Life Assessment of Deep-Sea Observation Windows under Different Design Considerations

As a key component of deep-sea manned submersibles, the observation window is usually constructed with polymethyl methacrylate (PMMA) material. During the design of the observation windows, the consideration of actual lifespan and its influential factors is insufficient. There are no clear provisions in the widely applied specifications. In this paper, based on the continuum damage mechanics model, combined with the viscoelastic relationship of PMMA material, a series of calculations were performed on the PMMA observation window. The parametric analysis of the fatigue crack-initiation life of the observation window at various thickness-to-diameter ratios (1.6, 1.4, 1.2, and 1.0), different friction coefficients (0.1, 0.2, and 0.3), and different transition arc radii (4000 mm and 6000 mm) was carried out. The calculated crack positions in the numerical mode used for validation closely align with those in the tested window. And simulation results show that the fatigue life of the observation window gradually decreases with the decrease in the thickness-diameter ratio and the increase in the friction coefficient. However, the increase in the transition arc radius will prolong the fatigue life of the observation window, which is higher than that of the original structure.