Fracture analysis is widely used to predict component failure caused by preexisting small cracks, allowing one to take precautions to prevent further crack-growth or to determine the remaining life of the structure.
To assess the fracture damage, stress intensity factors (SIFs) must be evaluated accurately. Because it is difficult to determine accurate SIFs using a closed-form analytical solution for cracks in complex structures, finite-element analysis is used instead.
Two approaches are available for evaluating SIFs:
Interaction Integral Method -- Performs the SIF calculation during the solution phase of the analysis and stores the results for later postprocessing.
Displacement Extrapolation Method -- Performs the SIF calculation during postprocessing. This method is limited to problems involving linear elasticity with homogeneous, isotropic materials near the crack region.
The interaction integral method is used here as it allows for the calculations to be performed during the solution phase. It is also more accurate, as the domain integral expressions are naturally aligned with the FE formulation.