Papers by Keyword: Friction

Abstract: Forging processes have been studied since years. However, recently these studies are gaining in importance because of the increasing emergence of non conventional forging processes such as LIF processes, in order to improve their efficiency and to fit the production requirements. In this work elementary forging processes are studied under plane strain conditions in order to evaluate the combined effect of strain hardening and friction in forces and contact pressure distributions by a FE analysis. For this purpose, different base to height ratios (b/h) of the workpiece have been considered, with different friction conditions. All cases have been solved for both a rigid perfectly plastic material and a strain hardened one. It is observed that the effect of the strain hardening on the forces and contact pressures is higher when the friction conditions become more extreme. The results do not depend on the base to height ratios when frictionless conditions are assumed.

Abstract: Present work applies the Upper-Bound Theorem (UBT) with Triangular Rigid Blocks (TRB) to metal forming compression processes like plane strain forge, offering an upper limit to required deformation energy. This analytical method, usually used by means of simplified models, is developed here incorporating different effects that impact in evolution of deformation process like shape factor and friction. By means of a new adaptive model, the shape and size of the rigid zones used for the UBT application are optimized according to the ratio of the width and the height of workpiece.

Abstract: Using air lubricants, wear tests of Si₃N₄-hBN composites with different hexagonal boron nitride (hBN) volume fraction sliding against Si₃N₄ ceramic were carried out on a MMU-5G type pin-on-disc tester. For comparison, Si₃N₄/Si₃N₄ pairs were also tested under the same conditions. The worn surfaces of specimens were observed under scanning electron microscope (SEM). Furthermore, the wear debris were analyzed by using X-ray diffraction (XRD). Wear debris layers are formed on the wearing surface when Si₃N₄-hBN composites slide against Si₃N₄ ceramic under air lubrication. In this situation, the friction coefficients are as high as 0.80-1.20 and the wear coefficients are above 10-5 mm³/Nm for all materials tested.

Abstract: The joint clearance on mechanism dynamic characteristics influence can not be ignored. This paper established a geometrical model of planar four-bar mechanism, it built the model of contact force and friction and embedded into the software of ADAMS dynamics analysis mechanical system, which analysis the dynamics simulation of mechanism. We obtain a accurate prediction of dynamic characteristics of mechanism with joint clearance effect from the analysis. What's more the results provide reference and basis for later mechanism design [1,2,3].

Abstract: A composite was produced from initial powder mixture of B4C (70 wt.%) and Al (30 wt. %) with WC-Co additives introduced during ball-milling and acting as catalysts by self-propagating high-temperature synthesis and followed by heat treatment of raw samples under gaseous nitrogen flow at 650, 800, 1000, 1150 and 1450 °C, respectively. Formation of different new superhard phases was detected via XRD investigation and analysis of microstructures. Micromechanical properties were tested by nanoindentation. The tribological behavior in dry sliding conditions of the composite was investigated using the ball-on-disk technique against alumina balls. The friction coefficient of the composite increased and wear rate decreased with formation of c-BC2N, c-BN, B13C2, W2B5, Al3BC, AlN, etc. contents during heat treatment at increased temperatures.

Abstract: Diamond-like carbon (DLC) films were prepared in-situ on top of hard coatings, namely, prior to the DLC deposition, CrN, TiCN and nanocomposite nACo (nc-AlTiN/(a-Si3N4) layers were deposited on WC-Co substrates. The Ra roughness of WC-Co substrates was 0.05 and 0.2 µm. Surface morphology of DLC coatings was investigated by means of profilometry and geometrical parameters Ra, Rsk, Rku and Rz were evaluated. Fretting tests were conducted with 3 mm in diameter alumina balls under 1 and 2 N load, at slip distance of 2 mm and frequency of 2 Hz. Statistical analysis shows significant correlation between Ra and Rz parameters corresponding to initial DLC surface and wear scar surfaces produced by fretting tests after 2400 and 4800 cycles, respectively. This finding indicates a relationship between friction (wear) and Ra and Rz parameters. Positive correlation between the coefficient of friction (COF) and kurtosis Rku indicates that surface flatness is an important factor for optimal friction of an alumina ball against DLC coating.

Abstract: Brake pads are composite materials which have been constantly improved by new materials that increase the quality and reduce the non-renewable raw materials. The goal of this work is to study the behavior of brake pads produced with replacement of phenol-formaldehyde resin by lignin up to 40% weight ratio. The Krauss method of characterization and SEM analysis were employed. The results showed an average friction coefficient approximately to μ_m=0.4 and a heterogeneous surface morphology. The satisfactory results are compatible with the current friction materials.

Abstract: In the traditional heavy-clay industry, compounds are usually prepared by the addition of organic waste material. These additives originate mainly from the wood, food or paper industries. The purpose of this study is to present the results of the examination of friction contact between the wall of the forming die and the clay compounds containing organic additives. Saw dust and ground sunflower seed shell were mixed to clay in 0 wt%, 3 wt% and 5 wt%. The water content of compounds was also varied. The clay and the additives were described by morphology, XRD, bulk density and equivalent diameter. Friction tests were carried out on a special tribometer up to plastic deformation of the sample. The coefficient of friction decreased when normal stress was increased for all the ten compounds. Average results showed that the tendency of change in the value of the coefficient of friction could be divided into three sections: a decreasing, a quasi constant and a shearing section. It follows from this that the coefficient of friction can be characterized with a number only inside the quasi constant section, i.e. between two definable normal stress values. Averaged coefficient of friction was between 0.17 and 0.21 for saw dust and between 0.19 and 0.21 for the compounds with ground sunflower seed shell.

Abstract: Based on the static load tests and stress tests results of two cases in Karsts area, the bearing behavior of piles were analyzed and compared in this paper, caves in the base of piles not only affect the base resistances, but also affect the frictions of piles. The finite element method was applied to analyze the influence of rocks in the base of piles on bearing capacities of piles, according to the calculated results; the modulus of rocks affects the bearing capacities greatly, bearing capacities increase with the modulus of rocks increasing.

Abstract: The tribological characteristics of nickel-aluminium bronze CuAl10Ni5Fe4 against 30CrMnSiA steel after the prior corrosion treatment was studied at the M2000A model wear tester. The wear rate of corroded specimen was less than that of uncorroded specimen at the early stage of prior corrosion treatment, while the wear resistances deteriorated and the average friction coefficient slightly declined with the extension of prior corrosion period. The tests of CuAl10Ni5Fe4 sliding bearing at PLS-100 swing tribometer were used to validate the results. The wear resistances of CuAl10Ni5Fe4 sliding bearing increased slightly after a short period of prior corrosion, and the average friction coefficient decreased slightly after a long term of prior corrosion. A suitable period of prior corrosion treatment can enhance the wear resistance performance of CuAl10Ni5Fe4 bearing. The tribological characteristics of CuAl10Ni5Fe4 sliding bearing tested by PLS-100 rack swing tribometer are consistent with the conclusions of the tests at M2000A model wear tester.