OPTIMIZATION OF SHELL- THICKNESS IN MULTILAYER PRESSURE VESSEL AND STUDY ON EFFECT OF NUMBER OF SHELLS ON MAXIMUM HOOP STRESS Niranjan Kumar Jadavpur University, Department of Mechanical Engg., City-Kolkata, State-West Bengal, ZIP/Zone-700032, Country-India Dulal Krishna Mandal Jadavpur University, Department of Mechanical Engg., City-Kolkata, State-West Bengal, ZIP/Zone-700032, Country-India Samar Chandra Mondal Jadavpur University, Department of Mechanical Engg., City-Kolkata, State-West Bengal, ZIP/Zone-700032, Country-India Sanjib Kumar Acharyya Jadavpur University, Department of Mechanical Engg., City-Kolkata, State-West Bengal, ZIP/Zone-700032, Country-India Abstract: Multilayer pressure vessel is designed to work under high pressure condition. In this paper, optimization of thickness of each layer in multilayer vessel is carried out by Genetic Algorithm and then stress distribution is analyzed under optimum shrink-fit condition. The fatigue life is calculated for shrink-fit multilayer vessel. Thickness of each vessel is considered as design variable and objective function is maximum hoop stress through-out the thickness at the given working pressure. Multilayer vessel is assumed to be constructed by insertion of different vessels with zero interference and zero clearance such that interface pressure at the mating surfaces is equal to the pressure generated at the same surface due to interference fit. The mathematical model is derived from basic governing equation of thick cylinder. The appropriate boundary conditions are applied to each successive layer. Effect of number of shells on the maximum value of hoop stress is analyzed. Apart from this, effect of overall thickness of pressure vessel on the effectiveness of multi-layering is brought into focus. Stress distribution and fatigue life for the obtained thickness of each vessel from Genetic Algorithm is nearer to that obtained from Lagrange’s multiplier method. Keywords: Optimization; Multi-layer vessel; Autofrettaged vessel; Shell thickness; Genetic Algorithm; Fatigue Life; FE Analysis. 1. Introduction Design of pressure vessel is done with an objective to minimize the maximum value of hoop stress. Various methods have been used by researchers to decrease the hoop stress. Autofrettaging is the method of reducing the hoop stress by introducing compressive residual stress within the material. Shrink-fitted multilayer vessel reduces hoop stress and decrease the difference between maximum and minimum stress value. Niranjan Kumar et al. / International Journal of Engineering Science and Technology (IJEST) ISSN : 0975-5462 Vol. 3 No. 4 April 2011 2693