Numerical modeling of ductile tearing for semi-elliptical surface cracks in wide plates

This study provides an engineering application of a continuum damage model to simulate ductile tearing of circumferential surface cracks in wide plates. Experiments were conducted to examine the behaviour of surfaced-cracked wide plates made of X-70 pipeline steel, subject to tension. The results of these tests were used to validate the proposed damage model. In the numerical model, progressive damage was restricted to a predetermined ductile tearing zone. The material damage behaviour in this tearing zone was described in terms of a Gurson-Tvergaard (G-T) isotropic constitutive model, which accounts for microvoid nucleation and growth. The measured load versus crack mouth opening displacement histories for three different surface crack configurations were numerically predicted using the damage model developed. The damage model was then used to numerically investigate the effect of stress triaxiality on crack initiation, and determine the site of crack initiation. The effect of crack growth on maximum load was also estimated through the damage model. It was shown that the maximum load in wide plates occurred after a large amount of crack extension, which confirms that tough ductile X-70 pipeline steel has considerable strength even when containing cracks. The model developed also provided a detailed description of plasticity in the crack plane.