Papers by Keyword: Friction

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Authors: Shuang Jin Zheng, Zhi Qiang Huang, Hong Jian Wu
Abstract: In the course of drilling fordirectional well and horizontal well,thefriction of drill string affects the WOBconducting directly,the WOBat bottom hole is often lower than the WOBexpected,whichaffects the drilling efficiency seriously.Therefore,analyzing the WOB conductingscientificallyand calculating the actual WOBat bottom hole accurately is the key for ensuring the drilling efficiency. The effectof mud on the axial force and the structural characteristicsof drill string are considered before analyzing the force of drill string in directionalwell. Then basedon the hook load, the actual WOB at bottom hole can be calculated by establishingthe WOB conducting model for directional well,which results in practicalsignificance for analyzing WOB conducting, guiding the drilling constructionand improving drilling efficiency.
Authors: Irene Guiamatsia, Giang Dinh Nguyen
Abstract: Failure develops and propagates through a structure via a complex sequence of competing micro-mechanisms occurring simultaneously. While the active mechanism of surface debonding is the source of loss of stiffness and cohesion, friction between cracked surfaces, upon their closure, acts as a passive dissipation mechanism behind the quasi-brittleness and hence can increase the toughness of the material under favorable loading conditions. In order to numerically study damage propagation, the constitutive response must be able to faithfully capture, both qualitatively and quantitatively, one of the signature characteristic of failure: the energy dissipation. In this paper, we present an interface decohesive model for discrete fracture that is able to capture the apparent enhancement of interfacial properties that is observed when transverse compressive loads are applied. The model allows to seamlessly account for the additional frictional dissipation that occurs when the loading regime involves transverse compression, whether during debonding or after full delamination. This constitutive model is then used to successfully predict the response of realistic engineering structures under generalized loading conditions as demonstrated with the numerical simulation of a fiber push-out test.
Authors: Mihail Botan, Constantin Georgescu, Lorena Deleanu
Abstract: This paper presents a comparative study upon tribological behavior of polybutylene terephthalate (PBT) and a blend of PBT + This paper presents a comparative study upon tribological behavior of polybutylene terephthalate (PBT) and a blend of PBT + 10% aramid fibers, in dry regime. Some of the properties of PBT grade CRASTIN 6130 NC010®. The tested materials they were obtained by molding at ICEFS Savinesti Romania. The aramid fibers added into PBT were supplied by Teijin, and have an average length of 125 mm. Tests were done with the help of a block-on-ring tribotester. The tests parameters were: three normal forces (F = 5 N, F = 15 N and F = 30 N), three values of sliding speed (v = 0.25 m/s, v = 0.50 m/s and v = 0.75 m/s) and a sliding distance of L = 5000 m, in dry regime, each test characterized by (F, v, L) being done twice. The conclusion of this research was that adding short aramid fibers in PBT improves the wear resistance, but slightly increases the friction coefficient. Also, the recorded temperatures near the contact are higher for the blend with aramid fibers. SEM investigation revealed particular processes within superficial layers of polymeric blend.
Authors: Chong Mu Lee, Kyung Ha Kim
Abstract: Diamond-like carbon (DLC) films have been deposited by radio frequency plasma enhanced chemical vapour deposition (rf-PECVD) with different Ar-CH4 mixtures. Nanocrystalline diamond films have been deposited by microwave plasma-enhanced chemical vapour deposition (MPCVD), using Ar-H2-CH4 mixtures. X-ray photoelectron spectroscopy (XPS) and nanotribological investigation (by scanning force microscopy) have been used to compare the mechanical properties and structures of these films. Highly orientated and non-orientated microcrystalline diamond films and MPCVD-produced amorphous carbon have also been studied by way of comparison. The diamond films exhibit a linear relationship between roughness and the coefficient of friction. The DLC and amorphous carbon have higher friction coefficients than the best performing diamond film, but may more easily be deposited as smooth coating. Possible applications for these various carbon-based films include microelectromechanical components, for which smooth, hard coatings are required.
Authors: Georg Peter Ostermeyer
Abstract: The analysis of friction in brake systems shows a complex dynamic dependence of friction and wear. Friction produces wear but wear affects the surface topography and by that the friction power itself. The wear in technical brake systems causes a dynamic equilibrium of growth and destruction of surface structures on the brake pad, carrying the friction power. This interaction between friction and wear generates a new dynamic friction law, which describes the effects on friction, wear and temperature on different time scales. For very slow processes the friction law reduces to the classical form, describing only the velocity and heat dependence of friction. For unsteady processes the dynamic friction law is able to describe and explain even complex measured friction events in brake systems.
Authors: Ji Qiu, Xiang Bo Suo, Shi Ning Ma, Gang Shuai, Hong Mei Wang
Abstract: Nano-particle reinforced composite coatings were prepared on 2A12 aluminum alloy by micro-arc oxidation and the effect of nano particles on wear performance of coating was studied. By means of SEM, CETR micro-nano-indenter friction and wear tester and white-light interferometer, the surface morphology and the friction and wear property were tested. Results showed that compared with the coating without nano-particle addition, the size and amount of pores on coatings were decreased substantially after additon with 20nm nano-SiO2 particles, 80nm nano-SiO2 particles and 80nm nano-TiO2 particles, and the wear resistance of the micro-arc oxidation coating was improved.
Authors: Bi Yong Li, Zhe Ming Zhu, Zhang Tao Zhou
Abstract: The existence of water affects the mechanical properties of cracked rock mass. Taking into account the friction generated by the crack closure, the stress intensity factor of the center cracked plate subjected to compression and seepage pressure was obtained through the theoretical analysis and numerical calculation of the boundary collocation method. The results show that crack tip stress intensity factor increases with the increasing of the seepage pressure, but decreases with the increasing of crack surface friction and the confining pressure. Finally a failure criterion for cracked rock mass under seepage pressure and confining pressure is developed.
Authors: Giovenco Axel, Frédéric Valiorgue, Cédric Courbon, Joël Rech, Ugo Masciantonio
Abstract: The present work is motivated by the will to improve Finite Element (FE) Modelling of cutting tool wear. As a first step, the characterisation of wear mechanisms and identification of a wear model appear to be fundamental. The key idea of this work consists in using a dedicated tribometer, able to simulate relevant tribological conditions encountered in cutting (pressure, velocity). The tribometer can be used to estimate the evolution of wear versus time for various tribological conditions (pressure, velocity, temperature). Based on this design of experiments, it becomes possible to identify analytically a wear model. As a preliminary study this paper will be focused on the impact of sliding speed at the contact interface between 304L stainless steel and tungsten carbide (WC) coated with titanium nitride (TiN) pin. This experiment enables to observe a modification of wear phenomena between sliding speeds of 60 m/min and 180 m/min. Finally, the impact on macroscopic parameters has been observed.
Authors: Ting Na Shi, Rui Liu, Hong Feng Li
Abstract: In this paper, a structure of friction feedforward compensation based on electromagnet torque feedback compensation is proposed to improve the speed performance of permanent magnet synchronous motor (PMSM), especially in a low speed range. First, this paper estimates the parameters associated with the friction model via an off-line identification method and compensates friction with the model. Then electromagnet torque feedback compensation is introduced to enhance the robustness of the system. The proposed control scheme is verified by computer simulation.
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