EFFECT OF ROUGH SURFACE ASYMMETRY ON CONTACT ENERGY LOSS IN HIP IMPLANTS

Abstract

Rough surface height distribution can be nonsymmetric, depending on the process of surface preparation. The prevalent processes for implant surface involve turning and milling, both resulting in surface height distributions of nonsymmetric nature. Asymmetry in a surface height distribution is manifested through a parameter known as skewness. Unlike Gaussian distribution, Weibull distribution permits characteristics such as skewness and kurtosis in data to be included in the mathematical description of a height distribution. This paper develops hip implant contact model based on Weibull distribution of surface heights. The elastic–plastic interaction of implant surfaces are considered as macroscopically spherical surfaces containing micron-scale roughness. Symmetric and asymmetric roughness height distribution are compared. The total contact force is related to the minimum mean surface separation of the contacting rough surfaces. The force is obtained using statistical integral function of the asperity heights over the possible region of interaction of the roughness of surfaces. Approximate equations are obtained that relate the contact force to the minimum mean surface separation explicitly. The approximate equations are used to derive hysteretic energy loss per load–unload sequence, contact frequency, and damping. It is shown that energy loss per cycle, contact frequency, and damping are lower for asymmetric surface roughness distribution.