Ali Salehi Nasab

Grade:  Master

Thesis Title:

Anisotropic damage effect on large plastic deformations and its application to metal forming

Year: Sept. 2014- May. 2017.

Abstract:

The use of highly efficient constitutive equations improves the prediction of physical phenomena occur during the simulation of metal forming processes. Plastic flow localization and micro-defects growth, which is called ductile damage and occurs during metal forming, has made the use of advanced constitutive equations which count damage unavoidable. In this thesis, anisotropic ductile damage model, which has high potential to predict damage, is implemented. Firstly, the constitutive equations are introduced and the non-associative plasticity model which includes nonlinear isotropic and kinematic hardenings is presented. Anisotropic plasticity is expressed by Hill yield function, and a symmetric second-rank tensor is used to describe anisotropic damage state variable. Total energy equivalence assumption and a symmetrized fourth-rank damage-effect tensor are used to apply anisotropic damage variable in constitutive equations. Secondly, the numerical integration of the constitutive equations is performed using a fully implicit and asymptotic integration schemes and return mapping algorithm is used for the implementation of anisotropic damage model. Next for the implementation of anisotropic damage model in the commercial finite element software ABAQUS, a VUMAT subroutine is developed. Then, anisotropic damage growth under simple tensile, cyclic and shear loadings are discussed and isotropic and anisotropic damage are compared based on their effect on elasticity. Finally, a square-cup deep drawing process of a steel sheet is simulated by the implemented anisotropic damage model. ABAQUS/EXPLICIT FE software is used for the simulation of this process so that critical damage zones are identified. After analyzing square-cup deep drawing process by the model, the outer surfaces of square box corners are predicted as crack initiation zones. The predicted failure areas by anisotropic damage model are in good agreement with experimental results qualitatively and this indicates the capability of anisotropic damage model for damage prediction of metal forming processes.

Keywords: Anisotropic ductile damage, Non-associative elasto-plastic model, Deep drawing process