The application of a kinematic hardening model for assessing ratchetting in pressurized pipes

Abstract

Concerns within the nuclear power generation industry regarding the possibility of incremental collapse or ratchetting incurred in pressure vessels and large pressurized piping runs during seismic disturbance has led to a programme of experimental work to simulate component and material behaviour under such conditions. As part of this programme, the plastic deformation of thin-walled cylinders has been experimentally examined for the loading conditions of ±1% cyclic axial strain with hoop stresses of approximately 0, 1 4 , 1 2 , and 3 4 of the initial unixial yield stress. Two materials similar to those used in the pipework of pressurized-water reactor nuclear plant in the UK have been tested, namely type 304S11 stainless steel and En6 low carbon steel. Under the loading conditions, both materials incurred plastic hoop ratchet strains to varying degrees. These ratchet strains were compared with the limiting ratchet strains predicted by the Prager-Ziegler model of kinematic work hardening. It was concluded that this model could not be satisfactorily used for design purposed as it did not consistently either overestimate or underestimate the measured ratchet strains. Furthermore, the manner in which the model reaches a limit is not observed in the experimental results.