Research And Simulation Of Mechanical Prestressed Autofrettage Technique Of Ultrahigh Pressure Thick-walled Cylinders

With the rapid development of science and technology, ultrahigh pressure vessel has become necessary pressure equipment for many industrial processes, and plays an important role in modern economic construction. However, the working environment and load forms of it is quite complex, which brings tremendous threat to its safety. How to ensure the safe operation of ultrahigh pressure vessels has become the primary problem of design and manufacture. Autofrettage is an effective way to improve the bearing capacity and fatigue life of ultrahigh pressure vessel.Since most pressure vessels can be simplified to the thick-walled cylinders, This paper makes a systematic theory and simulation research on the autoftettage of ultrahigh pressure thick-walled cylinders. The main contents include the following parts:1.Through systematically theoretical calculation of ultrahigh pressure thick-walled cylinders, promoted calculation formulas of stresses for thick-walled cylinders under three circumstances:Full elastic, partly plastic, full plastic, and obtained the calculation equation between thick-walled cylinders autofrettage pressure and elastic-plastic interface radius. Derived the calculation formula of residual stresses, total stresses.Discussed the optimum elastic-plastic interface radius and the conditions that don’t occur reverse yielding, and obtained the corresponding formula.2. Studied the relaxation of autofrettaged residual stresses. Made an overview of the mechanism of residual stress relaxation, summarized the features and causes of residual stress relaxation, discussed the influence of residual stress relaxation on the safety of ultrahigh pressurethick-walled cylinders. Proposed a method to recover the residual stresses by using reautofrettage, and obtained corresponding formulas through relevant theoretical calculation on reautofrettage.3. Based on ANSYS, taking the thick-wall cylinder of ultra-high pressure polyethylene reactor as the research object, using multiple load step as loading method, this paper simulated the stress distribution of thick-wall cylinder subjected to same operating pressure under three conditions: without autofrettage, after autofrettaged, after reautofrettaged.The simulation obtained the stresses cloud images and stresses distribution curves of thick-walled cylinders. In this paper, it also simulated the iMPact of different autofrettage pressure and different loading sequence on residual stresses and the bearing capacity of thickwalled cylinders, and verified partial calculation and conclusions of former two parts.