Time-dependent axial displacement of PMMA frustums designed for deep-sea manned cabin based on finite element analysis

The PMMA frustums applied as observation windows in the deep-sea manned cabins are vital substructures.The accurate measurement and calculation of the real displacement of PMMA frustums are important for designing the space between the window and the metal pressure hull. The total displacement during service of the submersible is time-dependent due to the viscoelastic properties of PMMA material. In this paper, the total displacement analysis of PMMA frustums with time-deformation behavior based on the viscoelastic model is conducted and parts of the results are verified by experiments. The displacement of the window during the load holding phases and the recovery behavior under different unloading modes are studied, in which the deformation recovery time for solving the residual deformation problem is recommended. Finally, an explicit formula to calculate the axial displacement of PMMA frustums with different thickness-diameter ratios at variable holding-time and pressures is formed for preliminary deep-sea window design.