The Iwan model is composed of elastoplastic elements and is widely used to represent the stiffness degradation of bolted joints under mixed-mode loading (normal and tangential loading). The latest static methods of parameter identification established the relationship between the elastoplastic elements and the contact pressure under normal loading. Under mixed-mode loading, the parameters of the Iwan model are dynamic for the evolution of contact conditions. Therefore, static parameter identification methods are not suitable for the dynamic Iwan model. A new technique was proposed to identify the parameters of the elastoplastic elements in this paper. Firstly, several different finite element models were established. The influence of the contact method and the thread structure were analyzed, and a reliable and efficient bolted-joint modeling method was proposed. Secondly, the evolution of contact conditions was studied. The dynamic elliptical contact model and the ellipticity discrete method were proposed. Finally, the residual stiffness of the Iwan model was analyzed to establish the mapping between the residual stiffness and the bending of the screw. The results can provide a technique for identifying the parameters of the dynamic Iwan model.

The nonlinear dynamic behavior has an important impact on energy dissipation and vibration damping characteristics of bolted joints. Firstly, the development of tangential dynamic models is summarized and analyzed. Secondly, a five-parameter Iwan model based on a truncated power-law distribution is proposed. The backbone and hysteresis curves are obtained. Thirdly, normalized and dimensionless analysis is performed. On the basis of the above, a more concise four-parameter Iwan model with stiffness continuity is proposed. Finally, the validity of the model is verified by comparing the energy dissipation vs excitation force amplitude curve with the experimental data.