To evaluate the collapse pressure of the steel–composite hybrid cylinders under external pressure without excessive computational cost, an analytical formula was derived in this study. The rationality of the derived formula was verified by the comparison with experimental and numerical results. The experimental results indicate that samples are manufactured and tested with good quality. The derived formula considered material failure and could reasonably predict the collapse pressure of the steel–composite hybrid cylinders with a maximum difference of 3.1%. Moreover, the effects of the wrap angle, thickness, and length on the collapse pressure of the hybrid cylinders were theoretically analyzed. The loading capacity of the hybrid cylinders was maximized under a wrap angle of ±55° for the composite layer. These findings are mainly because the hoop stress is twice the value of axial stress for a cylinder under uniform pressure.

The internal hydroforming of large stainless-steel eggshells from a stepped preform is investigated in this paper. The nominal major and minor axes of the eggshell were 1537 and 1070 mm, respectively. The stepped preform was fabricated from thin-walled (1.9 mm thick) stainless-steel sheets and comprised twelve conical segments inscribed inside the target eggshell. The preform was then hydroformed, and its wall thickness and shape were measured. The yield load distribution and material hardening of the hydroforming process were investigated analytically. Nonlinear finite-element analyses were employed to further investigate hydroforming behaviors and the effect of weld lines on hydroforming. The experimental, numerical, and analytical results were consistent. The results confirm that, during the hydroforming process, considerable springback occurs for large eggshells, which greatly affects forming precision. However, this effect can be reduced by accounting for the strengthening effect of weld lines.

This paper is devoted to the hydroforming performances of toroidal pressure hulls with octagonal cross-sections, together with the buckling performances of hydroformed hulls. The octagonal cross-sections of toroidal preforms are inscribed from the circular cross-sections of perfect toroidal shells with a 150 mm major radius, a 75 mm section radius, and a 1.058 mm wall thickness. The nonlinear finite-element method was employed to study the hydroforming and buckling performances under various hydroforming pressures. To verify the numerical findings, three nominally identical toroidal pressure hulls with discrete octagonal cross-sections were tentatively manufactured, internally hydroformed, and externally collapsed. The numerical and experimental data exhibited satisfactory agreement. It is indicated that the hydroforming technique could greatly enhance the loading capacity of toroidal pressure hulls.

To evaluate the stochastic characteristics of ultimate strength for spherical shells subjected to external pressure, uncertainty analysis is conducted in this study. Experimental measurements and result analysis of dimensions, as well as ultimate strength, are performed. The basic theories of the surrogate model and probability-box method for ultimate strength are introduced briefly. Uncertainty analysis of ultimate strength is completed utilizing double-nested random sampling based on the established Gaussian process model with high precision, and the results are compared with the experimental findings. The results show that the experimental empirical cumulative distribution function is contained in the probability-box obtained while considering the influence of welding, and the absolute errors of the mean value, as well as those of the standard deviation, are much smaller. The study verified that the influence of welding cannot be ignored, and the prediction of ultimate strength, considering uncertainties, can eliminate the occasionalities of simulations and experimental tests.

In this paper, strength prediction of spherical electronic cabins with pitting corrosion under external pressure was investigated. The finite element model of a spherical electronic cabin with random pitting was established using self-written code. The effects of the pitting distribution shape, pitting morphology and size on the ultimate buckling load were numerically studied. In addition, the analytical formula for predicting the ultimate load of spherical cabin with random pitting corrosion was proposed and verified by experiments. This study can be used by engineering designers for relevant design and evaluation basis and provides a reference for the development of a new design code for the buckling stability of spherical cabins with pitting corrosion.

In this study, we investigated toroidal shell wrinkling in free hydroforming. We specifically focused on toroidal shells with a regular hexagonal cross-section. Membrane theory was used to examine the distribution of stress and yield load in both preform and toroidal shells. The wrinkling moment was then predicted using an empirical formula of shell buckling. In addition, the wrinkling state was investigated using a general statics method, and the free hydroforming of toroidal shells was simulated using the Riks method. Subsequently, nonlinear buckling and equilibrium paths were analyzed. A toroidal preform was manufactured, and free hydroforming experiments were conducted. Overall, the experimental results confirmed the accuracy of the theoretical predictions and numerical simulations. This indicates that the prediction method used in the study was effective. We also found that wrinkling occurs during hydroforming in the inner region of toroidal shells due to compressive stress. Consequently, we improved the structure of the toroidal shells and performed analytical calculations and numerical simulations for the analysis. Our results indicate that wrinkling can be eliminated by increasing the number of segments on the inner side of toroidal preforms, thereby improving the quality of toroidal shells.