Current Issue : July - September Volume : 2018 Issue Number : 3 Articles : 5 Articles
CoCrMo alloy has long been used as a pairing femoral head material for articular\njoint implant applications because of its biocompatibility and reliable tribological performance.\nHowever, friction and wear issues are still present for CoCrMo (metal)/CoCrMo (metal) or CoCrMo\n(metal)/ultrahigh molecular weight polyethylene (UHMWPE) (plastic) pairs in clinical observations.\nThe particulate wear debris generated from the worn surfaces of CoCrMo or UHMWPE can pose\na severe threat to human tissues, eventually resulting in the failure of implants and the need for\nrevision surgeries. As a result, a further improvement in tribological properties of this alloy is\nstill needed, and it is of great interest to both the implant manufacturers and clinical surgeons.\nIn this study, the surface of CoCrMo alloy was laser-treated by a fibre laser system in an open-air\ncondition (i.e., no gas chamber required). The CoCrMo surfaces before and after laser remelting were\nanalysed and characterised by a range of mechanical tests (i.e., surface roughness measurement and\nVickers micro-hardness test) and microstructural analysis (i.e., XRD phase detection). The tribological\nproperties were assessed by pin-on-disk tribometry and dynamic light scattering (DLS). Our results\nindicate that the laser-treated surfaces demonstrated a friction-reducing effect for all the tribopairs\n(i.e., CoCrMo against CoCrMo and CoCrMo against UHHMWPE) and enhanced wear resistance\nfor the CoCrMo/CoCrMo pair. Such beneficial effects are chiefly attributable to the presence of the\nlaser-formed hard coating on the surface. Laser remelting possesses several competitive advantages\nof being a clean, non-contact, fast, highly accurate and automated process compared to other surface\ncoating methods. The promising results of this study point to the possibility that laser remelting\ncan be a practical and effective surface modification technique to further improve the tribological\nperformance of CoCr-based orthopaedic implants....
Three oilââ?¬â??miscible phosphonium ionic liquids with different structures were synthesized\nand used as additives for a Poly Alpha Olefin 10 (PAO 10) lithium lubricating grease. Different from\nother additives, the ionic liquids participated in saponification and were trapped in the entanglement\nnetwork formed by the thickener. The effects of the ionic liquids on the rheological properties of\nlithium lubricating grease were characterized through a small-amplitude oscillatory shear (SAOS)\nmeasurement. The tribological performances of the lubricating greases were determined on a four-ball\nfriction tester. The addition of phosphonium ionic liquids caused a decrease in the storage (G) and\nloss (G) modulus of lubricating grease. However, the ionic liquids were found to be effective\nlubricant additives for improving the friction-reducing and antiwear properties of PAO 10 lithium\nlubricating grease....
In this paper, we analyze the behavior of a single pad system in the presence of dry\nfriction. The goal is to investigate the path that leads a stable mechanical system to unstable behavior.\nIn doing so, we studied the behavior of a discrete three DOF model, a continuous model and a finite\nelement model of the pad. The numerical results are consistent with the experimental investigation\nconducted on a brake disk for railway application....
A flow of a thin layer of liquid is simulated on a flat surface of a body located in a stream of\nair. Liquid film on the surface of the body reduces frictional resistance and can be used as a boundary\nlayer control element. The paper presents a mathematical model of the film flow on a half-plane,\nlocated at an angle to the horizon. The fluid flow is determined by the force of gravity and friction\nfrom the external air current. A model of an incompressible viscous fluid is used in the boundary-layer\napproximation. The terms of the motion equation are averaged over the film thickness according to\nthe Leibniz rule. In the cross section of the film, a quadratic law is adopted for the distribution of\nthe longitudinal velocity, taking into account friction on the film surface. An analytical solution of\nthe problem is obtained in the form of series in powers of the small parameter for determining the\nfilm thickness and the average longitudinal velocity along the length of the plate. It is shown that the\nfriction decreases with flow around a half-plane with a film of liquid on the surface....
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