Mechanical structures with frictionally constrained interfaces often involve complex contact kinematics induced by tangential and normal relative motions. The tangential motion induces stick-micro/macro slip friction and causes energy dissipation. The normal motion induces normal load variation and possible separation of the joint interfaces. For effective analysis of dynamics of jointed structures, a reduced friction contact model is needed to characterize the nonlinear, coupled normal and tangential contact behaviors precisely. However, most developed microslip friction contact models considers only constant normal load.
In this paper, an improved microslip friction model with normal load variation induced by normal motion is proposed. The tangential stick-micro/macro slip friction is modeled by continuous Iwan hysteretic model. This model is characterized by a slippage uniform distribution density function and a linear stiffness at stick state. The coupling relationship between tangential nonlinear restoring force and normal load variation is built. This leads to generalization of the original Iwan hysteretic friction model to consider the effect of variable normal load. The proposed model is applied to model a 7-dofs frictional damping experimental system. The results show that normal load variation and tangential microslip motion exert an important effect on prediction of friction contact behaviors. The proposed model is capable of generating asymmetric hysteresis loops and intermittent normal separation. The numerical simulation fit well with the experimental results for the 7-dofs frictional damping system, which validates the effectiveness and accuracy of the proposed model.