Simulation of 3D non-planar fatigue crack growth in a turbine blade root

A case study of fatigue life predictions for the root of a turbine blade containing a initial flaw is presented. A fracture simulation system is utilized to perform simulations of low cycle (startup/shutdown) fatigue crack growth in the root. The turbine blade has a complex structural geometry, and the cracks have been observed to grow in a highly non-planar fashion. Simulation of these cracks requires the capability to model three-dimensional geometry and to allow for arbitrary non-planar crack growth. A geometric model of the portion of the root near the crack is created. Boundary conditions for this substructure are obtained from a finite element model of the entire blade (without a crack), loaded by centrifugal forces. One approach of transferring these boundary conditions to the geometric model is described. A small initial crack is added to the geometric model, and a linear elastic boundary element analysis is performed in order to compute the stress intensity factor variation (modes 1, 2, and 3) along the crack front. The crack growth rate curve for the blade material is used along with the mode-1 stress intensity factor variation to predict the number of cycles, and new crack shape, for a user-specified increment ofmore » growth. The model is then locally remeshed for the next boundary element analysis. Comparisons with experimental fatigue tests of this same configuration are presented. 39 refs.« less