Cyclic plastic and creep behaviour of pressure vessels under thermomechanical loading

Abstract

Structures such as pressure vessels are required to operate under thermal and mechanical loading and low-cycle fatigue conditions. Design of these structures is related to their response under these conditions. This work considers the cyclic plastic and creep behaviour of a thick-walled sphere and a cylindrical pressure vessel subjected to cyclic pressure and/or temperature. We investigate the steady state behaviour of the vessels using linear kinematic hardening in the plastic condition and Norton power law in the creep condition. Each loading cycle consists of four steps: loading, creep, unloading and creep. A numerical program has been developed to calculate final stress–strain state. We observe that because of the plastic strain and the creep strain in unloading, for both pressure and thermal loading, ratchetting is obtained. Thus, with these conditions secondary stresses lead to the ratchetting in the same way as the primary stresses.