Stress Analysis Of Composite Pressure Vessels Under Internal Pressure And Temperature Loads

The pressure vessel is a kind of special equipment that can possibly cause accidents such as explosion and poisoning. The design, manufacture, inspection and acceptance of pressure vessel need to be strictly based on relevant standards. At present, the existing pressure vessel design codes require that the vessel materials must be homogeneous, describing the stress level of the entire vessel with membrane stress. However, for non-uniform composite pressure vessels, such as composite steel pressure vessel, filament wound pressure vessel and pressure vessel with functionally graded coating, the design method is no longer applicable. As a result, these vessels are produced with simplified method at the expense of costs (material) for the purpose of security. Therefore, it is necessary and urgent to investigate the thermal-mechanical behavior and structural strength design method of these three types of new composite materials pressure vessel.In this thesis, the thermal-mechanical behavior of composite steel pressure vessel, filament wound pressure vessels and pressure vessel with functionally graded coating were investigated, respectively. Then, based on the finite element numerical technique, numerical models of the three types of pressure vessels were established to verify the accuracy of the analytical models. Finally, the structure and mechanical characteristics of these three types of pressure vessels were discussed and optimized in detail. The whole work would provide strong theoretical basis and technical support for the design of such new composite pressure vessels. The main research work includes:(1) By introducing an axial extrusion pressure as a boundary condition, the general formulation of the three-dimensional stresses calculation for the multi-layer composite steel pressure vessel under the internal pressure and temperature loads was derived, and its numerical model was established based on the finite element method to validate the analytical solution. In addition, on the basis of the numerical solution, the stress distribution characteristics of the composite steel pressure vessel were discussed in detail. Results showed that the axial stress is greater than the hoop stress for the multilayered structure under the temperature load, which is different from the stress distribution of the traditional pressure vessel. Besides, the edge stress of multi-layer composite steel pressure vessel holds the locality and self-limiting properties, and its peak stress range is nearly the same as the conventional pressure vessel. (2) Based on the linear elasticity and small strain theory, the three-dimensional stresses of the filament wound pressure vessels with an aluminum alloy liner under the internal pressure and temperature loads were derived considering the isotropic heat transfer conditions. And the analytical solution was validated based on finite element numerical modeling method. In addition, considering the demand of autofrettage process, the elastic-plastic numerical model for the filament wound pressure vessel with aluminum alloy liner was established using the finite element method. Stresses under autofrettage pressure, zero pressure and working pressure were calculated, respectively. Results indicated that the autofrettage processing can significantly improve the stress distribution of the fiber layer under the working load, giving full play to the characteristics of high strength composites and improving the strength and fatigue resistance of the pressure vessel.(3) By introducing the power law material model and the Euler method of variable coefficient differential equations for the functionally graded material, theoretical derivation of three-dimensional stresses of pressure vessel with an functionally graded coating under the internal pressure and temperature loads was conducted with simultaneous physical equations, geometric equations, equilibrium equations and boundary conditions. A finite element model was also established to verify the analytical solution. Finally, on the basis of the numerical solution, the interface effect and heat resistance of the coating was discussed in detail. Results showed that functionally graded materials can effectively eliminate the interfacial stress peak of the multilayer pressure vessel, and significantly improve the load-bearing properties of the vessel.