Simplified analysis of fracture behaviour of a Francis hydraulic turbine runner blade

Each welded connection between blades and band or crown of a Francis hydraulic turbine runner can be considered as a T-joint subjected to pure bending induced by the water action. A semi-elliptical crack is assumed to exist at the surface of one of the aforementioned welded connections. The actual geometry of the T-joint can be simplified, that is, only the cracked plate (representing the blade) under a given stress distribution acting on the defect faces is examined. A numerical procedure already proposed by the authors to compute the stress-intensity factor (SIF) along the crack front is here applied by introducing some changes to simplify such computations. The obtained values of SIF are compared with some results available in the literature.