The IBESS model - Elements, realisation and validation

The work presents the procedure developed within the German research project IBESS, which allows for the fracture mechanics-based prediction of the fatigue strength of welded joints under constant amplitude loading. Based on the experimental observations of the crucial failure mechanisms, the approach focuses on the short crack propagation, where elastic-plastic fracture mechanics and the build-up of closure effects must be considered, as well as the variability of the local geometry at the weld toe and the modelling of multiple crack interaction. Analytical solutions are provided for the approximation of the through-thickness stress profiles at the weld toe and for the determination of the crack driving force in the form of a plasticity-corrected stress intensity factor range Delta K-p. Proposals for the determination of the initial crack size and the crack closure factor are also included. The approach is validated against a large number of experimental data, which comprises fatigue tests on individual cracks monitored by heat-tinting and beach-marking techniques, as well as stress life curves. Three kinds of welded joints, two steels of significant different strength, two welding techniques and three stress ratios are considered. The results show that the procedure provides good estimations of the statistical distribution of the fatigue strength of welded joints both for the finite and infinite life regime. Furthermore, the predictions are compared with available benchmark data for structural steels. (C) 2017 Elsevier Ltd. All rights reserved.