Volume 3, Issue 1 (January 2006)
Modelling the Redistribution of Residual Stresses at Elevated Temperature in Components
In this study the effects of high temperature relaxation on the residual stresses has been examined for T-plate and tubular T-joint geometries by numerical analysis using elasto-plastic-creep finite element modelling. It is shown that residual stresses are important, especially at the early stages of lifetime before the residual stresses relax rapidly. A sensitivity analysis was carried out by varying the creep properties and geometric constraint under plane stress and plane strain conditions. A comprehensive residual stress profile derived from measured residual stresses of a range of steels and different geometries that have been welded, cold bent, repair welded, or overloaded, was used as a ‘Master curve’ of the residual stresses. In all cases compared, it has been shown that the transverse measured residual stresses were tensile at the surface The stress intensity factor (SIF) estimates using the master curve profile for the T-Plate, and tubular T-joint geometries are lower compared to current case specific residual stress profiles used in R6 and BS7910 procedures but is still sufficiently conservative when compared with experimental measured residual stress data. It has also been shown that the numerically calculated residual stresses induced by overload in this study compare well at the surface with the master curve but decrease more rapidly with respect to crack depth compared to experimental values. Furthermore, by considering creep stress relaxation rates from the present FE calculations, it is shown that the peak surface residual stresses drop rapidly to about 50% at the relatively short duration of the first 1000 h. The SIF values of the predicted residual stresses are found to be lower than the experimentally measured data, and they are also found to be insensitive to stress relaxation in the through depth of the T-plate and tubular T-joint geometries. It was shown that the master curve gives an overall conservative SIF, though reduced, for the weld residual stresses as well as for residual stresses derived from overload. Furthermore, where redistribution of the residual stresses is concerned, it is shown that present profiles may all be unduly conservative in their SIF estimations.