Research On Collapse Performance Of Single-Layer Grid Structure Based On Discrete Solid Element Method

Traditional numerical calculation methods based on continuum mechanics will encounter problems such as serious grid distortion,element disappearance,and discontinuity of displacement fields when dealing with structural strong nonlinear problems,which make the solution convergence difficult.The calculation methods that are limited by the deformation coordination conditions and the displacement continuity conditions usually require manual intervention and correction when dealing with complex mechanical problems,and their limitations are obvious.Based on this,this paper adopts a new type of numerical calculation method—discrete solid element method（DSEM）to simulate and study the structure’s large geometric deformation,material nonlinearity,crack propagation,structural collapse and other strong nonlinear problems.The effectiveness of this method in dealing with continuum structure failure and its superiority compared with traditional methods are verified,and new ideas and algorithm tools are provided for structural analysis.This paper firstly presents the complete calculation framework of the DSEM suitable for solving three-dimensional structural mechanics problems,and discusses the reasonable values of the number of sphere elements,damping,and calculation time steps in the calculation model.Based on the advantages of Grasshopper’s visual programming,the pre-processing module of the DSEM was developed,and operations such as geometric input,sphere division,and preprocessing file output were successfully realized.The calculation program is developed using Fortran language,and the solution module is divided into the main program and three subprograms for elastic calculation,elastoplastic calculation and fracture calculation.The corresponding subroutines can be flexibly called according to the specific requirements during calculation,thereby improving the efficiency of the solution.The calculation program developed in this paper is verified by a specific calculation example,and the influence of the size of the sphere element on the calculation accuracy of the model is discussed.Based on the characteristics and basic principles of the algorithm,the DSEM force control method and the displacement control method are established to calculate the nonlinear large deformation of the bar structure,and the respective applicable ranges of the two control methods are obtained.For the solution of the elastoplastic problem,the yield equation expressed by the contact force between sphere elements is introduced through the Mises yield condition,and the elastoplastic contact constitutive equation of the DSEM in incremental form and the judgment criterion of loading and unloading are given.Use self-programmed programs to simulate and analyze several classic examples,and track the complete deformation process of the reticulated shell structure from partial member instability to overall instability and multiple instabilities.It is verified that the method in this paper can effectively describe the post-buckling behavior of complex structures,and provides a simple and efficient algorithm tool for the analysis of nonlinear problems of continuum structures.The crack propagation is realized by breaking the connecting spring between the spherical elements.The basic principles of fracture mechanics and the DSEM are combined to determine the strain energy release rate criterion for judging the occurrence and development of the crack,and the spring softening model is established.Developed the DSEM fracture calculation module to simulate and analyze the fracture process of rectangular beams under tension and torsion load.The comparison with the results in the literature verifies the correctness of the fracture calculation subroutine developed in this paper,which can be applied to the treatment of strong nonlinear problems such as component fracture and structural collapse.Finally,the fracture calculation program is applied to the numerical simulation study of the collapse of the single-layer grid structure.Establish a single-layer grid structure calculation model based on the DSEM,and simulate the process of the single-layer grid structure from local member fracture to the overall collapse of the structure,and analyze the influence of material properties,loading methods and rise-span ratio on the collapse performance of the structure.The calculation results further verify the feasibility and unique advantages of the DSEM in handling strong nonlinear problems such as continuum structure fracture and collapse,and provide new technical means for solving complex mechanical behaviors of structures,which has certain guiding significance and scientific research value.