ABSTRACT
Design procedures within the nuclear power generation industry require that the possibility of incremental collapse or ratchetting incurred in pressure vessels and large pressurised piping runs during seismic disturbances be considered. This requirement has led to a programme of experimental work to simulate component and material behaviour under such conditions and to consider theoretical models so that predictive rather than codified design analysis can be performed.
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, ¼, ½ and ¾ of the initial uniaxial yield stress.
materials similar to those used in the pipework of PWR nuclear plant in the U.K. have been tested, namely 304S11 stainless steel and En6 low-carbon steel. Under the loading conditions both materials incurred plastic hoop ratchet strains to varying degrees. This ratchetting behaviour was compared to the behaviour predicted by the Prager-Ziegler model of kinematic work-hardening.
The experimental results indicate that there is a clear divergence with theoretical predictions. It is shown that when the cyclic plastic strains dominate, the model predicts the limiting condition is rapidly attained within a few cycles.
