Abstract:

Through the tensile tests of specimens and the finite element simulations of cylinder vessels,the effects of loading path and pre-strain quantity on the plastic instability pressure of strain-strengthening vessels were analyzed. The results indicate that the loading path has no obvious effect on the ultimate bearing capacity of the specimens and the pressure vessels,and that,though different pre-strain quantities make vessels produce plastic deformations to variable degrees,the material reinforcing effect may make up for the impact of vessel size change to a certain extent. Thus,only a slightly-decreased plastic instability load of the cylinder vessels is observed. Moreover,it is found that,at a diameter ratio of 1. 02 ~1. 10 for thin-wall vessels,the wall thickness has little influence on the decrease of plastic instability pressure. Considering the change of both the geometric shape of vessels and the stress-strain curve after the hardening,the strain hardening ranging from 4% to 12% may result in a decrease of the minimum safety margin from conventional 4. 76 to 2.21,which meets the demand for the minimum safety margin set by international standards,thus concluding that the vessels after strain hardening are still of relatively high strength margin.

Key words: pressure vessel, safety margin, strain hardening, plastic instability pressure