| The quasi-brittle materials are widely used in engineering application,and the common quasi-brittle materials include concrete,cement and cement based composites,etc.The complex microscopic characteristics and mechanical properties of quasi-brittle materials pose a challenge to the damage analysis of structures which are constructed by these materials.It has been an important topic of damage and fracture research.Based on the micro-structure,mechanical properties and fracture characteristics,the domain information transmission model for quasi-brittle cracking analysis is established in this paper.The multi-level analysis is carried out using the information transmission manner which is from domain to domain.It realizes exit criterion of the representative volume element(RVE)when simulating the damage evolution process of quasi-brittle materials.The proposed model presents an effective plan to the phenomenon that the computational cost keeps increase with the variation of the range of damage area in the model.The global numerical model in which the basic elements are material particles is established.The boundary displacement of the material particles are basic unknown of the global model.The displacement modes relating to crack are embedded on the boundaries of material particles,which realize the exact equivalence of crack band from micro-structure to the global model.In this paper,the enrichment functions with continuous steps are proposed.The enrichment functions describe the deformation characteristics relating to crack band on the boundary of material particle.It realizes a priori unknown way to capture the intersection of crack band and material particle boundary,and allows the crack band to enter and leave material particle at any position on the particle boundary.It can describe the crack characteristics on the global level effectively.The added equation to solve element status is established.It determines if the enriched degrees of freedom are needed to be introduced somewhere according to the deformation of global elements,which realizes the dynamic activation and exit of enriched degrees of freedom.It makes the degrees of freedom of the global model not to keep increase with the variation of damage regions and decreases the computational cost of the global model significantly.The domain information transmission process is established.By the information transmission between the material particle and RVE,the multi-level simulation with relatively high accuracy for the damage trans-scale evolution process is realized.It avoids the re-meshing,re-computation caused by the re-establishment the the entire model and variation and connection relating to the insertion and exit of models with different scales.The RVE is established using the Lattice model,which can reflect the complex microscopic characteristics of quasi-brittle material accurately.It reflects the distribution and mechanical properties of different components,which can simulate the damage evolution process of quasi-brittle material.By using the Lattice model,the full microscopic model of the specimen is established.It is used as the reference model and the damage and fracture process is analyzed.According to the damage and fracture characteristics,the mechanism of activation and exit of RVE is established.The local unloading phenomenon is studied.The exit criterion of perforative RVE is established by the machine learning and damage evolution rate method.The exit criterion of RVE with low deformation degree is established by analyzing its deformation.The model realizes the dynamic activation and exit of RVEs,which makes the degrees of freedom not to keep increase in the entire model and improves the computational efficiency of the domain information transmission model significantly.By using the proposed model,the damage processes of beam and L-shaped specimens consisting of quasi-brittle materials are simulated.The damage evolution process is analyzed.By comparing the simulation results from domain information transmission model and reference model,the accuracy and efficiency of the proposed model and the effect of the RVE exit mechanism on the improvement of computation efficiency are studied.The simulation shows that the results obtained by the proposed model are consistent with the reference model.Although the microscopic characteristics and fracture pattern of quasi-brittle materials is complex,the characteristics can be described by domain information transmission model accurately.The exit mechanism improves the computation efficiency significantly. |
