[SY-G5] Dislocation dynamics modeling of fracture behavior with considering dislocation shielding effect
Ductile-brittle transition (DBT) in ferric steels is a critical issue to ensure the structural integrity of nuclear power plants. The DBT is believed to be caused by the shielding effect of dislocations at the crack tip. Therefore, in order to make a deep understanding of the fracture behavior and the DBT mechanisms, it is necessary to develop a computational method that can take into account the dislocation nucleation, the dislocation behavior and the stress of dislocation around the crack tip, and can derive the fracture toughness as a result of dislocation-crack interactions. This paper presents a dislocation dynamics (DD) simulation technique for the fracture toughness calculation with the consideration of dislocation shielding effect. In this study, the crack is represented with discrete dislocations, and the crack problem is solved using the DD method. The dislocation nucleation from the crack tip is simply modeled with a critical shear stress in the immediate vicinity of the crack tip. The nucleated dislocations move in the material, and produce the stress at the crack tip. The complex system of crack-dislocation interactions can be solved only with the DD method. In the DD method, the stress intensity factor at the crack tip can be easily computed by calculating the Peach-Koehler force, which is normally calculated in the DD simulations, acting at the crack tip dislocation. When the stress intensity factor reaches a critical value, the fracture toughness is determined by the applied stress. To demonstrate the potential of the developed DD method, we performed a simulation of dislocation shielding with various dislocation mobility, which imitates the temperature dependence of dislocation behavior and fracture toughness. The numerical result clearly shows that the higher dislocation mobility gives higher fracture toughness, which is qualitatively in agreement with experimental results.