The Dynamic Properties Of Safety Valve And Fatigue Analysis Of Valve Membranes

For one type of safety valve under the action of the fault occurred is studied, the main reason for the failure of the safety valve is the fatigue damage of membranes through the analysis.First, this paper introduces the current research status of valve failure mode, the structure and the working principle. In the mean while this paper studies the nominal stress method and the local stress-strain method, combining the basic theory of fatigue in the classification of fatigue and the mechanism of fatigue, emphasizing the importance of fatigue damage theory.Second, set up a one-dimensional model, the safety valve is mainly made up by the main valve and the command valve with two similar quality-spring-damping system structure, because of the nonconservative system, it needs Lagrange method to deduce the motion equation of the one-dimensional model and the Newmark method to solve of The Dynamic Properties of the main valve and the command valve.According to the structure of the safety valve, using ABAQUS sets a finite element model, due to the compression in the assembly process and the thickness of the diaphragm is far less than the other diaphragm size, it must be considered to geometric nonlinear effects in the process of modeling analysis. Meanwhile, it needs to consider the collision phenomenon, using ABAQUS/Explicit solver gets relevant result curve. From the results, the stress of membranes can be divided into several obvious zone, the greatest stress appears in the fixed constraints, extracts the maximum stress in the corresponding node value combined with MATLAB rain flow count method calculating program, gets the stress process curve in a load period, considering the stress ration R≠-1, using the formula to calculate the equivalent stress with the stress amplitude and the mean stress, inquires the material S-N curve, estimates fatigue cycle, based on linear Miner calculation fatigue damage factor, through calculation formula estimates the fatigue life of the membranes.Finally, in view of the membranes surface defects, considers the two kinds of surface defects on fatigue life effect and sets finite element modeling, using the methods to estimate the corresponding fatigue life. The result shows that due to the existence of surface defects, membranes thickness reduced, the stress level has a certain amount of increase and the fatigue life of the membranes has a certain amount of reduce.