Numerical simulation of ductile damage in pipeline steels across different constraint conditions using a combined void growth and coalescence model

Finite element method (FEM) simulations using a two-surface Gurson-like ductile damage model were used to investigate the ductile crack growth behaviors on X80 and X100 pipeline steels, under a wide range of constraint conditions. The implemented approach combines models in the spirit of the Gologanu-Leblond-Devaux (GLD) and Thomason's models to create a combined void growth and coalescence model. The implemented model can account for several ductile damage anisotropies which cannot be accommodated by the widely used standard Gurson-TvergaardNeedleman (GTN) model, which is limited to constraint conditions similar to the data used to calibrate the model. It is demonstrated in the study that the implemented combined model significantly improves upon the GTN model and can accurately predict the ductile fracture behavior over a wide range of constraint conditions based on the same calibration data. The ductile damage model was used to analyze ductile crack growth behaviors in single-edge notched bending (SENB) and single-edge notched tension (SENT) specimens. Three different pipeline steels were studied. A wide range of SENT crack geometries were analyzed. These specimens represented a wide range of constraint conditions. The numerically calculated crack growth resistance curves were compared to experimental J-Delta a curves and curves developed using the GTN model.