Investigation On Nonlinear Buckling Of Egg-shaped Pressure Shell Under The Influence Of Imperfections

The pressure shell is one of the most important safety equipment for exploring marine resources in the field of marine engineering equipment,and is mainly used to protect scientific personnel and scientific research equipment in the cabin.The egg-shaped compression shell is the latest research hotspot.Its structural stress principle uses biological characteristics,and the whole has a very strong compression resistance.However,the structure of the egg-shaped pressure shell is similar to that of the spherical pressure shell,and it is more prone to instantaneous damage due to imperfect conditions.Especially the imperfections of initial geometry and corrosion thickness reduction after a period of work will have a fatal effect on its buckling instability.Therefore,this paper carried out relevant research on the nonlinear buckling caused by the egg-shaped pressure shell under different defect conditions,which are divided into the following three aspects:(1)Under the uniformly distributed external pressure environment,the buckling characteristics of the egg-shaped compression shell with long axis L = 256 mm,short axis B = 180 mm and thickness t = 2mm,with local flat imperfections and local egg-shaped imperfections.Through the rapid prototyping manufacturing technology,nine test models of egg-shaped pressure shells were produced.The test data showed that the egg-shaped pressure shells were manufactured with high precision and good repeatability.Several quasi-static curves and failure pressures prove that local flat imperfections are more sensitive than local egg-shaped imperfections.In addition,the structures of all the test models are very similar,showing a local crushing shape.According to the arc length method,the nonlinear failure modes of all the eggshaped compression shells produced are obtained.The numerical analysis verifies that the local flat imperfections are more serious than the local egg-shaped imperfections.At the same time,the egg-shaped pressure shell with no imperfections and the egg-shaped pressure shell with modal imperfections were compared together.(2)Then we discussed the failure results of the external compression egg-shaped pressure shell under the influence of corrosion and thinning imperfections.The long and short axis parameters of the egg-shaped pressure shell are the same as above.The corrosion location starts from the place where the radius of curvature in the latitude direction is the largest.The circumferential corrosion range of the circumference is set between 2.5 ° to 360 °,and the latitude corrosion range is set between 20 to 50 mm.The corrosion depth is 10% to 40% of the wall thickness.In addition to one non-corroded shell and four completely corroded shells,nonlinear numerical analysis was also performed on 96 partially corroded egg-shaped shells.On this basis,representative egg-shaped compression shell test samples were produced,including non-corroded,partially corroded and fully corroded egg-shaped pressure shell models.The results obtained can be used as the basis for the safety assessment of corroded egg-shaped pressure hulls.The results show that the non-corroded and completely corroded egg-shaped pressure shells have metastable damage characteristics and break at the worst position(where the radius of curvature is the largest).Partially corroded egg-shaped shells exhibit unstable collapse behavior and collapse occurs in areas of low stiffness.The ultimate strength of the partially corroded egg-shaped pressure shell can be conservatively evaluated according to the situation of complete corrosion.(3)Finally,the numerical analysis results of egg-shaped pressure shells under the influence of shape imperfections and thickness imperfections are discussed.By superimposing corrosion thinning imperfections on the basis of shape imperfection,numerical analysis shows that when the shape imperfections begins to corrode,as the degree of corrosion increases,the load-bearing capacity of the egg-shaped pressure shell decreases linearly.The egg-shaped pressure shell under complex imperfections is more prone to damage than the egg-shaped pressure shell with a single shape imperfections.In addition,when the egg-shaped pressure shell is corroded due to imperfections in the initial geometry in a small range,its bearing capacity is significantly reduced.