Dieless Hydro-bulging Mechanism And Buckling Characteristics Of Toroidal Pressure Shell

The toroidal pressure shell has good space utilization and high bearing capacity.This is an ideal form of pressure structure for deep-sea space station.The manufacturing of large toroidal pressure shell is the key technology to determine whether the integral equipment structure can withstand deep-sea high pressure and ensure comprehensive performance.The dieless hydro-bulging technology is a low-cost,high-efficiency shell forming technology.It requires no professional equipment.It is suitable for on-site processing of large shells.The research on this technology has been relatively complete and applied to the manufacturing of various shells.At present,there are few studies on the dieless hydro-bulging of toroidal pressure shell,and there is no research on the buckling of formed toroidal pressure shell manufactured by dieless hydro-bulging technology.Therefore,this thesis will systematically carry out the research on the mechanism of dieless hydro-bulging of pressure shell and the buckling characteristics after hydro-bulging.The main research contents are as follows:(1)Based on the principle of dieless hydro-bulging technology,toroidal preform structures with polygonal cross-section were designed,and numerical models of the two structures were established.The process of hydro-bulging was simulated.The geometric and mechanical characteristics of shells after hydro-bulging were analyzed.Five toroidal preforms with polygonal cross-section were fabricated.One preform was retained as the control group.Ultrasonic thickness measurement,shape scanning and hydro-bulging tests were carried out on these models.The characteristics of thickness and shape before and after hydro-bulging were analyzed.The comparison between the numerical results and the experimental results shows that the numerical analysis can effectively evaluate the hydro-bulging process.The cross-section of formed shell has a slightly smaller out-of-roundness.The feasibility of using dieless bulging technology to manufacture pressure shell with ideal circular cross-section by preform with polygonal cross-section is verified.(2)Based on the formed toroidal pressure shell obtained by dieless hydro-bulging,the buckling characteristics were studied.The buckling characteristics such as buckling load and instability mode of formed toroidal shell were evaluated by nonlinear numerical method.Hydrostatic external pressure tests were carried out on four formed toroidal pressure shells and one preform.The nonlinear buckling characteristics such as instability mode,critical load and loading time history of the shells were analyzed.Compared with the numerical evaluation and experimental results,it is shown that the experimental results can be effectively evaluated by numerical analysis.When the hydro-bulging pressure exceeds a certain threshold,the Jordan formula can conservatively predict the ultimate pressure of toroidal shell.The failure mode of formed shell is consistent with the instability mode of the numerical evaluation.The load capacity and quality of the shell can be improved by dieless hydro-bulging.That verifies the feasibility of manufacturing toroidal pressure shell by dieless hydro-bulging technology.(3)Based on the results of the hydro-bulging of the toroidal preforms with ideal circular cross-section,a more compressive toroidal pressure shell with elliptical cross-section was proposed and the corresponding preform structure was designed.The effect of variable thickness on the dieless hydro-bulging of toroidal pressure shell was studied.The effect of the thickness distribution of each surface of the preform on the forming shape of the shell was analyzed by numerical calculation.A set of thickness parameters was optimized and selected.An experimental model was fabricated and subjected to non-invasive thickness measurement,shape scanning,hydro-bulging tests and hydrostatic tests.The results show that the variable thickness can effectively improve the hydro-bulging effect of the toroidal pressure shell with elliptical cross-section.The variable thickness design is better than the equal thickness design.The toroidal pressure shell with elliptical cross-section is easier to form than circular crosssection and the forming effect is good.(4)Aiming at the phenomenon of wrinkling during dieless hydro-bulging of toroidal pressure shell,the causing reason of hydro-bulging wrinkling of toroidal pressure shell were studied in depth.Taking a typical toroidal pressure shell with regular hexagonal cross-section as the research object.Theoretical analysis was used to analyze the stress and buckling characteristic of the whole and part of the shell;The corresponding numerical model was established to analyze the bulging process using nonlinear analysis method;A toroidal preform with regular hexagonal cross-section was fabricated and free bulging test was conducted to analyze the changes in the surface of shell during bulging.According to the theoretical,numerical and experimental results,the preform structure scheme was improved and the numerical simulation was carried out.The results show that the wrinkling on the toroidal preform is caused by compressive stress of the inner shell.The wrinkling can be avoided by increasing the critical buckling load of the inner shell.By changing the wrinkles during the bulging of the shell into useful wrinkles,it can be expanded by high pressure to improve the forming quality of the toroidal pressure shell.