Abstract
Anisotropic friction likely exists in human natural/artificial joints as well as various engineering systems with articulating bodies. In this study, a new experimental apparatus is designed and fabricated to measure load-displacement friction properties at the metal-polymer interface. Anisotropic friction properties at the polymer-metal interface are measured under tangential loads applied at different directions. Two series of polymer specimens with different surface roughness are considered. Metal specimens with similar surface roughness are used in this study. The measured interface tangential load-displacements are highly nonlinear exhibiting relatively large displacements prior to ultimate shear resistance forces. This is in contrast to conventional Coulomb friction curves in which no relative displacements occur before the maximum resistance forces are reached. The interface ultimate resistant force varies with the direction of loading, suggesting an elliptic failure criterion and demonstrating the anisotropy of the interface friction. For example, the mean friction coefficient along two interface perpendicular directions is measured to be about 0.12 and 0.19. These experimental results are incorporated into our existing numerical models of interfaces with nonlinear isotropic and anisotropic friction properties. The good agreement between experimental and finite element model results confirms the nonlinear, nonsymmetric, coupled constitutive relations developed to represent anisotropic interface friction properties. In this study, we have observed that the friction coefficient could vary significantly depending on the direction of loading. The current work also verifies the accuracy of developed finite element model to predict the response of contacting bodies with anisotropic friction.