Wear Performance Of Materials Research Articles

Characterization of Sintered Bronze–MoS2 Composite With Solid Lubrication Effect

Abstract The most efficient method to reduce material loss and frictional energy losses is by using lubrication. An alternative is the use of solid lubrication, specifically by using solid lubricants evenly distributed in a metallic matrix, thus forming self-lubricating composites, which are capable to induce low coefficients of friction in mechanical systems. Molybdenum disulfide (MoS2) is a very versatile solid lubricant, suitable for lubrication in critical circumstances such as vacuum, high temperatures, and pressures. Therefore, the aim of this study is to produce samples of sintered composites consisting of homogeneously distributed MoS2 in a bronze matrix obtained by cold uniaxial pressing and to compare the wear-rates and friction coefficient between the MoS2-free bronze and the self-lubricating composites. Different MoS2 percentages were used to characterize the tribological properties of the composites as a function of the MoS2 content. At the end of the experiments, it was found that samples with 20% MoS2 did not sinter properly due to the large amount of lubricant between the bronze particles. It was also found that the mixture with 5.0 vol% MoS2 had proper sintering, satisfactory hardness, achieved lower friction coefficient, and better material wear performance due to the optimal amount and good distribution of MoS2 when compared with the rest of conditions studied.

Coupled effect of scratching direction and speed on nano-scratching behavior of single crystalline copper

The exhibited friction and wear performance of materials are closely related to scratching direction and speed at grain level. A crystal plasticity finite element model simulating nano-scratching process is developed. Experimental results of nano-indentation and nano-scratching are in well agreement with corresponding simulation results. Significant effect of scratching direction and speed on the friction and wear performance of single crystalline copper is observed. Specifically, simulation study reveals that scratching along the [110] direction is conducive to reducing the wear of (001)-oriented single crystalline copper, increasing ploughing coefficient in the meanwhile. The wear performance is improved with the increase in scratching speed, and the ploughing coefficient decreases as scratching speed increases.

Property Self-Optimization During Wear of MoS2.

Knowledge of their bulk physical properties often guides selection of appropriate tribological coating materials. However, these properties as well as the microstructure evolve dramatically under the extreme conditions imposed during mechanical wear. The dynamic response ultimately governs the material's wear performance; thus, understanding the dynamic evolution of the system is critical. This work characterizes the change in mechanical properties and microstructure as a function of wear cycles in model MoS2 films using a combination of nanowear testing, transmission electron microscopy, and site-specific nanopillar compression. Notably, mechanical wear enhances the mechanical properties of the MoS2 while simultaneously evolving a microstructure that reduces the coefficient of friction and wear rate. We hypothesize that this self-optimizing behavior underpins the exceptional lubricity and antiwear performance of MoS2.

자동조심 롤러 베어링의 재제조 공정 및 피로수명 향상

Dept. of Mechanical Engineering, Sun Moon University, Asan 336-708, Korea(Received; Setpember 23, 2014 Revised; November 2, 2014; Accepted; November 5, 2014)Abstract − This study proposes a sustainable bearing remanufacturing process using the ultrasonic nanocrystalsurface modification (UNSM) technique. The UNSM technique is a newly developed and sophisticated surfacemodification technique that can increase the mechanical properties and improve the friction and wear per-formance of materials. Taking advantage of the bearing manufacturing process is the most significant way ofoptimizing the life of a bearing. The proper maintenance and usage of repaired bearings can increase their lifeto be equal to or greater than that of new bearings. This paper discusses the restoration of certain mechanicalproperties of worn, damaged, and discarded bearings, and suggests a remanufacturing process for used bearings,which can impart them with a lifespan equivalent to that of new bearings. The most damaged part of the dis-carded bearings is the raceway, which is the site of accumulated fatigue. The existing polishing or barrel finishingprocesses can recover the accumulated fatigue only partially. Rolling contact fatigue tests performed on UNSM-treated new and used specimens polished after 4×10

Investigation of carbon–carbon composite brake pads in wet and dry sliding wear conditions

Purpose – The purpose of this study was to investigate wear behaviours of brake pads produced from carbon–carbon (C/C) composites in both wet and dry friction sliding conditions. Carbon is probably the most remarkable element in science and also C/C composites are a family of advanced composite materials. They are the most advanced form of carbon and consist of fibre based on carbon precursors embedded in a carbon matrix. In the present work, wear test specimens were prepared according to the related standards and they were exposed to pin-on-disc wear testing in wet and dry sliding conditions with different loads as 10, 20, 30 and 40 N with 1 m/s constant sliding speed. Wet friction process was conducted on all specimens by means of rain water collected from the nature. Design/methodology/approach – Pin-on-disc wear test tribology lubrication was used. Findings – Mechanical and physical property measurements of C/C composite brake pad materials: hardness, modulus of elasticity, density and water absorption capacity. Wear performance of materials were measured as coefficient of friction, volumetric loss and specific wear rate. Originality/value – C/C composite brake pads are used in railway vehicles. Wear performances of them are very important for safety. In this study, wear behaviours of these materials were investigated not only in dry sliding friction condition but also in wet sliding one. Because safety braking is important in all weather conditions for trains, and we used natural rain water to observe the wet sliding friction behaviour of brake pads. “Water lubrication” is an important aspect mentioned in tribology handbooks.

Effect of VC Content on Abrasion Resistance of VC/Fe Composite

Normal load can affect the wear performance of the materials. with the normal load increased, friction coefficient is firstly increases and then decreases, when the normal load is 80N, the minimum friction coefficient is 0.916; rotating speed can effect the wear performance of the materials with the change of rotating speed, the faster the speed, the bigger the friction coefficient When the speed is 60 rad/min, the minimum friction coefficient is 0.918.The content of VC can influence greatly for wear-resisting performance, when the content of VC was 55%, the wear performance of material is better, the friction coefficient is 0.916-0.918.The results show that: the microstructure analysis can judged that, in the wear process, iron is off first, then the particle phase, so VC grain can intensify the wear resistance.

Design and test of novel tribometer: investigation into wear performance of materials used in total hip replacements

A six-station, programmable load and motion wear machine was designed to further the tribological investigation into wear, subsurface plasticity, and debris generation of ultra high molecular weight polyethylene (UHMWPE). This paper describes the pin-on-plate device and validation protocol in accordance with ASTM F732-00 (2006). Unlike conventional pin-on-plate wear testing machines which commonly statically load a UHMWPE pin against a metallic/ceramic rotating disc or sliding plate, this new design incorporates programmable dynamic loading and motion profiles. There is a requirement for this type of machine in order to investigate the directional dependence of wear and debris generation of UHMWPE more accurately, where 'simplified' tribometers (adequate for constant load/constant velocity and constant load/sinusoidal velocity work) are not capable or suitable. To validate the machine, three orthopaedic polymers of clinical relevance: polytetrafluroethylene, polyacetal and UHMWPE were subjected to linear reciprocating and novel elliptical motion paths under a Paul type load profile. All three polymers showed higher wear factors under elliptical motion, by up to two orders of magnitude, agreeing well with explanted values. The UHMWPE elliptical wear factor was comparable to that reported for clinical, where Kelliptical=1·56×10–6 mm3 Nm–1. Wear rankings agreed with the ASTM standard: polytetrafluroethylene>>polyacetal≥UHMWPE. However, only under elliptical motion were the wear rate ratios comparable in magnitude to published clinical data.

Wear of commercially available plastic materials

This article reviews the data on the wear of commercially available plastic-based bearing materials. Much of these data were obtained during the course of a six-year project at NCT, using a purpose-built test facility. The wear performance of materials has been assessed in terms of the effect of bearing pressure and surface temperature rather than PV factors. Basic wear data are presented on a wide range of materials. The effect of bearing pressure on the wear rate of some composite materials is discussed and the influence of wear debris removal on the wear rate at high loads is also assessed. The wear performance of filled-ptfe composites and polyimides at elevated temperatures is compared. These tribological data are presented in a form which is intended to enable designers to select appropriate materials and to estimate bearing life under the conditions of a particular application