Secondary Development And Application Of ANSYS Based On Twin Shear Unified Strength Theory

ANSYS,as a general-purpose finite element software,has powerful exploitable performance to meet the needs of geotechnical engineering applications.The self-contained D-P(Drucker-Prager)criterion uses the outer circle of the corner points on the yield surface of Mohr-Coulomb,and the calculation results will have great deviations in the numerical analysis and calculation.Considering the influence of intermediate stress by introducing the influence parameter b of intermediate principal stress into the twin shear unified elastic-plastic constitutive model will remedy this shortcoming and be widely used in geotechnical engineering.In this paper,the twin shear unified strength theory is transformed into another expression by stress invariants(I₁?J₂)and stress angle?.The associated flow law is adopted to derive the ideal elastoplastic principal model of twin shear unified strength theory.The twin-shear unified model can correspond to different yielding criteria according to different values of the intermediate principal stress coefficient b.To facilitate the use of different criteria,a user-defined subroutine USERMAT.F dedicated to the calculation of the twin-shear unified strength theory can be written in the USERMAT program using the FORTRAN language through the user program feature interface of ANSYS'own secondary development platform.The specific steps of calling the subroutine by ANSYS software are given to finally realize the calling of the program USERMAT.F.In order to verify the correctness of the subroutine,a classical tunnel example is cited and its theoretical equation solution and the numerical solution calculated by the secondary development are analyzed to verify the correctness of the derivation of the elastic-plasticity principal structure relationship and the subroutine editing.The results show that the subroutine is correctly developed.Finally,the twin-shear unified strength theory is applied to the analysis of soil slope displacement problems to obtain the effect of displacement variation under intermediate stresses.