Finite Element Analysis of Machining Damage in Single-Grit Grinding of Ceramic Knee Implants

Alumina is a common biomaterial used for knee implants due to its excellent biomechanical properties. However, the complex geometry and required surface integrity make precision machining of knee implants very difficult. Machining mechanics and damage mechanism is not well understood. In order to better understand the mechanism of alumina grinding, this work presents a numerical simulation of single point grinding of alumina at a shallow depth-of-cut. A 3D finite element model of single-grit ceramic grinding has been developed using the pressure dependent Johnson-Holmquist constitutive model. Failure strain (FS) was adopted as a user-defined element removal criterion to reveal damage mechanism during the grinding process. The predicted machining groove topography correlated well with the experimental observations. Surface and subsurface microcracks were characterized at different FS. The thrust, frictional, and grinding force histories were also investigated. Furthermore, material behaviors at different locations below the machined groove were analyzed to shed light on subsurface microcrack initiation and propagation.