Stress intensity factor by combined perturbation method and universal weight functions

The stress intensity factors (SIF) of three-dimensional cracks are known exactly only for a very limited number of shapes and loading scenarios. In this work, the perturbation method is combined to the universal weight function approach to estimate the mode I, stress intensity factor of cracks with crack fronts obtained as perturbations of any known, reference crack shape. This work is limited to cracks and loading scenarios with two planes of symmetry for which the universal weight function could be established. The novel approach is illustrated for a quasi-square crack and long, flexural fatigue cracks in brittle plates. The accuracy and limitations of the proposed method are also discussed. The proposed approach provides the means to approximate the SIF for a variety of shapes and loads without relying on FEM. Furthermore, the proposed approximation is the only method that can accurately approximate the SIF's for cracks with large aspect ratios.