Papers by Keyword: Friction

Abstract: Ball screw is a high-precision and high performance linear drive of mechanical elements. The frictional heat of internal components what is very significant impact for platform transmission in high speed and the high axial load and causes the thermal expansion of element. In this research , the influence of different greases on ball screw is investigated in thermal rising of nut and driving torque in high speed and high axial load. A vertical motion platform was used for driving performance test. Thermal rising of nut of ball screw and the variance of transmission torque whose lubricated by high viscosity base oil grease is significant larger than the lower one. High viscosity grease is not easy to carry out the friction heat generated at ball and raceway contact area due to the bad flowing properties. It also has more serious wear occurred at contact area and high friction force, whose causes the large variance of transmission torque.

Abstract: The friction coefficient of tribology pair between silicon nitride ceramic and stainless steel was researched with bovine serum albumin, saline and water lubricants. The coefficient of friction of silicon nitride in bovine serum albumin is lower than those in saline and water. Using digital microscope, the worn surfaces of silicon nitride and stainless steel were viewed. The groove depths of worn stainless steel surface were measured. The depth with bovine serum albumin is shallower than those in saline and water. The results showed that ceramic in bovine serum albumin has good tribological characteristic. This research provides the reference for the development of ceramic artificial joint.

Abstract: Large amount of unsaturated and polar component of oils enhance the lubrication of ferrous materials. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, consequently improving the fuel efficiency and durability of these components. Therefore, the interaction between nonferrous coatings (e.g., DLC) and vegetal oil must be investigated. A ball-on-plate tribotester was used to run the experiments using stainless steel plates coated with amorphous hydrogenated (a-C:H) DLC and hydrogen-free tetrahedral (ta-C) DLC sliding against 440C stainless steel ball. Raman analysis was performed to investigate the structural change of the coatings. At high temperatures, the CoF decreases in both coatings but the wear rate increases in the a-C:H and decreases in the ta-C DLC-coated plates. CoF and wear rate (coated layer and counter surface) are mostly influenced by coating graphitization. The degree of graphitization increases with increasing temperature. Graphitization occurs in the tribological contact because of friction-induced heating under contact and high contact stress conditions.

Abstract: Using C/C composite and chrome bronze as a friction couple, the frictional wear properties of C/C composite with electric current is studied in this paper. The results have shown that current, velocity and load are important factors to affect the frictional wear properties of C/C composite with electric current. Wear rate of C/C composite increases with the increase of arc energy .The coefficient of friction and the wear rate increase with the increase of velocity when the electric current is constant of 100A. The coefficient of friction increases but the wear rate decreases with the increase of load when the electric current is constant at 100A. The coefficient of friction decreases but the wear rate increases with the increase of current when the load is constant of 80N. Comparing with no electric current, the coefficient of friction of C/C composite with electric current decreases but the wear rate of that increases obviously. The wear mechanism of C/C composite is mainly of electric wear caused by arc erosion under the condition of current-carrying.

Abstract: Ni-P-CNT nanocomposite coating was successfully co-deposited by electroless plating and the heat treatment was carried out at 200°C, 400°C, 600°C in nitrogen atmosphere respectively for a holding period of 1 h. The effects of heat treatment on the microstructure and mechanical properties of Ni-P-CNT composite coating were investigated. The results indicate that the heat treatment at 400°C can greatly improve the hardness and wear resistance of the composite coating. The reason is that Ni₃P hard phase is greatly precipitated after the heat treatment, which played a strengthening effect. On the other hand, the precipitated Ni, Ni₃P crystalline phases in the coating result in an increase of the amount of grain boundary. The increased amount of grain boundary broke the spread of shear force during friction process, and reduced the wear loss caused by friction pair. Compared with as-deposited coating, the coatings after heat treatment possess higher microhardness and wear resistance.

Abstract: Based on previous work on lubricant hard HfC_x film, the HfC_xN_yfilmswere deposited by sputtering from theHf target in a mixture of discharging N₂,Ar and CH₄, and the N content in films was accurately controlled by changing the N₂ flow rate.Theintroduction of N into the films contributed to the presence of solid solution FCC-HfC(N) and FCC-HfNphase appeared at high N content in films. In addition, the a-C content in the filmsdecreasedwith increment ofN content in the films. In comparison with HfC_x film, hardness of HfC_xN_y films were enhanced from 21 GPa to 25 GPa with N content rising to 6.8 at.% but then surplus N in the films impaired the hardness. The coefficient of friction and surface roughness for HfC_xN_y films increasedfrom 0.10 to 0.23 and 3.13 nm to 12.4 nm, respectively, with decreasing a-C content from 52.9 at.% to 46.3 at.%. However, the introduction of N into HfC_xFilm improvedthe wear resistance of filmseffectively, and the specific friction rate for this HfC_xN_yfilm deposited at 8 sccm N₂was only 6.17×10^-7 mm³/Nm about half of that of HfC_x film (1.09×10^-6mm³/Nm).

Abstract: Organic CHNO-containing high energy density materials have been widely used for storing large amounts of the chemical energies which can be rapidly transformed into heat upon various external perturbations during detonation. The sensitivity of the energetic materials is subjected to considerable concern for safety and maintenance. Periodic density functional theory with the all-electron basis sets were employed in this work to unravel the impact, friction, and electric-fields induced decomposition of HMX. The minimum energy paths for the N−NO₂ homolysis reactions of HMX in the bulk and gas phases were obtained. The surface-enhanced effect on the decomposition of HMX were calculated for both (010) and (100) surfaces. A general theoretical scheme has been proposed to assess the intrinsic mechanic and electrostatic sensitivities of the pure energetic materials.

Abstract: This work focuses on the acoustic emission signals related to three different tribological systems: a rotary sliding contact between WC-Co pins against alumina flat counterfaces, a fretting contact between alumina pins against alumina flat counterfaces and a reciprocating sliding flat on flat contact between thermoplastic polyurethanes (TPU) and a steel counterface. This document relates dependences observed between tribological behaviors and variations of acoustic emission signals. Therefore, a third body approach is used to explain these correlations and to highlight the aspect of nature and associated energy of acoustic emission sources.

Abstract: The third body concept is a pragmatic tool for analyzing and understanding the friction and wear of sliding materials. This approach is based on the dominating role played by the wear particles under dry sliding conditions. These particles constitute the major part of what is called the third body. The third body concept was introduced by Maurice Godet in the middle of the 70’s and developed by Yves Berthier since the end of the 80’s who added complementary conceptual tools as the tribological triplet, the accommodation mechanisms and the tribological circuit. The aim of this paper is to give a synthetic view of these concepts, which involves mechanical, material and physicochemical subjects. Concrete examples and case studies from various practical applications are given to illustrate the validity and the efficiency of such a phenomenological approach.

Abstract: A focus on the effect of friction condition on tube hydroforming during corner filling in a square section die is proposed. Three approaches have been developed: an analytical model from the literature has been programmed, finite element simulations have been conducted and experiments have been carried out. Effect of friction coefficient on the thickness distribution in the square section of the hydroformed tube is studied. Critical thinning is found to take place in the transition zone between the straight wall and the corner radius and this minimal thickness seems to be the more appropriate parameter for the evaluation of the friction coefficient.