The Influence of Load and Angular Displacement Amplitude on the Torsional Fretting Wear of a Ball-on-Socket Cervical Disk Model

The torsional fretting wear behaviors of artificial cervical disk were studied under different loads (50, 100, and 150 N) and angular displacement amplitudes (±2 deg, ±5 deg, and ±7 deg). The cervical prosthesis was simplified and designed as a ball-on-socket contact with the material configuration of ultrahigh molecular weight polyethylene (UHMWPE) and thermally oxidized titanium alloy. The fretting running regime changed from mixed regime (MR) to slip regime (SR) when the angular displacement increased from 2 deg to 7 deg. The frictional torque became larger with an increasing load at all of the angular displacement amplitudes. Larger load and angular displacement amplitude also led to more severe wear for UHMWPE ball. The damage patterns for titanium socket were only slight scratches and polished tracks on the raised oxide scales. However, the dominant wear mechanism was abrasive and adhesive wear as well as deformation for UHMWPE ball. Hence, titanium socket revealed less severe damage than UHMWPE ball due to the protection of oxide film. Arc-shaped wear scars and scratches appeared in both the central and edge zones of the ball and socket component, which were rather different with that of ball-on-flat. In addition, a new damage pattern, annular stress concentration damage, occurred on the edge of UHMWPE ball characterized by severe abrasive and adhesive wear.