Papers by Keyword: Friction Coefficient

Abstract: This paper presents a study regarding friction and wear comportment of sintered composite materials obtained by mixture of copper with short carbon fibers. Sintered composites are gaining importance because the reinforcement serves to reduce the coefficient of thermal expansion and increase the strength and modulus. In case of composites form by carbon fiber and copper, the thermal conductivity can also be enhanced. The combination of low thermal expansion and high thermal conductivity makes them very attractive for electronic packaging. Besides good thermal properties, their low density makes them particularly desirable for aerospace electronics and orbiting space structures. Compared to the metal itself, a carbon fiber-copper composite is characterized by a higher strength-to-density ratio, a higher modulus-to-density ratio, better fatigue resistance, better high-temperature mechanical properties and better wear resistance. Varying the percentage of short carbon fibers from 7,8% to 2,4%, and the percentage of copper from 92,2% to 97,6%, five dissimilar composite materials have been made and tested from the wear point of view. Friction tests are carried out, at room temperature, in dry conditions, on a pin-on-disc machine. The friction coefficient was measured using abrasive discs made from steel 4340 having the average hardness of 40 HRC, and sliding velocity of 0,6 m/sec. The primary goal of this study work it was to distinguish a mixture of materials with enhanced friction and wearing behaviour. The load applied on the specimen during the tests, is playing a very important role regarding friction coefficient and also the wearing speed.

Abstract: Because friction became a more and more important issue regarding its influences on economical trends and technological developments, causing energy waste, pollution and increased costs for production, this research is oriented towards developing new type of coatings (monolayer and multilayer) having dry lubrication properties. Presented work will refer only to friction coefficients variation for tested samples, trying to establish the direct influence of used deposition parameters and settings for obtained analyses results regarding dry lubrication properties and also trying to determine the best recipe for dry lubrication coatings depositions.

Abstract: A new cast-iron material was obtained by melting in an induction furnace. The material was microstructural and chemical characterized before and after a wear test. We analyze the chemical composition of the material at macro-scale using a Spark Spectrometer and at micro-scale using Dispersive Energy Spectrometer. Microstructure before and after the external solicitations was observed using a Scanning Electron Microscope. We also evaluate the influence of external force on the dendrites microstructural and chemical modification.

Abstract: Lead-free frictional materials are important components in safety and power transmission parts of automobiles. In order to avoid using lead-containing friction modifiers, non-toxic ceramic particles are considered to be used as reinforcements. In this research work, copper-based friction materials have been developed by using press and sinter method. Pre-alloyed bronze (Cu-10Sn) powder was admixed with iron (Fe), graphite (C) and varied amounts of silicon carbide (SiC) powders. The admixed powders were compacted into disc-shape samples, which were then sintered at different temperatures in the range of 800-950 °C. It was found that sintered density and hardness of the sintered copper-based friction materials reduced with increasing SiC content. Microstructures of the sintered materials showed inhomogeneity due to uneven distribution of coarse Fe and SiC particles. The coarse SiC particles also prohibited bonding between metal powder particles. However, the sintered materials showed high room-temperature friction coefficients, which were in the range of 0.50-0.90, particularly the materials containing 4 wt. % of SiC particles.

Abstract: The Ni/WC/G composite coating was fabricated through vacuum cladding. The effect of graphite content on the wear behavior was investigated, and the worn surface was observed through scanning electron microscopy (SEM). The friction coefficient decreased with the increasing graphite content until the graphite content was 6%, and then increased when the graphite content was 8%. The wear rate decreased with the increasing graphite content for all graphite content. The wear loss of GCr15plate decreased with the increasing graphite content until the graphite content was 6%, and the wear loss of plate was rising when graphite was 8%. There was a layer composed of wear debris that containing oxides and graphite. The covering area increased with the increasing graphite content, which agreed with the changing trend of friction coefficient and wear rate. The net texture-like structure was formed among the composite coating, which could be the main support for load during wear process. There was little single WC particle protruding for support the wear load. Therefore, the Ni-based substrate was not easily to be worn.

Abstract: Metal matrix composites are attractive light weight materials with potential attributes to substitute automotive materials without sacrifing performance. This present study aims to investigate the wear characteristics of aluminium (Al) 6061 reinforced with silicon carbide particles (SiCp) of three (3) different particle sizes. The reinforcement consist of coarse particle (80μm), intermediate (40μm) and fine particles (15μm) particle sizes with 10, 5, 5 wt% respectively. The composite was fabricated using the stir casting technique due to its simplicity and cost effectiveness. The wear test was conducted using the pin on disc tribo-system with steel disc counter surface. The outcome of this study reveals that the MPS-SiC AMC exhibit better wear and frictional characteristics for brake rotor application. The coarse particles have better contribution to wear resistance because the possibility of particle pullout from the matrix for both intermediate and fine particles is high due to small surface contact area. However, the intermediate and fine particle compensates for multiple shielding effect for the base matrix thus influences the impact energy and mechanical strength of the composite. The friction coefficient (0.32 - 0.46) of the MPS-SiC AMC falls within the acceptable deviation band for automotive brake rotor application

Abstract: In many technological processes, friction results strong wear of the tool set and causes defect forgings. Many experimental investigations started in XX century had shown, that there are some laboratory methods with trustable results, which can be applied for friction prediction in real processes of metal forming. Among them such tests like ring compression test, direct and backward extrusion test, double cup extrusion test and T-shape compression test can be selected. Each of them has limitations that do not allow distributing the results of one certain test on all metal forming processes. Moreover, the tests should be done in a proper way to guarantee the adequate results that could be time-consuming. With the help of FE-analysis, the authors investigated numerically the intensity of the pressure distribution on the tool's surfaces and coupled the results with the real situations, observed in the metal forming operations. For the relative young T-shape compression technique oriented on the high contact pressure values authors have examined the changing of the relative deformed material volume as the merit of the friction characterisation.

Abstract: The friction conditions are responsible of the thickness distribution in a part realized by tube hydroforming. Then it is essential to have a good evaluation of the friction coefficient for running predictive finite element simulations. The tube expansion in a square die is one of tests proposed for the friction evaluation. In the literature, several analytical models have been developed for this specific test. The present paper concentrates on one of this model and results obtained from the analytical analysis, FE simulations and experiments are compared. The repartition of the thickness over the shaped tube and its evolution during the process are studied. The tendencies are in agreement but some complementary evaluations are proposed for using the proposed approach for the evaluation of the friction coefficient with the analytical model.

Abstract: This paper presents experimental analysis of the phenomenon of friction that occurs between two surfaces, one of polyethylene and other ceramics. Alumina ceramic is being recognized like a good biomaterial for its high strength and toughness. This ceramic, is used to manufacture the femoral head for arthroplasty of the hip joint in association with an ultra-high-molecular-weight polyethylene (uhmwpe) socket. Wear-resistant properties of uhmwpe were screened on two principally wear devices: first made by polyethylene – alumina-magnesia ceramic and the second by polyethylene – alumina-magnesia ceramic covered with polyvinyl alcohol (pva) layer. Sterile physiological saline is chosen as the lubricant fluid media. After hydration the pva layer provide lubricant properties. Depending on the lubricant medium, the friction coefficient (cof) of polyethylene and alumina-magnesia ceramic-pva counterfaces was about 0.38 (24 times low that polyethylene and alumina-magnesia ceramic counterfaces). Polyethylene friction coefficient in contact with alumina-magnesia ceramic was more susceptible in saline solution in which was about 0.46 compared with 0.016 on alumina-magnesia ceramic-pva. On the other hand, fluid environment shows a strong effect on polyethylene wear in contact with ceramic surfaces, increasing friction coefficient by ceramic hydration. The wear particles obtained in dried conditions are aglomerated and well individualized compared with lubricated conditions which are poorly individualized and with fine structure.

Abstract: Due to the advantage on low coefficient and self-lubricant, PPS races-PTFE retainer hybrid polymer bearings can offer better service performance under certain condition. In our previous study, the relationship between friction coefficient and rotation speed was investigated, and formation of black layer was found. In the present study, EPMA was introduced to investigate the component and thickness of the black layers. Based on the observations, the relationship between friction coefficient, solid lubricant layer and thrust load was also discussed.