XFEM-3D Dislocation Dynamics Coupling Algorithms And Applications

The evolution of dislocation motion affects the plastic deformation of crystalline materials.The discrete dislocation dynamics method studies the plastic deformation of materials by simulating the motion state of dislocations,but the method is limited to infinite models.Discrete dislocation dynamics-finite element superposition method(DDD-FEM)and discrete dislocation dynamics-finite element coupling algorithm(DCM)using finite element method for solving boundary value problems have strong grid dependence problems.The discrete dislocation dynamic-expansion finite element(DDD-XFEM)coupling algorithm breaks through the grid constraints.However,this method is still insufficient for the research involving a large number of dislocations and interface problems,and the problem of three-dimensional dislocations has not been involved.In view of this,based on the research of the two-dimensional DDD-XFEM coupling algorithm,this paper proposes the XFEM-three-dimensional dislocation dynamic coupling algorithm,and uses Fortran language to write numerical calculation program,combined with Ansys finite element software,The wrong question is calculated.The research content and main conclusions of this paper have the following points:1.The XFEM-three-dimensional dislocation dynamic coupling framework is proposed,and two calculation schemes are given: a coupling algorithm with only three-dimensional dislocation step expansion and a coupling algorithm that increases the stress field correction term near the dislocation core.By comparing and analyzing several typical examples,it is found that the coupling algorithm with only three-dimensional step expansion has higher computational efficiency,but the calculation accuracy is not high in the region with high singularity near the dislocation core.Then,based on the existing problems,a coupling algorithm for increasing the stress field correction term near the dislocation core is proposed.The accuracy of the calculation results is significantly improved,but the calculation efficiency is reduced.2.The straight edge type dislocation model with different numbers of straight edge type dislocations and cylindrical holes is calculated.The calculated results agree well with the corresponding theoretical solutions,and the reliability of the algorithm and program is verified.Then,the algorithm is applied to models that do not exist in theoretical solutions,such as dislocations and spherical holes,two-phase materials and inclusions.The simulation results extend the understanding of complex dislocation problems.3.The straight edge type dislocation model and the dislocation loop model are calculated by the coupling algorithm which increases the stress field correction term near the dislocation core.The calculation results are compared with the calculation results and the theoretical calculation results only including the three-dimensional dislocation step expansion algorithm.Increase the reliability of the coupling algorithm for the stress field correction term near the dislocation core.In addition,the comparison results show that the proposed two algorithms are in good agreement with the theoretical results in the region far from the dislocation core,but in the vicinity of the dislocation core,the algorithm that adds the correction term has higher accuracy.