Effects of sliding kinematics and normal load on the tribological behavior of metal/polymer contact

Wear and friction simulator with metal cylinder on flat polymer was developed to analyze the tribological behavior of tibial insert used in Total Knee Replacement (TKR). For the kinematics, flexion/extension motion (F/E) was applied to the metal cylinder and anterior/posterior translation (A/P) was applied to the flat polymer. Tests were first carried out with polymethylmethacrylate polymer (PMMA) for which the tribological behavior has been well developed. High density polyethylene (HDPE) was also characterized. In fact HDPE has been firstly used in the tibial insert before the use of ultra high molecular weight polyethylene (UHMWPE). Sinusoidal motions were considered for the F/E and A/P with 8.185 and 5 mm amplitude respectively. F/E and A/P motions were generated separately under a constant applied normal load and 1 Hz frequency. For each test condition, the damage of polymer surfaces was analyzed by following the evolution with the cycle numbers of the friction coefficient, the surface roughness and the micrograph of the wear scar. Whatever the sliding kinematics is, the initial average value of the friction coefficient measured is 0.3 for the steel/PMMA contact and 0.07 for the steel/HDPE contact. These values are similar to those presented in the literature. Specific tribological behavior, which present direct dependence on the sliding kinematics, was identified for each steel/polymer contact.