Macro-mesoscopic Simulation Research On The Node Fracture Damage For Hybrid Structures

The purpose of this paper is to solve the problem of the separation of the whole analysis and the node analysis in the traditional structural analysis.This analysis method has the deviations brought by the simplification of the force and boundary condition of the node with less accurate.At the same time the current node analysis rarely consider the scrutiny of crack propagation.In this article,a series of multi-scale method of macro-meso-coupling method is explored.What's more the extended finite element method was used to consider the mesoscopic-crack propagation in the node analysis,thus came to realize mulit-scale coupling and cross-level association which not only makes up for the deficiency of traditional structural analysis,but also can consider the influence of mesoscopic cracks more precisely.In the end,the theory is applied to practical engineering analysis,this paper has both theoretical breakthrough in mechanics level and practical engineering significance.The main work includes the following five aspects:1.Mastered the latest technology of structure elastic-plastic analysis know as multi-scale analysis and to improve the technology.One of the trends in the structural elastic-plastic analysis of the current structure is to analyze the local mesoscopic failure process and the overall macroscopic behavior of the structure with the same model.The key to solve this problem is multi-scale method.Based on the existing research results,different mechanics model is adopted at different parts of the structure,and thecooperative calculation between different scale models is realized by the appropriate connection method.Besides the author introduced the sub-structure method in the multi-scale analysis,which greatly improves the calculation speed and the computational efficiency without affecting the accuracy of the calculation.In the case of limited computing ability,the method can quickly and accurately implement the high-definition.2.Focused on the simulation of the dynamic expansion of crack.It is found that the most effective method to deal with dynamic crack is extended finite element method(XFEM).The extended finite element method is a kind of discontinuous finite element method,after ten years of theoretical research,application of XFEM in the simulation of the crack problem has been quite mature.The authors used the XFEM method to study the fracture toughness requirements of high strength steel nodes with initial defects and concrete nodes with mesoscopic crack and the seismic performance of high strength steel joints with initial defects.The simulation of the expansion process under the action of static load and cyclic load is solved in the process of studying the breaking performance and seismic performance of the joint.3.Based on the multi-scale theory and XFEM theory,the effect of mesoscopic crack propagation on the overall performance of the structure is introduced for the first time in the time history analysis of the structure.The initial crack and crack propagation are introduced into the whole structure analysis,and the detailed analysis of 2D frames and3 D concrete frame is carried out.In this process,the author combined crack propagation process and the time history analysis together,while the steel frame and concrete frame elastic-plastic analysis technology has been improved4.In order to introduce the crack propagation simulation into the hybrid structure,the author explored the interface problem which belongs to the weak discontinuity problem.By comparing the research results with the relevant research,experimental and theoretical studies,the crack propagation in the hybrid structure simulates the good symbolic reality.The methods used in this paper to deal with the problem of continuous and the problem of discontinuities was conformed to the actual state of the structure,and it can be used to solve crack propagation simulations in interface problems similar to hybrid structures.5.On the basis of the theoretical breakthrough in the preceded four chapters,the author applied the method to the concrete engineering practice.The engineering structure system is the overrun frame transition structure,and the conversion beam and the conversion column are steel-reinforced concrete hybrid structure.In the structural elastic-plastic analysis,the influence of mesos-cracks or initial defects on the overall performance of the structure is taken into account,and the damage process at the critical nodes is also obtained.