BIFURCATION BUCKLING OF PRESSURIZED CONICAL VESSELS

Metallic thin shell structures are used in different branches of industry, and the components of these structures such as dished ends show different modes of failure depending upon the geometrical and loading conditions. These are mainly gross plastic deformation under static load, loss of stability (buckling), fatigue crack initiation at highly stressed locations under cyclic loading (especially in the low cycle regime), progressive plastic deformation (ratcheting) and creep at high temperatures. In this paper, failure modes of a conical pressure vessel subjected to internal pressure has been investigated. Also, to study the effect of vessel geometry, a set of conical cylindrical vessels with the cap-cone apex half angles of 20 to 85 degrees, internal radius of 500 to 1000 mm and thickness of 1 to 10 mm has been selected. The failure modes of these vessels which include gross plastic deformation and bifurcation buckling have been taken into account. In this work, a new plastic criterion has been established which is based on the plastic work dissipation in the vessel by increasing the internal pressure. This plastic criterion can be used for structures subjected to single or a combination of loading condition. The calculated plastic limit loads, which have been obtained using the plastic criterion, are determined purely by the inelastic response of the vessel, and they are not altered by initial elastic behavior. In addition, a design graph for designing pressure vessels with conical heads subjected to internal pressure has been presented via comprehensive parametric study. The results show that when the ratio of the internal pressure to the limit pressure (Load Factor) approaches 0.5, the material yielding initiates and with further increase in the Load Factor, the plastic regions develop. Also, by increasing the ratio of cylinder radius to wall thickness (R/t), plastic buckling failure becomes more dominant.