Fatigue crack growth in blade attachment of turbine disks: Experimental tests and life prediction

To assess residual life for those component parts where low cycle fatigue (LCF) design is adopted, especially for those critical regions where high stress concentrations cause cyclic yielding of the material, it is necessary to consider the presence of potential defects and their propagation during service. In order to represent the high stress concentration at the root of blade attachments in a gas turbine and the typical elastic-shakedown conditions, a notched specimen has been designed and tested. A series of experimental tests in three regimes have been carried out with the presence of small semi-circular micronotches and crack growth rates have been measured with plastic replicas. The results have shown that the initial over-load impressed by the spinning tests is able to double the propagation lifetime. The experimental results have then been successfully analyzed with Newman's crack growth model applied to the elastic shakedown stress fields at the notch root.