A combined critical plane and critical distance approach for predicting fatigue crack initiation in notched single-crystal superalloy components

The fatigue crack initiation in notched single-crystal components of material MD2 is investigated and analysed. A critical plane approach in combination with a critical distance method has been adopted, in which the total shear strain ranges on the discrete crystallographic slip planes are evaluated. To determine the critical distance two approaches were evaluated, a mean value approach and a cycle dependent approach. Furthermore, a Coffin–Manson type of expression (derived from the results of a set of 12 smooth specimens) is used to predict the number of cycles to fatigue crack initiation. The numerical procedure is applied to a series of experiments, in which notched single-crystal components were exposed to uniaxial cyclic loading in the nominal [0 0 1] crystal direction at 500 °C with Rε = 0. A good correlation between the experimental results and the simulated results was found.