Numerical Stability of the Cohesive Zone Approach in Simulated Initiation and Growth of Intergranular Cracks in Polycrystalline Aggregates

Understanding and controlling early damage initiation and evolution are amongst the most important issues in nuclear power plants. Integranular cracking has been known to occur in both austenitic steels and nickel based alloys. Modelling efforts are under way to understand this phenomenon on the grain-level scale where the influence of the microstructure plays an important role. Here, the initiation and evolution of integranular cracking can be modelled using the advanced finite element approaches with explicit account of the grains, their crystallographic orientation and explicit inclusion of grain boundaries. The cohesive-zone approach, with damage initiation and evolution, can be used for grain boundaries. However, the stability of such an approach can be problematic, especially in cases where there are a number of intergranular cracks. These cracks can form complex networks which can have a negative impact on the stability of the analysis. This work addresses some of the issues related to the stability. The influence of the finite element individual model parameters like convergence controls and numerical viscosity on the model convergence is looked at. The effects are demonstrated on a simple geometry containing 3 grains. It is shown that the numerical viscosity has the highest beneficial influence on the convergence. However values of numerical viscosity of more than 10\,\% of the time step should be avoided.

SIMONOVSKI Igor;  CIZELJ Leon;  MACHINA Gangadhar; 

2013-01-10

Nuclear Society of Slovenia

JRC77190

http://www.nss.si/ljubljana2012/images/phocadownload/papers/605.pdf,    https://publications.jrc.ec.europa.eu/repository/handle/JRC77190,