Nowadays wear is recognized as one of the main concern of metal-on-metal (MoM) hip implants, causing osteolysis and the release of dangerous metallic ions. Numerical wear simulations of hip implants are an attractive tool to investigate and predict long-term wear at low cost. A few wear models have been proposed in the literature for MoM bearings [1-3], all based on the Archard wear law, as adhesion and abrasion are considered the main wear mechanisms. The reliability of such models mainly depends on a dimensional wear factor k whose evaluation/choice is actually a critical issue. Indeed k depends on many factors, such as lubrication regime, bearing materials and geometry, loading and kinematic conditions and thus can vary during a wear test/implant lifetime. This complex scenario is simplified in wear simulations which typically assume two constant values of k - equal for head and cup - one higher for the initial running-in phase (kri) and the other lower for the steady state phase (kss), according to experimental observations (Fig. 1). Such k values are generally estimated by matching numerical and experimental wear volumes obtained by hip joint simulator tests [2-3], sometimes even simulating conditions different from the experimental ones [3]. For these reasons and because of a complete neglect of the comparison between numerical and experimental wear maps, the validity of the wear models can be disputable.
Estimation of Wear Factors of MoM Hip Implants from Simulator Tests
MATTEI, LORENZA;DI PUCCIO, FRANCESCA;CIULLI, ENRICO
2013-01-01
Abstract
Nowadays wear is recognized as one of the main concern of metal-on-metal (MoM) hip implants, causing osteolysis and the release of dangerous metallic ions. Numerical wear simulations of hip implants are an attractive tool to investigate and predict long-term wear at low cost. A few wear models have been proposed in the literature for MoM bearings [1-3], all based on the Archard wear law, as adhesion and abrasion are considered the main wear mechanisms. The reliability of such models mainly depends on a dimensional wear factor k whose evaluation/choice is actually a critical issue. Indeed k depends on many factors, such as lubrication regime, bearing materials and geometry, loading and kinematic conditions and thus can vary during a wear test/implant lifetime. This complex scenario is simplified in wear simulations which typically assume two constant values of k - equal for head and cup - one higher for the initial running-in phase (kri) and the other lower for the steady state phase (kss), according to experimental observations (Fig. 1). Such k values are generally estimated by matching numerical and experimental wear volumes obtained by hip joint simulator tests [2-3], sometimes even simulating conditions different from the experimental ones [3]. For these reasons and because of a complete neglect of the comparison between numerical and experimental wear maps, the validity of the wear models can be disputable.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
