Research On Ultimate Strength Evaluation Of Deep Submersible Sphere Shell Based On Heat Affected Zone

With the continuous exploration of the oceans in various fields,marine equipment called deep submersibles has been accelerating.underwater deep submersibles become a subject of intense scholarly debate at home and abroad.However,the main domestically-developed manned submersibles which is made successfully mainly concentrate at 4000-7000 m in the past,which has a long distance with manned submersibles of 10,000 m in the world.The spherical shell becomes the main factor that limit the depth of the deep submersible,and spherical shell is the key component of the long-term reliability of the internal system and components.Therefore,research on the ultimate strength evaluation method of titanium alloy pressure ball shell is of great significance to the development of deep submersibles.Titanium alloys are widely used in deep submersible pressure-resistant structures because of their low density,high strength,corrosion resistance,good strength and stiffness,and weldability.However,it is found that there are many differences between the traditional titanium alloy sphere shell ultimate strength calculation method and the factual result because of neglecting the influence of structural welding process on structural strength,which makes the submersible has a certain safety hazard.In addition,the welding defects of the titanium alloy pressure-resistant spherical shell have a nonnegligible influence on the ultimate bearing capacity of the structure.In view of the above problems,the research considers an ultimate strength evaluation method that considers the change of material properties in the heat affected zone of titanium alloy,and divides the structure into the base material attribute area and the weld equivalent material attribute area for ultimate strength evaluation.a relation between the heat-affected zone and the plate thickness is determined by the welding simulation and welding test.Secondly,the experiment of some titanium alloy plates is carried out.Metallographic test and hardness test are utilized to verify the accuracy of the numerical simulation results.At the same time,using the ultimate strength evaluation method of titanium alloy sphere shell proposed in this study to analyse the thickness-to-radius ratio t/ R,defects depth-to-thickness ratio?/ t,defect angle?,out-of-roundness.The relevant calculation results in the study prove that the evaluation method proposed in this paper can predict the ultimate strength of the medium-thickness pressure spherical shell more scientifically,which makes the finite element simulation results more consistent with the actual results.Therefore,the evaluation result of the ultimate strength of the pressure ball shell is more accurate,and the safety of the pressure ball shell structure is ensured,thereby providing a guarantee for the normal and good work of the deep submersible.It will have important theoretical and practical significance for the promotion of national maritime powers and marine defense capabilities.