What is the GTN damage model?

GTN damage model ( abaqus umat tutorial ): The ductile damage model and Gurson damage model are the two most popular models used in FE simulation to model ductile fracture of metal and polymeric materials. The Gurson-Tvergaard-Needleman (GTN) model is a material plasticity model in which the accumulation of ductile damage is represented by the nucleation, growth, and coalescence of microvoids.
The basic yield function of the GTN model is:

The GTN damage model has a total of nine parameters, which need to be calibrated for a given material. The GTN model is just one model from a particular class of pressure-dependent plasticity models in which the response is dependent on the development of the hydrostatic stress as well as the deviatoric stress tensor. In the model, the micro-voids are represented by a continuous internal variable, the void volume fraction, f.

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Modified shear-anisotropic 

A modified Gurson–Tvergaard-Needleman (GTN) damage model ( damage model abaqus ) was developed with the consideration of shear to predict ductile fracture in the (single point incremental forming) SPIF process due to void nucleation and coalescence with results compared with the original GTN model in SPIF.

The model has been implemented in full for the ABAQUS finite element code. It supports fully the nucleation, growth, and coalescence of voids, and differs from the porous plasticity model provided in ABAQUS/Standard. The model has been implemented as a Fortran 90 subroutine for use with the Abaqus/explicit (VUMAT) Finite Element code. It has a number of additional features and offers an alternative to the built-in porous plasticity model in ABAQUS. As well as predicting the void volume fraction, the model calculates the microscopic equivalent plastic strain in the fully dense material, the partitioning of the elastic and plastic strains, and the stress in the material. Integration of the constitutive equations is carried out using the backward Euler method. The incremental forms of the rate equations are nonlinear and coupled together, and robust numerical techniques are required to solve them.

In this work, a modified Gurson–Tvergaard-Needleman (GTN) damage model based on Gatea et al. paper was developed with the consideration of shear to predict ductile fracture in the SPIF process due to void nucleation and coalescence with results compared with the original GTN model in SPIF.  the main motivation of this study is to develop a GTN based model and to investigate its accuracy and effectiveness in predicting the ductile fracture in SPIF processing of typical truncated cone and pyramid shapes. In the original GTN model, the increment of void volume fraction is measured based on the nucleation and growth of voids. In this study, the Nahshon-Hutchinson type shear mechanism was incorporated in the GTN model to take into account the effect of shear in the increment of void volume fraction.

Advantages of the modified GTN damage model abaqus 

• Incorporate plastic anisotropy into constitutive equations of the GTN damage model based on the Benzerga and Besson, 2001 paper by Lankford coefficient.
  
• Consideration of shear to predict ductile fracture and improved the modeling accuracy of fracture over the original GTN model under shear loading conditions based on Gatea et al..
  
• You can choose Mises, Hill, or Barlat criterion independently.

Abaqus GTN damage parameters

GTN damage parameters for 14 engineering materials to use this criterion are available in Abaqus software. By purchasing this product, you will also receive these parameters.

1. Al 6061-T6
2. Pure Titanium
3. AA 6016-T4
4. AA 6111-T4
5. AA 5182
6. AA 6016
7. Al 5182
8. Al 5754
9. Mild steel
10. XES steel
11. ULC/Ti
12. DC 06 steel
13. AA 6016-T4
14. DP 600 steel