Fracture of eutectoid steel bars under tensile loading: Experimental results and numerical simulation

Construction steel bars tested under tension usually show a cup-cone fracture pattern. Nevertheless, some steels, such as the eutectoid one used for manufacturing prestressing steel wires, show a different pattern: a flat fracture surface with a dark region inside. This paper presents experimental work performed to identify the fracture mechanisms that trigger this particular flat fracture pattern and numerical simulations where it is reproduced numerically. The experimental tests are carried out on cylindrical specimens of three diameters, 3, 6 and 9 mm, subjected to tension. In order to analyse the fracture mechanism, numerical simulations are performed by using the finite element method and the cohesive zone approach. To that end, a cohesive interface element with mechanical properties that depend on the stress triaxiality is presented and assessed. This approach provides reasonably good agreement with the experimental results. In addition, when compared with other popular models such as the GTN model, it presents certain advantages since it requires a smaller number of parameters to be defined.