Development Of UMAT Subroutine For Rock Baserd On Mohr-coulomb Criterion

In recent years, a number of major rock mass projects have been destructed dueto instability, causing huge economic losses and a large number of casualties.However, the existing numerical methods cannot simulate well the stability of therock mass project. Therefore, it is an urgent major issue to develop a program whichcan take the rock crack initiation, expansion and pierce into consideration andsimulate the stability of the rock mass project. ABAQUS is now one of the generalprofessional finite element sotfware and has a powerful function of nonlinearanalysis. Meanwhile, ABAQUS provides the secondary development subroutineinterface by which the user can easily create their own subroutine as needed,expanding the ABAQUS application. UMAX subroutine interface is with goodstability, openness and other features and used by many scholars to study anddevelop the constitutive model. This paper builds a rock elastoplastic UMAXsubroutine and analyzes its parameters on the base of the study on the rock statisticsdamage constitutive model.When studying the rock statistics damage constitutive model, the paper uses anew measure method of the rock infinitesimal strength and considers the impact ofrock damage threshold. Besides, in order to obtain the damage variable expressionin the rock constitutive equation and analyze the determination of the rockconstitutive model parameters. At last, the paper describes the design process of therock constitutive program.In fact, the rock has entered the elastoplastic stage before it is damaged.However, the Mohr-Coulomb criterion that is used usually to judge whether the rockmaterial is yielded has such drawbacks as the complex numerical calculation andslow convergence. This paper applies the yield function to handle the comer andhyperbolic approximation yield function to improve the Mohr-Coulomb criterion.Then the paper calculates the expression of the first order partial derivative of theimproved yield function as well as the expression of the first and second orderpartial derivatives of the potential function. The obtained equations are used for theshaping correction of the elastoplastic constitutive model and the consistencycalculation of the tangent stiffness matrix. The paper programs the elastoplastic constitutive model UMAX subroutine forthe undamaged phase in the rock statistics damage constitutive model based on theimproved Mohr-Coulomb criterion. Then, the paper the contrasts the calculationresult of UMAX subroutine that is developed based on the improved Mohr-Coulombcriterion and that of Mohr-Coulomb criterion program with ABAQUS by theuniaxial compression test, pure shear test and uniaxial tensile test separately, inorder to verify the accuracy of the rock elastoplastic constitutive model UMAXsubroutine for the undamaged phase in the paper that is developed on the basis ofMohr-Coulomb criterion. Also, the paper applies the developed subroutine toanalyze the effect of transition angle change in the uniaxial compression test, pureshear test and uniaxial tensile test respectively on the stress-strain calculation results.Finally, the paper presents the calculation design thinking for the damaged phase inthe rock statistics damage constitutive model.