Design optimization for a three-layers shrink-fitted pressure vessel exposed to very high pressure

Abstract

In this paper, design optimization for a different materials three layers shrink-fitted cylinder subjected to very high pressure has been investigated. The optimum design of the cylinder has been brought into being by upsurge the advantageous compressive residual stresses, thus increasing the carrying load capacity of the cylinder as well as its fatigue life. A finite element model has been established to estimate the residual hoop stress, the equivalent von-Misses stress and the equivalent plastic strain. In this optimization problem, the design parameters have been taken as the thicknesses of the layers and the diametral interference between them. Also, the major constraint is that the equivalent von-misses stress for each layer does not exceed the yield strength of each layer material during the shrink-fitting process and when subjected to 750 MPa inner working pressure. Design of Experiment (DOE) and the Response Surface Method (RSM) have been joined together to obtain an effective objective function to be used in the optimization formulation. Two optimization techniques have been sequentially used to obtain accurate global optimum parameters, Multi Objective Genetic Algorithm (MOGA) and Lagrange’s Multiplier (LM). The hoop and von-Mises stresses distributions along the thickness as well as the mechanical fatigue life have been calculated for the cylinder before and after optimization. It was found that the residual hoop stress has been enhanced at the near bore area by 31 %, also the fatigue life for the cylinder is better than that before optimization by 10900 cycles.