-dimensional finite element (FE) analyses are carried out under internal pressure condition to simulate the failure behavior of SG tubes with different defect configurations; elliptical wear, tapered and flat wear type defects. Maximum pressures based on material strengths are obtained from more than a hundred FE results to predict the failure of SG tube. After investigating the effect of key parameters such as defect depth, defect length and wrap angle, simplified failure estimation equations are proposed in relation to the equivalent stress at the deepest point in wear region. Comparison of failure pressures predicted by the proposed estimation scheme with corresponding burst test data showed a good agreement.

Sedimentation casting of wear resistant metal matrix composites

A new sand casting technique to produce particle reinforced composites has been developed. It is called “the drawer casting technique”. The technique is based on sedimentation casting and gives a high concentration of particulates at and below the working surface of the component. Two models that assisted the development of the drawer casting technique are described. It is shown that WC reinforcing particles settle in the bottom of the mould quickly to form a sediment bed. The critical flow velocity required to avoid sediment bed particle motion as the mould is filled is calculated. The use of the technique for the production of materials with a flat wear resistant working surface consisting of a white cast iron matrix reinforced with ex situ (WC) and in situ formed transition and refractory metal carbide particles is described.

An efficient method for accurately determining wear volumes of sliders with non-flat wear scars and compound curvatures

Point contact is often used in unidirectional pin-on-disk and reciprocating pin-on-flat sliding friction and wear tests. The slider tip could have either a spherical shape or compound curvatures (such as an ellipsoidal shape), and the worn tip usually is not flat but has unknown curvatures. Current methods for determining the wear volumes of sliders suffer from one or more limitations. For example, the gravimetric method is not able to detect small amounts of wear, and the two-dimensional wear scar size measurement is valid only for flat wear scars. More rigorous methods can be very time consuming, such as the 3D surface profiling method that involves obtaining tedious multiple surface profiles and analyzing a large set of data. In this study, a new “single-trace” analysis is introduced to efficiently evaluate the wear volumes of non-flat worn sliders. This method requires only the measurement of the wear scar size and one trace of profiling to obtain the curvature on the wear cap. The wear volume calculation only involves closed-form algebraic equations. This single-trace method has demonstrated much higher accuracy and fewer limitations than the gravimetric method and 2D method, and has shown good agreement with the 3D method while saving significant surface profiling and data analysis time.

Mechanisms of ultra-low friction by hollow inorganic fullerene-like MoS 2 nanoparticles

Inorganic Fullerene-like (IF)-MoS 2 nanoparticles were tested under boundary lubrication and ultra-high vacuum (UHV) and were found to give an ultra-low friction coefficient in both cases compared to hexagonal (h)-MoS 2 material. Previous works made by Rapoport et al. with IF-WS 2 revealed that the benefit effect of the inorganic fullerene-like materials decreases at high loads and sliding velocities. Nevertheless, under the conditions used in our experiments using high contact pressure (maximum pressure above 1.1 GPa in oil and 400 MPa in high vacuum) and slow sliding velocities (1.7 mm/s in oil test and 1 mm/s in high vacuum), friction always decreases and stabilizes at about 0.04 for 800 cycles in both cases. Therefore, IF-MoS 2 material appears to be a good candidate for use in various environments in regard to other MoS 2 crystal structures. Wear mechanisms were investigated using both High Resolution TEM and surface analyses (XPS) on the wear tracks. Wear particles collected from the flat wear scar show several morphologies, suggesting at least two lubricating mechanisms. As spherical particles are found in the wear debris, rolling may be a possible event. However, flattened and unwrapped IF-MoS 2 particles are often observed after friction. In this case, low friction is thought to be due either to sliding between IF-MoS 2 external flattened planes or to slip between individual unwrapped MoS 2 sheets.

Patterns of dental wear in the early Maori dentition

AbstractThe levels of tooth wear were surveyed in 50 pre‐contact Maori skulls (23 of them female) from New Zealand. In addition to a generalized tooth wear index, we evaluated occlusal wear for erosion and abrasion. Occlusal microwear was also investigated using scanning electron microscopy (SEM) images and, finally, the occlusal slope was determined at the level of the first molar teeth. The general pattern of wear was one of severe occlusal reduction with no significant differences between males and females. Both silicone impressions and SEM views confirmed a large component (30%) of erosion. While most individuals had flat wear planes, 33% of males and 44% of females showed reversed Monson's curves. Accentuated Monson's curves were found in 23.8% of males. While these results confirm early studies of the excessive wear experienced by pre‐contact Maori, our study shows for the first time that erosion played a significant role in the dental wear of these people. Copyright © 2001 John Wiley & Sons, Ltd.

Wear simulation of UHMWPE for total hip replacement with a multidirectional motion pin-on-disk device: effects of counterface material, contact area, and lubricant.

The wear of nonirradiated ultra-high molecular weight polyethylene (UHMWPE) was studied with a circularly translating pin-on-disk (CTPOD) device. With this simple device, the wear of the acetabular cup is simulated. Two shapes of a polyethylene pin were used: flat wear faces of 3.0 and 8.9 mm in diameter. The load was always 70.7 N. Tests were done against stainless steel plates in serum, albumin, and gamma-globulin lubricants and against alumina plates in serum. With 3.0-mm-in-diameter wear faces, the wear factors were an order of magnitude lower than the average clinical wear factors of polyethylene acetabular cups. With 8.9-mm-in-diameter wear faces, the wear factors and wear mechanisms were consistent with clinical ones. The mean wear factor against stainless steel in serum was 1.46 times higher than that against alumina, and the difference was statistically significant. The mean wear factors in albumin and gamma globulin were close to that in serum; the differences were not statistically significant. The results indicate that albumin and gamma globulin are the fractions of synovia that influence the wear of polyethylene. A practical test parameter combination for the CTPOD device has now been established for future studies of modified and new materials and of lubricants.

Biocompatible and mechanical properties of low temperature deposited quaternary (Ti, Al, V) N coatings on Ti6Al4V titanium alloy substrates

A series of quaternary (Ti, Al, V) N coating layers were obtained by low temperature reactive plasma sputtering in differing deposition conditions to improve the wear resistance and the biocompatibility of a titanium surgical alloy, specifically Ti-6Al-4V. Characterization of the mechanical properties, structure and the chemical composition of the coating layer was explored by microhardness test, ball against flat wear test, scanning electron microscopy and X-ray diffraction. The biocompatibility of the optimum coating layer (as determined by mechanical performance) was examined by a modified MTT toxicity test and by monitoring cell growth assessed by quantitative stereological analysis. The experimental results are encouraging, indicating that this low temperature deposited, dense, quaternary (Ti, Al, V) N coating layer exhibits improved mechanical properties such as high hardness and excellent adhesion to a Ti alloy substrate and is highly biocompatible.

A multipass/scanning tribometer for on-line friction and wear mapping

A pin on flat friction test rig is presented allowing for simultaneous on-line monitoring of friction as well as pin on flat wear during linear unidirectional sliding. It can be run either in the simple multipass (identical track) or in the scanning mode. Detailed wear-induced modifications in surface morphology of the friction partners are studied by conventional, P.C.-driven, tactile 3D profilometry. Data presentation is done by means of 3D topographical projections of the real surface as well as “triboscopic” mapping of friction either versus sliding distance and pass number for multipass sliding in the same wear track or versus the sliding distance and track number in the scanning mode. This system is used to do wear mechanism analysis of hard chromium plated construction steel specimens as compared to standard pin on disc, rotational operation. The observed difference in wear is explained by the abrasive action of debris generated during friction.

Effect of Silicon Carbide Whisker and Titanium Carbide Particulate Additions on the Friction and Wear Behavior of Silicon Nitride

A Si3N4/TiC composite was previously demonstrated to exhibit improved wear resistance compared to a monolithic Si3N4 because of the formation of a lubricious oxide film containing Ti and Si at 900°C. Further improvements of the composite have been made in this study through additions of SiC whiskers and improved processing. Four materials—Si3N4, Si3N4/TiC, Si3N4/SiCwh, and Si3N4/TiC/SiCwh— were processed to further optimize the wear resistance of Si3N4 through improvements in strength, hardness, fracture toughness, and the coefficient of friction. Oscillatory pin on flat wear tests showed a decrease in the coefficient of friction from ∼0.7 (Si3N4) to ∼0.4 with the addition of TiC at temperatures reaching 900°C. Wear track profiles illustrated the absence of appreciable wear on the TiC‐containing composites at temperatures above 700°C. Microscopic (SEM) and chemical (AES) characterization of the wear tracks is also included to deduce respective wear and lubricating mechanisms.

Sliding wear rig

As a preliminary to studies on cam and follower systems, a rotating cylinder on reciprocating flat wear rig has been developed. This has turned out to possess a number of useful characteristics not available in more conventional rigs. The rig has been particularly useful in that it has produced wear areas large enough for detailed comparison of a range of quantitative surface analysis methods. Esca, sem/empa, sem/edax have been compared for the quantification of antiwear surface elements.

Wear Characteristics of Single Crystal Diamond Tool

The single crystal diamond tool has been used for precision machining, and microfracture and wear of its cutting edge have larger influence on surface roughness. The purpose of this report is to make clear the relations of wear to various crystal orientations as well as to surface roughness in cutting Aluminum alloy and Nylon with the diamond tool. Primary results obtained by observation under the scanning electron microscope are as follows: (1) In the case of cutting Aluminum alloy, a smooth and flat wear land is observed on each of the rake face and flank. With the progress of cutting, the wear lands grow in stepped geometry corresponding to feed rate but hardly influenced on surface roughness. (2) In the case of cutting Nylon containing the filler, microfracture by cleavage occurred on the flank and its surface is in parallel to the (111) plane of the diamond crystal orientation. (3) In the case of cutting pure Nylon, only slight wear occurs on the cutting edge.