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Research Papers

Transient Elastohydrodynamic Lubrication of Hip Joint Implants

[+] Author and Article Information
Fengcai Wang1

School of Mechanical Engineering, University of Leeds, Leeds LS2 9JT, UKf.c.wang@bath.ac.uk

Zhongmin Jin

School of Mechanical Engineering, University of Leeds, Leeds LS2 9JT, UK

1

Corresponding author. Current address: Department of Mechanical Engineering, University of Bath, Bath BA2 7AY, UK.

J. Tribol 130(1), 011007 (Dec 17, 2007) (11 pages) doi:10.1115/1.2806200 History: Received December 08, 2006; Revised September 12, 2007; Published December 17, 2007

A general transient elastohydrodynamic lubrication model was developed for artificial hip joint implants, particularly in which the three-dimensional time-dependent physiological load and motion components experienced during walking conditions were considered in the theoretical formulation, although only a predominantly vertical load combined with a flexion-extension motion was actually solved. A nominal ball-in-socket configuration was adopted to represent the articulation between the femoral head and the acetabular cup in both simplified and anatomical positions. An appropriate spherical coordinate system and the corresponding mesh grids were used in the general transient lubrication model. Additionally, an equivalent discrete spherical convolution model and the corresponding spherical fast Fourier transform technique were employed to facilitate the evaluation of elastic deformation of spherical bearing surfaces in hip joint implants. The general lubrication model was subsequently applied to investigate the transient lubrication performance of a typical metal-on-metal hip joint implant. The effects of both cup inclination angles in either anatomical or horizontally simplified positions and different lubricant viscosities on the transient elastohydrodynamic lubrication were analyzed under the predominant components of vertically dynamic loading and flexion-extension motion. It was found that the general lubrication model and the numerical methodology were efficient for the transient elastohydrodynamic lubrication analysis during walking condition in hip joint implants. Furthermore, the significant effect of squeeze-film action on maintaining and enhancing the total thin film thickness formation was discussed for the transient lubrication study of the typical hip joint implant.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

A ball-in-socket configuration for hip joint implants: (a) the simplified model for the cup positioned horizontally and (b) anatomical model for the cup with an inclination angle (β)

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Figure 2

Schematic diagram for spherical coordinate system with z axis passing through the poles

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Figure 3

Schematic diagram for three-dimensional loading and motion

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Figure 4

The angular velocity and angular position of flexion-extension motion during one walking cycle

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Figure 5

The dynamic load during one walking cycle

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Figure 6

Spherical coordinates and the corresponding mesh grids: (a) with a cup inclination angle and (b) z axis passing through the poles of the spherical coordinates

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Figure 9

The predicted three-dimensional film distributions (a), the cross-sectional film profiles (b), and pressure distributions (c) at the instant t=0.13s

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Figure 10

The predicted three-dimensional film distributions (a), the cross-sectional film profiles (b), and pressure distributions (c) at the instant t=0.33s

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Figure 11

The predicted three-dimensional film distributions (a), the cross-sectional film profiles (b), and pressure distributions (c) at the instant t=0.51s

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Figure 12

Comparison of the predicted minimum film thickness (a), central film thickness (b), and maximum pressure (c) between the different lubricant viscosities (Pa s) during one walking cycle

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Figure 13

Comparison of the predicted minimum film thickness (a), central film thickness (b), and maximum pressure (c) between two different cup inclination angle for 0deg and 45deg using the lubrication model shown in Figs.  11 during one walking cycle

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Figure 14

Comparison of the predicted film distributions (a), cross-sectional film profiles (b), and pressure distributions (c) at the instant t=0.13s for the simplified model with the cup positioned horizontally shown in Fig. 1 during one walking cycle

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Figure 8

The predicted three-dimensional film distributions (a), the cross-sectional film profiles (b), and pressure distributions (c) at the instant t=0.01s

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Figure 7

Variations of the predicted overall minimum film thickness (a), central film thickness (b), and maximum film pressure (c) versus the time in three walking cycles

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