Research On Simplified Modeling Method Of Bolt For Explicit Dynamic Analysis

Explicit dynamic analysis is widely used in impact problems because of its strong ability to deal with highly nonlinear problems such as large deformations and fractures.For explicit dynamic analysis,the time step and the amount of elements used in the calculation will significantly affect the calculation time.Among them,the time step will be affected by the minimum element feature size and material parameters.The smallest element feature size is usually controlled by small parts.Using a simplified analysis model instead of a detailed analysis model can effectively overcome the problem of too small feature size of the minimum element,and at the same time can reduce the amount of elements of the analysis model.Bolts are a common type of small parts.In the explicit dynamic analysis,if the bolt influence is not considered,the stiffness of the connection will be estimated too high,and considering the bolt influence,the minimum characteristic element size will be too small and the analysis will take too long.Therefore,the modeling method of the simplified analysis model of the bolt has received extensive attention in the engineering field.However,the existing simplified bolt modeling method is not suitable for the impact simulation based on explicit dynamic analysis.For this reason,based on the traditional bolt simplification method,this paper proposes two improved bolt simplification modeling methods oriented to explicit dynamic analysis,and uses numerical simulation analysis,experimental testing and other methods to verify the effectiveness and feasibility of the proposed methods.The main research contents of this paper are as follows.Firstly,for the LS-DYNA analysis platform,two improvements to the classical bolt modeling methods are proposed: 1)Improved method of bolt simplification modeling for shell-beam coupling;2)Improved method of bolt simplification modeling for beam-beam coupling.The specific improvements and problems solving are as follows: 1)The introduction of contact beam elements and shell elements solves the contact problem between beam elements and solid elements;2)The selection of multi-segment beam elements solves the problem of inaccurate deformation of beam elements;3)By increasing The stiffness method of the local shell elements overcomes the problem of abnormal deformation of the shell elements caused by stress concentration.After that,based on the quasi-static problem,numerical simulation tests and experimental verification were carried out on the improved simplified bolt modeling method,considering the axial tensile load and the transverse shear load respectively.Numerical analysis and test results under the two load models show that the results obtained by the proposed simplified bolt model are basically consistent with the results obtained by the detailed solid model and experimental tests.This result verifies the validity and feasibility of the proposed simplified bolt model.In this study,in order to improve the accuracy of analysis,the proxy model technology was used,and an auxiliary program tool for parameter optimization of exponential material model was developed based on Matlab.Finally,this study applies the improved simplified bolt modeling method to impact load analysis.In the research,firstly,the simplified model and the detailed model under different impact speeds were compared based on the simple analysis model.Numerical results show that the proposed simplified models are basically consistent with the detailed model results for the response of common engineering structures such as deformation history and stress level.Furthermore,in order to verify the feasibility of applying simplified bolt modeling technology to complex models,this paper applies the proposed method to a complete aeroengine model to carry out FBO load analysis.The analysis results show that simplified bolt modeling technology can not only ensure calculation accuracy,but also save analysis and calculation time and improve analysis efficiency.Therefore,the proposed bolt simplification method has good engineering application feasibility.