The stresses in a microstructured optical fiber are determined in tension and in bending. A model for the failure process in porous structures with applications to weak microstructured optical fibers with large flaws is proposed. The model assumes that a continuous crack front splits on contact with a hole and then propagates such that the direction of the front in contact with the boundary of the hole is normal to it. Three-dimensional finite perturbation analysis of Bower and Ortiz is extended to model the interaction of cracks with a periodic array of holes. Crack propagation in the cross-section is examined using the modified finite perturbation method. Test cases are presented for the stress intensity factor distribution in elliptical cracks, and periodic perturbations in straight cracks. During crack front interaction, the front can split upon contact with the hole or an array of holes, and then travel around them.
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