Damage tolerance design of a manned submersible spherical pressure hull

This paper presents a study on the application of fracture mechanics analysis- based damage tolerance design methodology to a manned submersible pressure hull. The first step in this methodology is the assumption of the initial crack length in the pressure hull. Then, the critical crack size at which failure would occur is calculated, based on the material´s fracture toughness. The damage tolerance design methodology uses the Paris equation to determine the crack growth life of the pressure hull. Fatigue crack growth life is the number of cycles required for the crack to grow from the initial size to the critical size. In a full compressive nominal stress cycle, the fatigue crack growth rate and crack growth life are estimated with an effective stress intensity range. The effective stress intensity range is based on the crack closure concept. For a 60mm thick spherical pressure hull, the fatigue crack growth life is estimated to be 100 years, with 200 dives per year up to a 6000 m water depth. From the fatigue crack growth life, the inspection interval can be set as 50 years.