Modeling And Identification Of Nonlinear Bolted Structures

Structures with bolted connections have found diverse applications in the aerospace engineering fields.If the effects of the bolted connections on the system dynamics are neglected when modeling the mechanical structures,a significant error may be produced between the theoretical and experimental results,especially in some cases with large excitation or motion levels.However,it is quite challenging to model these bolted structures accurately due to their complex and nonlinear dynamics characteristics.The thesis focuses on modeling and identifying structures with local nonlinearities introduced by bolted joints.The main contents and results of the thesis are as follows.1.The nonlinear modeling and identification of a system of two-degree freedom with a nonlinear boundary connection are investigated by using Valanis model and Bouc-Wen model,respectively.2.Experimental tests at low and high excitation levels are performed to reveal that the dynamic characteristics of the bolted beam are approximately in the linear and nonlinear state at low and high excitation levels,respectively.Therefore,two Valanis models are used to model the nonlinear behaviors of the bolted joint and the boundary connection,respectively.The equivalent linear material parameters of the beam is identified via experimental test with low excitation level;whereas the parameters of Valanis model are identif ied by us ing optimization technique in order to minimize the residual error between the measured and the simulation data at a high excitation level.F inally,the identif ied models are verified by comparing the results of the identified model and the experimental test under another exciting level.3.Finite element modeling and parameter identification are performed on the structure of Aluminum Honeycomb Panel with multiple bolted joints.Finite element method is exploited to model the panel and the bolted connection interface as a homogeneous,isotropic plate and a thin layer of a bilinear elastic-plastic material,respectively.The linear material parameters of the panel are identif ied via experimental tests with low excitation levels,whereas the nonlinear material parameters of the thin layer are updated by using experimental tests with high excitation levels.Finally,the proposed modeling and identification strategies are verif ied by comparing the results of the identified model and the experimental test under another exciting level.