Stresses in a structure are magnified at the tip of a crack, causing the crack to spread. This process is modelled by the Paris crack growth law or, more recently, by the Frost-Dugdale law. The methodology of this project is to compute stresses in a structure using a standard finite element code, insert hypothetical cracks and modify the stresses accordingly, and to predict the growth of the cracks under cyclical loading.

This approach was applied to an essentially two-dimensional problem, determining the optimal shape for holes required in an airplane wing stiffener plate. Hole shape were parameterised and Nimrod/O used to find parameters that optimise the fatigue life, assuming the Paris law. This work is reported here.

More recently the methodology has been extended to three dimensional structures and to the generalised Frost–Dugdale crack growth law. Results demonstrate that the procedure has the potential to be applied to structures with complex configurations.