The ratchetting behavior of pressurized plain pipework subjected to cyclic bending moment with the combined hardening model

A series of six tests have been conducted using carbon steel and stainless steel cylindrical specimens having mean diameter/thickness ratios in the range 8 <= D(m)/t <= 28. Each cylinder is pressurized up to its calculated design pressure and is loaded with an alternative bending moment at frequencies typical of seismic events simultaneously. Ratchetting of the cylinder wall has been observed and recorded in the hoop direction. A finite element analysis with the nonlinear isotropic/kinematic (combined) hardening model has been used to evaluate ratchetting behavior of the cylinder under mentioned loading condition. Stress-strain data and material parameters have been obtained from several stabilized cycles of specimens that are subjected to symmetric strain cycles. The finite element results are compared with those obtained from experimental set-up. The results show that initial the rate of ratchetting is large and then it decreases with the increasing cycles. The FE model predicts the hoop strain ratchetting rate to be near that found experimentally in all cases that MIM(P0.2) <= 1. Also, M/M(y) ratios for the onset of ratchetting in stainless steel specimens are less than carbon steel specimens with same D(m)/t ratios. (C) 2009 Elsevier B.V. All rights reserved.