Optimum Autofrettage Pressure for a High Pressure Cylinder of a Waterjet Intensifier Pump

This study presents analytical approach for the determination of optimum autofrettage pressure of a thick walled cylinder which is commercially used as a high pressure cylinder of a waterjet intensifier pump. Bilinear kinematic hardening model is used in the derivation of analytical model based on plane strain, Von-Mises yield criteria and incompressible volume assumptions. Elasto-plastic radius is dependent on autofrettage pressure and optimum value of autofrettage pressure is found as a value that will give minimum value of maximum Von-Mises stress on the wall of the cylinder under operating pressure. Hence, considering elasto-plastic radius as the design variable, its optimum value is determined for the specified operating pressure. Reverse yielding owing to Bauschinger effect is used as the only non-linear constraint, Matlab© optimtool finds optimum value of the elasto-plastic radius and the corresponding autofrettage pressure is then calculated. By using ANSYS 15©, stress analysis of the autofrettaged cylinder has been performed and the results obtained from both methods are found to be almost the same.