Research On Buckling Of Cold-Stretched Pressure Vessels Under External Pressure

As common equipment for the storage and transport of cryogenic liquid gas, cryogenic pressure vessel has been widely used in the field of chemical industry, machinery industry, aerospace and so on, the demand of which also has kept increasing. The technology of cold-stretching which can obtain thinner thickness and lighter weight, has been widely used in manufacturing cryogenic pressure vessels made of austenitic stainless steel, to achieve the goal of saving material and reducing emission.However, the influence of cold-stretching on the stability of vessels under external pressure is not clear. Though the technology of cold-stretching could increase the material strength and decrease the weight, the influence of which on the stability of vessels under external pressure may be the key restraining factors for its application. As a result, the research for the influence of cold-stretching on the stability of vessels under external pressure is quite necessary.On the support of Key Sciences and Technology Team of Zhejiang Province (Number: 2010R5001), Special Funds of Central University Basic Scientific Research Business Expenses (Number: 2014FZA4024) and National Postdoctoral Science Foundation (Number: 2014M551731), a case study of buckling of cold-stretched pressure vessels under external pressure is carried out. The main research of this thesis can be described as the following three parts:(1) Introduced the design method of vessels under external pressure, expounded the general solving strategy of buckling problem, the fundamental theory of buckling analysis and the common buckling analysis methods based on ANS YS, established the nonlinear analysis method to simulate the cold-stretching process, verified the rationality of the model by comparing the numerical simulation value with the data from products, discussed the influence of cold-stretching on this established model, and established the suitable nonlinear buckling analysis method for analyzing the stability of cold-stretched vessels under external pressure. Performed the buckling analyses of perfect vessels with above model and method, to find the type of instable bifurcation point buckling before and after the process of cold-stretching and necessity to consider the influence of the imperfection.(2) Contrasted two commonly used methods of considering the initial geometrical imperfection when the imperfection data of the actual structure can’t be obtained. Chose out of roundness as initial geometric imperfection form of vessels, established the finite element model with initial out-of-roundness which was similar to the shape of vessels in application, and on these basis, acquired the laws of how cold-stretching process influenced the buckling load of vessels with initial out-of-roundness by calculating the buckling load of vessels before and after the process of cold-stretching, found the stable trend of the buckling load of cold-stretched vessels and analyzed the reason of the trend.(3) Based on the laws of how buckling load affected by the process of cold-stretching, the paper analyzed the influence of load history on the buckling load with the material hardening model, and also studied the influence of the residual stress and deformation brought by the process of cold-stretching to the buckling load, and the result shows that the deformation brought by the process of cold-stretching have the most significant influence on buckling load of vessels, to put the laws of how buckling load affected by the process of cold-stretching further. Came up with the idea to simplify the influence the process of cold-stretching in analysis by only taking the deformation into account.