A simplified life estimation method for the spherical hull of deep manned submersibles

• Ti–6Al–4V ELI has creep behavior in the room temperature and its dwell effect is important during life estimation.
• A simplified prediction model for constant amplitude cyclic creep loading is proposed for the pressure hull of submersibles made of Ti–6Al–4V ELI.
• The prediction method is validated by the modified crack growth rate model with parameters determined by large amounts of experimental data.

Creep and fatigue are involved in the loading of deep manned submersible, which is a rather complex variable amplitude pattern. Dwell effects resulting in lower life than pure fatigue are observed in the prior experimental research while no proper prediction methods are available to explain the phenomenon. Recently, the authors proposed a modified crack growth rate model to explain the creep effect under the cyclic loading which is validated for the crack growth of some titanium alloys under cyclic creep loading, however, its application is restricted to the condition where lots of parameters have to be determined based on many experiments and it is not very convenient in the material selection and primary design stage of a component. In this paper, a simplified prediction model for the load pattern of constant amplitude cyclic loading is proposed aiming at one of the most applicable materials for the pressure hull of submersibles, Ti–6Al–4V ELI. The method can be easily used to estimate the life of the pressure hull based on two series of basic mechanical properties of the material and validated by the modified crack growth rate model with parameters determined by large amounts of experimental data.