Based On ANSYS Secondary Development Of Material Nonlinear Finite Element Analysis In The Underground Engineering

In the underground engineering mainly materials is the geotechnicalmaterials,geotechnical properties is very complicated,belong to the three-phase body frictionmaterial.Due to the geological characteristics of discontinuity, heterogeneity, anisotropy andgroundwater and initial stress characteristics,so many geotechnical problems is difficulted byanalytical method to solve,therefore could by numerical methods such as finite element tosolve.Soil have obvious elastic-plastic characteristics,must be elastic-plastic analysis canobtain the practical calculation results.Considering the above factors and in order to widen theapplication range of the finite element software ANSYS in underground engineering,in thispaper, by using ANSYS secondary development function — UPFs that User ProgrammableFeatures,to compile a subroutine that name of usermat.F based on the Mohr-Coulomb model,for geotechnical structure of material nonlinear finite element analysis.First of all,in the understanding on the basis of elastic-plastic theory including planestrain problem, yield condition, hardening model,the flow rule,uninstall criteria such as basicconcepts.Through the Mohr- Coulomb’s law,to deduce yield criterion in stressinvariants,Considering the isotropic hardening model and associated flow rule,using thesimple processing method to eliminate the expunction that uncertain singular point of plasticflow direction,convenient for numerical calculation of elastic-plastic stiffness matrix isdeduced.And then,according to the usermat subroutine has tasks of stress update and outputconsistent tangent operator matrix. Were elaborated in detail the fallback algorithm of solvingthe stress update about elastic prediction and plastic modification in mathematics andmechanics principle of these two steps;by incremental finite element consistent tangentoperator matrix is elastic-plastic stiffness matrix.On this basis, using structured programmingmethod,to compile the usermat subroutine usermat.F.,the subroutine of Mohr-Coulomb modelis imported to the warehouse of ANSYS by compiling linker.The last,through two examples to verify the correctness and reliability of the model inthis paper.By example 1 proves that the usermat subroutine can complete stress updatetasks,and can reflect the soil from on macroscopic began to stress shear broken up of thewhole process.By example 2,to illustrates the Mohr-Coulomb model can achieve the result ofDP model close,in addition from the safety factors and soil is the essential attribute ofconsideration,in the underground engineering,only to use,the elastic-plastic analysis canreflect the mechanics characteristics of geotechnica.