This paper on "Numerical Predictions of Residual Stresses in Fusion Welded Steel Submersible Hulls" was presented at the NAFEMS World Congress on The Evolution of Product Simulation From Established Methods to Virtual Testing & Prototyping - 24-28 April 2001, The Grand Hotel, Lake Como, Italy.

Abstract

Fatigue crack growth in fusion welded steel submersible hulls is driven by tensile residual stress locked in during welding. Current knowledge of fatigue crack growth rate is primarily based on model tests and on fracture mechanics predictions, which use experimental measurement of residual stress. This experimental data base indicates that the fatigue crack growth associated with current fabrication practice is acceptably low: but it does not allow rapid assessment of the consequences of any change to the fabrication route. This paper describes the development of a numerical method, using MSC.MARC 2000, to predict residual stresses in thick welded structures containing multi-pass welds.
Coupled thermo-mechanical finite element analyses have been carried out to evaluate the magnitude and distribution of residual stresses induced at a bulkhead to cylinder T-butt full penetration weld. Multi-pass welding has been simulated, with thermal loading applied to the models on a pass by pass basis. An attempt has been made to follow the complex temperature history experienced by the structure during welding. A pragmatic approach has • been adopted whereby the phase transformations that occur in the base material on cooling are ignored in order to obtain the general characteristics of the structure after welding simulation.
Comparisons with experimental results for longitudinal residual stresses acting through the plating thickness have shown reasonable correlation. This suggests that continued development and application of validated numerical modelling techniques, for prediction of welding residual stresses, will allow the quality of advice offered in relation to fatigue crack growth to improve significantly.