Two-stage planar approximation of non-planar crack growth

Mechanical components subject to multiaxial variable amplitude loading may experience non-planar crack growth, which usually requires three dimensional finite element analyses for high fidelity simulation of non-planar fatigue crack growth. This is computationally expensive and prohibits recurrent use of high fidelity models in further probabilistic life prediction analysis. This paper presents an efficient and accurate two-stage approach for planar approximation of non-planar crack growth that reduces the computational effort. In this method, the non-planar crack is first approximated using an equivalent planar crack. Then, using the equivalent representation, planar crack growth analyses designed to account for uncertainty in crack growth are conducted. The proposed methodology employs two surrogate models: the first surrogate model is trained using 3-D simulations of non-planar fatigue crack growth to capture the relationship between the applied load history and equivalent planar crack orientation. The second surrogate model is trained using planar crack growth simulation to calculate the stress intensity factor as a function of crack size, crack orientation, and load magnitude for use in planar crack growth analysis. Individual predictions of the two surrogate models, as well as their combined predictions are verified for accuracy using full 3-D finite element simulations. The verified two-stage approach is then demonstrated in an illustrative example of uncertainty quantification in 3-D crack growth prediction in a mechanical component similar to a rotorcraft mast.