Hydroforming Simulation With Strength And Stiffness Analysis Of Super Large U-shaped Expansion Joints

With the increase of industrial production scale,more and more large and even super large expansion joints are used in industrial production.However,there are few studies on super-large expansion joints.In this thesis,finite element method was used to simulate the hydroforming process of a super large U-shaped expansion joint with the diameter of 6 meters,and the strength and axial stiffness calculation formula in the expansion joint standard were analyzed.The main contents and conclusions are as follows:(1)The numerical simulation of the hydroforming process of the super large U-shaped expansion joint was carried out.Compared with the actual structural requirements in engineering,errors of wave height,wave distance and wave peak thickness of the expansion joint obtained by the hydroforming simulation were all within the allowable range,which means that the finite element method is reliable for the hydroforming numerical simulation of the super large U-shaped expansion joint.(2)The stress calculation based on the formula in the standard and finite element stress analysis of single-layer and double-layer super large U-shaped expansion joints were carried out under the pressure and the displacement cases.The results show that,compared with the finite element calculation results,the stress caused by internal pressure or displacement calculated by the formula are in somewhat deviated for both single-layer expansion joints and double-layer expansion joints.But considering the magnitudes of the stress and conservativeness of the deviation,it is reached that the present standard for expansion joints is applicable for the expansion joint with the diameter 6 meters.(3)The formula calculation and finite element analysis of the stiffness of the super large U-shaped expansion joint were carried out.By comparing the calculation results,it is found that the error between the stiffness value calculated by the formula and the stiffness provided by the manufacturer could be as large as more than 50%,while the calculated value by finite element method is closer to the actual stiffness.(4)The stiffness of expansion joint with nominal diameter from lm to 4m was calculated according to the stiffness calculation formula of GB16749 standard and analyzed with finite element method.By comparing results,it is found that for large expansion joints,the stiffness of the expansion joint calculated by the formula is clearly larger than that obtained by numerical simulation.Thus,the stiffness correction coefficient of expansion joints was defined.The influence of t/D,h/D and r/D on the stiffness correction coefficient was analyzed,and the function expression of stiffness correction coefficient was fitted.