Micro-macro wear-fatigue of modular hip implant taper lock coupling.

A multiscale methodology for fretting wearfatigue analysis of a prosthetic hip implant taper-lock assembly is presented. On a macroscopic scale, the stem and cap surfaces are smooth. However, on a microscopic scale, surface roughness undulations are employed to accentuate the frictional contact for an enhanced mechanical locking effect. Macroscopic (global) modelling for fretting wearfatigue prediction of two head stem material combinations, namely, Co-28Cr-6Mo against direct metal laser sintering Ti-6Al-4V (Ti64) and forged Ti-6Al-4V, is investigated. The significance of fretting wear and fatigue in a hip joint for 10 years of service in a normal-weight male for moderately intense exercise is predicted for both material combinations. A micro-scale fretting wearfatigue model of the surface undulation submodel is developed to predict wear and fatigue micro-cracking. A key aspect is the development of a multiscale wearfatigue algorithm using adaptive meshing. Both material combination joints are shown to have sufficient wear resistance with direct metal laser sintering Ti64 performing better in terms of both fretting wear and fatigue.