| Liquid gases, including liquid nitrogen, liquid oxygen, liquid natural gas and so on, are widely used in modern industry due to the rapid development of national economy and transformation of national energy strategy. Pressure vessels made of austenitic stainless steels(ASS) are the main storage and transportation equipments of liquid gas. Therefore, the application of those pressure vessels is widely used correspondingly, especially the cold-stretched ASS pressure vessel due to the advantage of reduction of the wall thickness, the weight of pressure vessels and the energy consumption. Head is one of the most important parts of pressure vessel, whose demand is also increasing dramatically. Among heads, the cold stamping formed elliptical heads have the characteristic of good surface quality, good outline, good accuracy of forming size, easy forming, as well as the quick forming speed which can make heads realize mass production. Therefore, the stamping formed elliptical heads have been extensively used in small and medium size ASS pressure vessels.However, the deformation of stamping formed ASS head is large. Some cases of pressure vessels result from the failure of ASS heads have been reported. Therefore, the research on deformation of head is important. However, nowadays, few studies have been reported on it. Only some standards, such as GB, EN, ASME, issued some calculating formulas for us to calculate plastic deformation. Through research, these formulas are not found to reflect the real deformation of heads. Therefore, the research on a good prediction of plastic deformation, including prediction for design stage and test in manufacture stage, is necessary. Ensuing the influence of forming process to mechanical property of head as well as analyzing the influence of cold-stretching process to plastic deformation of head, will be of a significant importance in ensuring the quality and safety of stamping formed head.Supported by National High Technology Research and Development Program (Number:2011BAK06B02-05), Zhejiang province key science and technology innovation team project(Number:2010R50001) and International Science and Technology Cooperation Program(Number:2010DFB42960), a case study of head made of S30408is carried out. The main research of this thesis can be described as the following four parts:(1) A numerical analysis of stamping forming process was carried out which is based on ABAQUS. The results were compared to the test result. Based on the analysis above, a numerical analysis method was established.(2) Considering the effect of plastic deformation of head in stamping forming process, a non-linear analysis of head for cold-stretching process was carried out. After comparing the non-linear analysis result and test result, a non-linear analysis method which took the effect of plastic deformation of head into consideration was established. Based on the analysis above, the influence of cold-stretching process on plastic deformation was analyzed.(3) Based on the research on numerical analysis of stamping forming process, the numerical analysis for different kinds of elliptical heads were carried out. The difference between numerical analysis results and calculating results with formulas from standards were analyzed, as well as the reason of the difference. Based on the analysis above, a prediction method of plastic deformation for the stage of design was put forward.(4) Based on the phenomenon of deformation induced martensite, a mathematic model showed the relation between plastic deformation and martensite transformation content was established. Then a test method of plastic deformation in manufacture stage was put forward. |
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