Parametric Analysis on Creep Deformation of Deep-Sea PMMA Observation Window

Abstract

Observation windows are core components of the submersible manned cabins. The strength and stiffness of the observation window during the loading and load-sustaining process are crucial to ensure the safety of the equipment and personnel inside the manned cabin. It is extremely important to accurately calculate the structural creep performance of the observation window under a long-period sustaining load in seawater. In the present study, finite element analyses based on a temperature-dependent time-hardening creep model are conducted to investigate the performance of the observation window. The mesh convergence is studied first and the parametric analysis is accordingly carried out, taking different combinations of temperatures from 2~30 °C, different loading rates of 2.3 MPa/min, 4.5 MPa/min, 6 MPa/min, and 8 MPa/min, and different friction coefficients of 0.05, 0.1, 0.15, 0.2, 0.25, and 0.3 into account. The results show that the displacement in the y-axis direction of the center point of the lower surface of the viewport window increases with the increasing temperature and loading rate. On the contrary, the axial displacement of the observation window gradually decreases with the increase of the friction coefficient, and the axial displacement is the largest when the lowest friction coefficient is applied. This study aims to offer a more unified analysis and design methodology for the creep deformation of PMMA structures in underwater facilities.

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

“…Du et al [16] analyzed the relaxation behavior of a multi-parameter PMMA observation window through an improved stress relaxation model and found that the numerical calculation outcomes closely aligned with experimental findings. Using the temperature dependent time-hardening creep model, He et al [17] carried out a series of finite element analyses on the observation window, offering a method for analyzing and designing the window's creep behavior. Zheng et al [18] characterized and measured the defects of the observation window, and gave the stress, strain and displacement distribution of the observation window glass during the hydrostatic external pressure test.…”