Numerical simulation and experimental investigation on a steam turbine blade fractured from the lacing hole

摘要

Failure analysis of a 17th stage blade of a steam turbine fractured in the vicinity of the lacing hole is discussed in this study. For this purpose, visual inspection, chemical and structural analyses, hardness and uniaxial tensile tests, macro and micro-fractography, fracture mechanics calculations, as well as computer simulations have been carried out. According to the results of the hardness and tensile tests and a comparison with the properties of AISI 410 martensitic stainless steel, it can be claimed that the blade did not experience any deterioration of mechanical properties during the service. Fractographic observations revealed the high cyclic fatigue as the main failure mechanism of the blade and showed that the fatigue crack is initiated and propagated adjacent to the lacing hole, from the brazing interface between the rod and the blade due to a lack of proper filler attachment as well as the presence of micro cracks within the brazing metal. In addition, estimation of the failure stresses based of fractographic observations, fracture mechanics and computer-aided calculations indicated that the failure of the blades has not been due to any abnormal stresses. Finally, a computer simulation of the fatigue crack growth indicated that after the crack initiation, about 3.75 h should be enough for the crack to reach the critical crack dimensions.