Nonlinear Dynamic Modeling Of Bolted Structure With Stiffness Degradation Feature

Welding,riveting and bolting are among the most commonly used connection methods.Bolted connection is a conventional connecting approach and widely applied in every engineering fields because of its flexibility superior to both welded and riveted joints.However,bolted connection may fail not only in the way of fatigue or strength failure,but also the failure cause by stiffness degradation under heat or vibration.In this article,a nonlinear dynamic modeling method of bolted structure with stiffness degradation feature is proposed,which includes following parts:Firstly,a nonlinear dynamic modeling method of bolted structure is proposed based on Iwan model.The bolted structure is considered as a continuous structure.Constitutive model of the material for the continuous structure referred is determined by the force-displacement formulation and the elastoplasticity hypothesis.Iwan model gives the force-displacement formulation of bolted connection structure,and the hardening property of target equivalent model under cyclic loading is specified by kinematic hardening rule.The proposed equivalent modeling method is realized by UMAT subroutine of ABAQUS,a commonly used commercial FEM software,and verified by comparing with both theoretical and experimental results reported in literatures.The proposed modeling method is flexible and practical,for this method can be realized and applied to common 3D meshing along with common FEM software in engineering.Secondly,experiments that quantitively measuring stiffness degradation of bolted joints under vibration and heat are completed.The stiffness degradation properties of both composite material joints and metal material joints are measured different ways.The stiffness degradation properties of composite joints is determined by measuring fundamental frequency of the structure,and the one of metal joints is by measuring clamp forces of bolts.The contributes of different heat and vibration loads are analyzed by comparing measurements under different load cases.The general rule of stiffness degradation properties under vibration is induced from measured time-clamp force data of metal joints under vibration.Lastly,the nonlinear dynamic modeling method of bolted structure with stiffness degradation feature is proposed based on previous works.The equivalent modeling method is advanced with time-dependent stiffness term,which determined by the general rule of stiffness degradation achieved previously.The equivalent modal parameters are achieved by experimental dynamic responses with neural network method.The proposed modeling method is verified by time-frequency analysis and frequency domain analysis of dynamic responses of an example specimen.