RESIDUAL-STRESSES IN ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE LOADED CYCLICALLY BY A RIGID MOVING INDENTER IN NONCONFORMING GEOMETRIES

The characterization of stress and deformation fields that incorporate moving cyclic loads and nonlinear material response in ultra-high mol ecular weight polyethylene components for total knee replacements is r equired to quantify mechanisms of surface damage. A simulation of stre sses in polyethylene components for total knee replacement subjected t o cyclic moving loads was performed with use of nonlinear finite eleme nt analysis. Convergence to a steady-state cycle of stress and deforma tion was observed within five cycles of loading. Differential plastic deformation under the surface of the polyethylene led to horizontal re sidual stresses that were tensile at the surface and compressive in th e subsurface. The magnitudes of the residual stresses indicate their i mportance in surface failure mechanisms. Horizontal residual tensile s tresses at the surface are consistent with the initiation and propagat ion of surface cracks that could cause pitting in polyethylene. Horizo ntal residual compressive stresses under the surface could cause such cracks to arrest or turn and thus limit damage to a region just beneat h the surface. The results emphasize the importance of incorporating n onlinear effects to simulate long-term stress fields associated with s urface damage in polyethylene.