Analysis On The Effects Of Material And Structural Defects On The Property Of Deep-sea Manned Spherical Hull

The technology of deep-sea manned submersible is an important part of the development of deep-sea high technology,and is also one of the key points in the development of marine equipment in China.At present,China has started the development of full-ocean-depth(11000 meters)manned submersible.To ensure the safety of the submersible,the establishment of the safety assessment theory of its key components is a very important task,which contains a number of key technologies.The most one is the design and manufacturing technology of the manned cabin and the safety assessment technology during its application.Based on the development of the full-ocean-depth manned submersible "Rainbow Fish" and the needs of the submersibles "Jiao long" and "deep-sea warrior" in our country,the effects of material and structural defects on the property of deep-sea manned spherical hull is analyzed.The analysis involves two kinds of materials,namely high strength titanium alloy and maraging steel.The test spherical model is used as the simplified analysis model of the manned cabin.The four kinds of factors such as the volume defect in the material,the geometric defect of the spherical hull,the welding residual stress and the crack defect are considered respectively as the "generalized defects",are analyzed in order to provide basis for establishing the safety assessment theory of the manned cabin.It is quite easy to find volume defects in welding and casting components.The volume defects will have effects on the material properties,including the material elongation and tensile strength.And the decrease of the material elongation may eventually lead to the decrease of the structure strength.In this thesis,a tensile sample made of titanium alloy is taken as an example to simulate the tensile test with volume defects based on ABAQUS.The effect of the diameter of the defect and the number of defects on the properties of the material is analyzed,and the dynamic crushing of the spherical hull is analyzed in order to study the effect of the elongation on the static strength of the manned cabin.The initial geometric imperfection and the method to include initial geometric imperfection will have significant effect on the strength of the spherical shell.Based on the test results of the model sphere of a man cabin made of maraging steel,this paper introduces the measurement method of the initial imperfection of the hull.By measuring the thickness along the grid points by three-axis measuring instrument,the overall roundness deviation of the spherical hull is calculated.By contrasting the imperfection form of actual spherical hull and the idealized spherical hull,together with comparing the experimental results with finite element results,the equivalent method to introduce the initial geometric imperfection of the spherical hull is studied as well as verifying the accuracy of ultimate strength calculation after introducing the initial geometric imperfection in the finite element method.Crack defect is the most serious and common defect in welded components.The propagation of cracks will seriously reduce the service life of the components.In this thesis,the crack propagation in a spherical shell is simulated by software ABAQUS and Franc3 D.The stress intensity factors of a semi elliptical crack under the interaction of fatigue load and welding residual stress are calculated,and the crack growth rate curve is obtained.The fatigue life of the spherical hull is according carried out based on calculation results.The research results in this thesis will provide a basis for the establishment of structural safety analysis theory in the design,manufacture and use of manned cabin.