Wear of dimethacrylate resins used in dental composites

Wear of dimethacrylate resins used as the matrix phase in dental restorative composites was characterized by two-body abrasion and singlepass sliding. Ranking of the resins was obtained by both tests. Two resins that had low values of tangential force and track width also showed relatively ductile modes of surface failure for the normal loads tested. A monomethacrylate fluorine-containing resin did not show improved wear properties by these methods of testing.     

Wear and frictional performance of polymeric composites aged in various solutions

The aim of the present work is to investigate the effect of aging process on the wear and frictional characteristics of polyester composites based on oil palm fibres. Prepared samples of treated oil palm fibre reinforced polyester (T-OPRP) composite were immersed in different types of solutions (i.e. water, salt water, diesel, petrol and engine oil) for three years. The samples were then tested on a Pin on disc (POD) machine subjected to a polished stainless steel counterface under dry adhesive wear at different sliding distances (0-6.72 km). Scanning electron microscopy (SEM) was used to observe the damage features on the worn surfaces. Results revealed that aging process has pronounced influence on the adhesive wear and frictional behaviour of the T-OPRP composite. Immersing the samples in water and salt water demonstrated poorest wear performance as compared to the ones immersed in engine oil and diesel. This was mainly due to the higher viscosities of engine oil and diesel solutions as compared to the rest.     

Wear of dental enamel

Teeth wear for a number of reasons. One of the causes for wear is the use of abrasive tooth pastes. A study is reported in which enamel was damaged by single pass sliding of a diamond indenter. In single crystals of fluorapatite, wear occurs by flaking out of chips of material and severely fractured substrate is left behind. On the other hand teeth are made of small rods of polycrystalline hydroxyapatite of the order of 5 μm in diameter oriented perpendicular to the tooth surface. This rod structure of human teeth prevents large scale flaking out of material. Apparently the subsurface cracks do not extend from one rod to the other so that subsequent passes do not result in severe wear. Small abrasive particles may do considerable damage to rods, but the overall effect is small. Large abrasive particles with high loads cause separation of rods, and cracks appear to propagate but without severe permanent damage.     

Wear mechanisms of polytetrafluoroethylene and its composites

It is shown analytically that the empirical wear law takes account of two fundamentally different wear mechanisms. Whether adhesive or fatigue wear predominates will depend on the selection of the frictional power. Comparison of the coefficients in the empirical law demonstrates the role of the filler in reducing the wear rate of composites.     

Wear mechanisms of diamond coated dental burs

Abstract

Wear mechanisms of diamond burs consist of diamond wear-out, diamond pull-out, clogging by debris and degradation of the diamond binder material. These have been reported in the scientific literature and several discrepancies were found by the authors, which in itself, justifies an independent study. Diamond coated dental burs before and after use on human teeth were, therefore, compared in order to identify the predominant cause of wear. Fifteen new diamond coated burs were characterised using scanning electron microscopy before and after use on human teeth. The study focused on the condition of the same diamond particles before and after use. Clear evidence of diamond particle wear was detected rather than evidence of diamond pullout, clogging by debris or degradation of the diamond binder material.     

Wear and abrasion of cast Al-Alumina particle composites

Wear rates for cast aluminium and Al-Si alloys containing up to 5 wt.% γ-Al₂O₃ particles (100 μm size) were determined under conditions of adhesive wear and abrasive wear against a hardened steel disc and an alumina abrasive cloth sheet respectively. The adhesive wear rate of aluminium containing 5 wt.% A1₂O₃ dispersions is similar to that of Al-11.8Si eutectic alloy and slightly higher than that of A1-16Si hypereutectic alloy. Al-3wt. %Al₂O₃ and Al-5wt.%Al₂O₃ composites perform better than Al-11.8Si and Al-16Si hypereutectic alloys under abrasive wear conditions. Al-11.8Si and Al-16Si alloys have a lower abrasive wear resistance than pure aluminium. The results indicate that Al₂O₃ particles can be used as a substitute for silicon as the hard dispersed phase in aluminium for wear-resistant and abrasion-resistant applications.     

Wear behavior of Al-Mg-Cu-based composites containing SiC particles

The friction and wear behavior of Al-Mg-Cu alloys and Al-Mg-Cu-based composites containing SiC particles were investigated at room conditions at a pressure of 3.18 MPa and a sliding speed of 0.393 m/s using a pin-on-disk wear testing machine. This study is an attempt to investigate the effects of adding copper as alloying element and silicon carbide as reinforcement particles to Al-4 wt% Mg metal matrix. The wear loss of the copper containing alloys was less than that for the copper free alloys. It was observed that the volume losses in wear test of Al-Mg-Cu alloy decrease continuously up to 5%. Also it was found that the silicon carbide particles play a significant role in improving wear resistance of the Al-Mg-Cu alloying system. The formation of mechanically mixed layer (MML) due to the transfer of Fe from counterface disk to the pin was observed in both Al-Mg-Cu alloys and Al-Mg-Cu/SiC composites.     

Wear of filled and unfilled dental restorative resins

The influence of double-pass sliding on the surface failure of filled and unfilled dental restorative resins was evaluated. Damage was more severe for double-pass than for single-pass sliding. Wear of restorative resins and composites was influenced by the resistance to penetration and by the mode of deformation during sliding.     

Wear behaviour of carbon nanotube reinforced epoxy resin composites

This paper deals with the effect of a multi-walled carbon nanotube (MWCNT) reinforcement on the wear behaviour of Epoxy (EP) composites. Firstly, various dispersion methods were compared. Secondly, the optimum CNT amount was evaluated. In a third step, dry lubricants were added to the optimised EP/CNT composite. Finally, the influence of the steel counterpart (martensitic bearing steel 100Cr6 and austenitic stainless steel X5CrNi18-10) was studied. The preparation method was found to have a decisive effect on the wear behaviour of the composite. A pre-treatment of the CNTs in concentrated nitric acid proved beneficial. Even more important was the mixing method. A dual asymmetric centrifuge delivered so good wear results that the pre-treatment could be skipped. The optimum CNT content was at about 1 wt%, regardless of the preparation method. The lowest wear rates were found after addition of 10 wt% graphite. MoS₂ proved to be less effective and Polytetrafluorethylene (PTFE) even increased the wear. The wear rates against the unalloyed martensitic steel were far higher than against austenitic stainless steel.     

Wear of PEEK composites related to their mechanical performances

A series of polyetheretherketone-based composites was investigated, blended with different contents of polytetrafluoroethylene and/or graphite, and reinforced with various amounts of short carbon fibres. The mixture of the PEEK with various fillers was achieved by twin-screw-extruders. Thereafter, the composites were finally manufactured using an injection moulding machine. Testing of the tribological properties of the PEEK composites was carried out on a block-on-ring apparatus. The dependence of mechanical properties, e.g. Charpy impact resistance, fracture toughness, flexural modulus and strength, on various filler contents of these composites was also investigated, which is believed to be of help towards a better understanding of the steps on how to improve the composite’s wear resistance.     

Wear performance of tribologically modified thermoplastic composites at elevated temperatures

The use of injection moulded thermoplastic composites is increasing, but without fillers, reinforcements, or lubricants, they are limited by their thermal behaviour. This study looks at four polymers — polyamide 46, polyphthalamide, polyetherimide, and polyphenylenesulphide — containing first glass fibres as reinforcement, and a second version with added PTFE. Two types of wear test were undertaken, sliding wear (pin-on-disc and block-on-ring), and reciprocally fretting wear. The test materials showed different wear rates both under different tests and at various temperatures.     

Wear and rolling contact fatigue of PEEK and PEEK composites

Wear and rolling contact fatigue were investigated on unfilled PEEK and on three PEEK short fiber reinforced composites. For this aim, roller-shaped specimens were subjected to rolling contact tests at different contact pressure levels. Wear rate-pv product and contact pressure-life diagrams were obtained, depending on material hardness. Microscopic observations of rolling contact surfaces and sections of the rollers highlighted damages at two different scales, surface and bulk, leading independently to wear and rolling contact fatigue. These damages were also of different typology for unfilled PEEK and composites: micro-pitting and deep transversal cracks occurred on unfilled PEEK rollers, while delamination and spalling phenomena where found on composite rollers.     

Wear mechanisms in polymer matrix composites abraded by bulk solids

An experimental study of the wear of polymer matrix composite materials subjected to abrasion from bulk materials has been conducted. Three examples of vinyl ester resin systems were considered: (a) unreinforced, (b) reinforced with glass fibres, and (c) reinforced with particles of ultra high molecular weight polyethylene (UHWMPE). Soft and hard bulk materials used for abrasion were granular forms of coal and the mineral ignimbrite. The bulk material was presented to the wear surface on a conveyor belt in a novel wear tester. While UHWMPE reinforcement enhanced the wear resistance to both hard and soft abrasives, the situation for fibre reinforcement was more complicated. With coal as the abrasive, it was found that glass fibre reinforcement reduced the wear rate, whereas in the case of the harder ignimbrite, fibre reinforcement increased the wear rate. Microscopy indicated significant differences in the mechanism of wear in each surface/abrasive combination. Wear textures, consistent with both two and three-body wear, were observed with, respectively, soft and hard abrasive particles.     

Wear characteristics of some internally lubricated and reinforced engineering polymer composites

An interesting characteristic of abrasion is the dependence of the wear rate on the particle size of the abrasive grits used to lubricate the abrasive papers. Three types of polymers, PTFE, PA, PI, several of their composites, and three metals were selected for studying the effect of particle size on wear rate. The pins were abraded against Sic abrasive papers of various mesh sizes under constant loading in multi-pass conditions. For some of the polymers and their composites (PA and PEI) the size effect on wear rate was similar to that for the metals. Beyond a critical particle size, no increase in wear was found with increasing particle size. On the other hand, PTFE, PI, and their composites showed the opposite effect. SEM and EDAX were used to investigate the related mechanisms.     

Wear of rotary carbide tools in machining of Al/SiCp composites

With the projected widespread application of Metal Matrix Composites, it is necessary to develop an appropriate technology for their efficient and cost-effective machining. This paper deals with the study of feasibility of rotary carbide tools in the intermittent machining of Al/SiCp composites. A rotary tool holder was designed and fabricated for this work. Experiments were designed using Taguchi Methods to analyse the influence of various factors and their interactions on the flank wear of rotary carbide tools during machining. A tool-life model describing the effect of process, tool and material dependent parameter on the magnitude of flank wear of a rotary carbide tool is proposed.     

Wear resistance of composites for sliding electrical contact from reprocessed bearing steel

The electrical contact characteristics are determined of model composites from bearing steel reprocessed from grinding waste. It is established that the tested sliding steel composites have a low contact electrical resistance and wear rate at current densities up to 300 A/cm². An assumption is made that efficient performance of these composites results from the superdispersed structure of the reprocessed bearing steel.     

高速铣削SiCp/Al复合材料时聚晶金刚石刀具的磨损机理

采用聚晶金刚石刀具(PCD),以600～1200 m/min速度对SiCp/2009Al复合材料进行了高速铣削试验,研究了铣削时PCD刀具的磨损机理.使用扫描电镜(SEM)观察加工材料表面和刀具前/后刀面磨损带,X射线衍射仪分析已加工表面物相,并使用能谱(EDS)和激光拉曼谱对后刀面磨损带进行元素分析.结果表明,增强颗...     

Wear behaviour of dental enamel at the nanoscale with a sharp and blunt indenter tip

Two different diamond nanoindenter tips, a rounded conical (～1200 nm radius) and a sharp cube corner (20–50 nm radius) were used to abrade bovine enamel. Square abraded areas (2 μm × 2 μm, 5 μm × 5 μm, 10 μm × 10 μm) were generated with loads that varied from 50 μN to 500 μN depending on the indenter tip. In addition normal and lateral forces were simultaneously measured along 10 μm single scratched lines with the sharp cube corner tip. SEM (scanning electron microscopy) and TEM (transmission electron microscopy) were also used to characterise the worn areas and debris. Two different wear mechanisms were observed depending on the geometry of the tip. The rounded tip generates a predominantly elastic contact that mainly compresses and plastically deforms the superficial material and generates severe shear deformation within the sub-surface material which, under certain conditions, fractures and removes material from the sample. The sharp tip cuts into and ploughs the enamel creating a wedge or ridge of material ahead of itself which eventually detaches. This sequence is repeated continuously for every passage of the sharp indenter tip. The different mechanisms are discussed in terms of abrading tip contact angle and enamel microstructure.     

Wear behavior of SiC particulate reinforced aluminum composites sliding against steel balls under dry and lubricated conditions

Wear behavior of Al–Si alloys reinforced with SiC particulate has been investigated under dry and lubricated reciprocating sliding conditions using a ball-on-block wear test method. It was shown that in the dry sliding wear of the composite/steel ball system, the wear mechanism of the composite was predominantly adhesive. With further sliding motion, delamination and abrasive wear occurred as a result of fracture and debonding of the SiC particles. Under lubricated conditions, the wear rate of the composite was drastically reduced due to the presence of the lubricant, and a boundary lubrication condition existed and dominated the normal wear process. The debonding of the SiC particles from the matrix of the composite was a predominant factor in determining the wear loss of the composite in the boundary lubrication sliding process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Wear resistance of composites based on ultrahigh molecular weight polyethylene filled with graphite and molybdenum disulfide microparticles

Tribological characteristics of ultrahigh-molecular-weight polyethylene (UHMWPE)-based compositions with graphite and molybdenum disulfide are studied under conditions of dry friction, boundary lubrication, and abrasive wear. It is shown that, under dry sliding friction, the wear rate of UHMWPE-graphite and UHMWPE-MoS2 polymer compositions is halved as compared to that of pure UHMWP, while their mechanical characteristics change only slightly. Under the conditions of abrasive wear, the wear resistance of these composites increases by 1.3–1.5 times. Concentrations of the fillers, which are optimum for improving the wear resistance, are determined. The supramolecular structure and the topography of worn surfaces of the UHMWPE compositions with various concentrations of the fillers are examined. A comparative analysis of the wear resistance of the composites under conditions of dry friction and lubrication is carried out. Mechanisms of the wear of the UHMWPE-graphite and UHMWPE-MoS₂ polymer compositions under conditions of dry sliding friction and abrasive wear are discussed.