Friction-induced squeaking has been reported in 1-20% of patients who have ceramic on ceramic total hip replacement, which is a subject of annoyance. Friction induced stick-slip phenomenon is the driving force behind squeaking.The friction behavior of the bearing surfaces is ruled by the lubrication conditions, which may be from hydrodynamic lubrication to mixed or boundary lubrication. In the latter two conditions, there is surface-to-surface mechanical contact which may give rise to the friction-induced&nbsp;stick-slip phenomenon. Essentially, stick-slip occurs when the film lubrication is broken. Stick-slip is an undesired phenomenon and is understood to give rise to the squeaking phenomenon in the hip bearing surfaces.Fluid film lubrication is a function of sliding speed, lubricating fluid viscosity, bearing roughness, clearance, and contact pressure. A breakdown of fluid film lubrication may result from edge loading, presence of wear particles during articulation, damage to the articular surface resulting in increased roughness, mismatched bearing diameters, etc.This work attempts to develop a predictive stick-slip mathematical model that can predict the dynamic behavior of the hip bearing surfaces to define the design parameters and understand the squeaking phenomena in them by developing a robust model. The mathematical model is proposed which combines the lubrication theory and the lumped parameter model. It is assumed that the bearing surfaces operate between mixed and boundary lubrication regimes and the asperities are in contact with each other during the squeaking phenomenon. The lumped parameter model with coupling stiffness was used to study CoC bearing surfaces with the inclusion of boundary lubrication in order to examine how dynamic parameters (mass, the moment of inertia, and coupling stiffness) are involved in stick-slip phenomena. The simulations were also performed using the parameters taken by a ceramic-on-ceramic hip explant. The objective of the study is to provide a practical design tool to predict stick-slip conditions and to choose the optimal mechanical specifications.Numerical simulations demonstrate how the critical conditions vary with design parameters. A larger size of the limit cycle represents squeak. The possible factors attributing to the hip squeak were investigated in which the stick-slip phenomenon is the primary contributor.&nbsp; Using numerical modeling and computation, the effect of the variation of coupling stiffness and lubrication on system stability was studied using a 2-DOF model. Phase space plots were used to illustrate the limit cycle motion of bearing surfaces for different sets of mass, stiffness, and damping, and demonstrated the significance of the coupling stiffness and the lubrication on the system instabilities with specific emphasis on squeak.

A Parametric Study: Influence of Geometry and Material Properties on the Response of the Femoral Head Through Biofluid

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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