Stress Analysis And Optimization Design For Carbon Fiber Wrapped Composite Cylinder With Aluminum Alloy Liner

In this paper, a model of carbon fiber wrapped composite cylinder with aluminum liner of 1.8L is created with the APDL language in the ANSYS 12.0 environment. The parameter of the model is set close to that in the real situation with the thickness and the wrapped angle of both head and transition section varied. For the production of composite cylinders, autofrettage is an important process. Residual compression stress occurs in the liner after unloading the autofrettage pressure. When the cylinder is working, the tensile stress caused by the operating pressure synthesizes with the residual compression stress caused by the autofrettage pressure. Because of their opposite sign, the maximum stress in the liner decreases and the stress in the outer fiber increases. Thus, the stress distribution of cylinder becomes more reasonable. The autofrettage process of the cylinder is analyzed and the range of the autofrettage pressure value is determined according to the DOT CFFC standard. MISES stress distribution in the liner and fiber direction stress distribution in the fiber layer are given at the operating pressure, the water-pressure-test(WPT) pressure and the minimum burst pressure, respectively. A Comparison of the stress distribution is conducted between the cases with and without autofrettage pressure added. The result confirms that proper autofrettage pressure can significantly improve the mechanical properties of the cylinder. It has also been considered in the model that the properties of cylinder is influenced by the geometrical nonlinearity. And the location of the fatigue damage is determined according to the stress distribution in the liner.In this paper, the composite cylinder model is optimized by the optimization module of ANSYS. The volume of the fiber layer is taken as the objective function to be minimized; the fiber thickness, the wrapped angle and the autofrettage pressure are taken as the variables; the stress range is taken as the state variable on different conditions according to the DOT CFFC standard. The zero order optimization method is adopted for the optimization process. After the optimization, the influence of the autofrettage pressure, fiber thickness and wrapped angle and their combined influence on the stress distribution and fiber volume are obtained.