1,721,211 research outputs found
Permanent magnet bearing design: optimising the magnetisation direction
No full textPermanent magnet bearings may be conveniently employed in several mechanical applications when friction and wear have to be avoided. The mechanical behaviour of these components is defined by the force acting between the elements of the bearing and by the stiffness of the system. In order to get the desired performance of the bearing a compromise of force and stiffness can be achieved, e.g. by selecting the magnetisation direction of the elements. The paper reviews some general criteria for permanent magnet bearing design and proposes a method for evaluating the most suitable magnetisation direction, based on the equivalent current method and employing Finite Element analyses. Three sample cases of annular and tapered bearing are reported, for which design maps for axial and radial bearings are also presented
Theoretical and experimental investigation on friction in lubricated line contacts with different materials and textures in presence of wear
Full text linkAn experimental investigation on the friction coefficient in line contacts under mixed and boundary lubrication regimes is described. Rectangular contacts between cylindrical specimens and the flat surface of discs of different material and surface roughness combinations were analyzed. Very low Stribeck numbers have been considered, resulting also in low dimensionless film thickness, so that the morphology of the surfaces and the material had a remarking role. In this work, the theoretical procedure for assessing the friction coefficient in the tested cases is described and compared to experimental results. Additionally, wear effects obtained in boundary lubrication conditions are shown. The surface conditions are put in relation with some particular trends of the friction coefficient obtained for certain combinations of materials and roughness
FE analyses of edge loading in ceramic-on-ceramic hip replacements with different rim design
No full textThis study presents a comprehensive numerical investigation on contact mechanics of ceramic-on-ceramic hip replacements under edge-loading condition. In particular, the combined effect of implant positioning and design on the contact pressure is analysed for different load levels. The final aim is to identify design/configuration solutions which minimize the risks associated
to edge-loading
Influence of the wear partition factor on wear evolution modelling of sliding surfaces
Full text linkWear of engineering components is crucial to assess their performance during all their service life. Numerical wear models are a promising tool, cheaper and quicker than experimental tests, both to investigate wear effects and to compare design solutions. However, frequently, numerical models assume that only one body gets worn or both elements undergo the same volume loss.
This study proposes a generalization of the Archard wear law, introducing the concept of wear partition factor to take into account a different wear behaviour of the rubbing elements of a coupling. The proposed approach is applied to the case of a cylinder sliding over a plane with different stroke amplitudes st. A numerical wear model has been developed in Abaqus®, exploiting the UMESHMOTION routine. Implementation procedures are described and discussed along with the model convergence. Twenty combinations of and st were simulated covering the cases both of unilateral/bilateral wear and fretting/sliding wear. Results provide important indications on the evolution of wear volumes, wear profiles and contact variables with travelled distance, revealing the remarkable role of .
The present study aims to an improved understanding and modelling of sliding wear evolution thus clarifying some critical issues slightly discussed by the literature
A novel approach to the estimation and application of the wear coefficient of metal-on-metal hip implants
Full text linkA novel approach is proposed to estimate and model the wear of metal-on-metal hip implants. The approach is based on two distinct wear coefficients for the head and cup, derived from separate measurements on the two components. This is in contrast to the usual assumption that a single wear coefficient (k) is valid for both bodies. Actually, the head and cup do not wear equally; thus, assuming equal wear leads to predictive errors. Additionally, in most papers, k is chosen considering only implant materials while neglecting geometry and testing conditions. It is suggested that experimental procedures designed for hip implants should measure the head and cup volume losses separately and that wear maps should be provided to validate numerical models
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