Analysis and Test of Tribological Behavior at Interface between Lower Residual Limb and Prosthetic Socket

The 3D models of the bones, soft tissue and prosthetic socket were reconstructed by using CT scanning, image processing and reverse engineering techniques. The stress and slippage of the residual limb skin in a gait cycle were calculated by applying the load of five typical phases, i.e. Heel Strike,Foot Flat, Mid-Stance, Heel Off and Toe Off, respectively. Consequently, the maximum critical parameters were determined on the basis of the above results. By using a UMT-II tribometer to simulate lower residual limb/prosthetic socket interface, the tribological behavior of residual limb skin was investigated in vivo under the critical parameters in a gait cycle. The finite element results show that the maximum normal stress and shear stress in the five typical phases occurred all at the position of patellar tendon. In the phase of Heel off, the maximum normal stress was 384.3 kPa and shear stress was 102.1 kPa. With decreasing normal force, the friction force reduced while the friction coefficient increased. When the normal stress was lower than the critical value of 39.5 kPa, the relative sliding occurred on the contact interface and the friction coefficient reached the maximum value. Frictional experiment results show that the residual limb skin was in a frictional state of adhesion when the normal loads were 17 N and 7 N. The adhesion degree increased with the skin elastic deformation increasing.