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Computational simulation analysis for torus radius of edge contact in hip prostheses

Li F., Chen H, Mao K.

Acta of Bioengineering and Biomechanics

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2015

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Vol. 17, no. 3

67--73

EN

Stripe wear occurs when the components of hip prostheses move a sufficient distance laterally to contact the edge of the acetabular cup, causing abnormally high contact stresses. In this research, edge loading contact of prosthetic hip is analyzed in the most commonly used material pairs. The contact dimensions and maximal contact pressure are investigated in mutative normal edge loading with 3 different inclination angles (15°, 20°, 25°) and in alterable edge torus radius with edge loading of 2500 N and inclination of 20°. A computational case was conducted for a 14 mm radius alumina ceramic bearing with a radial clearance of 0.1 mm using a normal edge loading ranged from 0 N to 3000 N. Additionally, the Hertzian theory successfully captures principal curvature trends of the edge torus on the influence of maximal contact pressure and obtains the appropriate edge radius range for lower maximal contact pressure. This work elucidates the methods of applying classical contact theory to design the edge radius of hip bearings to better resist severe edge loading contact stresses and reduce the stripe wear.

2

Analiza nacisków kontaktowych w procesie wygniatania regularnych nierówności powierzchni

Patyk R., Szcześniak M., Mioduszewski P.

Mechanik

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2012

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R. 85, nr 2CD

PL

W artykule zaproponowano nowy sposób przygotowania powierzchni do nagniatania gładkościowo umacniającego. Szczegółowej analizie poddano zagadnienie kontaktu narzędzia z przedmiotem obrabianym. Opracowano aplikację w programie ANSYS/LS-DYNA, która umożliwia dokonywanie obliczeń dla różnych modeli materiałowych z uwzględnieniem wpływu odkształceń sprężystych, tarcia, prędkości odkształcenia i temperatury.

EN

In the article was proposed was new method of the surface preparations to smoothness and hardness burnishing. The detailed analysis was subjected from work-piece and tools the contact problem. The results of theoretical considerations of plastic formation regular asperities process obtain on the ground characteristic method. It the application was has worked out was in FEM system ANSYS/LS-DYNA the enabling analysis of process for different material models with considerations of influence elastic strain, frictions, strain rate and temperature.

3

Cele i mozliwości stosowania korekcji w łożyskach wałeczkowatych

Raczyński A.

Tribologia

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1999

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nr 1

55-70

PL

Korekcja wałeczków i bieżni pierścieni łożysk wałeczkowych jest od dawna stosowana w celu wyrównania nacisków kontaktowych. Mniej są znane inne możliwości, jakie może dać korekcja. Poprzez korekcję bieżni głównych i wałeczków można wpływać na rozkład prędkości ślizgania. w efekcie można wywołać taki moment sil stycznych. że wspomaga on właściwe toczenie wałeczków po bieżniach. W kontakcie wałeczków z bieżnia pomocniczą dzięki korekcji czoła wałeczka i tej bieżni można osiągnąć hydrodynamiczny film olejowy i w rezultacie tarcie płynne. Tak więc dzięki korekcji można zmniejszyć prace tarcia w łożysku.

EN

It is well-known that the distribution of contact pressures is improved by the correction of working surfaces of roller bearings, since edge concentrations of these pressures are reduced. However, there are various kinds of correction of different degrees of manufacturing difficulties and different effects. Arc correction, chord correction and logarithmic correction with modification are most frequently used. In the paper, comparisons of the three correction types taken from the literature are quoted. In the comparisons different loads of contact and the tilt of the roller with respect to the raceway axis that can occur in practice have been taken into consideration. The diagram of the ,,contact load capacity" proves that logarithmic correction with modification generally gives the best effects. The second purpose of using correction is to reduce the friction work at the contact of the rollers with the side flange. Correction of this contact can consist in: - deflecting the generatrix of the side flange from the roller end plane, - replacing the flat roller end with the convex end, - introducing a convex generatrix of the side flange. In the article different forms of corrected contact have been analysed (basing on the figures given) and their advantages in the aspect of the formation of fluid friction on the roller end have been shown. The best conditions for the formation of an hydrodynamic oil film occur when the convex roller end and the side flange of the slightly tilted generatrix are combined. This is the case of a small sensitivity to the manufacturing errors and load changes. The possibility of the easy formation of an oil film has been assessed on the grounds of the shape of the bearing interspace and the rate of the lubricant inflow to the contact area. The third aim of using correction is the possibility to modify the moments of tangent forces acting upon the roller from the side of raceway of the inner and outer ring. This refers to bearings of the tilted axis of the rollers in relation to the bearing axis, since the correction of these raceways and the correction of the lateral surface of the roller affects the contact length, the distribution of the rubbing speed and the distribution of unitary tangent forces. By modifying moments of tangent forces one can control the tendency of the roller to skew and there by affect friction work in the bearing. In barrel bearings a reduction in the tendency to skew results in the so called self-stabilisation of the roller, i.e. the loss of the pressure force between the roller and the side flange. The preservation of such a state during operation of the bearing greatly decreases friction work. In cone bearings there is a tendency of the roller to skew, caused by the friction force on the side flange. The moments of friction deliberately generated and determined by the correction on the main raceways can compensate this tendency. This also results in a decrease in the total friction work. However, in order to achieve this goal a certain perturbation of the kinematic conformity in the cone bearing is necessary. In view of the purposes being so different, it is not easy to select the proper magnitude of correction. A certain compromise is necessary and it is for the designer of the bearing to decide about it.