Design and Mechanical Failure of Deep-Sea Pressure Structures

The article by Cao et al. investigated an analytical approach for global buckling of ring-stiffened sandwich cylindrical shells with layerwise theory. The strain energies of the inner and outer shells and the ribs and the work done by external forces are derived with the help of classical laminate theory, and the Rayleigh-Ritz method is employed to obtain the critical buckling load of ring-stiffened sandwich cylindrical shells. The results show that the proposed approach has high accuracy in predicting the global buckling behavior of ring-stiffened sandwich cylindrical shells.The article by Wu et al. explored the failure analysis on fully-transparent deep-sea pressure hulls used at 2,500 m depth. The compression test is carried on, in which the material samples are subjected to quasi-static compressive load until failure in tests at different loading rates. An equation for prediction of instability-type failure is described. When 5 times of safety factor is taken, the wall thickness of the pressure hull is calculated to be t/R0 = 0.0685 at 2,500 m depth. Ultimate strength and failure mode of a typical fully-transparent deep-sea pressure hull are simulated. The provided simulation procedure can be referred for failure analysis of fully-transparent pressure hulls.The article by Zhang et al. studied the fracture mechanism and failure strain of TA31 titanium alloy for deep-sea pressure hulls based on continuum damage mechanics. Considering the pressure sensitivity, the Modified Johnson-Cook (MJC) model and the Bonora damage model were used to study the fracture behavior. The comparison revealed that the Bonora model with constant parameters was not enough to predict the failure strain. The damage parameters were sensitive to the stress triaxiality. It is concluded that a higher stress triaxiality and shear mechanism lead to lower plastic deformation, and will inhibit the void growth on the damage evolution.The article by Sun et al. investigated the mechanical characteristics of a fibre reinforced flexible pipe under radial compression loading. The hoop reinforcement layer of the pipe is considered equivalent to an orthotropic circular tube. An analytical equation for calculating the radial stiffness of the circular tube per unit length is then derived based on the classical elastic theory. The load-displacement curves obtained from the tests and numerical model are linearly fitted to calculate the radial stiffness of the pipe. The radial stiffness obtained by the numerical model is very close to that obtained by the analytical method. However, owing to factors such as material defects and initial ovality, the radial stiffness measured experimentally is lower than the analytical result.The article by Yu et al. studied the cutting mechanism of 5052 aluminum alloy by means of process experiment, underwater sensor and numerical simulation. The effects of parameters were investigated on cutting current, voltage, and water depth on the underwater kerf formation. The visual sensing system was setup to monitor the cutting arc trajectory and the combustion process during the cutting process. Finite Element Analysis was performed to further analyze the underwater arc cutting kerf formation of aluminum alloy. The numerical results of temperature distribution and kerf shape were consistent with the experimental data, which revealed the cutting mechanism.The guest editors are highly thankful to all the authors for submitting their articles and submitting them on time. We also acknowledge the great service of the reviewers who had carefully reviewed the manuscripts and made constructive suggestions to improve the quality and readability of the articles. Finally, we are very grateful to the editorial office of Frontiers in Materials who had worked diligently to get all the reviewed manuscripts published in this special collection in time and in a beautiful format.