Local Approach to Fracture of an Aged Duplex Stainless Steel

The local approach to fracture (LAF) is a methodology aimed to calculate macroscopic fracture properties of a body, from the knowledge of the local stress strain field at the fracture site, and the modeling of the acting fracture mechanisms. In the present work, this method was applied to a CF8M steel, aged 30000 h at 325 °C, in order to elucidate if LAF could be able to describe the measured fracture toughness data. We have simulated the elastoplastic behavior using the Gurson model and the general methodology of Joly. The required parameters were obtained from the stress – strain curve and from the damage progression study by quantitative metallography. We extended the validity of that methodology for a material aged in a more realistic condition, i.e. at a relatively lower temperature and for a longer time. The model was found satisfactory because it was able to describe the experimental distribution of the fracture probability vs. fracture strain of notched axisymmetric specimens, without any parameter fitting. The model also predicted the lower bound of the experimental distribution of the crack resistance at 0.2 mm of crack extension (J02).