Numerical Analysis of Residual Stresses and their Influence on the Fatigue Strength at Block Joints of Ships

摘要

When evaluating the fatigue strength the consideration of residual stresses in larger-scale structures is generally done with a reduction of the FAT-class. The modern numerical analysis tools applicable these days, however, call for a more individual procedure. Due to this an investigation was performed to verify if the IIW-recommendations are still admissible for ship block welding. Therefore different ways of including residual stresses are compared with the IIW-procedure. For this purpose, butt joints at 250 mm wide and 15 mm thick plates made of higher-tensile steel were investigated at different stress ratios R with respect to their fatigue strength. The welding was performed under definite constraints corresponding to the stiffness of the surrounding ship structure that was measured in advance. For the residual stress determination a welding simulation of these specimens was done, involving the constraint conditions during welding as well as the welding parameters. Furthermore it was tried to simulate the whole block joint, which the tests were based on, including the surrounding part of the ship that possibly has an influence on the residual stress distribution when welding the blocks. The main goal of these investigations is to clarify the real influence of the computed residual stresses in a large-scale structure on the fatigue behaviour.