Size and geometry effects on ductile rupture of notched bars in a C-Mn steel: experiments and modelling

The aim of this work was to investigate the effect of specimen size and geometry on ductile fracture of a C-Mn steel with high sulphur content. Uniaxial tensile tests were conducted at 300 degrees C on axisymmetric notched specimens having different sizes and geometries. Geometry effects were studied using specimens with various notch radii, thus inducing different stress triaxiality levels. Size effects were evidenced using homothetic samples having the same geometry. Results show that ductility is reduced on specimens with sharp notches (which is a common observation). As specimen size increases, mean ductility as well as scatter are reduced (showing a clear size effect). In order to predict rupture, locally coupled (post-processing type) and fully coupled (continuum damage mechanics) Finite Element models were used. They are based on the plastic criteria introduced by Gurson and Rousselier. In order to model size effect (decrease of ductility and scatter), initial distribution of inclusion volume fractions, measured by quantitative metallography, was accounted for in the simulations. Comparison of experiments with simulations showed that both model types could predict mean values of ductility and scatter.