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 dynamic response of complex equipment under mixed-mode loading is significant for structural design. Bolted joints are the primary connection mode of subsystem assembly, and the degradation of bolted joints may reduce the safety and reliability of the equipment. The Iwan model is widely used to describe the degradation of bolted joints, which has been continuously revised and experimentally verified. The classic Iwan model is a static model that lacks predictive ability. The latest dynamic Iwan model can predict the softening process and reveal the physical mechanism of degradation. However, the function of dynamic pressure distribution needs to be determined for the model solution. We analyzed the contact boundary and pressure distribution under mixed-mode loading with the finite element method (FEM) and proposed the dynamic functions. Secondly, we put forward two correction methods to compensate for the loss of preload caused by simplification and to achieve consistency between the pressure distribution function and the contact boundary function. Finally, the influence of discrete order on the correction of pressure distribution was analyzed. The results show that the constraint method is more suitable for the modification of the pressure distribution. The research results can be applied to the solution of the dynamic Iwan model.

No abstract

No abstract